I have only worked with servos, never used DC motor driver.
My understanding is that, the DC motors driven by Sabertooth 2x5 do not need potentiometer unless you need CNC-level accuracy. Am I right?
My application does not require CNC-level precision but will have lots of fast stops and sudden reverses. At the time of sudden reverses, my DC motor will face about 30 kg-cm of sudden torque and I’m afraid too much of displacement may accumulate in time. Would I still get by without potentiometer?
Many savvy members in this forum seem to be very excited about Sabertooth motor driver. Is Sabertooth motor driver way to go among low amp DC motor drivers these days? (no competing products in this class at all?)
What exactly do you think a potentiometer does? I’m not sure how you expect a pot to enhance the accuracy. Please let us know.
As for other motor drivers, you probably won’t find anything significantly cheaper that will be as good as the sabertooth drivers. Not sure if anyone else knows of any.
I’m thinking of using SSC-32 together with Sabertooth motor driver to achieve a complex sequence of movements. And for this, I’d like to use regular DC motors instead of hobby servos.
So I was wondering if installing a 3rd-party pot would do the job (Sabertooth manual talks about this a little) but maybe I am totally off in that, there could be other ways that I am unaware of to achieve decent accuracy of angular position in the realm of DC motor drivers where I am a mere lost grasshopper.
I guess what I want to know comes down to this: What should I do to maintain hobby servo-level positional accuracy with regular DC motors? Do I use pot? If so, I would very much appreciate if you could recommend a good inexpensive pot that will work with SSC-32/Sabertooth and where to get it.
Thank you very much for your attention on this matter.
Ok, I think I understand now.
DC motors will turn continuously, so if you want it to go to a particular position, you will need some feedback. You can use a pot to get this feedbeck, and connect it to the analogue inputs of the ssc. You need to then write your own software to control the motors relative to the positional feedback.
The thing to remember is that the pot only turns about 270 degrees, so you will not be able to get multiple rotations out of the motor if you want feedback from a pot.
Is this the kind of thing you are looking for?
If you let us know what your application is, it might help with the advice we can give you.
The main reason I was considering DC motor over hobby servo was the cost factor. However I looked around today and found hobby servos are no losers in torque/dollar ratio anymore. Hitec HS-805BB (343 oz. in.) Mega Servo was being sold at less than $40 at ebay. Now this is nice value…
I would very much appreciate if you let me know discount DC motor shops so that I may compare price and make my decision.
If you are looking for precision control then please be aware that an HS-805BB has a plastic (nylon?) gear train and will wear some as it breaks in. I am not saying there is anything wrong with this, I am saying it may be something to be considered and may slightly impact your performance long term. Also please note the HS-805 is a quarter-scale sized servo and much larger than what is generally referred to as a standard sized servo. Again, not necessarily a problem but something to make note of.
I would suggest you go with a servo motor. When you add the cost of a motor, motor driver, and feedback circuit, I think you would be better off with a servo. Also, if you get cheap motors, you may have a problem with electrical noise. I used cheap gearhead motors in a project last semester, and it was diffinitely not worth the hastle. My microcontroller kept reseting because of it, and the readings from all of my sensors were ruined because of the noise from the motors.
You may get luchy, but I would still recomend servos.
Yes. However, the torque requirement in my application will be 500+ oz-in per joint and this means I will need 2 HS-805BB servos for every joint… The joint will look bulky this way…
Sabertooth board is not that expensive nor are decent pots… DC motor solution is still tempting.
Would you have recommendation for good inexpensive geared DC motors that are:
have you looked at the robotzone servo power gearboxes like this (sorry for the servocity link)? You may be able to meet your torque requirements with these and normal servos and they use an external pot by design. You may be able to replace the pot they use with an angular position sensor like these which are continuous rotation with output either as analog or 10-bit PWM.
If you are just going to be using motors, then all you need is the Sabertooth motor controller - it can use standard R/C style PWM signals for controlling the motors. If you are going to be using servos also, then you would also need the SSC-32, which can also be used to send PWM signals to the Sabertooth.
I don’t think this was pointed out in other posts, so I hope I didn’t miss something and repeat someone else.
