Wheel solution for those cheap stepper motors?

Oldbitcollector (Jeff)

I was challenged by @Prof_Braino a while back to come up with a sub $20 robot that incorporated two of those cheap stepper motors, a bluetooth module, and an ultrasonic sensor. At the time I wasn't buying in enough volume to meet this challenge.... I am now.. I think a low-end robot is completely possible.

I've almost worked out a mounting base and the third position will be a tail dragger (or cheap caster wheel).

Where I'm stuck is trying to find a wheel that fits those motors. Has anyone seen anything that fits?

Jeff

max72

I posted one here:
http://forums.parallax.com/showthread.php/138125-Erco-s-Figure-Eight-Challenge?p=1157894&viewfull=1#post1157894

They are 3D printed. The wheel itself is PLA, while the "rubber" is printed with soft PLA from Orbi tech.

Massimo

Prophead100

Here is a robot using the $3 stepper motors and a BOE. The chassis and wheels came from a toy truck at Goodwill for a couple bucks then I added a ping and a caster wheel completes it. Simple, cheap, fun and under $20 total not including the BOE

erco

Laser cut acrylic wheels on a stepper motor BoeBot!

Beau Schwabe

Jeff,

Whats the OD of the stepper motor shaft? ... If you don't have access to laser cutting, the "circle" cutting attachment for a dremel tool works nice. For the shaft connection I have found that a friction fit with 1/4 inch Polyvinyl "Aquarium tubing" works well.. especially if you use multiple acrylic disks stacked together for a single wheel.

...And for the size of wheel you would need, the Acrylic, Plexiglass, etc. can be FREE for the asking at your local hardware store since it would be considered scrap. I've hit up Ace, Home Depot, and Lowes before and all three have been very helpful when it comes to asking for their scrap material.

Oldbitcollector (Jeff)

Agreed! I've already started down the path of cutting acrylic to create the wheels. @erco you don't happen to still have the specifics on that wheel do you?

Grabbing my micrometer from the shop today.

Jeff

ajward

Those acrylic wheels are sweet!!!

I was looking for a way to mount wheels on the stepper motors and ran across these hubs on eBay:
http://www.ebay.com/itm/STEPPER-MOTOR-PREDRILLED-ALUMINUM-HUBS-5-PCS-/120660614713?pt=LH_DefaultDomain_0&hash=item1c17eede39

I haven't bought them yet 'cuz I haven't been able to get the stepper motors to run. :-(

Amanda

erco

@Jeff: I have the wheel file in ai but can't attach here (invalid file type). Can get it in Rhino if you prefer. The wheel is a beautifully tight press-fit onto the stepper shaft. That's a BoeBot chassis, and since the stepper's offset output shaft is higher than the servos' shaft (visible in pic), I reduced the wheel diameter to keep the chassis level using the stock roller ball. But those are the stock BoeBot rubber bands on the wheels for traction.

@Amanda: How can we help you and your steppers? We've mentioned them in threads a fair amount (see below). Those cheap steppers come with a ULN2003 driver board only good for one stepper, but you can see the 2803 I used in my breadboard. Works a treat for both motors.

I will say that these steppers have clear limitations. They are not fast, they have enough backlash to frustrate, and they likely strip very easily. When you put a BoeBot -sized wheel on them, there's a tendency to grab the wheel and rotate/backdrive the stepper. I honestly haven't done that yet, but considering the fragile tiny teeth on the plastic gears inside, one twist might be the end of them. I did a teardown on one at http://forums.parallax.com/showthread.php/141149-3-Stepper-Motor-amp-Board?p=1144016&viewfull=1#post1144016

My quickie BS1 Stepper Bot: http://forums.parallax.com/showthread.php/142831-Old-School-Rapid-Prototyping?highlight=stepper+motor

Oldbitcollector (Jeff)

@ecro, or email it to me jeffledger (at that free email google runs). Do you mind if I use that file to have a few of these made for Propellerpowered?

Jeff

max72

Erco, you can post any file as long as you zip it.
Being 2d a dxf profile maybe is the best solution.
If you don't mind posting it.. having a proven press fit profile would be nice.
Massimo

ajward

@erco Not sure what's up with them. I used your sample code which seemed to work quite well for you, but my motors just sort of vibrate without turning. :-|

Prophead100

If your trying to get the motor working, here is some simple code I was using for a BOE and $3 stepper robot....

Prophead100

ajward wrote: »

@erco Not sure what's up with them. I used your sample code which seemed to work quite well for you, but my motors just sort of vibrate without turning. :-|

Some reasons that I have seen that cause vibration instead of motion: (1) cycling through the sequence steps too fast and (2) wrong wiring, (3) bad UNL2003 board, (4) wrong step sequence and (5) low battery for the motor.

erco

Prophead100 wrote: »

Some reasons that I have seen that cause vibration instead of motion: (1) cycling through the sequence steps too fast and (2) wrong wiring, (3) bad UNL2003 board, (4) wrong step sequence and (5) low battery for the motor.

+1

ajward

Prophead100 wrote: »

Some reasons that I have seen that cause vibration instead of motion: (1) cycling through the sequence steps too fast and (2) wrong wiring, (3) bad UNL2003 board, (4) wrong step sequence and (5) low battery for the motor.

I was using a Stamp board, but I'll give your spin code a shot. (As well as verifying the other issues mentioned).

I know they're cheap, but I'd kinda expect one of them to work! :-[

@

max72

Check Prophead100 suggestions. If all of them have the same issue probably 3 is not you case.
Do a very slow step sequence (few Seconds between each pattern sequence) and check the leds light correcly (issues 2 and 4). this will also check bad wiring, broken connection, pin not working.
Use a working code.. the wrong pause in the sequence pattern makes the motor vibrate too.

nightwing

If still looking for wheels and even tracks try here...

http://www.pololu.com/catalog/category/24

erco

Attached is a zipped file with the Adobe illustrator file of my wheel. Sure Jeff, make all you want. I tried patenting the wheel long ago, but they just laughed at me at the PTO...

Oldbitcollector (Jeff)

Thank you @erco!

That'll save me a little time in "recreating the wheel".

As soon as I finish a base and mounting solution for the motors I'll have something interesting to offer. Finally I'm ordering enough of the the product lines to offer competitive pricing on this stuff.

Jeff

Gareth

Here is what i use on my sub $20 dollar robots :-
Left to right :-
lego ....not cost effective
Playmobile :- cost effective
Wooden local hobbyshop with rubber "O" ring :- very cost effective and for me preferable.

I use a lego coupling link.... just a few snips and presto an interference fit that hold very well.

Prophead100

If your cutting your own wheels, one thing to think about is matching the diameter to the step angle of the motor so that each step of the motor correlates to a precise distance. It can make navigation easier....

Prophead100

For those working on a stepper robot, here is my code for the line following "you've got mail" contest Sac Robotics is working on... It runs each motor in a separate cog with either 4 or 8 step cycles, runs a ping in another, serial comm in another, and the control loop in a final one. Doing the parallel processing leads to some interesting coordination such as when to wait for another wheel to do something.

-Prophead

mindrobots

Thanks for sharing the code, Prophead!

We have a growing army of these little stepper driven robots as I'm using them for 4-h projects this year. It will be fun to have some more code examples for the kids to see.

Prophead100

I cleaned up the code and made this into an object. Not too fancy but it makes good use of the parallel aspects of the processor. I have used the object methods on the same robot for both line following and autonomous wandering in the house. You can see it following a line and dropping off a business card in a "You've Got Mail" Challenge at http://www.youtube.com/watch?v=yzIWk8r3IwQ