For a college project I'm trying to make a set of legs that move with the user. The idea is to use the voltage that is made from a small motor when the output shaft is moved, pass that through an op-amp, and then use that to power the motion of the legs. This means that when the user lifts there legs it will power as long as they are doing so and then when they lower it will do the same.

The problem I have is that I can't figure out a way to the voltage high enough to power a decent size motor so I have altered the resistor values as much as I can and figure I need VCC and VDD is there a way of creating VCC and VDD from a battery (In my op-amp practical I used power supply which was attached to the mains) I want to make it as portable as possible. Am I out of my league here or there something I am missing

Below are the screenshots of my System so far I measured just over 5mV coming from the small motor (3v) when I moved the shaft.enter image description here

  • \$\begingroup\$ And what powers your op-amp? There is no such thing as free energy. \$\endgroup\$
    – Lior Bilia
    May 1 '20 at 16:42
  • 1
    \$\begingroup\$ your title says Using a motor signal to power a op amp to power another motor ... that is an incorrect train of thought ... it should be Using an op amp to amplify a motor signal to control another motor \$\endgroup\$
    – jsotola
    May 1 '20 at 17:16
  • \$\begingroup\$ are you hoping to use the small motor as a power source? are you hoping to use an op amp as a device which multiplies the energy available from the motion of the small motor? \$\endgroup\$
    – Ocanath
    May 1 '20 at 19:09
  • \$\begingroup\$ Yeah using the VCC and VDD \$\endgroup\$ May 1 '20 at 20:47
  • \$\begingroup\$ I'm sorry to say this but I really do think you might be out of your league with this project. You have some deep fundamental flaws in your understanding of how op amps work, conservation of power, how to control a motor electrically, and based on your reply to the answer below, angular encoders.I would encourage you to build your understanding with simpler projects first before trying to embark on this project idea \$\endgroup\$
    – Ocanath
    May 2 '20 at 19:55

You'll need some kind of control system, one problem that I see is the bigger motor also generating voltage in the smaller motor and creating a positive feedback loop. Because of this control theory will be needed to find a closed loop system response that is stable.

In my mind it would be better to use an encoder and use the position output from the encoder to control the larger motor.

If you do need an opamp to control the motor (also look into PWM control), the output can be boosted with a bipolar output stage

  • \$\begingroup\$ I just need the encoder to have 3 outputs one for up one for down and one for neutral if I used a motion encoder connected to a controller would that work? \$\endgroup\$ May 1 '20 at 18:07

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