Re: Modular Drive System
 

Looking good.

Re: Modular Drive System
 

The size factor is similar to my vex omnibot. With that size, you could use very grippy materials to get a good grip. The vex wheels are probably the most grippy wheels I've seen. The robot's ability to push is just like out 2013 robot. Have you tried to climb walls with it? (I mean going at the wall, full speed and scale it until the robot flips over)

Re: Modular Drive System
 

Not on purpose. :)

Re: Modular Drive System
 

Re: Modular Drive System
 

So what all reductions do you have going on?

What's the mecanum wheel size?

Custom, VexPro, or AM mecanum?

Re: Modular Drive System
 

Gearing: 1:5 planetary, 3:1 bevel = 15:1 total
Wheel is AM 8" MecanumAM Mecanum (am-2115)

Re: Modular Drive System
 

You'll be coming in at around 10 ft/sec which isn't too bad.

Pushing match current is 51 amps which isn't great but not bad.

Overall, a very good design and setup.

Re: Modular Drive System
 

How did you calculate these numbers.

Re: Modular Drive System
 

JVN

Re: Modular Drive System
 

What values did you use for drivetrain efficiency and speed loss constant? And wheel coeff of friction?

Re: Modular Drive System
 

Darn didn't even think that those could be different.

I used .7 for coefficient of friction (AM 8" forward cof) since most pushing matches are in the forward direction.

81% speed loss constant
90% drivetrain efficiency
Robot weight at 155 lbs

Results:
Unadjusted Speed: 12.36 ft/sec
Adjusted Speed: 10.01 ft/sec
Pushing Match Current (per motor): 51.08 Amps

Re: Modular Drive System
 

There is no reason to expect those numbers to be the same for all drivetrains, as they are substantially affected by the type of drivetrain design (chain and sprocket, belt and pulley, direct drive, type of gearbox, etc) and workmanship (chain or belt tension, proper assembly and lubrication of gearbox, wheel alignment including toe-in and camber¹, wheel axial offset², etc).

¹Toe-in and/or camber of a wheel causes the wheel sprocket (or pulley) to be non-coplanar with the driving sprocket (or pulley), and thus contributes to friction between the chain (or belt) and the sprocket (or pulley). Toe-in also causes scrubbing friction with the floor surface.

²"wheel axial offset" in this context means that the wheel sprocket (or pulley) is axially offset from the plane of the driving sprocket (or pulley), causing the chain (or belt) to be non-planar, thus creating additional friction between the chain (or belt) and the sprockets (or pulleys).

Re: Modular Drive System
 

I'd assume the way to calculate both are far too complicated.

Re: Modular Drive System
 

You can plug in swag values and get ballpark estimates for a drivetrain you haven't built yet.

Or you build your drivetrain and then measure them. Then you can use the model to generate reasonably accurate data for that drivetrain.

Re: Modular Drive System
 

Ether & geomapguy,

Great stuff! It didn't occur to me to model the system as part of the design process; I just used experience from previous designs. E.g., we used AM 8" Mecanums last year with the Toughbox Mini (am-0654). with 10.71:1 gear ratio. I picked 15:1 as the bot was plenty fast at full speed in tank-mode but we had issues with mecanum control and I wanted to begin conservatively. Fast is fun but I think good controlability should be achieved first.

For those of you like me, who didn't have a clue what Ether and geomapguy were talking about ;) , here's a link to information that Ether has posted:

Drivetrain Acceleration Model

This is excellent infromation!



Getting a model calibrated should be very useful for developing an energy management strategy.

Now if I just postpone sleeping for 3 months, I think I could work through all the study materials y'all have given me...