I've got a quick query regarding motor control.
To control the angle of a camera, I am using a geared motor, potentiometer for feedback, and a PIC running a PID control loop.
That all works fine - the system responds to an rc input. The motor is a **broken link removed** - with a 360:1 gearbox, it offers 7.4kgcm stall torque at 6v - mighty!
That's at 23rpm - OK for my camera control. However, as my PID loop pulses the motor mostly, it is actually much slower and weaker. My solution was to run the motor driver and motor at 12v, which increases the speed and torque to better levels.
As the motor is only being pulsed, the average voltage/current is low, so the motor stays cool and happy.
However - the problem:
- After a few weeks of successful operation, I pressed 'download' with out unplugging the motor driver - the outputs went to unknown states, and the motor went full speed in one direction. It moved the camera to the mechanical limit, and with the power of 12v, destroyed the motor's gearbox.
I replaced the motor (£15), and ensured the motor was unplugged for downloads.
- After a few more weeks of successful operation, while working on another part of the system, I turned off a BIG inductive load, which screwed up the power supply and caused a couple of PICs on the system to reset/crash. The motor (again) went in the wrong direction, jammed, and broke the gearbox.
I replaced the motor (another £15), added more capacitors, and have been OK for the past few months.
However, I'm constantly worried that I'm in a bad situation - if something does go wrong with the driver, I could easily loose another motor. The motor is rated to be stalled, but only at 6v, not 12v.
So:
- I realise running at 12v is a bad idea, but I don't want to redesign the system just in case of this unlikley event.
- I feel adding a dropping resistor is a quick (and acceptable) solution, as the motor is OK being stalled at 6v. The motor is driven by an H bridge, so adding an op-amp based solution or something at the motor is a big task.
Measurements:
Solution:
Adding a 10 ohm resistor in line with the motor would reduce the voltage to about 10v under normal operation (that's fine with me), while reducing the voltage my much more under stall condition.
What do you think of that idea? While a bit power-wasting, it seems to be a quick and workable solution to me. Does 10 ohms sound about right?
Any thoughts appriciated!
Thanks,
Andrew
To control the angle of a camera, I am using a geared motor, potentiometer for feedback, and a PIC running a PID control loop.
That all works fine - the system responds to an rc input. The motor is a **broken link removed** - with a 360:1 gearbox, it offers 7.4kgcm stall torque at 6v - mighty!
That's at 23rpm - OK for my camera control. However, as my PID loop pulses the motor mostly, it is actually much slower and weaker. My solution was to run the motor driver and motor at 12v, which increases the speed and torque to better levels.
As the motor is only being pulsed, the average voltage/current is low, so the motor stays cool and happy.
However - the problem:
- After a few weeks of successful operation, I pressed 'download' with out unplugging the motor driver - the outputs went to unknown states, and the motor went full speed in one direction. It moved the camera to the mechanical limit, and with the power of 12v, destroyed the motor's gearbox.
I replaced the motor (£15), and ensured the motor was unplugged for downloads.
- After a few more weeks of successful operation, while working on another part of the system, I turned off a BIG inductive load, which screwed up the power supply and caused a couple of PICs on the system to reset/crash. The motor (again) went in the wrong direction, jammed, and broke the gearbox.
I replaced the motor (another £15), added more capacitors, and have been OK for the past few months.
However, I'm constantly worried that I'm in a bad situation - if something does go wrong with the driver, I could easily loose another motor. The motor is rated to be stalled, but only at 6v, not 12v.
So:
- I realise running at 12v is a bad idea, but I don't want to redesign the system just in case of this unlikley event.
- I feel adding a dropping resistor is a quick (and acceptable) solution, as the motor is OK being stalled at 6v. The motor is driven by an H bridge, so adding an op-amp based solution or something at the motor is a big task.
Measurements:
Code:
6v 12v
No Load 34mA 73mA
Some load 100mA 250mA
Stalled 670mA 1.2A
Adding a 10 ohm resistor in line with the motor would reduce the voltage to about 10v under normal operation (that's fine with me), while reducing the voltage my much more under stall condition.
What do you think of that idea? While a bit power-wasting, it seems to be a quick and workable solution to me. Does 10 ohms sound about right?
Any thoughts appriciated!
Thanks,
Andrew
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