Turntable Product Purchasing Advice
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Turntable Product Purchasing Advice

by Pyriphlegethon on Mon May 06, 2013 2:05 pm

Please direct if this is not the appropriate place for this query.

Greetings!

I'm a fledgling Arduino hobbyist looking to build a simple turntable. I've got the concept working with some relatively simple code and a tiny servo motor. Motor turns, camera triggers, repeats. Now it's time to implement the idea on a real scale.

I have the lazy susan bearings for the turntable but have yet to construct the actual table. It seems like ideally a motor would sit in the base, below the table, with a direct physical connection of its shaft to the underside of the turntable so that I can directly set the rotation of the table by commanding the servo to turn in degrees. Or if this is impractical for any reason I could do some sort of belt driven system with a DC or stepper motor as well--I won't necessarily need the ability to send the motor to specific positions like a servo does. I see more people adopting the belt method though the direct drive seems a more intuitive application so I'm likely missing something there.

I'd be putting products up to 10 lbs in weight on the table and the table itself may add another pound, so I would need a motor capable of rotating that kind of payload maybe 5 degrees at a time. Speed isn't critical. Would you recommend getting the motor shield for the Arduino for that type of application? I know that, while the 5V USB power gets my mini servo going now, a 'real' motor capable of turning the table will require external power. I have some 12-volt Chinese Li-Ions that have worked well in the past. For this simple an application am I better of with an H-bridge and simple brushed DC motors maybe?

If more detail is required let me know. I look forward to a response and thank you for your time.
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Re: Turntable Product Purchasing Advice

by adafruit_support_mike on Mon May 06, 2013 8:25 pm

A stepper motor will allow you to control the turntable "open loop", meaning you just tell the motor to move so many steps and don't bother to measure the actual position of the turntable.

As for running the turntable directly from the motor's shaft, I think you'll probably run into some power and/or torque issues. Those are hard to characterize since they depend on how smoothly the bearings run, where you place the load on the turntable, how large the turntable is, etc.

IMO, you'd be better off using a belt drive to reduce the motion but increase the torque. There are 72 5-degree steps per circle, so one solution would be to have a two-belt system where the stepper motor has a 1" wheel on the stepper motor's shaft, a shaft with a 6" wheel and a second 1" wheel, and a second 6" wheel that drives your turntable. Arrange the belts so each of the 1" wheels drives a 6" wheel, and you'll get a 36:1 motion reduction and a 36:1 increase in torque. For each half-turn of the servo's shaft (180 degrees), the intermediate shaft will turn 30 degrees (1/6th of 180) and the turntable will turn 5 degrees (1/6th of 30).

You can vary the wheel ratios for other values, but that's the general idea.
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Re: Turntable Product Purchasing Advice

by Pyriphlegethon on Wed May 08, 2013 1:54 pm

Mike,

Thank you for your swift response. It's great to have an electronics supplier willing to take the time to help the ignorant not waste their money :)

It seems all the motors are of a high-speed, low torque design so you're belt recommendation may be the solution. Could I use gear reduction to increase the torque but have the fixed axel of the table running right down the middle of the final gear and attached to it--so that the final gear turns the table rather than worrying about a belt and its attachment point?

Would this shield be the one to get for driving the motor you referenced? And I did find this and this for the belt, but I couldn't find the gears/wheels on your site. I'm not yet understanding how it would all connect.

If I should need a much higher torque motor in the future for more substantial loads (100 lbs) in a larger version of the table, do you have any motor options for that? I think continuous DC motors might work unless the rotation is drastically inconsistent between steps. What type of shield with external power would I use for that?

Thanks again!
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