Re: Killer Bees - 2014
 

Thanks for keeping me honest Joe,

Shouldn't be a big deal to take care of this if it becomes an issue.

Re: Killer Bees - 2014
 

Congrats on the win at Southfield.

What are you all using for a "photon cannon" this year and what exactly are you using it for? Normal aligning to wall?

Re: Killer Bees - 2014
 

Since you already competed, can you share info about your drivetrain?

Re: Killer Bees - 2014
 

Thanks, we are generally happy with the robot performance this weekend.

The flashlight basically provides a line on the ground in front of the driver which allows us to line up with stuff on the field from far away. When we initially put the light on we immediately saw an improvement in driver performance. I contribute this to the driver being able to look at the light instead of the robot while driving. Effectively, it becomes intuitive to look where the robot is going to be rather than where is currently is.

The drivetrain this year is actually has a pretty interesting story behind it. I don't have time to properly do it justice right now, but maybe sometime later this week I'll type it all out.

Re: Killer Bees - 2014
 

So.... About that drivetrain.

Re: Killer Bees - 2014
 

This is one of the first mysteries that I set off to solve when I got to the pits in St. Louis. The answer surprised me: 4 omni wheels, each with a single gear reduction from a CIM motor, nothing more. I chatted with one of the students as they were going through inspection, and the rational for the design choice sounded reasonable. The consistency and range of their catapult seems like a big part of why they are so successful with this approach.

Re: Killer Bees - 2014
 

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.

Re: Killer Bees - 2014
 

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

Re: Killer Bees - 2014
 

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

Re: Killer Bees - 2014
 

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.

Re: Killer Bees - 2014
 

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."

Re: Killer Bees - 2014
 

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?

Re: Killer Bees - 2014
 

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?

Re: Killer Bees - 2014
 

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!

Re: Killer Bees - 2014
 

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.