ultrablaze
Hello,
We are a team of engineering students working on a robotics project about to participate in a robotics competition. We have only a few days to finish up and we are currently having a problem with the DC motors for our second robot. We are trying to drive two DC motors to move the robot using PWM signals sent from an arduino card. Using an H bridge we are able to deliver PWM signals with a controllable duty cycle from the arduino card, which are -24V/+24V. Thus in theory at 50% the motors are at 0V, and close to +24V or -24V at 100% or 0% respectively by average voltage. When the cables we use to connect to the motors are checked with an oscilloscope, the signals are fine and as expected.
When we connect our motors to them, the signals are significantly degraded (can tell its supposed to be a PWM cycle but it's not as clean as before) and the over all average voltage is lower then what we had before. In this situation, with the robot lifted off the ground and the wheels not touching anything, the motors seem to turn fine, at a decent speed etc. However the torque seems quite low, not as much as we should be getting from our motors.
The real issue is as soon as we place the robot on the ground, the wheels can not move. In this situation the expected rough 21.5V average voltage we measured previously drops to around 3 to 3.2V. If observed at this point the PWM cycles are totally degraged, can barely make out a square signal, and the average voltage is around 3V.
We can not figure out what is causing this problem. When we connect our generator directly to the motors without going through our electronic card, as soon as we go above 5V on a motor the wheel is able to move the robot easily, and at a decent speed above 7 or 8V. What adds to our confusion is another team last year used these motors and drove them with a -24/+24 V PWM signal in the same way as far as we know.
We are totally stuck, and are available to answer any questions or provide any data that could help debug our issue.
Thanks for any help!
We are using the 2322G/GP022C motors from this datasheet, the last one (24V/1621) : http://store.mdpmotor.fr/media/documents/pdf/2322g_gp022c.pdf
Is milliis() really an issue? We use it once or twice, but I thought only delay() really messed with timing, we will try without it later and see. However I doubt that is the problem, when we move the robot forward without powering the motors the encoder results are extremely accurate despite using a Millis wait cycle to transmit data to our screen.
These same encoders have been used several times before with an arduino mega with no problems as far as we know. When we roll our robot forward by hand the precision is perfect, over a 30 or 60 cm distance it's off by a couple mm. The arduino has no problem picking up the interruptions accurately So really there seems to be some issue with the way we are calling interrupts when we are trying to drive the motors, or some kind of interference from powering the motors