mechanically coupled DC motors

Hi all,

I am building a DC motor control demonstration panel. Apart from controlling the speed I also want to simulate variable load acting on the DC motor. Hence I thought of coupling another DC motor to the existing one and rotating it in the opposite direction just like in the figure.

If we say that motor A is the motor to be controlled (clockwise) and B is the torque generator, even though B is given power to rotate anti clockwise it will always be rotating in the opposite direction (because of A). This will cause B to heat up and I fear that it would get burnt.

The goal is to somehow dissipate the current generated by B. Can you all help me.

BTW both motors will be driven by H-bridges and both will have speed measuring ability.

Thank you !!!!!!!!!!!!!!

All you really need on B is a load resistor. B will act as a generator and provide the torque you are looking for.

Thank you very much for your reply SherpaDoug !!!!!!!!

But wouldn't the current comming from the PSU also go throgh the resistor and how can I determine the value of the resistor.

Regards

The B motor does not need any supply, just the load resistor. Calculate the voltage and current the motor will make as a generator at a given speed and torque. Then R = E/I gives the resistor. You probably want to use a rheostat if you can get one with the proper resistance range and power. Otherwise use a bank of switches and light bulbs to create the resistance you need. The light bulbs may actually make for a better demonstration. We are talking 100 year old technology here, but the physics hasn't changed.

The DC will act as a generator by itself if it is a permanent magnet type. (Most small motors are of this type).
If the motor has armature and field windings (universal motor) then you will need to power one of the windings and place the load resistor in the other. Then the torque can be controlled by the current that goes into the powered winding.

Hi every one !!!!!

I am VERY SORRY for this late reply.

Even though I asked this question a while back I am trying to implement it just now and I have a problem with selecting the motors.

Should I chose same motors for A and B or are there other factors that I have to weigh in?
Also, should I choose high power motors to get practical load resistor values?

Thank you !!!!!!!!!!!!!

You really ought to read a book about motors first.

If you target 12V 1A you should be able to buy motors and light bulbs at a good model train shop. 12W will give enough power that you can feel the torque but there is not enough voltage or torque the seriously hurt you.