| Electronics > Projects, Designs, and Technical Stuff |
| DC motor control response time |
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| Achu:
Hi I'm working on a project which uses two motors which spin at slightly different speeds which are derived from a reference speed which may change very frequently. I plan to use separately excited dc motor. Due to the rapid variation of rpm it requires a fast speed of response, say a settling time of .1 to .5 seconds.My questions is if that is possible to attain such high speed of response? If so I would like to know what method(s) to use. Thank you. |
| T3sl4co1l:
You need to obtain the electro/mechanical equivalent of the motor. https://www.modularcircuits.com/blog/articles/bridge-to-the-far-side/motor-modeling/ https://www.sciencedirect.com/science/article/abs/pii/S0142061512003262 (this kind of thing, but an actually-accessible article ofc) Tim |
| pwlps:
I once did it with a simple PID controller (to be more precise, students did it). There are (at least) two factors limiting the response speed: 1) the inertia of the motor itself: the settling time won't be shorter than the mechanical response time of the motor which itself depends on the available (or rated) drive current/voltage, you might easily get 0.1s for a very small and light motor but for a bigger one you will first need to measure the response time with the PS you are going to use; 2) the update rate of the rpm measurement: I was using a simple IR slot sensor giving the rpm once per cycle, this was enough at high rpm (100Hz) but at low rpm it limited the usable bandwidth and gain of the PID, for low rpm you would need a more precise rotary encoder. |
| jbb:
Watch out for backlash in any gearboxes etc. Suddenly slowing (or worse, reversing) the motor can lead to quite a lot of teth banging into one another. |
| Zero999:
Also be careful when breaking, as the motor controller will inject the energy back into the power supply which can blow up the controller, unless there somewhere for the energy to go to. If the energy can't be stored in a capacitor or battery, it will need to be dissipated in a resistor. Another thing which can help increase the response time is to use a higher supply voltage, than the motor can continuously take, which won't cause any harm, unless it's applied for long periods of time or is excessive, causing the commutator to arc over. |
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