servo

    how can i build my own servo? I need a stronger servo than you can by, and want to know how i would build my own. it needs to lift 30-40 kg with a 17cm arm. I expect i need about a 200 watt motor just to power this, and possibly bigger. but i have no idea where to get the controls for this. a normal servo only has 0,5 amps, and i probably need about 40 amps.

    Ive been playing with the idea of building a motorcycle for robot wars, but the only way to stear it would be weight transfer of the batteries, which must be able to rotate 180°. If you have another idea how i might acomplish this without servos, then i would also like to hear it. just keep in mind that it must be fairly easy to control, and half way fast.

    try, try, and try again

    hi bryan - ich weiss nicht, ob es nicht einfacher + billiger ist, einen linearvorschub (gibt es z.B. für Krankenhausbetten etc.) mit einem hebelsystem umzubauen. das hängt aber ziemlich mit deiner bauform zusammen, d.h. die frage ist, ob du genug platzt dafür hast und ausserdem ist die geschwindigkeit evt. nicht hoch genug ...

    gruss: frank

    Hi Bryan,
    the lowest-cost variant to build a crude high-power servo is as follows:

    You need a normal, cheap, used RC servo, 2 small (e.g. 5V) relays, and 2 more powerful relays. You also need a motor which is geared down significantly (to app. 60 to 120 rpm max.). The small relays have to be "directional" i.e. have to have diodes integrated, or you have to add them.

    The rc servo acts as the servo controller.
    The small relays trigger the big relays.
    The big relays trigger the geared-down motor, which then acts as a crude servo motor.

    First you must remove the gears from the rc servo so the tiny motor can spin freely.

    The 2 x 5v relays must have diodes so they have negative and positive inputs.

    Join them together like this:

    pos + of one relay to neg. - of the other and visa versa.

    You now have a pair of connections one + - and the other - +

    Take a wire from each pair to the motor connections of the small motor inside the servo. You now have two relays that will energize when the servo is activated - one of them will pull in when the servo motor spins clockwise and the other will pull in when it spins anti-clockwise.

    You now have a " left " and " right " relay.

    Now by further slaving off via the two larger relays a bigger motor can be actuated just clockwise and anticlockwise, no set off position.

    Now to make it self center and to a degree proportional (but a bit notchy) you must remove the tiny pot inside of the rc servo from the servo (unsolder the pot from its connections in the servo and extend the wiring) OR just disconnect it and wire in another pot externally.

    This must be connected to or driven by the motor output shaft BUT the speed of rotation of the pot should be limited to about 60- 120 r.p.m. or it will hunt i.e. run past its OFF position miss it and then return and do exactly the same ad infinitum.

    This is a crude and not a very "fine" servo, but it should work and be quite inexpensive. And best of all - simple! No electronics, no PIC programming etc.

    With a little more wiring, you might even be able to use car starter solenoids as relays.

    Regards,
    scotchco

    =) thanks for the help!!! everyone around here thinks i´m a little crazy. Ive got all the other problems work out with the motorclye robot, that was the only part i was haveing alittle trouble with. maybe ill actually get this thing running by next year. "???" I still have alot of planning to do before i start.

    @frank, thanks but i dont think it will work, because i wont be able to see the batteries, they will have to be enclosed in the frame. and without seening where they are at, i´d never get the control that i would need. it would only work if i could hook the sensors from a relay to them. and i couldnt figure out how to get the 180° from the linearvorschub, and i need that, and probably alitlle more. the room and the speed would be no problem though.

    try, try, and try again