FRC Blogged-Kit of Parts Drive System Option

[Kernaghan]

Just some ideas.

"Belt drive robot" - "direct driven center wheel"

Unless andymark has aquired new belts, there are currently only two sizes. The 20.47in belts are not large enough to accommodate 6in wheels or larger(and I imagine they might be using their new 6in HiGrip anyway). Because it is a direct driven center wheel, the outside wheels are the pulley center distance away from the middle wheel(minus the 1/8in center drop). Inferring we are using the current pulleys and the 31.5in belts, the center distance is about 11.5in.

Soooooooooooooo
(11.5in * 2) + (3in(HiGrip radius) * 2)
= 29in

Possibility the new drive train is at least 29 inches in length.

[z_beeblebrox]

Will it be possible for teams to buy a second kitbot for a practice robot?

[Racer26]

Historically, its been available from AndyMark after kickoff.

[Steven Donow]

Originally Posted by z_beeblebrox

Will it be possible for teams to buy a second kitbot for a practice robot?

Andymark usually puts the kitbot on sale sometime within the first week after kickoff

[MikeBrock]

I wish we had more information to base our decision off of. I'm generally not a fan of the kitbot, but if it has some new improvements, it would be a great option.

[Akash Rastogi]

Originally Posted by ErvinI

I'm hoping that the dimensions are increased this year. The dimensions last year severely limited what teams could design (although it meant less clutter on the field). The fact that they somehow fit 6 wheels in a wide configuration makes me hopeful the dimensions are increased this year.

I liked the new dimensions. The new limitations were really cool and forced kids and mentors to think harder and iterate more. It also made transportation easier, made more room on the field, and I felt it made everything a bit more fun.

I hope the new dimensions stay.

[Gregor]

Originally Posted by Akash Rastogi

I liked the new dimensions. The new limitations were really cool and forced kids and mentors to think harder and iterate more. It also made transportation easier, made more room on the field, and I felt it made everything a bit more fun.

I hope the new dimensions stay.

Agreed. Seeing the little robots beside the 2012 and earlier robots really showed me how inefficient teams were with their space.

[Chris is me]

Originally Posted by Ether

Does anyone know where the 81% number came from?

If I remember correctly, I once read a really, really old CD thread that said 81% was determined by taking one of 229's drive bases, running it to top speed, and measuring that speed. Ratio of that top speed to actual speed became the default "speed loss constant". I'm sure this number is somewhat correlated with efficiency, wheel size, tread type, etc etc. For most practical purposes it's "good enough".

Efficiency in JVN's calculator is used to calculate motor loading, not speed.

[Ether]

Originally Posted by Chris is me

If I remember correctly, I once read a really, really old CD thread that said 81% was determined by taking one of 229's drive bases, running it to top speed, and measuring that speed. Ratio of that top speed to actual speed became the default "speed loss constant".

I seem to recall reading that somewhere too, but I wasn't sure.

I'm sure this number is somewhat correlated with efficiency, wheel size, tread type, etc etc.

It's a lot more than "somewhat". In the real world, the top-speed to theoretical-speed ratio is correlated with playing surface, wheel type (e.g. pneumatic or solid) and tread type, chain vs belt, chain or belt tension, wheel alignment, wheel runout, torque-dependent friction in the gearbox and drivetrain, and speed-dependent friction factors such as large airfoils.

For most practical purposes it's "good enough".

It's quite useful as a rule of thumb. Whether or not it's good enough depends on what you're using it for. Students need to understand the limitations.

Efficiency in JVN's calculator is used to calculate motor loading, not speed.

That is true. In a physics-based model, the torque-dependent friction (gearbox "efficiency") would affect top speed.