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...... Tread Belts ......
The plan has always been to try to drive it by the tread belts, for now i've had to use internal wheels, but haven't given up the dream yet.
While still thinking about driving by the belts, i found this great neoprene, it's 16mm thick, tough like a car tyre, with nylon reinforcing at the bottom and enough rubber above to cut the grooves without encountering the reinforcing. It's used for conveyor belts in the mining industry and i picked up an off-cut, 50mm wide and long enough for 2 sets of belts for $40.
Instead of using a grinder to make the grooves i used a Tyre Groover. It's like a big soldering iron but with a blade on the end, they are used for cutting grooves in tyres for trucks or racing cars. It cost about $100-150 on ebay and afterwards i left it with the Robot Workshop so other builders could use it too, so overall it didn't add much to the cost of each set, but it's a lot cleaner and quieter!
You can get round or square blades, i went with the square as being closest to how the B9 looked. Even so the corners are just slightly rounded which helps to avoid splits in the rubber when bending.
They come in a variety of widths, but you can also get a slightly wider one and file the brass bit down to whatever width you desire. The depth of the cut is determined by how you position the disposable blades.
Made up a simple jig to hold the 4 strips of rubber so they are all cut at the same time.
With a gap in the wood on one side, and a piece of metal across the belts to guide the cutter in a straight line, it was just a matter of sliding the 4 belts (all taped together) 1 inch to the left before each cut. For that i had simply marked 1" marks on the rubber with a pencil.
Ready to begin.
You can see lots of the neat rubber strips cut out of the belts. (No i didn't cut them offset like that, they were all lined up but moved when the tape was taken off).
The reason for the 5th piece of scrap rubber at the back is to give a clean exit to the cut. The start of the cut was ok, and the transition from one belt to the next was ok, but if you finally exited into free air on the last belt it would stretch outwards as you were pushing on the blade, and then spring back as you broke through. This would make the gap where it exited a bit narrower, but having another strip of scrap rubber of the same resistance for the blade to push against kept the groove an even width across the belt.
Close up of the edge shows how the inside of the grooves are clean, smooth, and uniform.
Ground the taper by sliding the edge of the rubber tread past my small belt sander, which had a guide to stop it taking off too much rubber. Simply moved the rubber back and forth a few times until it was no longer being ground away, which left a pretty straight line between the taper and straight side of the tread belt. It took about 10 minutes per taper, or about 1.5 hr to do the 8 lengths.
With the taper having been sanded, it left the sides being pretty smooth, so the reinforcing didn't show very much. But what could be seen was soon hidden by colouring it with a black permanent marker pen.
Happy with the way they look in place, but it needs quite a bit of tension to get them to sit flat like that. The super glue is strong enough to hold them together, but they are too stiff to be driven effectively. So these must be only for show, in which case i could have used softer rubber and made the job easier. Oh well.
Since doing this i have now bought the rubber belts from Craig R., at the price they can't be beat. Available here:
i suggest you go there and buy most of what he is offering :-)
But i'm already thinking about a new plan to make motorised tread belts ...
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