Torticollis is a condition where an infant's neck muscle is tight or shortened on one side, causing the head to tilt in one direction. Congenital muscular torticollis (CMT) is the most common form and is typically identified in the first few months of life. Physical therapy with gentle stretching, positioning strategies, and parent education is the primary treatment.

Do you accept TRICARE?

Yes. Lead Pediatric Physical Therapy is an in-network provider with TriWest Health Care Alliance, which administers TRICARE West. Your provider can call 844-866-9378 to enter a referral. We are honored to serve military families in Fort Worth.

Do you offer in-home physical therapy visits?

Yes. In-home and daycare visits are available within a 15-minute drive of our clinic in the 76107 area of Fort Worth. Your child receives the same one-on-one care with Chrissy in the comfort of their own environment.

What is a PCS certification?

PCS stands for Pediatric Clinical Specialist, a board certification awarded by the American Board of Physical Therapy Specialties. Fewer than 3 percent of physical therapists in the United States hold this credential. It requires advanced clinical experience and a rigorous examination focused exclusively on pediatric physical therapy.

How much does a pediatric physical therapy evaluation cost?

The initial evaluation is $185 and lasts 45 to 60 minutes. Follow-up one-hour treatment sessions are $155 and half-hour sessions are $95. Packages are available at a reduced rate. We accept HSA and FSA cards, credit and debit cards, and Venmo.

What should I bring to my child's first physical therapy appointment?

Bring any referral paperwork from your pediatrician, a list of your concerns and questions, and your child in comfortable clothing. If your child is an infant, bring a favorite toy or comfort item. Chrissy will spend time understanding your child's history and your goals before beginning the evaluation.

Posts tagged:

home improvement

Personal Projects & Interests

Burning Weeds

Burning weeds is fun. It may also be cost effective, easy to apply than chemicals and just feels more natural. My neighbor once described a brief pass over weeds as “instant drought”. Maybe, but it works well. That is, unless your burner stops working.

The burner hooks directly to a propane gas tank. You just need a regulator, a flow value, and a wand. Light a spark and you have a nice torch.

In my case, I couldn’t get any gas to flow. I messed around trying to dissemble everything and then used compressed air to clear any blockages. This didn’t work. I started looking at new wands. They were > 100$ and repairing this was worth trying, but I needed to understand how this tool worked.

The key insight is that there is a small hole where the gas escapes. Mine was clogged. I put WD-40 on both sides of this hole and used a steel brush on my drill to clean this out and then compressed air until the blockage cleared. Next time, I won’t leave this wand out in the rain. Lesson learned.

The regulator is wrist-watch cool, it’s a mechanical feedback loop

The first part to understand is the regulator. In a typical direct-operated reducing regulator, outlet pressure pushes on a flexible diaphragm while a spring supplies the opposing force. A linkage connects that diaphragm to a valve at a restricted passage. The valve changes the opening through which higher-pressure gas enters the lower-pressure side.

Open the torch’s control valve and gas leaves the downstream side. As outlet pressure falls, its force on the diaphragm falls; spring force moves the mechanism toward a larger opening. When demand decreases, outlet pressure rises and the mechanism throttles toward closed. At a steady demand, it settles near a balance. The regulator responds continuously; it is not a pump or simply an on/off switch.

**Image 1** – You always see this thing, but what does it do?

I can’t follow paragraphs like this, so I built an illustration. Watch the linked diaphragm, stem and valve move together while the spring length changes. Motion is exaggerated to explain the feedback direction; this is not a pressure-response calculation.

Illustration 1 – Regulator

A small fuel outlet inside a much larger cup

Flame Engineering describes a fitting welded to the pipe end with a pin-sized central orifice. This detail was critical to fix this. There is much power in building a 3d model of a part. You can explore exactly how things work and then do a very surgical fix. Professionals gain this knowledge over years in apprenticeships, but weekend hacks like me can get the same wisdom from a model.

First, pressure drives gas through the restricted outlet. The emerging jet transfers momentum to surrounding air, drawing air into the mixing region. Fuel and oxygen then burn, producing a nice focused torch. The large air openings and the small fuel opening perform different jobs.

Illustration 2 – Watch fuel draw air into the burner, mix and form a flame. Use Pause and Speed to explore the flow.

The end of the wand is a mixing chamber, not a safety shield. The torch turns a narrow stream of propane into a broad flow of heat as it mixes in this tube. Pressurized fuel travels down the wand and accelerates through a small outlet into the burner bell, which is 2 inches (about 51 mm) across on the Weed Dragon VT2-23C. The fast-moving jet pulls surrounding air through the openings behind the bell a process called entrainment. The wider tube gives that air and fuel room to mix as the jet spreads. Once ignited, the mixture releases heat, expands, and continues mixing with outside air beyond the mouth, producing a flame much wider than the original fuel jet. The bell helps shape this flow, but the flame’s width and length also depend on fuel flow, air supply, and wind. The drifting haze in the illustration makes normally invisible gas motion visible.

The heat does not necessarily peak at the burner’s face, and it does not simply fall as $1/\text{distance}^2$. Near the torch, combustion, mixing, and the hot gas striking a surface all affect heat delivery. To understand the chemistry and the heat, let’s use NASA’s explanation of flame color. Blue in a real flame comes largely from light emitted by excited molecules during combustion. It is not a “cool” region. Yellow, orange, and red often come from glowing soot particles. Brightness and color alone cannot tell us the gas temperature or how much heat reaches a leaf.

The heat is not maximized at the end of the wand where fuel may still be mixing and burning. It takes distance for the reaction to increase. Farther downstream, the jet spreads, entrains cooler air, and loses speed and temperature. The concept here is heat flux:

q”_{\text{net}} = \underbrace{h(T_{\text{gas}}-T_{\text{leaf}})}_{\text{heat carried by moving gas}} + \underbrace{q”_{\text{radiation, absorbed}}-q”_{\text{radiation, emitted}}}_{\text{net radiant heating}}

Practically, this means you need to experiment on distance.

**Image 2.** Heat and distance from the wand

Why does a short pass of heat kill plants?

The trivial answer is that if you turn a plant into ash, it’s gone. That isn’t the idea here. I’ve learned a light pass that causes just a little wilt is best.

How does a pass of high heat kill a plant? A healthy leaf’s firmness depends partly on turgor: water pressure within living cells pressing against their walls. Membranes maintain the separation and chemical gradients that make normal cell function possible.

Illustration 3 – Watch heat damage the leaf’s cells, then follow its effects on the plant’s ability to recover.

The plant dies when damage exceeds its capacity to sustain itself and rebuild. Loss of support for the roots is part of that process, but damage to the growing points also matters.

Heat damages membranes and proteins, causing cells to lose function and water pressure. Leaves wilt and lose their ability to produce sugars that support the roots and new growth. The plant can recover if surviving leaves and stored reserves sustain it long enough for living buds to produce replacements. If that recovery fails, or heat destroys the growing points needed for replacement, the damage becomes fatal.

The S-curve describes how increasing heat exposure pushes more plants beyond that recovery limit. At low doses, most recover. Through the steep middle, more sustain fatal damage. At high doses, most susceptible plants have already crossed the limit. There is no universal percentage of leaf loss that kills every plant; protected buds and stored reserves change the outcome. Also, a curve measuring reduced growth must not be mistaken for a curve measuring death.

To do it right, pass the heat across the foliage and exposed growing points, the tips or buds producing new leaves. Burning through the stem could work if you really destroy it but that takes too much time.

From my reading on this, a good field check is to let the treated leaf cool, then gently press it between thumb and finger. A lasting thumbprint, dark watery appearance, or easily crushed tissue indicates sufficient heat injury in that area.

Why the same treatment can kill one weed and spare another

Burning doesn’t affect all plants equally. Small broadleaf seedlings are often susceptible because their growing points are exposed. Grasses can protect those growing points near the soil or within leaf sheaths. Established perennials can retain roots, crowns or underground stems that produce another shoot after the visible foliage is injured. A wilted top is not proof of a dead root system. [9] [11]

Nebraska experiments found that response changed with propane dose, species, growth stage and time of day; grasses generally tolerated more flaming than broadleaf species. So a universal pass speed or a single exposure will not kill every weed. [10]

Flaming also has practical limits. It is nonselective, can injure desirable plants, and can ignite dry vegetation or mulch. (Ask my wife about lighting the house on fire.) [9]

The useful question is not “How completely did I burn it?” It is whether enough vulnerable living tissue was injured to prevent recovery, and whether protected growing points can still restart growth. Several fast passes are a good experimental way to find out.

Sources & model notes

October 21, 2026 (updated October 22, 2026) By Tim Booher One Comment

Engineering & Code

Garage Door Simulator

My son had a physics assignment to estimate the power required to raise a garage door. He needed to make a video for this. I wanted to build an interactive simulation to teach about a simplified linearized model versus what differential equations can actually do in the real world.

Now that I’m using AI to understand the world around me, my son’s physics project provided an opportunity to understand how garage doors work. They’re super simple, just a motor that pulls on a door. But there’s a couple interesting things going on. The first one is that it’s possible when you disconnect the motor to just lift the several hundred pounds of door up with a single arm because the torsion spring is pulling it up. And the door starts to move horizontally after the door goes around the first turn, which gets it out of the way but also makes it easier to move.

Illustration 1 – Drag the slider to lift the case off, then run the motor and watch the worm, gear, sprocket and chain open the door.

The motor itself in my garage runs on 120 volt AC and spins really fast. It started and stopped by a start-run capacitor. Newer units use a DC motor feed from a transformer and rectifier to allow soft start and battery backup.

Inside the opener’s AC motor there are two separate coils of wire wound around the stationary outer part, the stator. Each coil becomes an electromagnet when current flows through it.

Illustration 2 – The rotor always chases the field from the coil that peaks first toward the one that peaks second. Drag the slider to watch it, then switch the capacitor to the other coil and the rotor runs backward.

The capacitor matters because household AC power alone is a simple sine wave that would just make the motor buzz back and forth, not turn. The capacitor delays the current into one of the coils by a fraction of a cycle. So the two coils peak one after the other instead of together. Let’s name the coils Coil A and Coil B. That handoff between the coils makes the magnetic field sweep around the motor, and the rotor follows it. This is just like two hands spinning a wheel one after the other.

To reverse the garage door, switch the order of the capacitor firing: the capacitor on coil A and A lags, so the field sweeps one way. Put it on coil B and B lags, so it sweeps the other way. In many openers the two coils are identical, and the capacitor is wired between them. The “up” relay feeds power to one end and the “down” relay to the other, which decides which coil gets the delayed current.

Since the motor spins at about 1,500 RPM, a worm on the motor shaft drives a larger worm gear, which is often made out of nylon, which reduces from 10 to 40 to 1. A worm drive is good because it’s hard to back drive, which helps hold the door in place when the motor stops. This worm gear turns the output shaft, and the sprocket on that shaft pulls the chain. A pretty simple drivetrain.

Illustration 3 – Drag the slider to open the door. Drag the model to turn it, or tap Close-up to see the forces at the door arm.

The arrows in the illustration show the forces on the door at each point in its travel. The red arrow is gravity: the door’s 78 kg pulls down with about 765 N from its centre of mass. Gravity matters less as the door goes more horizontal. The magenta arrows are the lift from the torsion springs, delivered through the two cables. With the door closed they carry almost the whole 765 N, about 380 N per cable. As the door rolls onto the horizontal track, the track takes over more of its weight and the magenta arrows shrink to match. Because the springs balance the door, the opener only has to make up the difference. The dark cyan arrow is the opener’s force on the door, pushed through the door arm. At the start of opening it is only about 20 N, just enough to overcome roller friction and the drag of the bottom seal. The light cyan arrows split that force into a lift and a pull.

With the door closed the arm leans about 42° from vertical, so it pulls up and back at once, and the arm carries about one and a half times the chain’s pull. The springs do the heavy lifting; the motor steers and tops up.

The torsion spring is cool because it is not a normal spring with a linear constant that increases its force. It doesn’t pull on anything directly; it twists. One end is bolted to a bracket on the wall and cannot turn. The other end is clamped to the steel shaft that runs above the door. When the door is closed, the spring has been wound about seven turns.

Illustration 4 – Drag the slider to open the door. The wound spring twists the shaft, the drum reels in the cable, and the cable lifts the door. Watch the coils loosen as the spring gives up its twist.

Like a wound-up rubber band it is always trying to unwind, and the only part free to move is the shaft. So the spring twists the shaft, about 19 newton-metres from each spring in this example. At each end of the shaft is a small drum, about 10 cm across, with a steel cable wrapped around it and running down to the bottom corner of the door. As the shaft tries to turn, the drums try to reel those cables in. A twist of 19 N·m on a drum with a 5 cm radius becomes a pull of about 380 N on each cable, and two cables together roughly equal the door’s own weight (78 kg, or about 765 N).

The door is effectively hanging from a pair of wound-up springs, balanced. As the door rises, the cables wind onto the drums and the springs give up their twist. They lift less and less, which is fine, because the horizontal track is taking over more and more of the door’s weight. What a cool, balanced, system.

You can see a full simulation of all the forces at garagedoor.theboohers.org/ but you can get a small sample of everything together below. (Btw, perfect introduction to differential equations.)

Illustration 5 – Drag the door or press Open & close. Change the spring, door mass and friction to see how the forces and power change.

The Math

This is a great chance to show differential equations in action. The model has a single coordinate, $ s $: how far the bottom roller has travelled along the track. Every other position follows from it.

The whole door has one moving part as far as the math is concerned: $s$, how far the bottom roller has travelled along the track. Every section, roller, cable and the trolley can be worked out from $s$, so one equation describes the entire door.

In words: the force needed to speed the door up equals what the opener supplies, minus gravity, plus the spring, minus friction.

\begin{aligned} M(s)\,\ddot s + \tfrac12 M'(s)\,\dot s^{2} &= F_{\text{op}} \\ &\quad – G(s) \\ &\quad + S(s) \\ &\quad – F_f\,\operatorname{sgn}(\dot s) \end{aligned}

The left side is the door’s inertia: $M(s)$ is how heavy the door feels at position $s$, $\ddot s$ is its acceleration and $\dot s$ its speed. On the right, $F_{\text{op}}$ is the opener’s push, $G$ is gravity, $S$ is the spring’s lift and $F_f$ is friction, which always opposes the motion. The simulation runs this equation backward: it knows how the door moves and solves for $F_{\text{op}}$, the force the opener must supply at each point.

The door’s effective mass adds up every section’s sliding and turning:

\begin{aligned} M(s) &= \sum_{i=1}^{4} m_s \left\lVert \frac{d\mathbf c_i}{ds} \right\rVert^{2} \\ &\quad + \sum_{i=1}^{4} \frac{m_s h^{2}}{12} \left( \frac{d\phi_i}{ds} \right)^{2} \end{aligned}

Each of the four sections has mass $m_s$ and height $h$. The first sum is the sections sliding, with $\mathbf c_i$ the centre of section $i$. The second is the sections turning, with $\phi_i$ its tilt and $m_s h^{2}/12$ a flat panel’s resistance to rotating. Because the sections speed up and tilt as they round the curve, $M(s)$ changes along the track, and that is where the $\tfrac12 M'(s)\,\dot s^{2}$ term in the main equation comes from.

Gravity is the slope of the door’s potential energy:

\begin{aligned} U_g(s) &= \sum_{i=1}^{4} m_s\, g\, \bar y_i(s) \\ G(s) &= \frac{dU_g}{ds} \end{aligned}

$\bar y_i$ is the height of each section’s centre. $G$ is largest when the door is closed and hanging straight down, and falls toward zero as the sections lie flat on the horizontal track, where the track carries their weight.

The torsion spring unwinds as the cable winds onto the drum:

\begin{aligned} n(s) &= n_0 – \frac{L_0 – L(s)}{2\pi r_d} \\ T_c(s) &= \frac{k\, n(s)}{r_d} \\ S(s) &= -\,T_c(s)\, \frac{dL}{ds} \end{aligned}

The springs start wound $n_0$ turns, about 7 here. Every $2\pi r_d$ of cable wound onto a drum of radius $r_d$ gives back one turn, so $n(s)$ is the wind left. The spring’s twist is $k$ newton-metres per turn, and the drum turns it into the cable pull $T_c$. $S$ is that pull measured along the door’s travel. It is positive because the cable shortens as the door rises. A balanced spring makes $S$ track $G$ almost exactly.

Friction comes from the rollers pressing on the track:

\begin{aligned} N_j &= w_j\,\lvert t_z(r_j) \rvert + \frac{m_j v_j^{2}}{R} \\ F_f &= \mu \sum_{j} N_j \left| \frac{dr_j}{ds} \right| + F_{\text{seal}} \end{aligned}

$N_j$ is how hard roller $j$ presses on the track. On the vertical track $t_z = 0$ and the cables hold the door, so the rollers only guide it. On the horizontal track $t_z = 1$ and the full weight share $w_j$ rests on the roller. On the curve of radius $R$, a moving roller is also pushed outward by $m_j v_j^{2}/R$. Rolling friction is a small fraction $\mu$ (about 0.03) of that, plus a steady drag $F_{\text{seal}}$ from the bottom seal and hinges.

Finally, the opener and the electric bill:

\begin{aligned} F_{\text{trolley}} &= \frac{F_{\text{op}}}{\zeta'(s)} \\ P &= F_{\text{op}}\,\dot s = F_{\text{trolley}}\, v_t \\ P_{\text{wall}} &= P_{\text{standby}} + \frac{\max(P,\,0)}{\eta} \end{aligned}

The chain pulls a trolley, and the trolley pulls the door through the door arm. $\zeta'(s)$ is how far the trolley moves per unit of door travel, so where the trolley moves less than the door, the chain must pull harder. Power is force times speed, the same at the door or at the trolley (moving at $v_t$, about 0.18 m/s). The motor and gearbox are about 55% efficient ($\eta$), and the board and radio draw about 8 W on standby ($P_{\text{standby}}$). The $\max(P,\,0)$ means that when the door pushes back on the motor, that energy is lost as heat rather than returned to the wall.

October 10, 2026 (updated October 11, 2026) By Tim Booher 0 Comments

Engineering & Code

Understanding and Fixing my Gate

Texas introduced us to cowboy hats and electric gates, in our case a a Nice Apollo 1500LA. It’s a long-running linear actuator swing gate: simple enough to be something I can repair, but just complicated enough to be difficult. The whole gate is really two different parts: a 636 control board and a 816 actuator. In the past, I documented how I connected our gate to Alexa through a WiFi connection in Gate Automation. This post is about how our gate works and how to fix it.

Our gate started opening past the limit switch and now I have to fix the 816 actuator, it’s a 12-volt DC motor that turns a pinon and spur gear which drives the central Acme lead screw. I had just fixed the broken spur gear and the old motor that lost much of its usable torque under load. After a couple of successful months after I replaced the motor and the spur gear, the limit screw broke and the gate only stopped at at absolute min extension. Slide below to see all these parts and how they work.

Illustration 1 – Drag the slider to open the housing and run the gears.

I opened up the housing to find that the A2019 limit screwwas broken and the key was broken as well. The A2019 limit screw threads directly the end of theACME lead screw so they move together. The illustration below shows how this works. A travellercarrying amagnetrides on the limit screw‘s thread. Two guide bolts keep the magnet from turning.

Illustration 2 – The traveller walks along the A2019 limit screw until a switch trips.

As the arm extends or retracts, the traveller walks slowly along the tower. Its position mirrors the gate. At each end of its travel sits a proximity switch on a limit block. When the magnet reaches a switch, the switch trips and tells the control board to stop the motor, one switch for fully open and one for fully closed.

**Fig** 1 – The traveler uses the guide bolts to stay vertical

So how does a magnet generate a signal to the controller board? A magnet induces an electric field. As the magnet approaches, the field strength $B$ at the switch climbs steeply, roughly as $1/d^3$, but continuously. My guess is that the gate has a Hall-effect sensor where current through a thin semiconductor is pushed sideways by the field, producing a tiny voltage proportional to $B$. On its own that’s still analogue. An on-chip Schmitt trigger (a comparator with two thresholds, on above one and off below a lower one) flips its output transistor fully on or off.

Another interesting thing: the lead screw moves about 5 tpi (threads per inch) or 0.20–0.22 $in$ per turn to fully open the gate, but the limit screw moves about $ \frac{1}{8}^{\text{th}} $ that distance. In all, whole 2 ft of arm travel is shrunk into about 3 in of traveller movement. Simply, the screw goes a distance $L$ which is each spiral thread winding around the screw $n_{\text{starts}}$ $\times$ the pitch $p$ of each screw.

L = n_{\text{starts}} \cdot p = \frac{n_{\text{starts}}}{\text{TPI}}

In this setup, both screws turn together. The limit screw is fixed to the end of the lead screw, so after a common set of $ N$ revolutions each screw goes a total length $s$ of:

s_{\text{arm}} = N \cdot L_{\text{lead}} \qquad s_{\text{trav}} = N \cdot L_{\text{limit}}

For the full stroke the revolutions are the same,

N = \frac{24\;\text{in}}{0.21\;\text{in/rev}} \approx 114\ \text{rev}

\, L_{\text{Lim}} = \frac{s_{\text{trav}}}{N} = \frac{3.6 \, \text{in}}{144\, \text{rev}} = 0.025 \,\text{in/rev} = 40 \, \text{tpi}

So the lead screw has 8x the thread density and goes 8x shorter in length.

**Fig** 2 – Lead screw versus limit screw threads

The geometry of the setup can teach us a lot about how stuff works. The lead screw pushes the rod out several feet, but it pushes only about 4.5 ft from the hinge, so a short push near the pivot becomes a long sweep at the gate’s far end. Two feet becomes 25 feet: about 20 in of stroke swings a 16 ft gate through 90°, and its tip travels about 25 ft, a quarter of a 100 ft circle. That is about 15× multiplication: the actuator’s average lever arm is about 12.7 in, compared with the tip’s 192 in, so each inch of push moves the tip about 15 in.

But nothing comes for free. The trade-off is force: holding the gate against a push at its tip takes about 15 times that force at the rod, which is why the motor’s torque is multiplied first by the gears and the ACME screw. All together, the whole chain: about 840 motor turns leads to 114 screw turns leads to 24 in of arm travel which is about 25 ft at the gate tip.

The most interesting thing for me is the offset arm. Without it the lead screw would just pull on the hinge and not push out. The bigger the offset arm, the more force transfers to the tip of the gate. How big should we make this offset? The manual recommends 6 $\text{in}$ which has enough lever arm to break the gate away from closed, while keeping the stroke inside the actuator. More offset means a longer stroke for 90°. The actuator swings through a bigger angle, and past a point it runs out of its 24 in, which is the demo’s warning.

Arm offset	Lever arm at start	Hinge torque	Force at tip
0 in	0 in	0 lb·ft	0 lbf (stuck)
2 in	≈ 2.5 in	≈ 73 lb·ft	≈ 4.6 lbf
4 in	≈ 5.0 in	≈ 146 lb·ft	≈ 9 lbf
6 in (manual)	≈ 7.5 in	≈ 219 lb·ft	≈ 14 lbf
9 in	≈ 11.4 in	≈ 333 lb·ft	≈ 21 lbf

The experiment below brings all this together. Move out the pivot arm to see the effect on the force.

Illustration 3 – Change the pivot arm and drive, then open the gate.

Now that we know how everything works, I actually have to fix this gate and put the washers and spur gear together.

**Fig 3** – The spur gear and screws form a rigid system

The washers in the A2087 include two needle thrust bearings. Every time the actuator pushes or pulls the gate, the gate pushes back along the lead screw, trying to shove the whole screw lengthwise out of the housing with hundreds of pounds of force. A thrust bearing takes that end-to-end load while still letting the screw spin freely. Each bearing is a sandwich. In the middle is a flat steel cage holding about twenty tiny hardened needle rollers, arranged like the spokes of a wheel. On either side is a hardened, polished race: the thin washers, plus one thicker race for the screw’s shoulder. The needles roll between the races instead of sliding, so the friction stays low even under heavy load. The races matter as much as the rollers, because they give the needles a hard, smooth track; without them, the needles would quickly dig grooves into the softer housing and gear. When a gate is making bad sounds opening and closing, it’s generally overlooked parts like this.

**Fig 4** – Nice Apollo Bearing Kit (A2087)

The biggest problem for me is that little piece on the bottom right. Known a key, it’s the smallest part that does the most work: ensuring the torque is transfered from the rotating shaft to the spur gear which sits on a round, smooth section of the shaft. On its own it would just spin in place, or slip under load. To make this work, a small slot is milled lengthwise into the shaft (the keyseat), and a matching slot runs through the gear’s bore (the keyway). The square key sits half in each, bridging the two parts. All of the motor’s torque passes through that little 3/32 $\text{in}$ bar. The Flexloc nut only stops the gear sliding off the end; it isn’t what makes the gear drive the screw.

As an engineer, I look at parts like this carefully. The key is like the derailleur hanger on your bike, strong enough to work, but weaker than the expensive parts around it. If the gate jams hard, it tends to shear the cheap key, saving a costly stripped gear or a twisted screw.

The final experiment is the diagram that matters for my current fix. Explode the assembly to see how the key ties everything together.

Illustration 4 – Explode the stack; click any part to hide it.

Hopefully this post gave you new appreciation for the beauty and thought that goes into the simple stuff around you. Today the combination of AI, youtube and Amazon/e-commerce let you understand, learn and find any part you need. These are amazing days to be a builder.

September 28, 2026 (updated September 28, 2026) By Tim Booher 0 Comments

Personal Projects & Interests

Gate Automation

Our gate is the most important motor in our home. It’s critical for security, and if it’s open, the dog escapes. As all our kids cars go in and out, it’s always the gate opening and closing. It matters.

The problem is that we have to open it and we don’t always have our phones around. We use alexa for home automation and iphones.

We have the Nice Apollo 1500 with a Apollo 635/636 control board. This is a simple system with only three states: opening, closing, and paused. The gate toggles through these three states by connecting ground (GND) to an input (INP) on the control board, which a logic analyzer would observe as a voltage drop from the operating level (e.g., 5V or 12V) to 0V.

To automate this I purchased the Shelly Plus 1 UL a Wi-Fi and Bluetooth-enabled smart relay switch. It includes dry contact inputs, perfect for systems requiring momentary contact for activation. It’s also compatible with major smart home platforms, including Amazon Alexa, Google Home, and SmartThings, allowing for voice control and complex automation routines. You can get most of the details here.

There are many ways to wire these switches. I’m setting this up for a resistive load with a 12 VDC stabilized power supply to ensure a reliable, controlled voltage drop each time the Shelly activates the gate. With a resistive load, the current flow is steady and predictable, which works perfectly with the gate’s control board input that’s looking for a simple drop to zero to trigger the gate actions. Inductive loads, on the other hand, generate back EMF (electromotive force) when switching, which can cause spikes or inconsistencies in voltage. By using a stabilized 12 VDC supply with a resistive load, I avoid these fluctuations, ensuring the gate responds cleanly and consistently without risk of interference or relay wear from inductive kickback. This setup gives me the precise control I need.

Shelly Plus 1 UL          Apollo 635/636 Control Board

      [O] --------------------- [INP]
      [I] --------------------- [GND]
      [L] --------------------- [GND]
      [12V] ------------------- [12V]

Settings

The Shelly Plus 1 UL is set up with I and L grounded, and the 12V input terminal provides power to the device. When the relay activates, it briefly connects O to ground, pulling down the voltage on the INP input of the Apollo control board from its usual 5V or 12V to 0V, which simulates a button press to open, close, or pause the gate.

To get this working right, you have to set up the input/output settings in the Shelly app after adding the device. In the input/output settings, the detached switch mode is key here, as it allows each button press to register independently without toggling the relay by default. Setting Relay Power On Default to Off keeps the relay open after any power cycle, avoiding unintended gate actions.

With Detached Switch Mode, Default Power Off and a 0.5-second Auto-Off timer, every “button press” from the app causes a voltage drop for 0.5 seconds. Adding the device to Alexa means I can now just say, “Alexa, activate gate,” which will act like a garage door button press.

November 3, 2024 (updated November 3, 2024) By Tim Booher 0 Comments

Engineering & Code

Kerf Mounted Corner Brackets

Kerf Mount Corner Brackets are great. But it takes some thinking if you are working with larger lumber. I recently purchased these and these from amazon.

The corner bracket looks like this:

The trick is figuring out where to cut the leg at 45 degrees and the kerfs, especially if the leg isn’t square. I was going to work out the geometry of this, but instead I measured the bracket, drew a horizontal profile in visio and then measured the geometry. Since the leg isn’t square, I had to decide where the bracket mounts flush. I included my drawing here in the hopes that it may be helpful to you.

There are instructions here.

August 27, 2021 By Tim Booher 0 Comments

Personal Projects & Interests

Lauren’s Bed

Overall Design

Lauren was disappointed when we had to take 30" away from her already small room to build a bench for a duct after adding a furnace to the third floor.

Lauren did an initial sketch of what she wanted to build. Her overall goal was to maximize the space available in a smaller room. This meant we needed lots of storage and that we wanted to use the surface area of the bed.

lauren's bed

We looked around for some design ideas. We decided to match the trim color of the room and use the bottom for storage.

design ideas

I drew this up in Sketchup and decided on a design that used pine 2×4 and 2×6 to make the frame, with poplar sides. By using an internal frame and a several stage layup, we could make lots of adjustments.

We decided on three drawers on the bottom using full extension hardware ball bearing side mount drawer slides. I found these on Amazon, which have been excellent quality. For my shop shelves, I purchased two Everbuilt drawer slides at Home Depot for 3x the cost that were inferior in quality.

bed layout

All this would be supported by an internal frame that would allow us to adjust to all the non-level components of the room.

frame

I like notching the pine board with my 5-1/2" Craftsman C3 19.2v Circular Saw. While an old tool, it is super light and I can use my speed square as a guide to notch out the pine quickly. I tried using my table saw with a crosscut sled, but the handheld saw was a lot easier.

drawers

For all joinery we used pocket screws and also #10 biscuts.

We laid out the frame on the floor and ensure the top frame was level, but we also should have leveled the bottom. Not leveling this created a lot of issues when we had to put in the drawers and build the outside frames.

The frame for the inside was built using lots of lap joints, held together by wood glue and pocket screws.

interior frame

I don’t build my own face frames. It’s awesome to order them professionally finished. I ordered them from the cabinet door store, which I can’t recommend enough.

Shaker Cabinet Door
Wood Species:Paint Grade Maple w/ HDF Panel
Frame Width:2 1/4"
Finish ($11.97):Simply White OC-117
Door Width (in):18.75
Door Height (in):10.75
Total Area (sq. ft.):1.3997395833333

or $44.23 a face.

One big mistake of my design was failing to account for non-straight boards and my over-optimism in everything lining up. Since the purple boards below were rigid, any mismatched angle would effect two drawers. This trapped me in the middle of a highly coupled problem where adjusting one drawer would cause problems with the others. I solved this by cutting 1 inch out of the middle of each purple board so I could adjust each one independently. Lesson learned: designs should always account for reality and provide the ability to adjust.

drawer slides

In order to get the drawers to sit at the right height, I cut out spacers for each of the drawers before installing the sliding tracks.

Result

The end result was awesome. Lauren loves her bed and we learned a lot putting it together.

May 9, 2021 By Tim Booher 0 Comments

Engineering & Code

Wiring for 3HP 220V (for Laguna Tools 18|Bx)

I recently purchased a Laguna Tools 18|Bx 3HP 220V 18″ Bandsaw, specifically a MBAND18BX2203, and needed to wire a 220 Volt outlet. I’ve done a fair bit of electrical work (both low and high voltage), but I had a couple questions.

Just for the record, I enjoyed this video to make sure everything was setup correctly and this unboxing video was helpful. Also, here is the manual. The instructions weren’t great, but the wiring digram in the manual was helpful. YouTube and web forums are incredible for learning how to do new things like this. This article, Understanding 240V AC Power for Heavy-Duty Power Tools, was super helpful.

The 18BX2203 has a 12-amp 3 HP 220 volt 1 phase Leeson motor, with a 20 Amp recommended breaker. (Engines use more current on startup. Why not more Voltage?). 220V is a somewhat outdated nomenclature for the US system, but tools like this have adequate tolerance to take 240 without problems.

Laguna made this confusing since their website for the 18BX, differed from the manual. The website recommended a 20 amp breaker, while the manual recommend 15.

mismatch

The machine’s wiring diagram showed me a couple important things. First, I have no need for a neutral wire and the saw has a NEMA 6-15 plug.

wiring

The single phase motor will need at least 12-amps of continuous current at 240V (hot 120V + hot 120V) plus a ground. Here in the US, we have 240V single-phase residential, with a center tap. The center tap is called neutral. This is called “Split-phase” since you can grab the outer “phase” wires (hot-hot) or grab one phase and neutral for half the voltage.

This diagram cleared everything up for me:

Where I found myself confused was on the “single-phase”, if a “normal” outlet grabs one phase, and a neutral for half the voltage, wouldn’t a 240V setup have two phases? There actually is a 2-phase, but it’s weird as heck. It was basically two single-phase circuits set 90 degrees apart, and requires 4 wires instead of 3 but only carries about 14% more power for 33% more wires. Needless to say it wasn’t popular.

This diagram cleared it up for me. The amplitude of 120V on each leg adds to 240V at the same frequency. The current doesn’t add since the flow remains the same. A 240V-only piece of gear connects to two hot legs and a ground (no neutral), so if it pulls 20A, that 20A has to be going in one hot leg and out the other hot leg — there’s nowhere else for it to go! (In other words, it draws 20A, period — the legs do not “add together”.)

In setting up a 20-amp circuit, I had to make sure this worked with my setup. Per the table in the manual, I need at least 14 guage wire, so I went with 12 guage which I needed for the 20-amp breaker anyway.

wire thickness

How many wires?

I initially was going to use 12/2 wire, but I decided on schedule 40 conduit with Thermoplastic High Heat-resistant Nylon-coated THHN wire. I like this reference on wires.

I initially thought I would need to have 4 wires (a 12/3 wire), both a neutral and a ground in addition to two hot wires. After thinking about it a little bit, it made sense two use three wires total, since I was setting up a dedicated circuit and the ground and the neutral will have the same purpose. (The neutral is connected to the ground in the panel.)

What receptacle do I use?

The bandsaw came pre-wired with a 220V NEMA 6-15 3-pin plug. I used this page to make sure I used the correct outlet. One of the decisions I had to make was if I wanted to use a twist lock plug, but I didn’t consider the benefit worth the extra work to re-wire the saw.

For this setup, I needed a NEMA 6-20.

By the way, I learned that due to an exception in NEC, I’m allowed to plug 15A-plugged loads into either a 15A or 20A circuit. Further, a 20A circuit is allowed to have 15A sockets on it (as long as there are 2 or more sockets, e.g. the above NEMA 6-15 will suffice).

I decided on 20 Amp Commercial Grade Double-Pole Single Outlet, White which has two connections for hot and one ground wire and is a NEMA 6-20R, 2P, 3W.

Breaker

This is the most simple part. I need two 20 amp breakers that connect to different leads to get both parts of the split phase. This one will work.

November 29, 2020 By Tim Booher One Comment

Engineering & Code

Three Way Troubleshooting

Tonight, I was rewiring switches to a more modern set of switches. These days I don’t have time to learn by experience, I have to think my way through this. Without experience, I have to go back to first principles. Funny enough, understanding a four way switch is very similar to understanding digital logic and computation in general.

A three way switch is an electrical component that lets you turn a light on or off from three or more locations. Any one toggle should change the state of the light. To control a light from one location, all you need is a simple on/off switch. The switch either closes the circuit, in which case the light goes on, or it opens the circuit, in which case the light goes off. Essentially, the switch takes two ends of a wire and connects or disconnects them. This is different than a one-switch circuit where the position of the switch correlates with the state of the light. In the examples below, up will mean on, and down will mean off.

First, there are $2^n$ states for $n$ switches. A 4-way switch has three lights or eight states. Mine were wrong. Lauren (my 12 year old) and I measured three switches: 1,2 and 3. Switch 2 was the four-way switch. Our measurements produced:

Case	1	2	3	Light	Ideal
1	0	0	0	off	off
2	0	0	1	off	on
3	0	1	1	off	off
4	0	1	0	on	on
5	1	1	0	off	off
6	1	1	1	on	on
7	1	0	1	off	off
8	1	0	0	off	on

Two states are off: cases two and eight. They should be closed, but are open.

To think about this more, I was helped by Rick Regan at exploring binary

The next piece was to understand how the circuit actually works so I could look at what configuration might be causing the current state machine. This simulation (credit to falstad.com) was awesome.

The key insight was that both failing states should have counted on the four way to close the circuit but the circuit was staying open. With that knowledge, I was able to put the four-way together per the diagram below.

4 way wiring

And, for my switches in particular:

helpful links

finding function
exploring binary
three way switch troubleshooting
some nice diagrams
another nice picture for the three way

March 10, 2017 By Tim Booher 0 Comments

Personal Projects & Interests

July 4th Home Project: Thermostat Bracket

This post is about how to use design tools to save time and build nice stuff at home using computer controlled machines (CNC). In addition to describing my design process, I’ve also included the helpful references I found along the way.

Our old thermostat was too small for our wall. I could have replaced the drywall, but I needed a starter project to help me understand 3D CNC work with wood. Replacing the drywall would have taken a good bit of time because of the lath behind the old thermostat. The bracket took a long time because I had to learn wood CNC and spent way too long finishing the surface. In the end, this was a great use of a wood CNC machine. It would have been difficult to get the corners right and route out the pocket inside. Additionally, I could prototype and correct parts of my design with the rapid iteration that CNC machines provided.

We have a programmable thermostat with z-wave, the 2gig CT100 Z-Wave Touch Screen Programmable Thermostat. It works perfectly and is easy to control with our Mi Casa Verde VeraLite Home Controller. This gives us the ability to set our temperature from our phones or do nest-like things like learn our patterns and adjust temperature. We can also set up multiple thermostats to regulate temperature throughout the different regions of our house.

In case you are working with the CT100 or the VeraLite, you might find the following links helpful:

First I measured the thermostat from the manual.
nice install video

Design

I designed the bracket in Fusion 360. I’m still figuring out how to use Fusion, but it is a computer-aided design application for creating 3D digital prototypes including design, visualization and simulation. Fusion 360 is easy to use and it provides the ability to go from design, render, analysis and production in one tool. Most important, it is free for hobbyists.

The design was pretty straightforward. It is a one inch offset with fillets that matched the radius of the CT100. One problem with CNC routing is that I tend to design features that take advantage of the CNC features and this tends to lead to more curves. I just had to get the measurements right. I shouldn’t need to do this, but I used a laser cutter to cut out the frame from a piece of cardboard to check the fit. I’m glad I did, because I hadn’t accounted for some of the curves and the opening was too small. In general, I love using the laser-cutter to prototype designs. The prototype let me see how the final design would look on the wall. This would have been helpful to test different designs. Chrissy and I tend to like 18th-century English and 19th-century neoclassic millwork, but I didn’t put too much thought into this design, partly because I could change it so easily.

Here is the final, dimensioned, design:

Construction

I found a piece of scrap plywood at TechShop that I cut on the ShopBot buddy.

ShopBot Buddy

To cut the workpiece I used the 1/4″ High Speed Steel Two Flute Downcut. You can see the purchase page here. As this was my first cut, I had to understand the definitions and the different cutter parameters to build the tool in fusion.

For the High Speed Steel Two Flute Downcut I have the parameters are:

CED: 1/4
CEL: 1
SHK: 1/4
OAL: 3

Here are some terms that helped me:

CED: CED is abbreviated for cutting edge diameter or the width of the cut the tool should make through the work piece. CED has a tolerance in thousandths of an inch or .xxx decimal places.

CEL: CEL is abbreviated for cutting edge length and is the maximum thickness of the material it can cut. CEL has a tolerance in hundredths of an inch or .xx decimal places.

SHK: SHK is abbreviated for shank diameter and is the nominal size of the shank which should match the collet size of the spindle the tool will be used in. SHK has tolerance in the ten-thousandths of an inch or .xxxx decimal places.

OAL: OAL is abbreviated for overall length and is the total nominal length of the tool from end to end. OAL has a tolerance in hundredths of an inch or .xx decimal places.

HSS: High Speed Steel, typical applications in Non-Abrasive Plastic, Solid Wood & Aluminum where keen edges perform best. High Speed Steel tools perform well in hand routing applications where a tough core is necessary to prevent tool breakage.

Carbide Tipped: Used for a variety of applications in composite woods, hardwoods, abrasive plastics and composites plastics to hard aluminum. Limited by geometry in some applications due to the brazed nature of the tool. Carbide Tipped tools work well in hand routing applications due to the tough HSS core and hard carbide cutting edges.

Solid Carbide: Typically used for widest variety of applications including man-made board, solid wood, abrasive plastics, and some aluminum’s. Solid Carbide does not deflect allowing the tool to be fed at higher feedrates than PCD or straight insert cutters decreasing cycle times. s typically. Solid tools also have major edge keenness advantage thought only possible in HSS until a few years ago.

Chipload: Chipload is simply defined as the thickness of a chip which is formed during the machining of a material. Chipload is critical because if the chip is the proper size, the chip will carry away the heat promoting long tool life. If the chip is too small, the heat is transferred to the cutting tool causing prematurely dulling. Too high of a chipload will cause an unsatisfactory edge finish, or part movement.

The most important reason to understand cutter parameters, is to set the correct feed rates, which is a combination of rpm and cutting speed. In order to get this right, I consulted this reference from ShopBot and read up on end mills in general at makezine. I also was able to incorporate some information from destiny tool that was helpful to verify my settings.

These links also helped:
* hardwood cutting data from Onsrud
* A great video tutorial from ShopBot

After understanding endmills, I had to get everything in the right format for the machine. I found the open sbp reference to be very helpful and the command reference also taught me how to understand the resultant g-code.

I summarized my research below:

Table

Name	SB#	Onsrud Series	Cut	Chip Load per leading edge	Flutes	Feed rate (ips)	RPM	Max Cut
1/4″ Downcut Carbide End Mill	13507	57-910	1 x D	0.005-0.007	2	3.0-4.2	18,000

You can see the final product here:

July 3, 2016 By Tim Booher One Comment