Let's Make Robots!

360bot - Stepper motors are cool!

So far just a Stepper motor hooked up!


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Strange, some Google videos are down. Link to the one down now when writing this, here.


So I thought; With 360 degrees overview, I am unbeatable, I can navigate anything. I took an old toy-tractor and in amazingly short time got everything fitted onto it. That tractor was made for this, I thought.

I knew that it would be crap at steering, as the wheels where big, and the rear wheels (or front sometimes, this is 360!) where locked to each other, giving no differential steering, and slow turns.

But after a short while I got really tired of it; It is turning not on a plate, but on a big football stadium! :)

So it is going to die now, 360bot will not be on a tractor. Still I thought it looked cool :D And so I took some snaps just before I now go back and tear it apart. Click on image for more images..






I wanted to transfer power and signals to the moving part. I tried all sorts of stuff, but did not relly manage. So in the end I just gave up and used a 3.5mm jack-stick. Simple and easy.. but only 3 lines open.. So i had to give up on my first thought of having several LED's spin around. The thought was that they should sort of draw a rotating "radar image": Closer objects would make LED's closer to the axle light up.

However, I really like the sound of it spinning, and I will make something up! Added new video with the jackstick-trick. The LED on it is simply using the Sharp signal directly - that is actually quite a nice hack in itself :) I will always add a LED on the sharps from now on, nice indicator!

For a long time I wanted to hook up a stepper motor, and finaly I got to it!

Wow, these are cool! I enter this as a robot because I simply have to make a robot with this. I do not have much time, but now I have told you all that I am going to make a robot with a stepper motor, and so I will have to find the time :)

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i'm really glad to see someone do somethign with steppers.  These motors are soooo cool.  Very versatile and easy to control...very accurate and torquey and teh different stepping modes (half/full/double step) make it very versatile and good for different situations, sacrificing accuracy for torque (rather than speed).


The only downsode for  steppers is that you will usually need a seperate circuit to drive them (the microprocessor will only supply the triggers)...and you must be very careful as they swallow up huge amounts of current, and you need to use soem pretty high-grade resitors with them.


I've had cases where the resistors generate so much heat that they melt the surrounding wires...so be cautious!



Nice. I've always been curious how fast a stepper motor can spin. Floppy drives were spun by stepper motors, weren't they? The electronics store downtown has a 'grab bag' with 4 or 5 random stepper motors for about $25. I've considered picking one up to play with them, but I'm not sure if that's a good price or not. They sound fun though.


If you want something cheap and aren't too particular you can usually find decent stepper motors from surplus dealers.  A few months ago there were even some small stepper motors somewhere for $.50 each.  BGMicro had some excellent motors for $2.75 (instead of $8 from Jameco) but they sold out.  Actually, most of the surplus sites seem to be out of good stepper motors right now, so it could be a good deal if they are big or high quality motors. 

The "grab bag" sounds very fair. I think I gave $25 for one. And I think you want as few amps and ohms as possible unless you want to drive something with it - I just like it to turn. Apart from (and including) this, I have no clue.

I just hooked it up to a standard 28 picaxe board, no special H-Bridge or anything. It says 12V, but I give it 5, and do not feel much difference if I give it more. It has 4 "signal" that I feed 2 by 2 with pause between, and 2 "Volt", that I have just short circuited and give both 5V.

I may learn some more and tell about it. For now I am looking into making some sort of cool radar with it. I think :D

In work, my colleague and I have just completed a stepper driver. It drives a 4-wire motor 50 steps per rev with 64-microsteps per step. Get this: it has feedback using a Rotary Variable Differential Transformer. My colleague did the electronics (three H-bridges: two for the stepper and a third for the RVDT excitater. I did the software (including PID) in an FPGA. It took us nearly 8 months, but it's a sexy piece of kit.

Guess what? He's one of the ones who couldn't explain FETs ina language I understand. Maybe I'm just thick?

I don't understand why you'd need an H-Bridge for the steppers.  Can't you just reverse the firing pattern on the steppers' input pins?
That is what I do.

Indeed. The H-bridge is used for controlling the currents through the coils in both direrctions while micro-stepping.

Rather than pulsing each of the coils on and off in sequence, they are actually fed with a pair of out of phase sinusoidal currents . This means that even though the stepper only supports 50 steps per revolution, we can microstep, giving us a resolution of 0.1125 degrees!

Told you it was a bee-atch! 

So you are saying that you first atract the thing like "normal".. but instead of atracting in a row, just in between each attraction, you push away from the one leaving?

I'm saying tha instead of switching the "attraction/repulsion" on and off, you ramp it up/down gradually. But in addition to that, yes, the current reverses so that the permanent magnet gets pushed away. I thikn your solution probably doesn;t do any pushing - only pulling.