SparkFun Forums

[chris890]

I am currently working on my Mechanical Engineering Senior Design Project and now need to figure out how to drive a small turn table device (8 inch diameter x 1/4 inch thick aluminum wheel).

I need to meet the following requirements:

-Move Disk 45 degrees, stop for a set time and repeat movement (each cycle moving in same direction)
-Time between each of these cycles adjustable from 1-10 seconds with 0.1 second accuracy
-Time adjusted using knob or preferably an analog display with increase/decrease button

I was thinking of using a stepper motor but do not know how to setup up a controller to meet the requirements. Any advice on how to do this would be greatly appreciated! Also, please forgive my ignorance of electronics, Thanks!

[waltr]

Lots and lots of info on driving running stepper motors in the forums here and on the web.
Search and read.
Hint: There are many chips designed just to drive and control steppers, look these up and read the data sheet and app notes.

[Mee_n_Mac]

I need to meet the following requirements:

-Move Disk 45 degrees, stop for a set time and repeat movement (each cycle moving in same direction)
-Time between each of these cycles adjustable from 1-10 seconds with 0.1 second accuracy
-Time adjusted using knob or preferably an analog display with increase/decrease button

Pretty much any simple microcontroller (MCU) will do; to take the user input, update a display and feed the stepper driver. The driver will offer a number of parameters to be set by the MCU; including speed, acceleration, etc. The driver must be sized (voltage, amperage) to the motor. And the motor sized (torque curve) to the load and it's moment of inertia to meet the speed and timing and accuracy reqs.

More reqs to be filled in ;
- How much time to move 45 deg ? +/- ?? secs
- 45 +/- ?? degs

So first learn about steppers and their torque characteristics and pick one that can be made to work. Then pick the driver and then the MCU (likely some Arduino due to existing code base) and auxiliary stuff.

http://www.nmbtc.com/step-motors/engine ... ationship/
http://users.ece.utexas.edu/~valvano/Da ... ection.pdf

[chris890]

Thanks for the replies, here are the additional reqs:
- to move 45 degrees needs to be around 0.5 to 1 second.
- the accuracy of the movement should be +/- 2 degrees

I'm thinking maybe I need to include a proximity switch to guarantee the correct stopping point.

[Mee_n_Mac]

I'm thinking maybe I need to include a proximity switch to guarantee the correct stopping point.

No need to, that's the beauty of a stepper ... so long as it stays in sync. You command a number of steps and it turns that number. Each step is some # of deg. A typical stepper might be 200 steps/revolution or 1.8 deg/step. Higher resolutions are available and microstepping (Google it) can be used too. You just need to ensure the motor can develop enough torque to move the load and complete the step in the time allotted.

My guess is that getting that mass accelerated to speed and then decelerated to a stop to rotate 45 deg in 0.5 secs is one hell of a motor (of any type). But you're the ME student, that's right up your alley.

http://homepage.cs.uiowa.edu/~jones/step/

[oldtemecula]

A little Arduino code to a driver and I could have fun all week.

My worm drive idea would be way too slow. Something like this image using the gear ratio for speed and 25x 1.8 degree count to get to a close ~45 degree stop point. Maybe motor 1:2 disk ratio to speed up disk movement and stay in the stronger torque range of the motor. Use the max motor current with higher voltage, this is better at starts and stop,helps prevents over rotating or start up sync slip. On the faster side one 360º disk revolution must be done in 8 seconds? Sounds like a rodeo to me. I am new to this so just guessing.



Christopher