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Would like to convert a baby bouncer (like this one), which requires continuous manual effort to rock it, into one that use electro-mechanical means to auto-bounce. However, my aim is to make these on the cheap (as all of my other projects so far have). So I am on the look out for alternative design approaches or parts.

My idea is to place a low RPM, high torque (unable to quantify, since I've not work with DC motors, beyond the ones found in small toy cars etc.), DC motor (brushless?), which periodically winds (like a winch) pulling the bouncer seat to the low-position, and then (here is where, I am not sure, it is right or feasible to do with standard DC brushless motor), just de-energise the motor, for the bouncer to bounce up, and have few naturally dampened oscillations (bounces), and then repeat the process.

Is the above approach correct ? Will de-energising the motor, and the rapid unwinding in opposite direction, make it act like a dynamo and feed current back into the circuit ? Can that harm the motor ? Will stepper motor be a better approach ?

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  • \$\begingroup\$ There's a really good chance that such devices are DESIGNED to require continuous manual effort for safety reasons. Before you put too much time, effort, and money into this idea, if your goal is a consumer product you might want to look over consumer safety issues in such devices. It sounds to me like it might be an expensive recall waiting to happen. \$\endgroup\$ – Scott Seidman Sep 7 '12 at 22:47
  • \$\begingroup\$ @ScottSeidman, good point and thanks for bringing this up. My desire for this solution stems from a real personal need, and commercialization is a far-cry. Since this involves my own baby, you can bet I'd be careful to the extent of over-engineering safety. However, I am at loss as to what all safety implications the thing might have. My idea shouldn't involve anything more than 12VDC, and definitely not high rpm motor. As for torque, I am happy to work with a motor, which provides, just enough. \$\endgroup\$ – icarus74 Sep 10 '12 at 8:24
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How about an alternative approach? Use a solenoid.

Solenoid baby rocker

You only need to inject a little bit of energy into the system to get it oscillating. Wind up a big coil. Attach a steel rod to the back of the rocker, and when you energise the coil, it will pull the rod into it. Switch the current on and off, and you'll cause the rocker to bounce up and down. If you time it correctly, you'll achieve resonance. The best way to do this is to have a little sensor to detect the position of the steel rod. Energise the coil when the rod is all the way out of the coil, and de-energise it when it's all the way in. This has the advantage that it'll be quiet.

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  • \$\begingroup\$ I have zero experience with solenoids, but couldn't such a solution be pretty rough/"bumpy"? I.e. the solenoid pulls too fast? \$\endgroup\$ – exscape Sep 7 '12 at 21:22
  • \$\begingroup\$ @exscape - Not if it's very gentle. The idea is to build up the oscillation gradually. It's a non-contact mechanism. The steel should be allowed to pass through the coil without touching anything, or banging into anything on the other side. \$\endgroup\$ – Rocketmagnet Sep 7 '12 at 21:37
  • \$\begingroup\$ Like the idea Rocketmagnet, however, echoing @exscape's concern, most solenoids I've seen, have an instant push-pull action. Can't imagine how to make it work "gently" without things like "dampening springs" etc. I think the key is in "building up oscillations gradually", but I'm probably missing the physics of how to go about this. \$\endgroup\$ – icarus74 Sep 10 '12 at 8:27
  • \$\begingroup\$ @icarus74 - You see the instant action because the mass of the plunger is low compared to the force. If you attach a baby to the plunger, then you have a very high mass. Now the acceleration will be quite slight, and you will achieve a gentle rocking motion. Trust me on this. \$\endgroup\$ – Rocketmagnet Sep 10 '12 at 8:56
  • \$\begingroup\$ Thanks Rocketmagnet. This is starting to make sense (to me). Would you suppose a 12VDC direct-action solenoid (the small ones used in fluid control valves / irrigation valves), work ? If you have a specific part in mind, do let me know. \$\endgroup\$ – icarus74 Sep 10 '12 at 13:36

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