Stepper Motor Robot

A quickie testbed to demonstrate these $2.50 stepper motors and ULN2003 driver boards from Ebay China: http://www.ebay.com/itm/271025356632

They are slow and have some backlash, but they get the job done and are good for experimenting. Currently driven by a simple BS1, which is slower and fewer (8) I/Os than my favorite PICAXE 20M2. That upgrade is coming!

square: http://www.youtube.com/watch?v=TLdkKKMfUP0

figure 8:

hi
from servo's to steppers their's no end to your talents look forward to reading your write up sir.
jinx

Brief discussion and pic in thread at http://www.picaxeforum.co.uk/showthread.php?22230-Very-cheap-stepper-and-driver-to-play-with&p=218336&viewfull=1#post218336

That chassis was a quick slam-build just to see how well the steppers work, I had not used steppers previously. I must admit, I'm pretty impressed how easy to use and accurate they are. On the down side, they are slow, get warm in use (pull lots of current) and they require 4 I/Os per motor. But for certain applications, they may be a useful option.

Faster run, 38 seconds versus original 56 seconds. Eliminated 1-second stop at center. Shorter timing loop on the stepper pulses increases motor speed at the risk of stalling the motor by skipping pulses. Slight acceleration (velocity ramping) used here at start, finish, and center transition from left to right turns. Might be as fast as these can go at this voltage (7.4v) with a light load on them.

erco said:

. . . . and they require 4 I/Os per motor.

Click to expand...

Not all stepper motor control methods require 4 PICAXE IO pins.

For example, there is the On Electronics AMIS30622 stepper motor chip which has a current rating of 800 mA. These are i2c bus controlled and available in an SOIC package (not DIP format).
It can be programmed for half, quarter, eighth and sixteenth stepping. There are settings for min and max velocities, acceleration and deacceleration, running and holding current, etc.
It operated over -32768 to +32767 steps (in 16 th micro-stepping mode) which with a 200 step per revolution stepper motor gives you -10 to +10 revolutions (around +/-42 with a 48 step per rev motor), but you can reset the position and resume for something near continuous rotation.

Thus with just 2 (i2c comms) signal wires you could control up to 32 stepper motors. No doubt there are other i2c based stepper motor controllers available as well.

I posted a “Getting Started… “ tutorial for the AMIS30622 chip back in April 2010 here:
http://www.picaxeforum.co.uk/showthread.php?15071-Using-the-AMIS-30622-Stepper-Motor-Driver-IC&highlight=AMIS

Great chip, westaust55! That looks quite capable with lots of features. It's interesting that according to http://www.onsemi.com/PowerSolutions/product.do?id=AMIS30622C6228G , the price is $ 3-4. I can get a 20M2 for $4 (phanderson, RIP). That's a bargain. At $4, the Picaxe is cheap enough to be used as a standalone stepper driver, servo controller, or anything else. Makes the stepper motor & driver board look even better at $2.47.

What's not to like about PicAxes?

I opened up one of these motors to have a peek inside. Details & pics at http://www.picaxeforum.co.uk/showthread.php?22230-Very-cheap-stepper-and-driver-to-play-with&p=223606&viewfull=1#post223606

Hi erco! Very nice project U have big talent. I habe in plan build something like this but I dont have too many time. Work... :/

Just a quick experiment to use those very cheap stepper motors. A robot with stepper motors can do fairly accurate dead-reckoning navigation without wheel encoders.