Domino Robot H-Bridges: Common Wiring Problems Solved

Quick answer

Most domino robot wiring problems come down to four things: a motor pair plugged in backwards, a jumper seated one row off, a loose power or ground lead, or a channel that never worked at all. Check those in that order before you touch anything else. If the board still misbehaves after reseating every connection, stop troubleshooting and replace the H-bridge rather than keep poking at it.

A domino robot that twitches, drives in circles, or does nothing at all is almost never a mystery. The H-bridge sits between your power source and the motors, so nearly every wiring fault shows up as a predictable movement symptom. Learn to read those symptoms and you can fix most builds in a few minutes.

This guide walks through the wiring problems we see most often, what each one looks like in motion, and the exact fix. It also tells you when to stop and swap the part, because some faults are not worth chasing.

Start by reading the symptom, not the wires

Before you unplug anything, power the robot and watch what it does. A robot that drives forward when you press reverse points to swapped motor leads. A robot that spins in place usually means one motor channel is dead or unpowered. A robot that does nothing at all suggests the H-bridge is not getting power or ground. Each symptom narrows the fault to a specific set of pins, which saves you from reseating the whole harness.

Write down what you see, then match it to the diagnosis table below. This keeps you from fixing a problem that does not exist and creating a new one in the process.

• Power the robot before touching any connector so you have a baseline symptom.
• Note whether the fault is direction, one side only, or total silence.

Reversed motor leads: the most common domino robot wiring problem

If the robot drives backward when it should go forward, or spins instead of going straight, one motor pair is almost certainly plugged in with its two leads swapped. The H-bridge reverses current direction to change motor direction, so swapping the two output leads flips that motor's behavior. This is the single most frequent h-bridge wiring problem, and it is also the easiest to fix.

Power down, swap the two leads on the affected motor channel, and test again. Do not swap the input signal wires, only the motor output pair. If the robot now drives correctly, you are done. If it still spins, the problem is not the motor leads and you should move to the next check.

• Swap only the two motor output leads, never the signal or power inputs.
• Retest forward and reverse before moving on.

Loose or off-by-one jumpers

A jumper seated one row off looks perfectly fine but sends the wrong signal to the H-bridge. This produces erratic behavior: the robot may stutter, respond to only one direction, or ignore commands entirely. Wiggle each jumper gently. If any one moves, reseat it fully until you feel it click into the header.

Check the signal, power, and ground rows one at a time rather than all at once. If reseating fixes the symptom, run the robot through a full forward, reverse, and turn cycle to confirm the fix holds under movement and vibration.

• Reseat one row at a time so you know which connection was the culprit.
• Run a full movement cycle after each reseat to confirm the fix.

Power and ground faults that look like a dead board

When the robot does nothing, the H-bridge may simply not be powered. Check that the battery or power source is charged and that the positive and ground leads are firmly seated at both ends. A ground lead that looks connected but is not can make the whole board appear dead even though the motors are fine.

If you have a multimeter, confirm voltage at the H-bridge power input. No voltage there means the fault is upstream in the power path, not in the H-bridge itself. Restore power first, then retest. Do not replace the H-bridge until you have confirmed it is actually receiving power.

• Confirm voltage at the H-bridge input before blaming the board.
• A missing ground can mimic a completely dead board.

When to stop and replace the H-bridge

Some faults are not wiring problems. If one channel never worked from the first build, or if the board gets hot, smells, or behaves differently every time you power it, the H-bridge itself is likely damaged. Repeated reversed connections or a short can kill a channel permanently, and no amount of reseating will bring it back.

At that point, stop troubleshooting. Continuing to power a damaged board risks damaging the motors or the controller too. Replace the H-bridge and rebuild the wiring carefully, double-checking polarity before you power up again.

• A channel that never worked is a hardware fault, not a wiring fault.
• Heat, smell, or inconsistent behavior means replace, do not repair.

Keep a spare on the bench

If you build often, keeping a spare Hack Pack Stand-Alone Robot or a spare H-bridge on hand means a failed board does not end your session. It also lets you swap a suspect board into a known-good build to confirm the diagnosis in seconds.

For builders who want a second robot to test against, the Laser Tag - Light Collimation kit runs on the same Hack Pack platform and gives you another working board to compare against when something misbehaves. That comparison is often faster than any meter reading.

• A known-good board is the fastest diagnostic tool you own.
• Swap, do not guess, when you suspect a dead channel.

H-bridge wiring diagnosis table

• Drives backward or spins in place: One motor pair is plugged in with its two output leads swapped, so the H-bridge reverses that motor's direction. Power down, swap only the two motor output leads, and retest forward and reverse. If it still spins, move to the next check.
• Stutters or ignores one direction: A jumper is seated one row off or is loose in the header, sending the wrong signal to the H-bridge. Reseat signal, power, and ground rows one at a time and run a full movement cycle after each. Stop when behavior is consistent.
• Completely dead, no movement: The H-bridge is not receiving power or ground, often because a lead is loose or the battery is depleted. Confirm voltage at the H-bridge input. If voltage is present and the board still does nothing, stop and replace the H-bridge.
• One channel never worked from the start: A damaged or dead channel on the H-bridge itself, not a wiring fault. Stop troubleshooting and replace the board. Do not keep powering a suspect H-bridge.
• Board gets hot or smells: Internal damage from a short or reversed connection. Disconnect power immediately, replace the H-bridge, and recheck polarity before powering up again.

Parts that help with domino robot wiring fixes

• Laser Tag - Light Collimation: This is a Hack Pack Toys kit that runs on the same Hack Pack platform as the domino robot build. Having a second working Hack Pack board lets you swap parts and confirm whether the fault is in the H-bridge or elsewhere in your build.
• CrunchLabs Logo Hoodie (Black): The hoodie is part of the CrunchLabs creator community, made for builders who spend time at the bench. Long wiring sessions mean leaning over a workbench; a comfortable layer keeps you focused while you trace connections.

Work through the symptoms in order, fix the simplest cause first, and stop when the board shows signs of real damage. Most domino robot wiring problems are a swapped lead or a loose jumper, and both take under a minute to correct.