This season taught me something new: While thinking outside the box is good, reaching beyond one’s own box of ability is a very poor choice. This season also taught me another good lesson: The ability to design a crab drive does not give one the ability to machine it to acceptable tolerances.
That being said, here goes: Introducing the Bullet Proof Drive!
Here are the concerns that go into this design:
Little to no CNC work needed. All you need to build this is a manual mill. Don’t even need a DRO, if you’re good enough!
Scalability. A team with advanced CNC ability can cut the weight down significantly, and up the features, while a team with only manual mills can make it function quite well.
Weight. 40 pounds without a battery for a bulletproof modular chassis.
Modularity. With either 4 bolts, or 8 1/4" rivets, one can remove and entire side of the chassis. Machine yourself a spare chassis side, and repairs can be done while the robot is on the field.
Cost of Materials. The chassis is designed to allow AndyMark components to be put in at almost any stage, from wheels to gearboxes to sprockets.
Durability. This is the fourth evolution of this chassis. All the weak points have been designed out, while still keeping weight and size down.
Balance. The Chassis itself is perfectly balanced, which allows for one to shift components around as needed.
Ease of maintenance. Tensioning a wheel is as simple as turning two nut drivers. Once you get the feel for the system, this can be done insanely rapidly should the need arrive.
This drive first reared its head in 2006, back when I was on 114. We had sliding pillow blocks inside chassis members, and that let us tension fairly easy. The next season we added in the bolt-pulled tensioning system, and smaller wheels. In 2008, we added the Unibody Extrusion to the module. This significantly cut down on weight, while keeping the number of parts to be machined fairly low.
If the game allows, I have a feeling 1595 may be returning to the BPD next season, unless Mecanums are called for. Questions and comments on the system are more than welcome, and I’m very willing to give out the CAD for the chassis to any who want it. Just email me and I’ll add you to the list of people to send it out. You can email me at iron spork AT gmail DO com.
I am sure that the rules will have to be fairly tightly constrained to cover most of the preferred 5- and 7-leg options, but still flexible enough to permit the magnetic impellers.
Thanks! Those exact gearboxes aren’t Supershifters. The Supershifter works for this, but needs a little bit of tweaking on the mounting plate (By tweaking I mean drilling two holes and countersinking two more). Also, encoders are mounted elsewhere in the drive. There’s a handy-dandy mechanism that will measure left side and right side speed directly off the ground, rather than off the wheel speed. If one really wants to add encoders to the drive system as well, it WOULD open up some interesting traction control ideas… I’ll have to look into this.
Who says we’re not?
But seriously, our team is looking at going green as much as possible from the chassis up, and implementing as much bamboo and other woods as possible. The weight is unbeatable, same for the strength.
Good good good. We are officially hooked on wood. You should be able to build a killer wooden frame with a table saw and mill, especially if you want to get into biscuiting the joints and even laying it with glass. We used okoume this year and the weight savings is incredible. The density is only.018lbs/cubic in. The only problem with it is that its super expensive and difficult to find. I think for next year we will just go with 12mm baltic birch since we can get it 2 miles from our school and its 1/4 the price of okoume. We also used MAS epoxy to attach everything.
It wouldn’t ACTUALLY take a bullet… Though if someone machines one for me, I’ll take it out to the range next week, and open up on it with some 5.56x45’s!
It’s both a possible design for our team, and something that other teams could make. It’s really not too bad machine-wise, all you need is a manual mill and some AM parts.
