All Terrain Robot Build Blog

I’ve installed some gear reduction motors I had laying around. I used some 9/32″ brass tubing to slip over the output shaft of the gear box, then I drilled a hole in the shaft and installed a set screw. After drilling the wheel hub hole out to 9/32″, I inserted the axle and motor assembly through the drilled out bushing in the suspension arm. Next I pressed the wheels onto the axles by hand. I soldered a twisted pair of wires to each motor and routed them up to the batteries on the main chassis.

It crawls over things fairly well considering the lack of torque and over all weakness of the gear box.

So, I now have proof of concept for a six wheeled drive train. Now I need to find some higher torque gear motors.
Here’s a video of it in action:
http://www.youtube.com/watch?v=FxE4sayLlV8

I found a light weight fold up baby stroller at a yard sale for $7.00!!

The wheels that came on it are perfect for this prototype. I’ve mounted them up and they fit great. The tire is made of high density closed cell foam so they should grip well enough.

Now it’s all about fabricating the drive mechanism. I might experiment with some gear reduced electric motors I have just to test the traction. Eventually, I want stepper motors on all six wheels, preferably built into the hub. We’ll see about that one… so far my searches haven’t turned up anything affordable. Electronics “salvage yards” will be the place I’ll end up finding what I want.

I had a very busy build session today involving a trip to the hardware store for some more hardware. I found I had less play in everything if I used a bolt with an unthreaded shank on it. After retrofitting a few, I built the box chassis with a cross member for the rocker arm. This is a component that lends itself to the name Rocker - Bogie Suspension. I mounted the suspension arms and rocker and gave it a wiggle. It worked great!

Next, on with the wheels. For now, all I need is a simple wooden wheel, so, I re purposed a painted  pine plank I had laying around and cut out six four inch diameter wheels. After a little sanding, I installed them on the legs and gave it good look. I put it in a few different configurations in an attempt to simulate what it might go through in a boulder strewn terrain. It performs quite well and deals with a wide range of positions thanks to the way the rocker links the two suspension arm assemblies.

Of course, when you start looking at a prototype, things pop up you didn’t expect. That’s part of the process though so I pay attention in those moments even though my builder ego may be bruised. Ego schmego… work the problem. Anyway, you start to think “what if a drive motor failed on one of the two bogie wheels? What keeps it from just snagging on something and rotating 360 degrees and ending up useless?? ” Yeah.. what if? So now I’m thinking a limit of travel is in order, but I would need some data on maximum angles and such, hence, this prototype.

So now I can collect suspension angle data ,  operating parameters, and continue forward to the next phase, powered locomotion.

I took my PVC pieces into the machine shop and drilled all my 1/2″ holes for the nylon bushing to press into. They’re all straight and fit tight!

The trick here was to keep everything on plane while assembling the PVC with the solvent weld cement. There’s very little time to work so planning ahead makes a big difference. I pre assembled and adjusted everything, then I put a line on each joint with a red Sharpie marker. I rigged up a jig to help hold everything in the right place then set about gluing it up!

I’m very pleased with the results. I have the right and left suspension arms complete for less than $25. These are prototyype arms and they won’t steer, but they’ll demonstrate proof of concept.

Next task is to attach wheels and then bolt both arms to a central chassis. After that, there’s the rocker arm to install that links the two suspension arms.

PVC pipe is easy to obtain and it’s inexpensive. So, I’m building the prototype suspension parts with 1/2″ PVC pipe and various fittings.

I drilled holes in the pipe at the pivot points and inserted some 1/2″ x 1/4″ nylon bushings along with some 14″ x 20T bolts.
Each side took about 20″ of 1/2″ PVC, 4 - 90 degree elbows, 3 - 45 degree elbows, 2 nylon bushings, 7 washers, 2 bolts and 2 nuts.
Next I’ll add the arms that extend down to the axles and the wheels. Then,  the whole assembly gets mounted to the main chassis.

Click the pics to enlarge them.

 All Terrain Robot  =  ATR.

Well, the Maker Faire is over and I proudly walked away with an Editor’s Choice Award from Make Magazine for my Rumble Robots with an Arduino. I built two more while there and had a real blast with everyone. Now it’s time for a new project!

I’ve set a new robotics goal for next year:
Build a roving robot based on the six wheeled Mars rovers. There are three generations of these rovers. The latest is called the Mars Science Laboratory  , AKA “Curiosity”, and it’s big! About three times the size of Spirit or Opportunity. All three generations of the Mars rovers have a common component. The Rocker Bogie Suspension. I really like this suspension design and I’d like to experiment with building one so here we go!

I’ve started by producing some drawings:

Most of the mechanical construction of the chassis involves the suspension components. The main body is just a box that houses the electronics and batteries and carries a solar panel on it’s back. After a few more drawings are completed, I’ll begin building a prototype model to test the suspension geometries.

I’m still considering materials for the chassis. Aluminum, steel, PVC pipe, composites… all have come to mind. Steel would make welding things together very easy but I would have it’s weight to contend with. Plastic and composites are a lot of work and expensive. Aluminum would be great but I don’t have easy access to a TIG welder. I like the idea of PVC because it’s so readily available. For now, I’ll just focus on building a scaled down prototype.