[mowbot] drive and chassis design

DON AUTRY (Don.L.Autry nospam at msfc.nasa.gov)
25 Oct 1996 09:20:53 -0500

to either chassis design or start to talk about locomotion methods, i.e.
tracks or wheels or legs, differential drive or some sort of steering
wheel etc..
I really don't have too much to say about this at this point other than
let the discussion begin.

skar9500 nospam at mach1.wlu.ca

Does anyone know of any cheap mobile platforms we could adopt?
Or suggest a low-tech way to build one? I envisage a solid square of
chipboard, say 0.5x0.5m (20"x20"), with two motors bolted to it and crude
wheels made from something suitably round (like the ends of a large tin
can perhaps).



I have given some thought to chassis and drive design. My basic thoughts have been that wheels should be fairly wide to maximize traction on slick grass. Although they are expensive, some from large RC model trucks might work. Finding a cheap source is the hard part here. For drive I was thinking of using a two motor drive with each motor driving both wheels on a side by a small belt. Perhaps a small car timing belt. A tracked system would be great for me as I have that ditch to contend with, and I may have to build a tracked bot for it, but I have not been able to come up with a way to mow close to a edge with a tracked system. Wheels can be recessed on the front and back so that the blades attack area is outside the wheels. Additionally a small wheel could be put on each drive line with holes in it for use with a ir led system to count pulses for positional and control information. This would eliminate the need for stepper motors and the problems which they can introduce.

The chassis could be anything, but I believe a design which is simple to build is ideal. A dome shape would be perfect as it would be self righting if mowbot should flip, but these shapes are hard to build unless you are handy with fibreglass. This is a good option as fibreglass can be made to any shape, is fairly durable, lightweight, and weatherproof. Unfortuantely it is also messy to work with. I may go this option myself even though I have never worked with it. I was planning to use cheap angle stock, probably aluminum, for my frame. It is cheap to buy at any hardware store. Sheet metal is extremely easy to work with and can make a weatherproof enclosure. Aluminum here as well to avoid weathering. Any seams can be sealed by putting strips of rubber in the joints. The perfect cheap material here is that round stuff that holds the screening into household window screens. I bet that stuff is even sold in britain and down under. Another good material for the enclosure would of course be platic, but I have never seen a place where you can just buy sheets of it cheap. I would avoid wood because it will not weather well, has nasty habits of swelling, shrinking, cracking, etc. Also chip board will melt if wetted unless you use marine grade, in which case metal is cheaper.

Another idea I had for a cheap, easy way to make the blade decks was to get two melamite, (cheap plastic) salad bowls about 7-8 inches diameter. Cut about 1/2 inch of one edge each, and join them. drill a hole in the center for blade drive shafts, use two pluming grommets on each side of the bowl on the drive shaft, and mount a pully on the back, and blades in the bowl. voila, cheap weatherproof blade decks. Now you only need to cut round holes in your bottom sheeting material and glue them in.

Any other ideas?