Why did you decide to ditch the drop down perpendicular omni wheel this year? I would think strafing would be the only upside to this whole switching drivetrain
Im not sure that they did: Looks like they can go side to side
if im mistaken and it does not have a 5th omni to go side to side… here it shows the robot “auto magically” lining up to the pole.
From the blog on the drive module, he states that there is a reduction through gears and another through chain. This essential provides a two speed transmission with two different driving characteristics. This will allow for a change of speed and torque. The omni-wheels still provide more degrees of freedom for the robot to move in, than IFI traction wheels.
There are plenty of advantages to this system. I really like this system and hope to develop something similar in the off-season.
If there is no powered movement in the lateral direction, they don’t. However, I’m tempted to believe that 148 did put in the “kicker drive”. I just don’t see why they would choose an articulating drive like this if they couldn’t strafe controllably.
I really like how the traction wheels are geared differently than the omni wheels. Simpler than shifting indeed!
@ Chris, you do bring bring up a valid point. However, the omni-wheels will allow for a more maneuverable robot. This is what I was trying to say. Thanks for catching that
I can imagine that the all-omni wheel drivetrain would create a nice “drift” effect when turning around during high-speed motion, a maneuver that can be seen at about 1:44 in their video. I can imagine that this will come in handy, due to the “back and forth” nature of driving in this game, and that this may have actually been hampered by the kicker wheel.
CAD drawings that flash by all feature a kicker wheel, as well as many practice bot pictures. But all footage of the final robot seems to place the battery in the center of the robot, in place of the mass of sheet metal that (presumably) supported the sideways wheel.
Also, John mentions a major change to subsystem 1 (the drivetrain) here. Coincidence? Or iterative design?
You got it.
The original drivetrain was a full Nonadrive system, but we ended up removing the sideways wheels around Day 31 (see the blog post linked above). After a week of practice we decided it wasn’t necessary. In my mind, all our work and testing since that point has confirmed we made the right decision.
When we removed the middle wheel our original plan was to swap out the 4 primary omni wheels with 6" traction wheels, however… well… we were impressed with what our driver Connor can do with it.
We call this configuration “Butterfly Drive.” Which is a joke in reference to how this robot can be pushed sideways while on all omni wheels (obviously when we drop the traction wheels she stops floating like a butterfly and stings like a… you know.)
I don’t think all of it’s virtues are readily apparent. I assure you there are more reasons to do an articulating drive than moving sideways. Though I realize most other teams may not value the same things we do, and as such may not make the same tradeoffs we did.
We love “traction mode” and it’s virtues in autonomous and driver control. We love the simplicity and modularity of this module design. We love how the drivetrain performs on all omni-wheels (super efficient geartrain + 4 omni wheels = smooth like butter). We’re very happy with what we ended up with…
I remember way back to 2003, team 980 had a similar drive system in which they raised or lowered two different sets of wheels to essentially have two different final drive speeds/ratios.
Team 810 did the same thing in 2002, from what I remember.
While I think its cool shifting wheels instead of shifting gears, I don’t really see how it is simpler at all. A transmission is quite compact and requires a small amount of force to shift versus needing enough force to lift the robot to drop down the traction wheels. The only potential benefit I see of this system without the perpendicular omni wheel is the ability to change the center of rotation although the benefit of that wouldn’t necessarily be worth the added weight of the system.
JVN given that you ended up taking out the 5th omni wheel would you stick with this drive if you could do it over or go with a more conventional 6 or 8wd with shifting transmission?
From a fabrication standpoint for a team with limited resources, it is far easier. Having worked through the “fun” of getting the speeds right for multiple gearboxes, it is also nice in that it is easier to change the difference between high and low gear.
Utlizing COTS gearboxes and wheels, a team with a drill press (or even a hand drill), could make such a drivetrain.
While it can be done with less resources, I’d be worried about these low resource teams trying this, mainly because wheel pod side loading is a pretty big concern with this style of drivetrain.
By the way, the above blog post refers to large performance gains with the removal of the 5th wheel. What are those gains?
Depends on the way you place your wheels. Obviously if you use omni wheels as your dropped wheels you will slide rather than break the pods. If you use traction wheels the problem becomes more significant.
Yes, but the system is designed around giving the traction wheels a higher reduction, so they aren’t the natural choice to be directly driven / the pivot point.
Unless, of course, you’ve put the CIM on the module… like 148 does…
This was something we learned last year, which is why the Generation 3 & 4 drivetrains have stationary traction wheels and actuated omni wheels. When we’re in traction mode if we take a hit, all the load gets transferred straight into the chassis.
This layout comes with its own set of challenges and constraints, but we like it a lot more.
Not to hi-jack, but that’s how we did it, Drill press and bandsaw. Only machined parts are the two plates. Traction wheels direct drive, larger mecanums raised and lowered. 1-CIM 1-775 per module.
Side loading is not a problem, as the traction wheels are mounted conventionally with a bearing on both sides of shaft, and the mecanums are braced with sideplates/slides. Obviously not all is shown in this rendering.
Another in this series:
Want to retain a flanged bearing? Drill some holes and rivet a washer over the flange.
Did you also replace the bolts in the AM omnis with rivets?
Yes we did and they haven’t failed us yet. Not sure how much weight we saved by doing this but anything we can do to save a little bit is worth the effort. Additionally by doing this it was and opportunity to check each roller to make sure it rolled freely.
810 used 9" Bead-lok wheels for its main drive and lowered two absurdly wide belts to the ground for pushing. I don’t recall the overall ratios, but the difference between the wheels and belts was 3:1.