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Unread 27-06-2016, 14:20
Steven Smith Steven Smith is offline
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FRC #3005 (RoboChargers)
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Re: pic: Another Belt-In-Tube Drivetrain

Hopefully not de-railing the conversation, but if anyone could humor me and take this discussion up a level, or link the relevant threads if it has been adequately discussed before, I'd certainly appreciate it.

#1: What are the pro/con of going to belt in tube if you are currently running chain in tube?
#2: Do you believe the differences are significant? And why?

As a data point, since I've been on 3005:

In 2014 we ran a WCD style 3.25" 6WD tank with internal 9mmxHTD5x20T pulleys (Vex) on the inside of the robot. Never had any ratcheting issues (or would expect). Used VexPro/WCP bearing blocks (without retention cams) and had enough slippage issues (block vs. tube, our fault) to cause pulley misalignment and the press-on walls of the pulleys to come off.

In 2015, we ran a chain in tube for an H drive configuration in 1x3x.125" extrusion, #25 chain, ~22-25T sprockets as I recall, geared at maybe ~10ft/sec. No issues to note.

In 2016, we ran a chain in tube, 8WD with #35 chain, 8" pneumatic tires, in a 2x3x.125" extrusion. No real issues to note.

Looking forward, though we may play around with "other" drive train options, it is highly likely we will prefer to similar drivetrain styles. We have the manufacturing capability to handle most designs (lathe, cnc mill, Al welding, etc), it just requires the investment of resources to create in the offseason and prove out. We value robustness over maneuverability, and think we can make up for any loss of mobility with extra driver practice in most games.

What advantages might we be missing out on by continuing to run chain in tube?

The things I can think of:
- We have run 3" high tubing two years in a row, to accommodate extra center drop as well as a slightly larger sprocket to reduce chain loads/sprocket wear/etc. I have justified this in my head by saying the extra profile yields a stronger frame (torsional), but is it needlessly stronger? Would running belts make it easier to go to 2" profile and maintain the high safety factor I would like, even at large diameter wheels?
- Are belts (when properly tensioned) more accurate with less slop when it comes to measuring distance traveled (for auton)? Or is the difference to chain not worth mentioning?
- Is the system more efficient? More robust? Overall lighter (I know the belts are, but the hubs look heavier than an equivalent plate sprocket).
- Other?

Any rate, we will probably do another iteration of our drivetrain before build season next year, and the discussions on the belt in tube have me intrigued. Thanks for any input!
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2014 - 2016 - Mentor - FLL 5817 / 7913
2013 - Day I Die - Robot Fanatic
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