Hi Jared,
I believe I recall you are using a KMotion board, DC Servos, and KMotionCNC.
No the speed is not directly controlled by the supply voltage, however the supply voltage limits the maximum speed that the motor can move. The speed should be determined by the motion trajectory. For Rapid moves (G0) in KMotionCNC the max speed, acceleration, and jerk are determined by the parameters Vel, Accel, Jerk in the KMotion Step Response Screen and are in units of counts. For coordinated moves (G1,G2,G3, etc..) the max speed is set in the KMotionCNC Tool Setup|Trajectory Planner screen in units of inches.
If the planned trajectory moves faster than the possible motor speed then the position will fall far behind. Normally we would have the Max Following error set to a small value and as soon as we began to fall behind by a significant amount the system would Disable with a following error fault. However if you have the Max following error set to a huge value, then the position will continue to get farther and farther behind until the trajectory comes to a stop. Then the position will finally be able to catch up and depending on the servo tuning may or many not violently overshoot.
You can use the Step Response Screen to understand exactly what is going on. Set the Size, Vel, Accel, and Jerk parameters to be the same as the type of move you are making in the GCode. If you are making G0 moves in GCode then the Vel, Accel, and Jerk parameters will be the same. Otherwise you will need to set these to the KMotionCNC trajectory planner settings multiplied by your counts/inch. Since coordinated motion doesn't limit the System Jerk, set the Jerk to a big value (ie 100X the acceleration value) to simulate a motion trajectory with unlimited Jerk.
Now Set the Plot Type to Command, Position, Output vs Time and push "Move". The Blue plot will be the desired motion trajectory. The Red plot will be the actual motor motion. The Green plot will be motor voltage commanded by the Servo (in PWM counts where 255 represents your full power supply voltage). If you can see that the red plot is not keeping up with the blue plot while the green plot is "pegged" at max of around 255 then this indicates that your velocity settings are too high for the motor and power supply you are using.
Please post a screen shot of your Step Response, Filter, and Configuration Screens.
Also If you increase your power supply voltage from 12 to 55 volts, besides increasing the possible speed, this will also increase the servo loop gain by ~ 4.5X and may make your servo unstable. So reduce your PID gains by 4.5X to have the same response.
Regards
TK
| Group: DynoMotion |
Message: 300 |
From: Jared Tesmer |
Date: 4/12/2010 |
| Subject: Re: Speed |
Before I go any more indepth into the motor tuning I have to ask. Should I mount the motors to my axis before trying to tune the system? |
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| Group: DynoMotion |
Message: 301 |
From: Tom Kerekes |
Date: 4/13/2010 |
| Subject: Re: Speed |
Connecting your system to the motors will of course change the tuning. Adding mass will have the effect of reducing the loop gain (for the same motor effort, the encoder will move less).
In some cases it can add resonances that can make the system go unstable. (that is something the Bode Plot can be useful to help understand).
But I would make sure that I had reasonable motion before connecting the motors to the system.
TK
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