Help with DC motors and motor drivers

Thread Starter


Joined Oct 20, 2007
Hi all:

I am trying to control two Maxon DC Brushless RE035-071-34EAB200A motors attached to encoders from US Digital: E6 Encoder Kit (Differential Encoder): part number: E6-2500-079-I-D-H-D-B:

The controling board I am using is Quanser Q8 boards:

I will be using Quanser simulink toolbox to signal process and control the system.

I am still in the design phase and I am wondering if i can get some input on what type of motor drivers or amplifiers to use?

I want to be able to generate a range of torque from the motors. That means, correct me if i am wrong, I need to control the current delivered to the motors.



Joined Jan 9, 2009
My first recommendation for simplicity is to go with an all in one solution, where the controller card and amplifier are in the same package. These packages, as in the ones I design, come with a real-time bus for commanding positions/velocities etc..

If you require the flexibility and control of a separated solution, as it seems this Quanser board allows (multiple controls, lots of Analog inputs etc..), than you need only get a power stage which supports the appropriate voltage, power and can directly take PWM inputs (as I believe the Quansar board gives out as per the description).

Depending on the accuracy required, many control boards will just give out a +-10V analog signal to command torque with and the amplifier needs only to read this and it generates the PWMs itself.

You will probably want to choose a default amplifier for the motor, so othat the current loops come pre-tuned. Tuning current loops is ugly.

Option number 1 is the easiest.

Thread Starter


Joined Oct 20, 2007
Thanks for the reply Skeebopstop.

What type of board are you using? The ones that has the contoller and amplifier in one package?

Also, the main purpose that Quanser is being used, is that it comes with a very handy simulink library that, once the system is setup properly, many experiments and tuning and signal processing can be done.

Here is what i am thinking from looking at various projects:
The Quanser card will be connected to an amplifier (which is powered by a power supply) commanding the motors and controlling them. The encoders on the motors will be communicating with the Quanser board to give position, spead, etc...

The Maxon motors being used have the following features:
Maxon RE035-071-34EAB200A


Low Inductance - much longer brush life and extremely low electrical noise
Low Interia - low mechanical time constant for fast acceleration
High Efficiency - low current consumption for extending battery life
Ironless Core - no cogging for smooth rotation even at low speeds
No Magnetic Saturation - linear speed-torque constants for simple, accurate control

90 Watt, Maxon DC motor, Graphite Brushes

Motor Data
Assigned power rating 90 W
Nominal voltage 42.00Volt
No load speed 7540 rpm
Stall torque 1070 mNm
No load current 71.5 mA
Starting current 20300 mA
Max. continuous current 2150 mA
Max. continuous torque 113 mNm
Torque constant 52.5 mNm/A
Speed constant 182 rpm/V
Terminal Inductance 0.62 mH

So i need a setup that can deliver the full range of torque.


Joined Jan 9, 2009
Ok, so since you want the board to work on some new controls you're setup will be the following:

1. your quansar board which receives the motor feedback (make sure your board can take the type of feedback your motor gives). Please note that the higher the resolution, the better luck you'll have. If it is a robotic application don't forget to investigate absolute encoders. If it is not a robotics application and homing procedures are acceptable, generally 1 Volt peak to peak sin/cos encoders give you the highest resolution. Generally to get even better precision you need to make sure your controller supports calibration of these, although that can be quite sophisticated and even just supporting them at all is better than anything digital can get you.

2. For the amplifier. Get a 100W or so amplifier. Make sure it has over current protection in case your motor gets a fault. The amplifier will have a PI current loop running in it. This generally will need to be tuned. There exist some theoretical formulas that can get this tuned, or you can contact Maxon and ask them for one 'recommended' for that motor. They'll probably give you a maxon one. The amplifier would normally take a +-10V 'torque' (i.e. current) command. The quansar board does the controlling of position/velocity and outputs the torque command to the amplifier as a voltage. I did read that your quansar board gives PWM outputs directly? This would be more ideal and it means that the board is able to do commutation. This would mean you could tune your current loop etc.. from the quansar board and all the amplifier needs is a way to accept the PWM signals and drive them out to the motor (in effect, it is just a much of MOSFETs). Either should work, I am more familiar with the +-10V approach when you segregate the amplifier and controller.

Take great care with shieldings and ground loops in these types of systems. The phase current lines out of the amplifier will be noisy as anything, switching 2-5A at probably 20kHz with <1uS rise times.