Need some help with a design for a powered eccentric cam toy

Hi everyone! I’d really appreciate some expertise on the best way to go about building the below, if you wouldn’t mind:

My idea is a toy / moving sculpture, based on those eccentric-cam toys (the ones with a set of rods in a row, following a set of eccentric cams on a drive shaft, typically cranked by hand: they make a little scene above move).

I’d like to make such a thing but have the individual “rods” driven by electronics so that each one is capable of independent (accurate) movement to pretty much any height.

My thoughts so far:

  1. Is that going to involve a small stepper motor or similar for each rod?
  2. Is there some kind of linear actuator capable of this sort of thing? The total travel distance required for each one is probably in the range of around 3in at most.
  3. Is there any way to save on the number of “driver” mechanisms beyond having one per rod? I have no idea how it would work but I’m almost wondering if there’s any kind of multiplexing mechanism theoretically possible??

Any thoughts welcome, and thank you!

  1. as described? it’s the quickest to build, but might not be necessary
  2. 3in? with precision within the range? worm gear (slow) or rack and pinion (can be very fast)
  3. depends…

if the motions are continuous (EX:ship bobbing on the sea) you can probably do it all with one motor, even if the rods move at different rates (just a matter of gearing), likewise if it’s fixed positions in a set sequence (potentially more complex gearing). any particular part that is independent (not sequenced or continuous) will require either a separate motor, or some sort of clutch (so it only engages when you want)

basically, for any sequenced/continuous motions you only need one motor. for anything that fits that description but is occasional engagement, a clutch mechanism will be needed (either automatic, manual). anything requiring independent manual control gets it’s own motor.

for clutches, it’s probably easiest to do those electronically, via limit or reed switches and a separate motor, but they can be done purely mechanically (cams, pinwheels, cones, etc)

In theory it’s possible to do everything from one motor, old time clockwork animatronics certainly did, but the cost there is complexity (and precision, and fragility) of the gearing. using one motor for sequenced/repetitive motions (with optional cluthes) and one or more for independent motions makes for a nice balance in build complexity

Thank you, that was really helpful. I have two comments / questions:

  1. Could you elaborate a bit or link me to the kind of thing you mean around clutch mechanisms from reed switches etc?

  2. I think really my requirement is actually arbitrary independent motion: there’s no fixed sequence ahead of time because the intention of the project is the ability to make arbitrary patterns. I think what you’re saying is that that pretty much means one driver per rod?

for the first question, a reed switch clutch you could have part of a gear covered with a magnet, when the gear comes around it will trigger the reed switch, which can power something to engage with the main motors gear train such as an electromagnet that moves a gear or arm or rod, or even a a separate motor that does.

for completely arbitrary positions (essentially random chance of of any next configuration) a motor each is probably what you are looking at, unless you are willing for each to move one at a time (then it would be something like one to drive, and one to engage, but you’d need to both lock them when not engaged, and track their position so you know how much to move them

Motors with rotary encoders might be an option for the one each scenario. they’re usually cheaper than steppers, but usually only rotate one direction, and require a bit more wiring/code