Well it happened our (new team 9713) first competition. We competed as team 9999 as we did not get our funding and team number until friday about 4pm. Thanks also to 714 for some CIM motors and Victor controllers and to the pinebush team in NY for a roborio and PDB on loan
So we competed with a 3dp robot that was originally designed by me and some members of the now defunct team 1989 I used to mentor and it was the first bot of that kind to actually compete.
First the bad there was a design flaw on the key way of the bevel gears connected to the CIM motor as we were initially use an 1/8 in key filed down to 2mm to give more grip in the plastic but then could not get a 1/8 in key and i had 2mm keys in stock so we used that and it promptly fell out. We solved that problem - luckily had another key by filling the excess gap in the 3dp key slot with hotglue and were “golden” for the rest of the competition
We were not able to finish to cone/cube manipulator - it is difficult to finish a bot with a new team in about 3 weeks with low resources. So we decided to push some cubes around but mainly play D and get in the way of and hit some bots to see if something would break
Nothing broke and we got bounced around good as we were stripped down to a skateboard and the whole bot did not break 50 lb in weight.
One short coming was that in the future if we get onto acrylic type surface we will use a softer TPU when printing the tires. We had excellent grip on the carpet but poor traction on the teeter toters.
Frame held well as expected and that came down to the design I think
As you can see the 3DP part has 13.5mm square holes (1/2 in plus clearance) and in those in the outside of the frame are 1/2 in square 1/16 in wall thickness steel bars. The structure on the inside has same dimension aluminum instead of steel where they meet they are bolted together and to the plastic with m5 bolts and nylock nuts. So should you by magic remove the plastic you still got a bolted steel/al frame. All bolts are countersunk (printed that way) on the outside so the wood of the bumpers is flush on the steel/plastic combo and is bolted to the steel bars
This pic shows how the bumpers are flush to the frame and also allow a look at one of the drive wheels. We have a CIM motor with a 3dp bevel gear setup (19 : 41) feeding into a planetary that sits inside a 6 in wheel. All 3dp the ring gear doubles as rim for the TPU 3dp Tire - the one we need to make grippier if we get onto acrylic like material agin. The gears were printed in HIPS PETG and NYLON to allow evaluation of different materials. All 3 materials survived a 48 hour bench test and at least for a competition like Brunswick erruption none of them showed any wear or tear. So it might not be necessary to spend the $$$ to go nylon.
The frame was mostly HIPS and the motor mounts PETG. No wall was less than 5mm most were 6mm thick solid prints. As I buy hips/petg in quantity at about $10/kg there was about $110 worth of Filament in the frame about $90 Aluminum and Steel and some 608 and 688 bearings in the drive wheels. None of them loaded in excess of 20% of its rating. 5/16 hex bolts doubled as axles for the planets as that is about 8mm (7.9375) which means 8mm ID bearings will slide on nicely.
Cad is available on my Grabcad and I will most likely set up an account with print on demand companies to make them qualify as COTS.
With 3 printers and Nozzles ranging from .6 to .8mm the whole thing was printed in less than 72 hours. All parts should fit on an Ender 3.
