I'm manufacturing a "running boar" target for my local shooting club. The boar will have an on-board 12 V battery and drive a wheel via a wiper motor. The boar starts its run on the end of a track, runs the length of the track, and returns to the start.

SW2, 3 and 4 are on the boar, and are momentary.

Sprung contacts are to be positioned for SW1 (momentary), this is a remote switch, so only connected at the start and finish position. Pushing SW1 starts the boar run, and connectors will physically disconnect SW1 on short boar movement, say 50 mm.

The boar runs until SW2 is hit; this disconnects the motor. Inertia is expected to move the boar on a little, and I didn't want to immediately switch into reverse.

Very shortly after SW2 is hit, SW4 is hit and this reverses motor direction.

The boar travels back to the start where it hits SW3 and stops, hopefully in contact with spring loading connections of SW1.

I have added diodes to prevent feeding the motor directly from SW1 and SW4.

I'm a mechanical engineer, so would like to ask some questions.

  1. Will this work?
  2. Can I add an RC snubber in parallel with the motor? Will an RC snubber work in reverse polarity?
  3. Are there any simplifications?
  4. Do relay coils need protecting?



1 Answer 1


the circuit looks good,

The RC snubber shpould be connected at the points where the current is switched (at the isolation switch, and on the relays contacts both normally open and normally closed)

on the motor a suppression capacitor can be used to reduce EMI.

When the limit switch is activated and the relay switches back off the motor will be short-circuited so it will slow rapidly.

  • \$\begingroup\$ Thanks Jasen, So can I just check, does it matter which way around the snubber is fitted? \$\endgroup\$
    – Jeff
    Nov 30, 2020 at 10:17
  • \$\begingroup\$ it does not matter the order of components in a series circuit has no effect. \$\endgroup\$ Nov 30, 2020 at 10:26
  • \$\begingroup\$ Hi Jasen, Many thanks, your help is much appreciated. Regards Jeff \$\endgroup\$
    – Jeff
    Dec 1, 2020 at 12:56

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