Looking on opinions about using stepper motors for drive

[mjhilgerokc]

Hi,
I have decided to begin my first robot.  I am planning on using stepper motors for the drive, but was curious about others opinions regarding using these as opposed to general DC motors.  The electronics and micro are not an issue and I already have several steppers I can use.  I am mainly interested in opinion regarding stepper with no feedback vs DC motor with some form of rotational feedback (either shaft encoder $$$ or just movement detection $).  But, I am open to other comments regarding the choice as well.  I will probably either gear or belt reduce the output drive to provide a boost in torque to the wheels.

Thanks,
Mitch

[Soeren]

Hi,

I am mainly interested in opinion regarding stepper with no feedback vs DC motor with some form of rotational feedback (either shaft encoder $$$ or just movement detection $).

Steppers are heavyer than regular DC motors for the same power and they need to be ramped up and down in a controlled way, to stay in reasonable sync with the commanded steps, so I'd use DC motors.

Encoders can be made for next to nothing - a reflective IR sensor or a slotted opto-coupler is all you need to buy (if you don't have one already).

[photomark]

Stepper motors can be a real pain in the back .

But hey can also be a lot of fun to play with 


If you have stepper motors laying about then you have nothing to loose by using them and there are plenty of good driver circuits around .

They may not be suitable for your needs or they may be perfect but either way by the time you either get them working or throw them away you will no a lot more about motors .

Personally I love stepper motors .

[mjhilgerokc]

I already know much about both types of motors.  I'm just looking at it from a resource and implementation perspective.  If I use stepper motors, I feel comfortable monitoring its progress by the number of rotational pulses I send to the motors (If I send a pulse and the motor does not turn is ok for the moment) this will mainly keep the direction straight.  If I use DC motors, then I must monitor the rotation (with the micro) of each and adjust the drive power (PWM or whatever).  So for ease of implementation, I am leaning toward steppers with gearing sufficient to provide torque to drive my body mass sufficiently.  As I said earlier, the electronics and motor information is not an issue; I am fine with that knowledge. 

Just mainly looking for feedback on pros and cons regarding each.  Weight is a valid issue for comparison, but in this case, it will not make a difference in my design.  Actually I am more concerned regarding mechanical connections.  Trying to find parts to couple belts, gears to the wheels and motor are probably a bigger concern for me.

[photomark]

so what was your question ?

if a stepper is best use a stepper , if a DC motor is best use a DC motor

Only you know what your application is and what will work best

[paulstreats]

dont forget that stepper motors need either an additional set of control electronics to run the steps in sequence or if you are implementing the stepping sequences software wise, it takes up more resources on the microcontroller.

Most stepper motors usually come with predrilled mounting holes for mechanical connections, whereas other dc motors dont usually.

 You may find that you also want to add a gearbox onto the stepper motors output, the better your control system the better torque performance you will get out of them (usually though the faster you run the stepper motors, the less torque they have).

 As soeren mentioned above, if they are not ramped down correctly then you lose sequence quite of resulting in the stepper motors stalling and just spinning freely until the sequence slows down enough to "recatch" the rotor. The same occurs if they ae ramped up too fast and also if the motors stall for any other reason the same also happens(your sequence might still be energising the stator, but the rotor isnt in phase with the rapidly changing field so it just spins freely inside the body).

 If you have stepper motors available to use then this is a great advantage of course.

 I enjoy using stepper motors, and like the positional control they can provide. Why not try them out if you have them available.

Another disadvantage is that along with extra control circuitry(or additional uc resources for a software implementation) they also require more H - bridges to run than a basic DC motor.