pic: 2791's Chassis

[Nemisis]

Nice use of Inventor!!

[JackS]

You can view some preliminary pictures with electronics here.

We are planning on using Anderson connectors to enable us to put the Victors much closer together than otherwise possible. Wire paths have yet to be drawn out.

[Navid Shafa]

A) Are you planning on running the chain on the inside of the frame?
B) Are the bumpers going to be mounted right onto the standoff blocks, without any other support?

[Sh1ine]

Originally Posted by Navid Shafa

A) Are you planning on running the chain on the inside of the frame?
B) Are the bumpers going to be mounted right onto the standoff blocks, without any other support?

Yes and Yes.

The spacing between the edge of one stand off and the edge of the next closest stand off is always less then 8". Which is to say that the center points on the standoffs may be a bit more then 8, but if I am reading the rules correct "and no section of BUMPER greater than 8” may be unsupported)" just having material behind it suffices. And with a bolt holding it in place, and a generous amount of stand off to support the bumper from twisting, they should be good.

[Chris Fultz]

Nice work.

Something to consider. It looks like very little ground clearance.

If you have anything stick through the bottom plate, it could rub the carpet.

And, there is a small step in the carpet around the towers. There is a plate under the tower base, and then a layer of carpet covering it.

[Justin Montois]

Looks great. I love the belt running through the tube. Very slick.

[Leav]

Originally Posted by 340x4xLife

Looks great. I love the belt running through the tube. Very slick.

I would actually say that is my least favourite feature about this chassis.
it's cool no doubt, but looks like a pain to maintain if you throw a chain...

A lesson I learned from my mentor a while back was to design for maintainability, as well as performance and looks.

[Chris is me]

Originally Posted by Leav

I would actually say that is my least favourite feature about this chassis.
it's cool no doubt, but looks like a pain to maintain if you throw a chain...

A lesson I learned from my mentor a while back was to design for maintainability, as well as performance and looks.

It took about 7 minutes to change a belt on our prototype chassis.

This one will have a removable easy access window over the middle wheel. That and practice / belt changing drills should bring it down to 5 minutes - twice as fast as our previous dead axle drivetrain.

We also stress tested the drive. Stalled the wheels multiple times, ran it forward and back a bit with no signs of slipping or failing.

[rahilm]

Looking at the CAD with electronics, I just wanted to point out that the only legal bridge this year is the DAP-1522 included in the kit.
Looks like a pretty cool drive design with the 6 motors

[Matt H.]

Why did you choose to use six motors in your drive train?

4 CIMs at a 7.4:1 ratio gives a maximum of 634 in-lbs of torque at the wheels. With 4 inch wheels, that becomes ~315 lbs of force to accelerate the robot. However, with a generous coefficient of friction of 1.5 your robot will spin its wheels at 180 lbs of accelerating force.

[Chris is me]

Originally Posted by Matt H.

Why did you choose to use six motors in your drive train?

4 CIMs at a 7.4:1 ratio gives a maximum of 634 in-lbs of torque at the wheels. With 4 inch wheels, that becomes ~315 lbs of force to accelerate the robot. However, with a generous coefficient of friction of 1.5 your robot will spin its wheels at 180 lbs of accelerating force.

We're assuming about 1.3 for traction.

Essentially, pushing power. 4 CIMs geared at 12 FPS draws a LOT of current. 4 CIMs and 2 BB isn't quite traction limited (60some amps last time I checked) but at least we won't stall out pushing mecanum bots and kitbots around a bit, and we'll have great acceleration.

[JesseK]

Originally Posted by Chris is me

We're assuming about 1.3 for traction.

Essentially, pushing power. 4 CIMs geared at 12 FPS draws a LOT of current. 4 CIMs and 2 BB isn't quite traction limited (60some amps last time I checked) but at least we won't stall out pushing mecanum bots and kitbots around a bit, and we'll have great acceleration.

Looks like a very solid setup.

If you use the line following sensors, where would you put them?

I only ask because the first words out of the student programmer's mouth was "I want my line followers here, here, and here", which correlated to the front corners of the robot and the center of the robot. In this setup, it looks like those sensors would interfere with the live axles (they're about an inch tall), though other modifications could be made.

[sdcantrell56]

Id be real careful gearing at 12fps. We did that last year with 4cims and 2fp's and often times our battery was totally dead with around 30 seconds left in the match. We later dropped down to 9.5fps with the 6 motors and it was much better. Just be ready to swap out gearing after testing. Otherwise this looks super awesome!

[Teched3]

I've always been an advocate of using smaller diameter wheels for a little better grip on the carpet. You also obtain a little lower CG, which helps on Sat afternoon. Was there a reason that your standoffs appear to be reversed from one side to the other, or just an oversight. are you using belt or chains to drive your front/back wheels? Your rendering is awesome, and is motivating me to learn a 3D modeling program. any suggestions for an old-timer?

[Chris is me]

Originally Posted by JesseK

Looks like a very solid setup.

If you use the line following sensors, where would you put them?

If we opt to use line followers (I'm thinking an ultrasonic sensor and a gyro for dead-straight tracking is as good as we'll need), we'll probably cut a hole in our electronics board and mount them a little above the bottom of the front of the chassis.

Originally Posted by sdcantrell56

Id be real careful gearing at 12fps. We did that last year with 4cims and 2fp's and often times our battery was totally dead with around 30 seconds left in the match. We later dropped down to 9.5fps with the 6 motors and it was much better. Just be ready to swap out gearing after testing. Otherwise this looks super awesome!

One of the really cool things about this transmission is the belt reduction - we can adjust with a new belt and output pulley between 9 and 14 FPS without taking up as much space as a chain run would. It also lets us mount our motors in a very compact configuration - the two-motor model is literally 3 inches from the ground.

That being said this is a valid concern - does anyone know how I could predict battery discharge rates using math? I have no idea how to do it.

Originally Posted by Teched3

I've always been an advocate of using smaller diameter wheels for a little better grip on the carpet. You also obtain a little lower CG, which helps on Sat afternoon. Was there a reason that your standoffs appear to be reversed from one side to the other, or just an oversight. are you using belt or chains to drive your front/back wheels? Your rendering is awesome, and is motivating me to learn a 3D modeling program. any suggestions for an old-timer?

Our drivetrain's CG last year was about 5 inches from the ground.

This year, it's just under an inch and a half.

With the 9 foot tall arm we're working on, that could be pretty important.