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I'm looking for a very slow motor. Like half a round in a second, or even less. The movement must be as fluid as possible. I don't care about velocity variation on start or on stop, but I care about the constant velocity.

I've tried with a small DC motor, powering it with both 5V and 3V and a 5 and 10 kohm potentiometer but slowing down after a while it does not move anymore.

Then I've tried with a small stepper motor and an Arduino motor shield and with micro step I'm getting the desired velocity but the movement is no fluid at all and I can see the steps.

I think that I need to use a full velocity DC-motor with some reduction gear but I don't know how to get the right ones. Can someone advice me some pre-made gear set for very low-velocity motor or at least how to calculate them and try to make by myself (3D printing?)

EDIT: no particular torque is needed, I'd like to rotate really light object (lddd then 100g)

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closed as off-topic by Olin Lathrop, JYelton, Leon Heller, Scott Seidman, Daniel Grillo Oct 7 '14 at 16:18

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    \$\begingroup\$ Is this question actually "where can I buy a gearbox or geared motor?" Cheap wall clock mechanisms might do what you want.. \$\endgroup\$ – pjc50 Oct 7 '14 at 15:10
  • \$\begingroup\$ Also called gearhead motors. All sorts of speeds. \$\endgroup\$ – George Herold Oct 7 '14 at 15:38
  • \$\begingroup\$ Motors geared that slowly will likely be expensive. \$\endgroup\$ – Matt Young Oct 7 '14 at 15:45
  • \$\begingroup\$ Look for a gear motor, motor with gearbox or things of that nature. A couple of places that have such things: ServoCity, All Electronics, and Adafruit; not to mention usual suppliers like DigiKey and Mouser. \$\endgroup\$ – JYelton Oct 7 '14 at 15:47
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    \$\begingroup\$ @Matt Not necessarily; a 0.5 RPM 3-12V DC gear motor at ServoCity is $25 US. \$\endgroup\$ – JYelton Oct 7 '14 at 15:48
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Along with the comments about gearhead motors and gearbox motors, for links see JYelton's comments to your question, you can also use a "360 degree Servo" or a "Continuous Servo" with the fun of it having a PWM interface. It's really just a cheap servo with the limitation removed. The smallest ones can be had for about $3 and come quite close to 10 to 30 RPM (= half a round per second or less) with pretty decent continuous motion and a good amount of strength as well.

Of course this does depend on whether you'll be wanting to drive it with PWM or not, but even if you don't, you can remove the back housing, snip out the PCB that controls it and put 1 to 5V on the motor yourself directly to control rotational speed, torque and direction with your own electronics.

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  • \$\begingroup\$ This may not be a great solution - these are effectively a crude hack to give bidirectional control with a low parts count. But the application may not need that, and it may need more consistency than these open loop, prone to calibration drift devices may offer. \$\endgroup\$ – Chris Stratton Oct 7 '14 at 18:34
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    \$\begingroup\$ @ChrisStratton Firstly, if the OP is fiddling with resistors in the kiloOhm range on normal DC motors, this will have infinitely better control. Second of all, the question is about open loop, so using an open loop servo is a perfect answer. If you use a continuous rotation servo and drive it at 0%, 50% and 100% I have not yet, ever, seen one of them not, respectively, rotate CCW, stand still or rotate CW (although CW and CCW may be reversed depending on manufacturer) and with pretty good motion continuity. \$\endgroup\$ – Asmyldof Oct 7 '14 at 19:29
  • \$\begingroup\$ The problem is that you're making a highly unstable open-loop bidirectional velocity controller, by breaking a closed loop position one. Even if what is wanted is simply a stop-start control, this is a very crude and unreliable way of doing it - people end up doing it for fiddly hobby projects because it's easy - not because it works well. \$\endgroup\$ – Chris Stratton Oct 7 '14 at 19:33
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    \$\begingroup\$ @ChrisStratton If the OP wanted high absolute accuracy, I'd expect that to be in the question. Again, I'm just answering what I read, not what I want to read. If he wants super high accuracy and torque I might just advise an expensive Panasonic motor with 1000:1 titanium gearbox, but that isn't asked, so I don't advise that. The outgoing shaft of a cheap servo already has pretty decent motion continuity and if the OP doesn't want the PWM control, my answer clearly states you can drive the motor directly, if that's not good enough or too cheap only the OP will know with this phrasing. \$\endgroup\$ – Asmyldof Oct 7 '14 at 19:46
  • \$\begingroup\$ Given the hobby-ish nature of the problem statement, a continuous motion servo is a perfect solution. At no stage has the OP asked for precision control, closed loop control, or any degree of fine control: Their only critical need as expressed is for hihg fluidity of motion. It's tempting, yet a waste of time, to presume requirements of an industrial or high precision nature and insist upon expensive professional solutions, instead of actually reading what the OP is asking. \$\endgroup\$ – Anindo Ghosh Oct 8 '14 at 2:36

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