I am trying to design a mechanical system which will allow ~2mm of movement (against only its own friction of movement) when an electrical signal from logic circuit is given. Think: a coin suspended from the ceiling by wire, dropped when an arduino drives logic high.

A simple solution would be to have a small solenoid with the wire looped over the core set up so that when the voltage is applied the core retracts into a housing forcing the wire off the core and to fall. The problem with this is that most solenoids require fairly high currents (I have a 'small' 5V solenoid which requires ~1.1A to retract) and are quite bulky.

Another solution I've considered is to use muscle wire, which contracts ~3% upon electric heating. You could have a spring loaded bolt that is pulled back but the datasheet suggests that 320mA would need to be applied for ~1s to a 66mm wire to gain 2mm of travel — this is viable but I'm wondering if there's something better?

I don't need any particular speed to drop my coin (a second's lag would be fine) but the lower power and the smaller the better. Generating mechanical movement from electrical impulse is generally not a low-power endeavour, but am I missing anything simple?


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    \$\begingroup\$ Does the device need to be self-resetting? \$\endgroup\$ Sep 27, 2017 at 21:50
  • \$\begingroup\$ RC miniature servo. \$\endgroup\$
    – user16324
    Sep 28, 2017 at 10:11

1 Answer 1


I think you could strip down a small relay and use the actuator movement to withdraw a pin or similar. You don't need as much force as is generated by a solenoid if you are only overcoming the friction caused by the weight of a coin.

  • \$\begingroup\$ I'll see if I can find any relays that only require a little current to trigger! \$\endgroup\$
    – JP.
    Sep 30, 2017 at 7:22

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