Running two DC motors at same speed.

Thread Starter

sahil-siwatch

Joined Jan 12, 2021
43
Hello. I am designing a new product that will have two motors attached to two different rollers on a metallic base. It is a button controlled device and will be used to rotate rear wheel of belt driven heavy bikes(at very low RPM). I am using planetary gear motors(45kgcm, 60rpm). I am sure that there will be some difference in their speeds which can cause problems such as slip etc to the whole system. How can I synchronize the speeds of these two motors?
I was also reading at some places where some people used incremental encoders connected to motors and arduino to control the speed(closed loop system). Any ideas on the encoders that I can use??
 

dendad

Joined Feb 20, 2016
3,835
And you will need to specify the power of the motors and what accuracy is needed.
Will both motors have to run exactly the same and what is he problem if they do not?
Using stepper motors may make it easier as you have full control over the rotation speed and direction.
It does help if you post as much info on your application as you can.
 

Thread Starter

sahil-siwatch

Joined Jan 12, 2021
43
And you will need to specify the power of the motors and what accuracy is needed.
Will both motors have to run exactly the same and what is he problem if they do not?
Using stepper motors may make it easier as you have full control over the rotation speed and direction.
It does help if you post as much info on your application as you can.
The wheel will be resting on the two motors and putting equal load on both the motors. If motors rotate at different speeds, there might be some problems. I haven't tested this setup yet. Steppers motor will be expensive for us as compared to normal DC planetary geared motors. It will be a product so cost matters to the client.

these are the motors that we are using - https://robokits.co.in/motors/rhino...avy-duty-ig32-planetary-dc-geared-motor-60rpm

I used this motor for a single motor setup. There are basically two cylindrical rollers. We have motor on one of them already but second one also need a motor. Imagine this setup.
1612944925502.png
 

dendad

Joined Feb 20, 2016
3,835
Is this a motor attached to encoder??
No. This is just the encoder.
You will need to link it to the roller drive shaft.
They are available in various pulses per rev. I think the 100 pulses per revolution will be plenty.
But, tuning two DC motors to run together may be quite a task. I would use steppers myself, if I was doing it. Or, find a way to just use the one motor.
 

Thread Starter

sahil-siwatch

Joined Jan 12, 2021
43
No. This is just the encoder.
You will need to link it to the roller drive shaft.
They are available in various pulses per rev. I think the 100 pulses per revolution will be plenty.
I was looking for it online here in India. This is too expensive. My motor is cheaper than this :p Is there any way that I can make something similar like this? or use some IC to find out speed.
 

Thread Starter

sahil-siwatch

Joined Jan 12, 2021
43
It will be a one directioned motor system. Honestly I am not sure about the accuracy that the system needs. I am yet to try this 2 motor system. How can I access the gear wheel ??
 

dendad

Joined Feb 20, 2016
3,835
You may have to add a gear wheel to the gearbox shaft to sense the rotation.
Do you have any experiance in programming, maybe an Arduino, to control this device?
 

LesJones

Joined Jan 8, 2017
3,168
Why not just couple the roller together using a toothed belt and pulleys or a chain drive and use a single more powerful motor ? As you are using DC motors (And assuming that they are permanent magnet types.) why not run the motors connected in series. In that way they will share the required torque as torque is proportional to current (To a good approximation.)

Les.
 
Last edited:

MaxHeadRoom

Joined Jul 18, 2013
23,084
I don't see why a single motor and gearing wouldn't work, together with the suggested timing belt method.
What is the gearing ratio? and have you measured the torque required, this should be able to be easily read?
This would avoid complicated servo electronics syncing.
Max.
 

KeithWalker

Joined Jul 10, 2017
1,778
You don't need a fancy load control circuit. If you connect the two motors in series, they will run in sync because each will produce a back EMF proportional to speed. If there are any differences in the motors, they will balance themselves out.
Regards,
Keith
 

MaxHeadRoom

Joined Jul 18, 2013
23,084
Have you measured the RPM you need?
The stated limit on the motor is 7amps.
I would first establish the torque you need instead of designing from the wrong end.
Max..
 

Thread Starter

sahil-siwatch

Joined Jan 12, 2021
43
Have you measured the RPM you need?
The stated limit on the motor is 7amps.
I would first establish the torque you need instead of designing from the wrong end.
Max..
I have meausured the required torque and rpm. RPM is not a hard constraint. Torque required in my case is roughly 40-50kgcm(I am sure the design of roller and other bike factors are adding some extra torque as well.) The motor I am using right now is working well for 2-3 mins but then I see smoke coming out of it. There were few problems in our design as well. I will get a clearer picture once the design is corrected.
Yes. The current drawn in my case is 5-5.5A. But I guess multimeter might not be detecting the irregular peaks when the load is increased or in case of overheating.
 

Thread Starter

sahil-siwatch

Joined Jan 12, 2021
43
You don't need a fancy load control circuit. If you connect the two motors in series, they will run in sync because each will produce a back EMF proportional to speed. If there are any differences in the motors, they will balance themselves out.
Regards,
Keith
Hi. Thanks for the reply. I read this at few places in forums. Can you shed more light on it??
 

Thread Starter

sahil-siwatch

Joined Jan 12, 2021
43
I don't see why a single motor and gearing wouldn't work, together with the suggested timing belt method.
What is the gearing ratio? and have you measured the torque required, this should be able to be easily read?
This would avoid complicated servo electronics syncing.
Max.
In my case right now with single motor, we are using one motor with one roller and the other roller is rolling free. It works with medium load bikes. but not heavy belt driven cruiser bikes.
 

Thread Starter

sahil-siwatch

Joined Jan 12, 2021
43
Why not just couple the roller together using a toothed belt and pulleys or a chain drive and use a single more powerful motor ? As you are using DC motors (And assuming that they are permanent magnet types.) why not run the motors connected in series. In that way they will share the required torque as torque is proportional to current (To a good approximation.)

Les.
That's a good suggestion. Thanks. In my case one roller will be free and other will be connected with a motor(if I use a single motor)
 
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