pic: Team 148 - 2011 - Raptor

I wonder if there is any maximum allowance of people/teams per pit. Looks like 148 is going have a crowd. Non-stop. :slight_smile: Again.

How do you generate the tooth profiles? Does IFI just have a piece of software that spits it out, do you do it by hand :ahh: , or is there a handy SW feature that I’ve missed that does it for you?

Well 148 would be nagged about the safety issue of too much people crowding your pit.

Actually, it’s always a pleasure to notice how planning committees work to make the pits efficient and, at the same time, a showcase for teams like 148 and 118, allowing space where there is some to be had. It’s also nice when rookies are placed between veteran teams or are placed in an area together where they can be accessed and helped easily by veteran teams and volunteers who will help. Teams like 148 are very aware of their draw and they work hard not to infringe on other teams’ space. I’ve seen it on Championship level and Regional level. It’s also the job of the pit volunteers to help keep things orderly and running smoothly.

There are lots of ways to do this. Some of my favs:

  1. Pull out your handy Machinist’s Handbook and sketch the tooth profile by hand.

  2. Buy one of those gear profile generation programs and get it to spit it out for you.

  3. Download the gear from somewhere online. bostongear.com has all their gears available online.

For this year’s robot we used option 3. I downloaded the gear I wanted from Boston gear, then traced over the tooth in Solidworks (eliminating splines with simple arcs, so it would import cleaner into our laser cutter’s NC program). I grabbed this sketch, dropped it into a new sheetmetal part and away we went…


A few more options:

  1. It’s surprisingly easy to generate a real involute using equations; this and this explain how to do it in Pro/E (but any CAD software ought to be able to do the same).
  2. If you can make do with an approximation instead, either follow the second method in the link above, or get GearGen (I think it’s shareware*) from here or here. (It’s a DOS program, so the interface might be a little unfamiliar nowadays…) This makes a sort of segmented polyline when exporting, with arcs that (as near as I can determine) are approximate. But thanks to modern, fast computers, you can create an arbitrarily large gear and scale it down to whatever degree of precision you need—so this isn’t a problem so long as your CAM software won’t choke on the geometry. (Note that all of those facets will make 3-D CAD really slow to regenerate; use the equation in that case, or just approximate it for visual purposes.)

*Does anyone even use that term anymore?

Another from this series which highlights the Drive Module layout.


Nice drive module!

for making that strange gear for the arm lifter…you could also get the arm gear from a door window regulator from a car, and trace it onto the aluminum


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?