Slider & turn table: indication of motors

Hello all,

I am new to working with small-scale motors in general, and I really needed the indication of the right motors to buy in order to do the following simple tasks.

I am working on a project where I will need:

  • A motor capable of moving a Sharp IR sensor vertically, more or less like a slider. I need something that can move very smoothly, in a movement that goes up and down modulated by a sine equation, simulating a "wave" moving only up and down. I have tested a couple of slider potentiometers and they did not fit very well, due to the low sensibility and power of the motors.

  • A second motor that turns a circular table of 30cm diameter continuously, slowly and very smoothly, similar to a turn table but slower. Such table will hold in the end a couple of objects that will altogether weight from 0.5 to 1kg. Thus it cannot be a very low torque motor to do the task.

Both motors will have their acceleration changed in realtime by other components.

I am thinking that I can solve both problems with the right DC motors, but it would really be great to have an idea of the right ones for each task, since both must be able to turn very slowly & w/ the right torque.

Thanks a lot! : )

For the first motor, it might be best to use a stepper motor driving a threaded rod (ACME thread would be best and cheapest for your app - you might try regular threaded rod, but depending on what kind of smoothness and accuracy you need, it may be more trouble than it is worth). The rod would have a follower nut, on which the platform the IR sensor would be attached. Note that you'll likely want to incorporate some end-of-travel sensor switches or such when using a stepper.

You could also use a regular DC gearmotor, of course - but you would need to implement some kind of positional feedback mechanism. This could be a couple of limit switches (like the stepper) and a slotted disc on the motor (so many slot pulses would equal one rotation of the output shaft, which would equal so much travel of the follower nut on the threaded rod).

For the second motor, another DC gearmotor would work ok. You could attach this directly to the center of the turntable, or you could use the turntable as a large "gear", and have the motor rotate the turntable from the outside or inside of the edge - using a geared or friction drive (the latter would be easier to implement, and likely smoother - but there could be slippage). Just make sure that the whole of the turntable is mounted in such a way so that its weight, and the weight of the objects on it are distributed over a broad surface. Look at how laxy susans are made (and/or use such a bearing) - as well as how the turntables of a microwave are supported (fairly easy to homebrew as well).

You could probably get by with motors with a gear output ratio between 50:1 and 200:1 - but you should calculate things first before you purchase a random motor.

First task is to replace as many of those adjectives by numbers, phrases like "like a turntable but slower"
are meaningless. Acceleration isn't relevant for a very slow turntable BTW.

You seem to confuse a motion system with just the motor - you are needing linear motion for the
IR sensor so you need more than a motor, perhaps a leadscrew or servo arm. A slow turning
turn table will probably be geared down, so a low torque motor may be perfectly fine (whatever
"low" means here.)

Some sketches of the mechanical parts of the system are a good place to start. Then once the mechanical
parts are decided you can think about sizing the (gear)motors.

Thank you hugely, cr0sh! I have not yet thought about a threaded pole, and your suggestions were great and certain. I am just not confident in using a Servo to run it: I only need a good control of its speed, put not exactly its positioning.

MarkT, thank you for your input. Indeed, I lack knowledge and vocabulary to describe this. This is not my area, and I am learning. I will think about the setups cr0sh suggested, and come back here to ask more specifically with sketches.

Thanks!

Hey all,

Just checking here back to say once again thank you for your help. The project I was working on is finished, and can be seen here:

http://digitalmedia-bremen.de/en/project/the-new-velocity/

I finished up using two stepper motors. One, to rotate the “turntable” with controllable speed and direction. The other, to control the vertical slider on a threaded pole.

Thanks!