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### Topic: motor for fast stop/run frequency turntable (Read 448 times)previous topic - next topic

#### walkingrames

##### Jun 16, 2015, 01:39 pm
I want to build a turntable with a 40 to 50cm diameter (ca. 15-20 inch), and a load of about 1 - 2 kg.

The table should make 360° in 1 Sec. Not in a continuous rotation, but with 25 ‚stop an goes'. Each stop should be at least 30ms (x25). So the motor should turn the 360° in 250ms, or each 14.4° in 10ms.

I've tried a setup with arduino, big easy driver and a stepper with planetary gear stepper specs. The specs for the motor are 904 rpm, but I only managed to run the 14.4° in 30ms. Besides the whole thing is really noisy and vibrates and jumps a lot, obviously because of the fast stop and go and the centrifugal forces.

Does anyone have a suggestion, what motor would be most suitable: a stepper or would a brushless motor or servo be a better option? What driver would I need?

Thanks!

#### MarkT

#1
##### Jun 16, 2015, 02:03 pm
First do the maths....

You want to accelerate and then decelerate going 2pi/25 radians in 1/25th of a second

Just the acceleration takes you pi/25 radians in 20ms, and w = 0.5 a.t^2, gives a = 628 rad/s/s.

Lets say your turntable weighs 1kg, with even density, radius 25cm.  Then its MoI is 0.25 M R^2,
or 0.0156 kg m^2.

torque = MoI x angular acceleration, ie 628 * 0.0156 = 9.8 Nm

Peak angular velocity is 0.02 x 628 = 12.5 rad/s (120 rpm).

torque x speed = 122W peak mechanical power required.

So you need a servo motor of 150W or more.  Yes it will vibrate like crazy, because you
are vibrating it like crazy...

So what are you actually trying to do?
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