How to derive/measure force feedback with a servo or motor?

Using Arduino Motors, Mechanics, Power and CNC
#1

I have been hacking away at this problem and would like your suggestion on alternative solutions.

Problem

I want to rotate something through a distance, but want the rotation to stop if a [specified level of resisting] force is "felt" on thing being rotated. I don't want to use additional sensors.

...so far:
The current drawn by a servo has been observed, but characterizing it to detect the force in a reliable way is proving complicated.

So my thoughts are to use Arduino's motor control shield and a motor to rotate the thing I want to rotate. However, I am scratching my head on how I can detect any force this thing encounters based on the motor's signals? Remember, I don't want to use any additional sensors.

Your suggestion will be appreciated.

Thanks!

#2

ard_automatica:
So my thoughts are to use Arduino's motor control shield and a motor to rotate the thing I want to rotate. However, I am scratching my head on how I can detect any force this thing encounters based on the motor's signals? Remember, I don't want to use any additional sensors.

Are we talking DC or 3 phase motor?

#3

Power_Broker:
Are we talking DC or 3 phase motor?

DC

#4

You will need to sense current, that's inescapable, but if you have a motor driver with built-in
sense-resistors that will help as you then only have to use analogRead(), although the resolution
in terms of current may be quite low (you don't want to waste much voltage across the sense
resistors, or they get very hot and steal power from the motor).

#5

MarkT:
You will need to sense current, that's inescapable, but if you have a motor driver with built-in
sense-resistors that will help as you then only have to use analogRead(), although the resolution
in terms of current may be quite low (you don't want to waste much voltage across the sense
resistors, or they get very hot and steal power from the motor).

On observation, I can't seem to identify a change in the current (i.e. unique amplitude/pulse period) that I can map to a resisting force in the path of the servos motion. In a nutshell, if the servo is rotating and I apply little resistance by tapping it with my finger, I can detect something unique that tells me a force is being felt.

I'm thinking of using a strain gauge for force measurement instead.

Thanks

#6

ard_automatica:
On observation, I can't seem to identify a change in the current (i.e. unique amplitude/pulse period) that I can map to a resisting force in the path of the servos motion. In a nutshell, if the servo is rotating and I apply little resistance by tapping it with my finger, I can detect something unique that tells me a force is being felt.

I'm thinking of using a strain gauge for force measurement instead.

Thanks

I think that will mean the motor mounting plate will need to rotate slightly. probably held by a spring.

Paul

#7