pic: Frog Force 503 Omnitank Drivetrain (rAC)

[Electronica1]

Originally Posted by evand4567

Since it's a form of butterfly, theoretically only the omnis or the tractions should be touching the ground at once, therefore they can use the omnis as a high "gear" and the tractions as a "low" gear. That being said, I'm not exactly sure how the front set of wheels switches from tractions to omnis. Maybe the back traction wheel extends down far enough to pitch the robot up on the front tractions.

The reason I bring this up is that every iteration of the rear drop (my name for this style) hybrid drive I have seen has the wheels all geared the same and has a transmission to switch speeds. I believe that in a pushing match/change of direction the piston would give a little and all the wheels would be on the ground.

Originally Posted by Bryce Paputa

In this revision, the drop was 1/8" and we ran into scrub issues. In the next revision, which I'll posting in a week or so, we increased this to 3/16" which should work pretty well. The omniwheels are off of the ground in traction mode. We haven't done enough testing to determine if much energy is lost in drag, but the idea is that when we are pushing or accelerating in omni mode, we rock on to the traction wheels and gain torque, but these traction wheels don't have enough traction to do this effectively, the next revision uses roughtop and will be able to test this better. We've been driving this for a while, and even with its issues it's a huge improvement over our past drivetrains. As for chain tension, we did exact c-c with no tensioners, and it's been very loose since we made it, however, we have not thrown any chains. We think that the looseness will be fixed by adding a bit (.018") to the c-c distance and fixing some spacing issues that left the sprockets a little loose on their axles. The shifting wheel moves in an arc that is always the same distance from the gearbox.

Please tell me you aren't using 25 chain for this. From what you described, you might run into the issues the mk1 version of my teams octocanum had. It worked fine in the shop, but in a competition setting, the stresses on the 25 chain from shifting caused our chain to stretch every match, we later found that during defense it could even shred the chain. We tried switching to 35 chain that summer and haven't run into the issue since. If your chain is getting loose now, it won't stand a chance at competition.

(Just an fyi, we had this issue with a drive that only had 4 cims of power, I have a feeling that the 6 cims might make this issue more prevalent)