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Originally Posted by topgun
Art,
What was the design intent or advantage with the bent in corners on the hostbot?
Also, can you give us some of the specifics on the sheet metal drive train this year?
Thank you for posting the model again Our CAD team uses GUS models to study design and CAD techniques.
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Go back and watch video of 177 or 1503, both of which picked up tubes from the feeder slot almost exclusively. It's not uncommon for them to catch the corner of their robot on the tower when they enter or exit the lane and get hung up for about a second.
We predicted that tube starvation would be used a lot*, so that would mean we'd have to go into the lane a lot to pick up tubes. Using 2D geometry simulations in a SolidWorks sketch, and then testing in real life with the Kitbot chassis and a tower base, we confirmed that shrinking the width of the robot to 25" and making the corners angled at 60 degrees eliminated nearly all of the hangups going into/out of the lane. The shorter wheelbase from the knocked off corners wasn't a stability issue for us since we went with an elevator/short arm design.
Some details on the drive train:
- Base chassis 0.125" 5052 aluminum sheet metal
- 6WD with 4" modified Colson wheels
- Direct-drive, 0.125" dropped center shaft
- 25p roller chain to end wheels, all live shafts
- Custom 2-speed gearboxes (each weigh less than a stock ToughBox) made from a la carte AndyMark gears, geared for 6/16 ft/sec
Here'a a photo of our competition robot drive train:
While we did design to use an exact number of 25p roller chain links, chain stretch from breaking it in required us to throw in some floating idler sprockets (
like this one). This was predicted ahead of time, which is why our chassis standoffs were stepped and had a small Delrin sleeve over the inside end. While we had previously used floating idlers on various mechanisms, this was our first time using them on a "real" drive train (I'm not counting 2009 due to the very low loading that year). They worked flawlessly, never once popped out, and at just a few hundredths of a pound each are the lightest chain tensioner we've found.
Overall, we were very pleased with our drive train this year (once we broke in the gearboxes, the drive train literally required absolutely zero maintenance, repairs, or attention). Even without a belly pan, this chassis was rock solid and had literally no warping or flexibility.
Quote:
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Originally Posted by JesseK
In highsight, were there any mechanisms or dimensions you should have proofed or prototyped more before starting the CAD? (e.g. the roller claw width to maintain grip or roller claw height to ensure it 'pinched' but not too much)
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We pretty extensively prototyped the Minibot and deployment, and went through about a half dozen iterations of roller claw designs. We tried wide ones, we tried narrow ones, we tested how much we should pinch the tube. The only thing I would change had we another change was to test the length of the roller claw, as making it about two inches shorter would have been perfect. But we ran out of time to do this, and we pretty much only have one shot per season at sending parts out to our machine shop sponsors (they help us, but it's not like IFI-level involvement where we can keep going back to them again and again with new revisions).
Nothing for the elevator or drive train was prototyped, for those we just did the math, designed and checked the geometry in SolidWorks, and sent it to manufacturing. All in all, we were pleased with the outcome (by STL), as until that weird radio issue popped up about halfway through Friday in STL, we were putting up an ubertube, two logos, and 1st or 2nd minibot nearly every match, and had three qual matches over 120 points.
* Frankly, we were completely surprised at the amount of tubes thrown onto the field after watching Week 0 and 1 events. But after seeing how widespread it was, we also made sure we had good human players and ended up picking up 90% of our scored tubes from the floor near our home zone.