Let's Make Robots!

CRAB - a 4WD bot - now industrial yellow/black :)

Got it moving around


Hi all,

Behold my new little toy, the CRAB. This is my attempt at creating a 4WD rover like bot, the main target here beeing making use of the little motors I had lying around for quite a while. 

These motors are quite small, model FF-30PK Mabuchi (http://www.mabuchi-motor.co.jp/en_US/cat_files/ff_030pk.pdf) very fast, pretty low torque. So to get any usable output out of them I needed reduction gearing. 

The reduction ratio I have chosen is 20:1 total in two stages, 5:1 first then 4:1. The 20:1 ratio applyes to each wheel pair. 

All mechanichal parts except the rods, the plastic spacers and the black rubber tires are cut on the Phoenix CNC. 

I'm almost finished creating the driver board(s), it is a stacked design dues to the very little space available.


From 4wd

Below we have the driver board featuring an L293D and 7805 regulator:


From 4wd

And the driver "brain" the ATTiny2313 board:

From 4wd

I won't show the back ... it's ugly as hell :D

The idea behind this "smart" driver is to separate the driving functions (speed control, handling encoders, etc) from the main brain which is to be built yet, so it will be able to issue simple commands to the driver like go forward X mm. 

Update - July 6 2011 - Movin'

Added a short video testing the driver electronics. PWM is working, the speed in the video is probably close to the lowest I got.

Going straight forward or backward, I think I can lower the speed some more, for turning I have to increase it with 20 to 50 percent (just guessing now). 

Next is adding encoders ... 


Update - Sep 19 2011 - I haz brainz and claw 

Past week and this weekend I worked on getting the crab ready for RoBotX's challenge, I got the following going on so far:

- added encoders and found an use for them: I'm controlling the bot in steps

- manufactured and added a Master Control Unit aka brain - based on an Atmega 328 running the Arduino bootloader

- the brain can talk to the motor driver trough I2C so the actual driving of the motors and handling of the encoders is offloaded frm the brain.

- I managed to create a (working!) claw for the crab, checkout the testing video, I think I will need to add some limit switches in there ... construction details later on. 

- I have created IR sensors to use them as obstacle/range detectors ... still have to mount them and test them but I think they will work great. The idea behind this comes from this tutorial on www.gioblu.com, it works pretty well in my tests so far.

Next is to put everything toghether and maybe make the deadline 2011-09-23 06 :)

And some pictures: 

From 19.09.2011
From 19.09.2011

Update - Sep 20 2011 - I haz claw mounted

Quick update:

- mounted the claw into it's final position

- added 2 IR detection sensors for front/side collision - untested I might also want one right under the claw to sense something got in there

- removed encoders for rewiring ... I somehow missed the fact I could not replace the batteries with them mounted this way ... need to rewire

- tidyed up all wiring on the bot to make it look nicer 

TODO: the whole lotta programming ... :/

Update - Oct 14 2011 - I haz been painted dude

While CTC lectured me pretty good on how painting should be done (thanks again for taking the time Chris), I just could not resist attempting to paint it without dismantling, grounding, sanding etc, etc especially because I got my daughther excited about helping me out :)

Se we painted it together first in white, and then in yellow/black. It came out very amateur looking but hey it's painted :)

From 4wd

On the programming side I think I'm pretty close to done, but I still have to write a calibration routine so the sensors are adapted to variable ambient lightning.  

Will update....

Update - 05-03-2012 - EOL 

The CRAB is officially E.O.L. it's still in one piece but the mechanics failed after some hair got stuck in the gears causing the super glue to unglue and the gears to rotate freely around their axes. No fun fixing it so I'll leave it to rest as a remainder of the times I did not own a 3d printer ;) 

I'll probably will have to get the motors and the brains out of it but I'll keep the case in one piece. 

So RIP CRAB you were fun ... maybe I'll revive it 3d printed sometime.

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That's an idea, JAX. He looked like he got more travel backing up that going forward (at least in the first video).

Great robot, though.

Amateur, bah. It looks so official now. Perhaps it needs one of those backup beepers like forkifts have lest it back up and kill someone :)

Beautiful! When will it save the Teddy bear? We want to see it in action!

are you going to upload a video with your crab witha claw ?test drive? ty

... as soon as i get to it :)

Wow those gears are very impressive! What size bit did you use for that? I agree you should put up some video the CNC it seems like an amazing machine.

I use a 1mm bit for the gears, it's a standard Proxxon end mill.

Yeah a time lapse will be done but not on this one :)

I love the wooden gears.  I presume the unused holes at the ends of the claws are for mounting some sort of rubber grips or something?

... as you see in the new picture I added the missing part.

Ah, I see.

 But could be for both...    :-)