DC motor control

Thread Starter

bug13

Joined Feb 13, 2012
2,002
Hi guys

How tell if a small DC motor is blocked?
And how do I hold the position of the motor at the blocked position?

The DC motor I am dealing with is a small 3V-6V brushed DC motor, like the one you can see in a small RC car.

The motor is likely to be controlled by a H-bridge.

Thanks
 

Thread Starter

bug13

Joined Feb 13, 2012
2,002
What is a blocked motor and blocked position ?

Timescope


hope my (hopeless) drawing will explain it better.

motor driving wheel -> wheel attached to rope -> rope attached to weight.

so the motor will pull the weight up, to the horizontal dash line, something will block the weight go any further. how do I detect that?

and how do I keep the motor at that position.
 

timescope

Joined Dec 14, 2011
298
A solenoid has a coil and a metal plunger that moves when current flows through the coil. This could be used as a brake to hold the mechanism at the desired position.

The current through a motor that is blocked will be much higher than the normal load current. You can tell if a motor is blocked by measuring the current through the motor.

A better method would be to use a sensor to detect the position of the weight and use it's signal to stop the motor and energize the brake.

Timescope
 

Bernard

Joined Aug 7, 2008
5,784
If the wheel had a toothed wheel attached, then a solenoid operated paul would require little power to hold. Sensor might be IR beam break. or a low value resistor in series with motor with comparator can give an adjustable current limit. Your drawing is worth 100 words.
 

Thread Starter

bug13

Joined Feb 13, 2012
2,002
Is there a way to hold the motor in position without mechanical means? will PWM the motor at a certain duty cycle work?
 

tubeguy

Joined Nov 3, 2012
1,157
Is there a way to hold the motor in position without mechanical means? will PWM the motor at a certain duty cycle work?
You could use two sensors set up to detect the desired stopped position only when they are both activated Then use a pwm circuit to hold the motor position. Additional sensors could be used to detect when its getting close to the desired position.

Will the motor be geared down ???
 
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