Which motor to choose?
Which motor to choose?
(OP)
Hi everyone,
For a project in Linear Fresnal Mirrors - Solar power at the universiry UFSC (Brazil) I need a motor to position the mirrors. I have estimated the desired torque, which is about 30 Nm. The desired rpm is very low. An rpm of order 10^-1 would satisfy. The desired accuracy is about 0.1 degree. However, our budget is very limited.
I think servo motors (controlled via an arduino board) would be a very good choice to control the position of the mirrors, but I have no bloody idea where to buy cheap decent servos (max $100 each); what is a good site or servo brand/type? Or is it maybe better to choose for another type of motor?
Regards,
Harm
For a project in Linear Fresnal Mirrors - Solar power at the universiry UFSC (Brazil) I need a motor to position the mirrors. I have estimated the desired torque, which is about 30 Nm. The desired rpm is very low. An rpm of order 10^-1 would satisfy. The desired accuracy is about 0.1 degree. However, our budget is very limited.
I think servo motors (controlled via an arduino board) would be a very good choice to control the position of the mirrors, but I have no bloody idea where to buy cheap decent servos (max $100 each); what is a good site or servo brand/type? Or is it maybe better to choose for another type of motor?
Regards,
Harm





RE: Which motor to choose?
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: Which motor to choose?
The most common stepper motors have an accuracy of .9 or 1.8 degrees. The more precise but powerfull steppers are actually equivalent to servos right?
And is there any website where you can find a motor on base of specs? Like min. torque, max. price, min. accuracy et cetera?
Thanks,
Harm
RE: Which motor to choose?
Though you can get lots of cheap gear box versions:
DC Gear motors
Another possibility is standard HEAVY DUTY R/C servos.
Heavy duty classic R/C servo
You can get Arduno shields that drive armies of them.
Arduino Servo Sheilds
Cautionary tail of R/C servo usage
But back to steppers. Look at "gearbox steppers".
Ebay geared steppers
Keith Cress
kcress - http://www.flaminsystems.com
RE: Which motor to choose?
The speed reducer will, at the same time, better the resoluion så you can easily have the 0.1 degree that you need. The accuracy is often a lot better than 0.9 or 0.18 degrees - it is the resolution that has those typical values.
Microstepping improves resolution a lot. It is not difficult to have 0.01 degre resolution when motor shaft is unloaded. A speed reducer, without backlash, will improve that further.
But, do not try without gear/speed reducer with any motor. It can be done, but at a high cost - you are using less than one percent of the motor's capacity if you run without speed reducer at these low speeds.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Which motor to choose?
RE: Which motor to choose?
Two more questions;
1. Is the accuracy related linear to the gear ratio? (I do think so, but just as a check)
2. Would I need metal or titanium gears? As I think plastic gears will break under these forces.
Regards,
Harm
RE: Which motor to choose?
Resolution gets better with higher gear ratio.
Accuracy may get worse, if there is backlash and/or stiction in the gear. But, in general - accuracy improves also. But that is highly dependent on the quality of the gear.
Re plastic or titanium (why titanium?, there is also steel and brass to chose from): You must, of course, select a device that can handle the forces involved. Titanium sounds quite expensive. I usually see steel and brass in different combinations.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Which motor to choose?
So the resolution increases a lot, but what I need is an accuracy of 0.3 degrees.
I found one very cheap servo with integrated gearbox here (I also found two geared steppers on robot market place, thanks itsmoked, but unfortunately they were out of stock). However, the backlash is >=1.5 degrees. That means my accuracy is 1.5 degrees (so not even close to the .3)?
If I search for other motors / gearboxes, what is the direct influence of the backlash?
RE: Which motor to choose?
RE: Which motor to choose?
RE: Which motor to choose?
RE: Which motor to choose?
RE: Which motor to choose?
any precision planetary gearbox that can produce 30nm continuous output will be approx. 3-4" in diameter x 3-4" long.
any precision planetary gearbox of this torque with 6 arc min or less backlash will cost you approx $ 1500.00
NOW figure out whether you want servo or stepper.... you will likely want >100:1 ratio; any ratio over 10:1 will add approx. 30% more to the cost.
NOW pick your motor and add that to the gearbox price.
You will NOT get 30nm <.1 degree accuracy for $ 100.00 unless you steal it.
If this is for a client, walk away NOW.
www.KilroyWasHere<dot>com