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Suppressing Motor EMI

I'm building a Khaos for a client. It runs on 3S and has an ammo counter from triggered by an IR gate. The counter is running on a separate PP3 battery so it's isolated from the blaster's power supply.

All works as it should but the counter doesn't register reliably when the blaster is firing. The code seems to be fine and the counter can 'see' the balls. I tried it on 2S and it is better so I assumed the issue was with the rate of fire. To test this theory, I loaded 25 balls into a length of pipe and blasted them all through the IR gate with my air compressor. The counter registered the shots so it's not the ROF that's the problem.

This leaves me with the motors and the Electromagnetic Interference (EMI) they produce. I've placed a ferrite bead on the ribbon cable between the IR gate and the counter board which seemed to help a bit so now I'm considering adding a snubber to the motors themselves.

My question is, will a simple capacitor suffice? If so, what type of capacitor do I need? is there anything else I could try beyond encasing the counter electronics in a Faraday cage?

A capacitor across the terminals and/or from each terminal to the motor can should help reduce noise (one from each terminal to the can is better than a single cap across both terminals but all three would be better still). A capacitor across the VDD and ground near the electronics should help at that end aswell (although there should already be capacitors on the board for this purpose if the ammo counter is worth it's salt) as would an EM shield/Faraday cage.

For the motors you'll want ceramic caps of something like 0.1μF whereas I've seen caps used for this purpose on boards with values anywhere from 0.1μF to 500μF - sometimes ceramic and sometimes electrolytic.

If you can't route them further away from the motors you could also try twisting and/or shielding the individual pairs of wires to the IR diodes/other board components.

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