# Choosing right motor

Hi all,
Im doing project like this Image .

My rotating table is bigger radius od 0.7M ( thats an outer gear radius) and i need to pick up right motor to do it. Precision is very important, thats why i want to use stepper.
Weight on table could be aroung 100kg ( human).

Ofc, motor is not handling all that mass, he is handling fricition and momentum for rotation.

Do you have some advice, or hunch what king of motor would do this job ( power, amps etc...)

Maybe it would be overkill for this task, but better more power than less

What kind of driver should i use for this motor?

Thank you

Can you do some tests to measure the torque needed to turn the table? That is the best way to get an estimate that can be used to select a motor.

How fast does your table need to turn?
What gear ratio will there be between the motor and the table?

Keep in mind that a stepper motor that needs more than about 1.5 amps per coil will also need an expensive high current stepper motor driver.

also look up the AccelStepper library

So, this is way i calculated it.
Because of imperfections in gears and with friction i estimated max of 100N of force ( i think this is above real values ) but there is no practical way to find real values, so this needs to be estimation.

Radius of driven gear is 350mm. So max torque is 100N*0.35m = 35Nm.

Gear ration between driven gear and operating gear would be between 12/20. ( still not designed)
So my calculation says that torque of operating gear needs to be 35Nm/15=2.9Nm.

I know we are dealing here with rought estimation, but it is better to spend little more money but to be sure it works.

Is my math good or i missed something?

I found this drive, it has motor name in itself so i think it might be good. Driver link.

Thank you!

djuro11:
Is my math good or i missed something?

I don't trust my own maths sufficiently to offer an opinion. I make too many silly mistakes.

Hopefully someone else will come along.

there is no practical way to find real values

Can't you do some tests - try rotating the base with a string wrapped round it and a spring balance pulling the string?

If you have a 700mm diameter gear why not drive it with a 10mm gear for a 70:1 reduction? Or maybe use some form of worm gear drive?

...R

I will try to make some tests tomorrow. So ill come here with results

Just want to know, is the driver and motor from my last post good pair?

Robin2:
If you have a 700mm diameter gear why not drive it with a 10mm gear for a 70:1 reduction? Or maybe use some form of worm gear drive?

...R

Unfortunately, reduction on gear is calculated by dividing number of teeths of both gears, we are unable to create that small teeths on gears.
On 10mm gear teeth would be very small and im afraid they would snap under that force. (we are creating gears on 3d printer) so it wouldnt be hard as steel ones

djuro11:
Hi all,
Im doing project like this Image .

My rotating table is bigger radius od 0.7M ( thats an outer gear radius) and i need to pick up right motor to do it. Precision is very important, thats why i want to use stepper.
Weight on table could be aroung 100kg ( human).

Ofc, motor is not handling all that mass, he is handling fricition and momentum for rotation.

Do you have some advice, or hunch what king of motor would do this job ( power, amps etc...)

Maybe it would be overkill for this task, but better more power than less

What kind of driver should i use for this motor?

Thank you

If you have a human on the table you'll have to handle the torque generated by
the subject, which can be suprisingly large (the first thing people tend to do on a turntable is try to
turn it, people are like that).

Anyway you need further reduction gearing of about 10:1 based just on the size of your existing gears
and my guess that 30rpm is a suitable top speed. Most motors are around 4000rpm, so about 100:1
total reduction is about it, split into 10:1 gearmotor and 10:1 for the drive gear (estimated from
the example image). I'm assuming a standard DC motor here. A stepper might be more like 1000rpm
top speed, note.

Once you have 100:1 reduction, that changes your desired torque in proportion. Then pick a motor,
then pick a driver than can drive the motor chosen.

Se, unexpected behavior of humans on table isto one more reason why leđa Power wouldnt be waste.

As i cant measure forces i guess Thatcher motor i mentioned be more than capable od doing that job.

Justin a question about the driver i mentioned on one of posts above.
How is it powered? Some special adapter?