Let's Make Robots!

Moo Bot v1.1

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Moobot Update 3, Oct. 1, 2012 (Version 1.12)

I'm waiting on a mail order for a bunch of the electronics that will go into OddBot's motor controllers, but in the meantime I attempted to finish the "body" work for the bot (still have a bit more to go) as well as to begin to write some of the code for the robot using an Arduino-simulated version.

That included making a small robot head that would contain the Ping ultrasonic distance sensor, two LED arrays to indicate "happiness" and "sadness" and, just for the heck of it (not even sure what I'm going to use it for yet), a button -- er, tri-color LED -- nose. The head is also able to rotate using a small servo motor. In total, the head will rotate to calculate the direction in which it is supposed to move.  

I posted a video of the simulated robot, which should hopefully show the direction I'm attempting to go in. 


Moobot Update 2, Sept. 25, 2012 (Version 1.11)


Not much of an update to the robot itself, other than I finely crafted a lovely cardboard remote control for the Moobot strictly for the purposes of putting a demo video together of the mechnical nature of the Moobot. Admittedly it was also just pure fun to actually get the thing moving a bit. I uploaded the video to this project page. Enjoy, or mock me, at your leisure. Both are welcome (I have a pretty good sense of humor!)


Moobot Update 1, Sept. 21, 2012 (Version 1.1)

To the best of my knowledge so far, I have overcome the problem of having proper wheel mounts for the drill motors by hack-sawing the hell out of the original drill chucks that came with the 18V Harbor Freight drills I had purchased for the purposes of gutting their motors. Long story short, I hack sawed the plastic cover of the drill chucks to reveal their inner metal parts, which turned out to be a suitable  motor-to-wheel mount, so long as I torqued the crap out of the drill chucks to hold the screw axels I'm using for the front wheels.

I've made quite a lot of overall structural/mechanical progress since making the change. It turns out that the thing definitely drives, after testing it by directly connecting the drill batteries that came with the Harbor Freight drills to the terminals on the motors. Like others have suggested, it almost drives TOO much, haha. The motors very well may be overkill if the motor controllers and microcontroller can't tame this thing a bit.

As you may be able to see in the photo above, I did have to drill in some "grub" screws into the driving wheel in order to get better traction on the tank tracks.

Thanks to this recent post by Oddbot I believe I'm going to be able to soon hand-make the motor controllers that will ultimately tie the Harbor Freight motors to an Arduino. I have been using the program Fritzing to redesign Oddbot's circuit such that I can print out some custom PCB templates. In turn, the controllers will connect to the Arduino, which will connect to an ultrasonic distance sensor, which I will use to write a wall-avoiding AI for the bot. Yet the closer I get to a working bot, the more ideas I have for extra sensors, remote control, etc....just trying to keep it as simple as possible for now, as I know even getting a basic working robot out of this design will be some work.

After connecting the motors to the wheels, I also made the motor mounts with some scrap hobby wood and some plumbing pipe clamps, which secure the motors to the chasis:

And lastly at this point, I'm attempting to cut and fit the outer shell pieces, which I have decided will also house the microcontroller and the motor controllers once complete:


At this point, it's at least starting to look like a robot!  I'll post some vids of me demoing the speed of this thing at some point tomorrow (or soon after ) to demo the power this thing has.

Could be interesting trying to harness that power appropriately :)

The premise of the robot:

I was inspired by armando96's robot, which he called the AATV, and have since made an effort to the best of my ability to duplicate his build in a new robot, which I've dubbed the Moo Bot ("moo," because my last name is "Mumau," pronounced "moo-mah"). 

My general design for the robot is something like this:

I started by building the PVC tank tracks as armando96 described in this tutorial. I did not have rollerblade wheels like the kind that armando used, but I was able to find some relatively cheap caster wheels at my local Lowes (which is where I got most of the materials for my robot). 

I decided to use some weld steel for the chassis/frame. The wheels are mounted on the bottom with some wooden dowls that I drilled a center hole through.

The top of the chassis will hold the two Harbor Freight 17v drill motors, which I have tweaked using the "o-ring" hacked described in this tutorial from Dale's Homemade Robots. I plan to using plumbing pipe clamps to mount the drill, with some dowls/scrap wood as the base for the drills to give them some lift.

Altogether, the thing would look something like this from the top-down view.

The main mechanical problem I've had with building this bot is with the wheel hubs. I've tried a great many of different designs, but they all seem to fail. I'm hoping by posting my design here that someone can offer some help or ideas. At this point, I believe I may have to try to find someone who works at a machine shop to create some custom couplings with set screws.

Ultimately, I plan to use the Arduino to be the "brains" for this thing, and I'll have to devise/buy some sort of motor controller for the thing. I hope to make it autonomous by using a sonor-based sensor, which I have already purchased and tinkered with (seems to work fine). 

I plan to use this robot to test sensors and programming techniques for the Arduino. 


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If you have the space why not use the drill chuck to hold the axle of the wheel? might work if you have the space available.

I think I'm going to try this before I go too much further. Tonight, I actually took the outer plastic off of one of the chucks to see if I could reduce its size, and it does seem to be a good fit. Will update will new images after I experiment a bit more with this.

Ideally the adaptors should be metal, not wood or plastic as neither of these materials have the strength required.  What are the two shaft diameters?

Best bet may be to find someone with a lathe to make them for you - do you have a local model engineering club near you? Looking at the small size I'm guessing they could make it from their scrap bin materials.

The two shaft diameters are 1/4"-20 screw going into the wheel, and 1/2" which is the size off the flatter, wider part of the drill motor shaft.

I actually was looking for a group or a small shop locally that I might be able to ask for help from. So far, no luck, although I did find a group who I think does model train stuff (is that kind of a "Sharks" vs the "Jets" thing, among modelers, i.e. robot guys versus model train guys? Haha just kidding). 

In any case, I wonder if you have a such a group nearby, and if so, I wonder if you'd be willing (or if anyone who lives in an area that has one) to ask them for some help on my behalf? I'd be happily willing to pay someone to make the exact part I had in mind. 

In the meantime I'm going to probably mess around with some of these other ideas. Thanks for the feedback!

Something like this is what you are probably looking for:


Although I don't know the exact size of the shafts you are trying to couple. There is also a style of a solid aluminum coupler here:


These have a spiral cut into them to allow for flex which ensures a good connection even when the two shafts are not perfectly aligned. They come in many sizes. I just searched for "CNC coupler" to find these quickly and referenced your "1/2 -1/4 coupling nut" that you were considering using.

At the end of the day it is basically the same part that you designed, just pinches the coupler around the shaft instead of driving a set screw into it, and made of metal instead. While I haven't tried the ones in the first link (love-joy couplers), I actually use the solid ones with the spiral cut into it on my 3D printer, and they are much stronger then theey appear with no backlash whatsoever.

Yeah that's what I'm going for, I think. That is essentially the size of coupler I need -- the screw going into the wheel is a standard 1/4"-20 machine screw, while the outer dimension of the thicker part of the rod coming off of the drill is 1/2". I'm not exactly sure what the thread size of the threaded part of the drill shaft is -- I believe I have seen elsewhere that it fits a 3/8" nut. I like the idea of the sprial cut in those one-piece couplers, as I don't have great alignment, for sure, overall (about the best that a 1/32" ruler can give me, haha). 

Thanks very much for the suggestions!

also, the axle from the motor to the wheel look very long.  If is possible, move your motors close to the wheel, may be install the wheel directly on the motor shaft ?

if you can, use a ball bearing much as possible, friction = torque = amps

I really like the idea of spring-loading one of the wheels! I agree that would help increase friction, as it would increase the tension on the treads, which I think is another mechanical problem. Thank you very much for taking the time to check out my design and to offer advice!

I just answered your other thread, so I'm not gonna repat it here. I just wanted to say that your plastic coupler broke because the wheel shaft was not supported close to the wheel (with a ball bearing for example). Even if you make a coupler from metal, you need to support the wheel as close to the wheel as possible or you'll have problems in time. You need a support between the coupler and the wheel in your current design.

What more can I say at the moment? :) Glad to see things are moving for you.