Im having trouble getting brushless motors in myRC car to run at the same rpm. i give one motor a signal of 180 ( making it go forward) and give the other motor a signal of 180 (for strange reasons, giving it 0 makes it go other way)
Question: does a sensored motor run at the SAME RPM at 0 and 180?
It depends exactly what pulse length 0 and 180 are mapped to and how well calibrated the ESCs are. If your ESCs have reverse then roughly speaking 0 should give full reverse and 180 should give full forward but if 0 and 180 don't correspond to the expected pulse lengths then the speeds will be a bit off. The defaults in the standard servo library are a bit wide for most ESCs.
What motors/ESCs are you using ?
Steve
slipstick:
It depends exactly what pulse length 0 and 180 are mapped to and how well calibrated the ESCs are. If your ESCs have reverse then roughly speaking 0 should give full reverse and 180 should give full forward but if 0 and 180 don't correspond to the expected pulse lengths then the speeds will be a bit off. The defaults in the standard servo library are a bit wide for most ESCs.What motors/ESCs are you using ?
Steve
If i give it a pulse of ....say 200 (so now its way above 180) will it move at max speed? I noticed that for my ESCs, i can do a max reverse when i feed it a value of 16 (it doesnt move when i give it a 15 or less). so does that mean that the max my motor can go to is 180+16)?
It's going to depend on the ESC. Many will simply do nothing if you send an out-of-range signal but some will do odd things. My guess (and I do mean GUESS) is that you've probably got a working range of something like 16 to 164 (i.e. 180-16 not 180+16).
I think I would try using a modification of the simple servo.Knob sketch with a pot and some debug serial writes so you can see the value you're sending. That way you can calibrate the ESCs so you know exactly how they respond to each value you write to them.
But if you're using the standard servo.h library to control the ESCs don't try writing a value outside 0-180. You'll find it does something unexpected if you try to write a value much greater than 180.
Steve
masterfo:
Im having trouble getting brushless motors in myRC car to run at the same rpm. i give one motor a signal of 180 ( making it go forward) and give the other motor a signal of 180 (for strange reasons, giving it 0 makes it go other way)Question: does a sensored motor run at the SAME RPM at 0 and 180?
A sensored motor ESC does not do any sort of control PID loop to maintain a specific speed, unless it was programmed specifically to do so. What it controls is power to the motor depending on the input. This does not guarantee a certain running speed.
If you calibrate both esc's the same and have identical motors and exactly the same ground conditions under each wheel it will be close. Otherwise expect variance.
In order to run a motor at a certain rpm and have it be the same for the other motor you would have to monitor the rotation speed and have a control loop to adjust the input to the esc to maintain that speed.
The control feedback can be from an encoder, the hall sensors themselves, an optical tachometer or you can even use a gyro to maintain a heading if the goal is to get a vehicle to move straight.