I would like to have a small battery operated motor controlled by a microprocessor with the following: 1 - battery operated, so small current draw when not used. 2 - once positioned, would hold the position 3- could operate in either direction 4 - could operate with 3.3 volts or less (6 is possible, but would rather 3.3) 5 - would need to pull a cable up to 3 inches (either by winding on a pully or a linear pull)
Unknowns: how much torque is needed. would experiment.
I know it would work with a stepper, but the current draw to hold the position is not desired.
This would be used to replace a shifter cable on a bike. the device would operate in close proximity to the derailer and only pull the cable a short distance. The microcontroller would operate on Bluetooth and would operate from my phone initially.
August 25, 2020
If you are looking for a latch movement (set/reset), you can explore the use of a Nitinol wire ( muscle wire). It is a memory metal wire which, basically change its modulus of elasticity ( Young modulus ) from the one of lead, when cold (relatively speaking, that is), to the one of aluminum, when hot (again, relatively speaking). Since its electrical resistance is high, that change of temperature is easy to get by passing a small current in it.
To give an image, imagine that you suspend a weight W from a cable, then, if the cable is a weak spring, the deformation is great, but for a strong spring, the deformation is small. Change the strength of the spring, from a weak one to a strong one, and the weight can either raise, either fall back, like ... a latch. More details at musclewires.com or on Youtube where you could see robots and hands (of automaton) build on that motorless principle.
August 26, 2020
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