Hi,
I have a question concerning a general appraoch of manually moving an object that is driven to a certain point or in a certain direction by a motor or servo.
lets say you have a spinning wheel spun by a motor or servo and you grab it and force it in the reverse direction. If I understand correctly (and I don´t understand that much about Arduino and electronics) the motor would overheat and break.
Or if you had a robot arm which was controlled by a computer to go to a certain point and you´d force it with your hand to go somewhere else for example in an arm wrestling match. Would the servos/motors be destroyed? Would you have incorporate some other sort of mechanism for such a devecie? How would you do that?
A lot depends on the sort of motor and how it's powered.
I suspect you are likely to break most servos if you try to move them away from their desired position. There is a huge gear reduction within a servo and the gears would probably break, rather than the motor burn out.
DC motors take their maximum current when they are stationary so, if you have a useful voltage to power them at speed they are likely to draw too much current and overheat if held stationary. This problem could be overcome with electronics that ensure the current stays within limits that don't cause damage. In that case it probably wouldn't do any harm to force the motor in the opposite direction. This is not a simple option, however.
Another possibility might be a stepper motor. They are designed to move in discrete steps and stay in position until the next step instruction arrives. They are unlikely to suffer damage if they are made to move by an external force that exceeds their holding force. However the computer that was controlling the motor would no longer "know" where it was.
In saying all this I am assuming you are not thinking of moving the motors at high speed or for a long time in the "wrong" direction.
Thank you very much for the answer.
I wasnt thinking about any specific use just the problem in general. I am just starting to learn and familiarizing myself with different concepts.
Since there are things like force feedback steering wheels for computer games it seems to me that there must be some commonly applied solution to this problem.
Ah, thank you very much for the link, Hotcut, very interesting.
Shpaget: If I understand you correctly you would use the cluch to declutch the motor in case of overloading it and the rotary encoder to send information about the angle back to the controlling device in order to compensate for the step motors lack of a position output which would be present in a servo.
Cardboard:
to compensate for the step motors lack of a position output which would be present in a servo.
You are right about the stepper motor. But servos have no position feedback either - assuming you mean hobby servos as used for model aircraft, rather than expensive commercial alternatives to stepper motors.
Since there are things like force feedback steering wheels for computer games it seems to me that there must be some commonly applied solution to this problem.
Can you clearly state the problem you need a solution for? If the question is can overloaded Motors be broken, the answer most likely is yes, depending on the setup and situation. How to prevent motor damage depends on how they are being used, what kind of motor, etc.
Yes, the clutch would provide enough friction for the motor to transfer the torque during regular operation, but would slip if someone tried to force it out of position. The actual position of the moved part would be monitored by the encoder.
@Robin2: I´m a bit confused now. After reading the following link I thought that there are common servos that provide feedback:
@zoomkat: I can not really clearly state the problem because there is no clear problem. I was wondering about how to avoid motor damage in case of overloading it but not in a specific case.
If "It depends on the setup and situation" is the answer and there is no standard solution then that´s answered the question.
Sorry for not being comprehensive. Yes you can get special servos with an extra wire for position feedback. The vast majority of hobby servos don't have that. I have never had a feedback servo and I wonder what benefit they offer in practice.
It seems to imply that the servo is undersized for its load. If it had enough power it would just move to the commanded position.
It seems that the extra wire just makes the internal potentiometer voltage available to the microprocessor. You could probably modify any servo to do that. I wonder how the external microprocessor could make better use of that data than the internal circuitry - especially if you get a regular digital servo.
What I said earler about the risk of breaking the servo's internal gears still applies.
