Power Query and Speed Control Question

9 years 5 months ago #29525529 by wakestrap
Couple of questions:
Oh and I\'m using the ax2550

1) After reading around the forums I THINK I understand but correct me if I\'m wrong. When querying for power applied to the motor, the value being returned (0-127) corresponds to the PWM duty cycle (0-100%). So If I know the duty cycle then I know the average voltage as seen by the motors (50% duty cycle with a 12V supply means the motors see 6V). If I know the average voltage as seen by the motors and I query the amps consumed by the motors then I can calculate the power consumed in watt\'s. Using that I can get the Amps consumed from the supply. Is this correct?

2) I\'m using the controller to control a winch type setup. When lowering, the load will pull the motor faster then I want it to lower, this causes back EMF which is sent to my supply which isn\'t happy about it. I realize I can filter that back EMF with a battery or a power dumping circuit but I\'d rather just control the lowering speed. In closed loop mode will the controller take care of this? If so what exactly is it doing? I\'d rather not run in closed loop mode but have my uC take care of it. I could query the battery voltages and when i see them rising I could apply a reverse current but I think this is going to make the lowering very jerky. Any ideas?

Please Log in or Create an account to join the conversation.

9 years 5 months ago #29525531 by wakestrap
If I were to go with closed loop speed control, does anyone have suggestions for cheap analog tachometers?

Please Log in or Create an account to join the conversation.

9 years 5 months ago #29525533 by roboteq
Replied by roboteq on topic Re:Power Query and Speed Control Question
The reported Amps are battery amps, so you can compute the watts as

reported volts * power out / 127 * reported amps

Regeneration can be a very serious problem.

There is no way to measure the regen amps (ie negative amps) on the AX2550, so there is no easy way to limit the regen current with your external micro.

Best is to set a decceleration rate that you find slows things down to a comfortable level.

For the tachometer, you may be able to use a small motor as a generator.

Please Log in or Create an account to join the conversation.

9 years 5 months ago #29525535 by wakestrap
Will closed loop speed control mode stop run away acceleration? ie If the commanded speed is 20 and the motor starts going above that speed will the controller slow it back down?

Please Log in or Create an account to join the conversation.

9 years 5 months ago #29525537 by roboteq
Replied by roboteq on topic Re:Power Query and Speed Control Question
that\'s the idea. Power will automatically be increased or decreased as needed to maintain the desired speed

Please Log in or Create an account to join the conversation.

Moderators: tonysantoni
Time to create page: 0.207 seconds