pic: Sheetmetal 6WD

[JamesCH95]

Originally Posted by sgreco

I was under the impression that that temper is what really matters to bending. You want a soft temper to bend ideally. I was planning on using 2024-O which will bend fine. If I were to use 2024-T3 or 2024-T351 (to name common tempers of 2024) I wouldn't have as much luck. It does say that 2024 welds poorly, which is why I'm riveting the frame.

I like your choice of 2024, but unless you use a tempered 2024 alloy, 5052-0 will bend easier and be slightly stronger in fatigue, yield, and ultimate strengths compared to 2024-0 (I looked this up on Matweb.com, great resource). Maybe make the bent pieces from thinner 5052 and make your gussets and reinforcement (like Don suggests) out of 2024-T4/T351 to utilize its strength appropriately.

You could definitely use zip-ties to tensions your chain, but a spring would probably be better. A constant-force spring or a gas spring would be great because you could maintain a constant tension on the chain. It might have to be a fairly high load spring depending on your gearing. The gas spring also has the advantage that if anything failed the spring wouldn't go flying around, they are damped.

Keep rolling with this, it's looking pretty good so far!

[Chris is me]

Originally Posted by JamesCH95

You could definitely use zip-ties to tensions your chain, but a spring would probably be better. A constant-force spring or a gas spring would be great because you could maintain a constant tension on the chain. It might have to be a fairly high load spring depending on your gearing. The gas spring also has the advantage that if anything failed the spring wouldn't go flying around, they are damped.

Spring loaded chain tensioners are fairly notorious for not working in more than one direction. There aren't exactly many successful spring loaded tensioners designs in FRC. Unless you happen to have experience in the area I wouldn't recommend something as "better" that you haven't successfully run yourself (and if you have, I'd love to hear about it).

[apalrd]

Instead of zip ties or springs, we have used screws to tension dchains like this:

Our axle blocks were made out of 1" wide 1/4" thick aluminum plate, cut to length. We had a hole for the axle (3/8") and a hole for a securing bolt. In the frame, we had two slotted holes, one for the axle bolt and one for the securing bolt. We then made the axle block longer then needed to hold the axle, and drilled/taped a hole down the long end for a 10-24 bolt. When you tighten the bolt, the axle slides and the chain is tight. You could then tighten the securing and axle bolts to make everything nice and tight.

[AdamHeard]

Originally Posted by Chris is me

Spring loaded chain tensioners are fairly notorious for not working in more than one direction. There aren't exactly many successful spring loaded tensioners designs in FRC. Unless you happen to have experience in the area I wouldn't recommend something as "better" that you haven't successfully run yourself (and if you have, I'd love to hear about it).

I believe he is referring to using the spring to pull on the dead axle; which would work in both directions.

[JamesCH95]

Originally Posted by Chris is me

Spring loaded chain tensioners are fairly notorious for not working in more than one direction. There aren't exactly many successful spring loaded tensioners designs in FRC. Unless you happen to have experience in the area I wouldn't recommend something as "better" that you haven't successfully run yourself (and if you have, I'd love to hear about it).

I haven't done anything like this myself. I was basing my recommendation on this: http://www.popsci.com/invention which is an incredibly fast tracked vehicle, and it uses a spring/piston to tension the drive tracks, and hasn't thrown a drive track in 3 years, even with a broken suspension mount. Though perhaps not a great parallel to a FIRST robot.

I would be interested to see these designs that didn't work well, I bet there were issues where the drive wheel's tractive forces was also compressing the spring that was tensioning the chain. A workable design might be as simple as an adequately stiffer spring/piston/gas spring. Like I mentioned before, a piston or gas spring with constant force vs deflection (unlike a typical coil spring) would not slacken as long as it's force rating was not exceeded.

I think it would be a very cool idea to design and implement, but it certainly won't be as trivial as throwing some springs into your robot. Having thought about it for 10 minutes I think that one could design a cam with a 1-way clutch bearing that could eliminate the need for a spring entirely.