Inexpensive crab module?

I’m looking to design a crab drive robot over the summer… on my own budget. That budget? A McDonald’s check… sigh So… here’s my question. Can somebody design a relatively cheap and innexpensive crab drive module? Or atleast give me ideas on what to use. The entire robot will be 28X28. I’ll be using 4" diameter wheels. I don’t know what kind of wheels to use. If anyone can provide me a link to innexpensive wheels that’d be great. Also be using drill motors geared down for the drive… b/c I can get them very cheap. So… if anyone needs any more information then ask. I know I probably didn’t provide enough info but it’s the best I can do on what I know.

PS - I would ask some of the engineers on my team to help but they are mostly on vacation for a few months from robotics.

You say that you will be using drill motors. Will you also be using the drill transmissions?

If you are you may be able to direct drive the 4" wheels to the drill output and save the cost of chain/belt/pulley/gears.

A chunt of plastic such as Delrin or Nylon can may a good inexpensive pivot/thrust bearing for your crab module and it is much cheaper than roller bearings.

Matt B.

i think wildstang’s crab drive from 2003 is a good bast to copy from it had 4 delrin bushings around a bottom plate that had some pillow blocks the wheel and a transmition and the weight was supported from the top by what i believed to be something like a lazy Susan bearing, not good for side load but it didn’t matter with the delrin at the base. i wish i could find the pictures of it but it looks like nobody has tagged them in CD media yet im shure Raul Could elaborate further.

You can find many pictures in our gallery. Here are some albums that have some shots of the modules and mounting points. If you want more information, I would suggest contacting Raul. He’ll be able to give you more details than I could.

(Note that in the side-by-side album, you can see our mythical stacker that was removed early on at Great Lakes)

So… to use Nylon… I would put the Nylon between the frame and the module to reduce friction? And then a bearing on the shaft between the shaft and frame. I think I understand what you’re trying to say. Anyone know where I could get some of this stuff? in the plastics section.

Does anyone know where to get a microcontroller and operator interface/radio for cheap? Needs analog outputs and C programability. I found one… but I just wanna shop around before commiting.

RobotCombat is a great place to look for anything related to robotics.

Thanks… I’ve been to this site multiple times.

Question: If I buy an R/C transmitter and receiver… How do I incorporate that with the controller? And also… how would I go about making my own transmitter? With joysticks and all… I know how to do it with the FRC operator interface but what about with a different one?

I don’t know, you should probably try Greg Needel, he might know.

I PMed Greg.

I also found a transmitter/reciever package from RobotMarketplace but would prefer to make one identical to ours from this year and the past couple of years.

I’m using the MTJPRO11a microcontroller from

The best deal on a combination radio controller and C programmable microcontroller right now is the VEX kits selling for $150 at radioshack.

Will the VEX kit radio and microcontroller work for a bigger robot? I have a VEX kit ordered… but for a VEX robot.

You can use the Vex transmitter/receiver/microcontroller to drive Victor speed-controllers, which can then be used in a manner similar to FRC to drive motors on a big robot.


Hm… how many Victors can I run with one VEX microcontroller?

I’m pretty sure it’s eight, but you’ll need a second power source to use 12V, 18V, whatever, (or a converter) the controller runs on 7.2V

The VEX/Victor combo is out of the question anyways. Victors are waaaay too expensive. $100+ a piece?!?! I don’t have to use Victors do I?

Well, that depends on your situation. You might be able to get away with an R/C car controller if you’re not drawing too many volts or amps–look at a site like or for some non-Victor speed controllers. (Scaling down your design might help here.)

You could also go with relays of varying sizes, which are cheaper–but you do that at the expense of maneuverability. (Would you drive your robot with Spikes, current issues notwithstanding?)

It can be done on a budget–it just takes time and a keen sense of bargain hunting.

Spikes have been thought of on different occasions. They go full forward/reverse and neutral right? So would spikes still work for crab drive? And relays… I don’t know what they do.

Don’t use relays. You’ll regret it. You need smooth proportional control.

With that said, a cheap 12 volt pwm forward and reverse speed control with decent current handling ability is something everyone in this world needs but no one in this world can find.

The cheapest you’ll get is $50 which will run maybe at 9.6 volts and I have no idea about Vex or other controller compatibility.