Killer Bees - 2014

[apalrd]

About the drivetrain:

The drivetrain is very simple. There are 6 pieces of sheet metal (0.050" 6061 T6) which make up a fairly standard square with 2 wheel bays of approximately standard width (I believe 3", don't quote me on that). At each corner, a stiffener plate (0.050" 6061 as well) is used to maintain the center-center distance between a single large CIM with Vex 11t pinion and the Vex omni wheel and 72t gear (held together with versakey parts). The axle is 1/2" 7075 round, dead, taped in the end for a 1/2-20. I can give more details on the exact fabrication if you want.

The omni wheels were replaced every 2 tournaments or sooner, we simply replaced the entire axle-bearing-wheel-gear assembly and had a complete set of identical spares (including axle spacers) in the pit.

We found that the CIM could twist, so we added wood blocks between the CIM and front/rear chassis rail to keep the gear spacing correct. This was done manually by sound, the whole drivetrain is very quiet when running.

We initially used Vex encoders with Vex 2.75" omni wheels as floating odometry wheels, but quickly removed them for weight savings and ran time-based autonomous programs (we did do voltage compensation to try to keep it reasonably consistent). There are no sensors in the drivetrain.

The catapult is a single welded frame, which bolts on top of the chassis to provide significant stiffness. With the 4-omni drive, we don't care about stiffness nearly as much as we did with drop-center traction wheel drives.

The strategy behind the drivetrain was basically to be able to maneuver out of any situation easily enough to prevent direct pushing. We believe this achieved it in the lights, simplest way possible, without any articulating systems. By preventing direct pushing, we also removed the need for a multi-speed gearbox, allowing the 'corner modules' which are extremely light, simple, and efficient.

I can answer more questions if necessary.

[Zebra_Fact_Man]

Are there any better pictures of the drivetrain system posted anywhere?

[apalrd]

Originally Posted by Zebra_Fact_Man

Are there any better pictures of the drivetrain system posted anywhere?

I don't have any. I'll see if anyone else does.

[Jim Zondag]

Here are a couple of pics.
As Andrew said, it is very simple. The minimalist design freed up a lot of resources we could then use on other features of the machine such as a giant spring bundle in the catapult and huge catching wings. The lack of chains or belts means we do not need much rigidity in the frame, allowing it to be even lighter. There is a single 6:1 rear reduction to each wheel.

Our priority this year was to make the best catapult possible. The drivetrain needed to take a backseat to this objective.

A lot of people thought we were crazy and/or stupid when we revealed this. Admittedly it is a bold choice. It has its pros and cons, but for this game, I think the pros were an advantage overall. It does require a very good driver, and Ellen is pretty awesome. (7 blue banners, 175/46/1 record over 2 years)

There is more than one right way to design a robot. The right choice depends on many factors including: experience, driving ability, weight, complexity, and game strategy. I think our 2014 experience proves that you can sometimes step outside the box if you have properly thought through the question.

[jagen31]

Nice! Very interesting design philosophy. We have a really good driver, but if I told him we were putting omni wheels on the robot he'd punch me square in the face.

Funny story, during Archimedes, whenever someone would mention 33 in the team 20 stands, a bunch of mechanical people would say, "don't worry, we can just push them around," and finally someone said, "Then do it, if its so easy."

[Mike Marandola]

This is my favorite robot by far. The drivers are so good. Are you guys able to alter the trajectory of the shot with your choo-choo mechanism?

[AlecMataloni]

So, what's the standard bend radius on the .050 sheet you guys use? I've read that 6061-T6 bends poorly/ cracks below a bend radius of double the material thickness. Is this the rule of thumb you follow?

[chiefsfan67]

By the way, thank you Killer Bees, from 1730 Team Driven, for all of the free bee antennae, at the buffet Saturday night, and for wishing our drive coach a happy birthday! That was awesome!

[tim-tim]

Originally Posted by AlecMataloni

So, what's the standard bend radius on the .050 sheet you guys use? I've read that 6061-T6 bends poorly/ cracks below a bend radius of double the material thickness. Is this the rule of thumb you follow?

I can't speak for 33, but the typical rule of thumb is twice the thickness for 6061-T6. We don't use much .050" or 6061-T6 on our robot, but at work we typically just use a 1/8" bend radius or 3/32" (.094") if we are in a pinch.

[Phyrxes]

Interesting read, thank you for posting. This was our first year using a sheetmetal frame and our sponsor suggested 5052 sheet over 6061 as thats what they use for most of their paying customers and can generally make our parts of of scrap. Any insight on what alloy properties to look for in this application?

[Ed Sparks]

Originally Posted by Jim Zondag

..... There is more than one right way to design a robot. The right choice depends on many factors including: experience, driving ability, weight, complexity, and game strategy. I think our 2014 experience proves that you can sometimes step outside the box if you have properly thought through the question.

Absolutely ..... and your drivers were awesome. When I first saw the bot on it's back in the pits, I kept looking for the secondary wheel system to provide traction. What are the two green omni wheels doing?

The proof is in the performance and no doubt 33 had it this year (as always). Looking forward to seeing you next time.

[z_beeblebrox]

Originally Posted by apalrd

About the drivetrain:
We initially used Vex encoders with Vex 2.75" omni wheels as floating odometry wheels, but quickly removed them for weight savings and ran time-based autonomous programs (we did do voltage compensation to try to keep it reasonably consistent). There are no sensors in the drivetrain.

Omni wheels are for position measurement.

[yash101]

Originally Posted by z_beeblebrox

Omni wheels are for position measurement.

I believe you can use omni wheels to create quite creative drivetrains. They are not solely for position measurements. You can make an omni drive, a kiwi drive, and possibly even a tank drive capable of drifting!

Jim posted a picture, showing how omni wheels were used for the drivetrain, not just odometry!

[cadandcookies]

Originally Posted by yash101

I believe you can use omni wheels to create quite creative drivetrains. They are not solely for position measurements. You can make an omni drive, a kiwi drive, and possibly even a tank drive capable of drifting!

Jim posted a picture, showing how omni wheels were used for the drivetrain, not just odometry!

I think he was referring to the question about the purpose of the green omnis in the middle of said picture, which do not appear to be driven.

Another fantastic robot from 33. I remember seeing your 2012 robot at Championships and being immediately inspired to push my team to create more aesthetically pleasing robots. Your robots have been excellent examples of both form and function in a killer package.

[apalrd]

The green wheels were intended for odometry but were later removed. The gray omni wheels are the drive wheels.

We use 6061 T6 as it is a harder than 5052, in FRC this translates into the need for a thinner sheet for the same overall stiffness. In the thicknesses we use (0.050" and 0.063") it does not crack when bent properly, but we have issues bending anything thicker (we have successfully bent a few 0.090" pieces, but also cracked several). 5052 is usually used by sheet metal shops as it is easier to work with, many teams use 5052 successfully in FRC (some on CD will say it's impossible to bend 6061, that is not true). I have only ever seen 6061 and 5052 used for FRC sheet metal applications.


We can in fact be pushed, we intentionally do not resist and instead spin out. That was part of the strategy.