Hi Inkmark,
The problem at low speed could be a number of factors.
If at low speed the motor turns unevenly - i.e it struggles round part of the turn then jumps or speeds up then the root cause of the problem is probably some asymmetry in the drive train or a tight spot. You are more aware of the effects of this at low speed because you can actually see the variation in speed. The problem is worse at low speeds than at high speeds because the torque of the motor is much less and so you get a greater loss of speed as it goes through the tight spots - just like you cranking something with a tigt spot - it gets easier to maintain a smooth speed the faster you crank because the inertia of the object helps.
The best choice of ESC probably comes down to trial and error - finding one which suits the characteristics of you setup the best - see if you can borrow a number of types and see what does the job the best.
<!!!!!! SCIENCE ALERT !!!!!!>
Here I am going to disagree with the illustriuos Stallspeed. Experimentally I have found that a high frequency ESC is not the best choice for a slow running motor. The speed of a motor driven by an ESC is determined by the mark-space ratio of the signal from the ESC - that is the proportion of the time that the pulse is switched on to the proportion of the time it is switched off. The greater the proportion of the time it is switched on the greater the average output voltage and the faster the motor spins.
At low speeds though, these pulses get very narrow and a second factor comes inot play - the inductance of the motor. When you put a voltage across an inductor the current is not direclty proportional to the voltage - its rate of change is (V = L.dI/dt) - so when you switch the output of the ESC on, the voltage across the motor jumps to the battery voltage but the curent does not immediately jump to its maximum value but climbs up at a rate of V/L amps per second where L is the inductance of the motor.
The maximum torque of a motor is obtained (to a first order) at maximum current - you will not achieve that maximum torque unless your ESC pulse is wide enough that the current will be able ot rise to its maximum value. If you have a High speed esc, then the pluses, particularly at low speeds are very narrow and you may not be able reach the maximum current - so you lose torque at low speeds and the effects of any tight spots in the drive train are masde worse.
THe effects of this will be seen more with large low speed motors because they have large armatures and lots of turns - therefore they have a lot more inductance and the current rises to its maximum value more slowly than with a smaller motor so the minimum pulse width required to achieve maximum current is greater. With a high frequency ESC you need to go further up the speed range to hit this point.
Wom
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Topic: Which ESC (Read 7786 times)