IC for remote motor drive control

[trailrider]

hey

i'm doing my final year project at qut in australia and need a bit of help. i need to design a motor drive circuit to control the motor forwards and backwards in 20 degree steps and was wondering if anyone would know what sort of ic would be best for this kind of thing. any help would be much appreciated.

thanks

zac

 

[Nigel Goodwin]

Re: IC for motor drive control

hey

i'm doing my final year project at qut in australia and need a bit of help. i need to design a motor drive circuit to control the motor forwards and backwards in 20 degree steps and was wondering if anyone would know what sort of ic would be best for this kind of thing. any help would be much appreciated.

You need to give far more details, you have two obvious options:

1) A stepper motor, this would be expensive and fairly low power, but give full rotation if required.

2) A servo system, this would be far cheaper, give much more power, but only give a limited rotation.

A simple motor wouldn't do, you need some way of knowing where it is, a servo does it by feedback, a stepper by precise and exact movements.

You could do it with a normal DC motor by arranging some sort of signal at each 20 degree step - a micro-switch triggered by a cam, or something like that - VCR's use similar methods for system control.

 

[bmcculla]

To use a DC motor as a servo motor you can use a pot as your feedback device (the same thing that RC servos use for feedback). Just buy a large pot that you can couple to the shaft. This scheme will work as long as you don't need continuous rotation. You might be able to find a pot with out the end stops for continuous rotation. The best method for feedback uses an optical encoder. Optical encoders use a metal disk with holes in it to block and unblock light to output a quadrature signal that lets you detirmine rotation. You can buy comercial optical encoders but they tend to be a bit pricy. you could try a mechanical encoder with a bit of gearing to give more precision. You would have to move slowly or the mechanical switches would bounce and generate errors. You could also try to make your own optical encoder. Its hard to get good resolution though. If you have access to CNC machine tools you could probably come up with something that was more than adequate doing it by hand would be possible though difficult (again gearing could give you more precision). The commercial optical encoder disks are chemicaly etched to give tiny holes - 2000 counts per revolution is fairly ordinary.

On the control side you can set up a microcontroller to implement a simple PID controller. You should be able to find tons of info on google about PID controllers.

For power control you can buy 3Amp H- bridge driver ICs that are perfect for this type of motor control project.

Hope this helps. feel free to post more specific questions as you move along (These sort of projects are a lot of fun to hear about).

Brent

 

[trailrider]

hey

a few more details: it'll be a remotely actuated device, and probably can't have a voltage greater than about 9V.

the motor will most probably be just a streaight DC one, using a worm gear to slow it down and up the torque, and then some sort of gearing mechanism to transfer the power.

i'm looking at using remote control car tx/rx with a range of about 2 metres.

sorry i can't be more specific, but it's something pretty special and i don't really want anyone to know exactly what i'm doing just yet.

thanks
zac

**Edit**

I want to use two signals at different frequencies, one to power the motor forwards, the other backwards. I have tried to think about how I can do this using filters, and I can, but that way I can't tell the motor to run for a caertain amount of time.