pic: Frog Force 503 Omnitank Drivetrain (rAC)

[Bryce Paputa]

This shows how the chain stays the same length:

The shifting axle pivots around the gearbox axle and the chain doesn't change tension. The triangular plate highlighted in the back has the bearing and slides up and down on bronze bushings in the smaller slots.

This shows the delrin piece it slides on:


In the physical shifting mechanisms we powdercoated the linkage plates which makes the shoulder bolts bind up, in the next iteration we're accounting for this with undersized spacers.

[Electronica1]

Got any video of it?

[Bryce Paputa]

Originally Posted by Electronica1

Got any video of it?

I'll try to get some tonight

[Kevin Ainsworth]

Design looks great, we have a group of kids that want to prototype one of these chassis as well. Keep posting your results as you go so we can learn with you.

Chain stretches over time, it's going to happen.
You can also use pre-stretched chain like the type from US Tsubaki.
Part Number RS25, it's shiny silver, not black like other chain.
We run this chain exclusively and it stretches much less.
And #25 chain is fine if you keep your sprockets aligned.

[AllenGregoryIV]

I like this drive train concept a lot. We were working on something similar earlier this year and never really got it finished.

I definitely would like to know how much the omni's are in the contact with the ground when shifted to traction with a fully loaded robot and if they slip during pushing matches.

Can you show a picture of the ground clearances in both omni and traction mode. We played around a lot with getting both omni wheels off the ground and it seemed like we would need to move the traction wheel a lot to get that done.

[Bryce Paputa]

Here's a sketch of it

In reality, the omniwheel still touches the carpet but should still carry significantly less weight. I'll get a picture tonight.

[AllenGregoryIV]

That's what I was expecting. That's about what we were looking at doing as well.

Our thinking was that since so little of the weight would be on the omniwheel it would slip pretty reliably and not really interfere with anything during traction.

We were also considering putting the traction wheels on dead axles and having the chain reduction on the outside of the frame form the omniwheels to the traction wheels.

[wilsonmw04]

What's the distance from the axle to axle in the middle of the transition?

[Paul Richardson]

Originally Posted by Bryce Paputa

We are using 25 chain, it isn't getting loose, it began loose. The tension on the chain doesn't change when shifting with this setup. Once we get the next iteration of this built with the initial chain tension issues fixed we'll be able to test if the 25 is sufficient or not, but teams have shown that it is (118).

Originally Posted by Electronica1

Didn't 118 have double strands of 25 chain like this?

While not a member of 118, I have had their systems explained to me by their students, so I can provide a little insight into why they do what they do.

They like the chain in tube because of the small space savings (and no bearing blocks to manufacture) but mostly because it requires no tensioning. The chain may stretch, but there is nowhere for it to go, so losing a chain isn't possible. Note that this doesn't mean the chain is necessarily strong enough for whatever load you are applying, it just means it won't derail as long as you stick it in a small enough space.

The double sprockets don't actually run double chain. Remember that the center wheel(s) are connected to the wheel in front of and behind it, so they have two chain runs on their axles. The people designing/building the drive found it simpler to just put double sprockets on all the axles rather than make spacers just for some of them.

[ajlapp]

While not a member of 118, I have had their systems explained to me by their students, so I can provide a little insight into why they do what they do.

They like the chain in tube because of the small space savings (and no bearing blocks to manufacture) but mostly because it requires no tensioning. The chain may stretch, but there is nowhere for it to go, so losing a chain isn't possible. Note that this doesn't mean the chain is necessarily strong enough for whatever load you are applying, it just means it won't derail as long as you stick it in a small enough space.

The double sprockets don't actually run double chain. Remember that the center wheel(s) are connected to the wheel in front of and behind it, so they have two chain runs on their axles. The people designing/building the drive found it simpler to just put double sprockets on all the axles rather than make spacers just for some of them.

This info is accurate. We don't run tensioners as they're not needed. We don't run double chains, but there is a double sprocket and two runs easily fit.

118 runs a modified version of the production units available from www.Team221.com. 118 has used them for the past two seasons with excellent results.

Editorial Note:
If you're breaking #25 chains in your drive base, you're doing something wrong.

It is very hard to generate a enough force in your drive base to violate the working load rating. Especially if you avoid master links...

[Bryce Paputa]

Sorry I didn't get any video, one of our newer drivers hit a forklift sideways in a drift without bumpers on and broke one of the omniwheels

We're getting new wheels and I'll get some video then.