How to Build the Domino Robot: H-Bridges Explained Step by Step

Quick answer

Building the Domino Robot is a matter of assembling the frame, then wiring the H-bridge so the motors can spin both ways. Follow the kit instructions in order, keep battery power off until every connection is checked, and test one motor at a time. If a wheel spins backward, swap that motor's two wires rather than rewiring the whole board.

The Domino Robot is a build that rewards patience more than speed. Most of the frustration people hit is not in the frame or the wheels; it is in the H-bridge, the small circuit that lets a motor run forward and backward. Once you understand what the H-bridge is doing, the wiring stops feeling like a guessing game.

This guide walks through the build in the order that keeps mistakes easy to catch. You will assemble the body, wire the H-bridge, connect the motors, and test before you run the robot. Each step includes a checkpoint so you can confirm things work before moving on. The same habits apply to other CrunchLabs builds like the Robot Ranger or the Repeating X Bow.

What an H-bridge actually does

An H-bridge is a simple switch arrangement that lets current flow through a motor in either direction. Picture four switches around a motor in an H shape. Close two switches one way and the motor spins forward; close the other two and it spins backward. That is the whole idea. In the Domino Robot, the H-bridge is what lets the robot drive forward, reverse, and turn instead of only rolling one way.

For kids, the useful mental model is a set of gates. You are not changing the motor; you are changing which gate the electricity goes through. That is why a motor that spins the wrong way is usually a wiring issue, not a broken part. If you keep that picture in your head, the H-bridge wiring guide below will make more sense as you go.

• Checkpoint: point to the H-bridge board and name which side connects to the battery and which side connects to the motors before you plug anything in.
• Common mistake: assuming a motor is dead when it is only wired backward.

Gather your parts and clear a workspace

Lay out every part from the kit before you start. You want the frame pieces, wheels, motors, the H-bridge board, the battery holder, and the wires within reach. A clean, flat surface matters more than a big one. Small screws and jumper wires disappear fast on carpet, so a tray or a shallow box lid helps keep everything contained.

Read the kit instructions once from start to finish before you assemble anything. You are not memorizing them; you are looking for the order of operations. Knowing that the motors get mounted before the H-bridge is wired, for example, saves you from having to take the frame apart later. This is the same approach that works for any CrunchLabs build, from the Flywheel Motorcycle to the Domino Catapult.

• Checkpoint: every part is accounted for and the instructions have been read once through.
• Common mistake: starting to assemble before checking that all parts are present.

Assemble the frame and mount the motors

Build the frame first, following the kit's order. Attach the motors to their mounts before you tighten anything down fully. You want a little wiggle room so the wires can be routed without strain. Once the motors sit flush, snug the screws. Do not overtighten; plastic mounts can crack, and a cracked mount is harder to fix than a loose screw.

Route the motor wires toward where the H-bridge will sit. Leave a little slack so you can move the board into place later. If the wires are pulled tight now, you will fight them when you connect the H-bridge. Think of this step as setting up the plumbing before you install the faucet.

• Checkpoint: both motors are mounted and the wheels spin freely by hand.
• Common mistake: overtightening screws and cracking a mount.

Wire the H-bridge to the motors

Connect each motor to its output pair on the H-bridge. The order of the two wires on a single motor determines which way it spins, so it does not matter which wire goes to which terminal as long as you keep track of it. What matters is that each motor gets its own pair. Do not cross wires between the two motors; that is the most common cause of a robot that only turns in circles.

If your kit uses a terminal block, loosen the screw, insert the wire, and tighten it down on the bare metal, not on the insulation. Tug gently on each wire after tightening. A wire that slides out now will cause a mystery problem later, and intermittent connections are the hardest kind to diagnose.

• Checkpoint: tug each wire gently. None should pull free.
• Common mistake: clamping down on insulation instead of bare wire.

Connect power and the control signals

With the motors wired, connect the battery holder to the H-bridge power input and the control wires to the board that sends signals. Keep the battery switch off or the batteries out during this step. Polarity matters here: match positive to positive and negative to negative as shown in the instructions. Reversing power at this stage can damage the board, and that is a much bigger setback than a backward wheel.

Once the power and signal wires are in place, do a visual sweep. Look for stray wire strands touching neighboring terminals, and confirm that no bare wire is bridging two connections. This thirty-second check prevents most of the smoke-and-sparks moments that make builders nervous.

• Checkpoint: power polarity matches the diagram and no bare wires are touching.
• Common mistake: leaving batteries in while wiring the power input.

Test one motor at a time

Power on and test a single motor before running both. If it spins, note the direction. If it spins the wrong way, power off and swap that motor's two wires at the H-bridge. Do not rewire the whole board. Then test the second motor the same way. Running one at a time isolates problems so you always know which connection is at fault.

If a motor does not spin at all, check three things in order: battery charge, wire seating at the terminal, and signal wire placement. Most no-spin problems are one of those three. A motor that twitches but does not turn usually points to a weak battery rather than a wiring fault.

• Checkpoint: both motors spin, and each one spins the direction you expect.
• Common mistake: testing both motors at once and not knowing which one failed.

Run the robot and fine-tune

With both motors verified, set the robot down and run it. If it veers instead of driving straight, one motor is likely reversed relative to the other. Power off and swap that motor's two wires. If it drives straight but turns weakly, check that the wheels are seated firmly and that nothing is rubbing against the frame.

This is also the moment to think about the H-bridge as a reusable idea. The same forward-reverse control shows up in the Robot Ranger and the Repeating X Bow, just applied to different mechanisms. Once you have wired one H-bridge, the next one goes much faster because you already know what to check.

• Checkpoint: the robot drives straight and turns in both directions.
• Common mistake: assuming a veer is a motor problem when it is a reversed wire.

Build steps at a glance

1. Step 1: Read the instructions end to end: Skim the full kit manual before touching a single part so you know the order and where the H-bridge fits. Checkpoint: you can describe the build order out loud.
2. Step 2: Lay out and inspect all parts: Sort frame pieces, motors, wheels, the H-bridge board, battery holder, and wires on a flat tray. Checkpoint: nothing is missing and no part looks damaged.
3. Step 3: Assemble the frame and mount the motors: Build the frame, attach the motors, and snug the screws without overtightening plastic mounts. Checkpoint: wheels spin freely by hand.
4. Step 4: Wire each motor to its own H-bridge output pair: Keep the two motors on separate output pairs and tighten terminals onto bare wire, not insulation. Checkpoint: a gentle tug does not pull any wire free.
5. Step 5: Connect power and control wires with batteries out: Match polarity to the diagram and sweep for stray strands bridging terminals before applying power. Checkpoint: no bare wire touches a neighboring terminal.
6. Step 6: Test one motor at a time: Power on, test a single motor, and swap that motor's two wires if it spins the wrong way. Checkpoint: both motors spin in the expected direction.
7. Step 7: Run the robot and correct any veer: Drive it, and if it pulls to one side, reverse the slower or backward motor's two wires. Checkpoint: the robot drives straight and turns both ways.

Parts and builds that pair well

• Domino Robot - H-Bridges: This is the Hack Pack Toy built around H-bridge motor control, listed at USD 39.98 with a catalog comparison price of USD 79.95. It is the exact kit this guide walks through, so the steps map directly to the parts in front of you.
• Robot Ranger - Time Of Flight: Another Hack Pack Toy at USD 39.98 with a catalog comparison price of USD 79.95, focused on time-of-flight sensing rather than H-bridge motor control. A good next build if you want to reuse your wiring habits while adding a different kind of sensor.
• Repeating X Bow - Latch: A Toys-category build listed at USD 16.48 with a catalog comparison price of USD 32.95, centered on a latch mechanism. Shows how the same motor-and-switch thinking transfers to a mechanism that stores and releases energy.
• CrunchLabs Logo T-shirt (Black): Apparel listed at USD 14.98 with a catalog comparison price of USD 29.95, available in multiple sizes, and described as a way to show you are part of the CrunchLabs team of creators, artists, scientists, and engineers. A practical option if you want shop-safe clothes for messy build sessions or a gift for a young builder.

The H-bridge is the part of the Domino Robot that turns a pile of parts into a machine that can move in two directions. Build slowly, test one motor at a time, and treat every backward wheel as a wiring clue rather than a failure. Once you have done it here, the same forward-reverse thinking will show up in almost every robot you build next.