Trouble-shooting Low Traction

[alecmuller]

Has your team experienced difficult-to-diagnose traction problems?

I built an off-season drivetrain as part of a tutorial project, and every time I try to measure the traction force, the wheels slip on the carpet with far less traction force than expected. Here's the set-up:

1. 4-wheeled robot with 4" rough top wheels (actually it's an octocanum, but I've confirmed that the 4 traction wheels are the only thing in contact with the carpet); the wheels have slipped a few times but still look rough to me.
2. weights added to bring total mass to ~148 lbs
3. nylon parachute cord running from robot to 2 pulleys to (barely) lift 3 garden bricks; wheels slip when trying to lift 4.
4. each brick weighs ~20 lbs alone and requires about 26 lbs of tension to lift through the pulleys (measured with bathroom scale)
5. carpet is good-looking used scrap of actual FRC field carpet

I've read this thread and this whitepaper, which suggest I should expect coefficients of friction in the 1.2 to 1.6:1 range, compared to the (78/148 = 0.53:1) I'm actually getting.

I have video of the 1st test here (ignore the fact that I have the wrong carpet - I forgot to video the 2nd test after replacing it with the correct carpet).

Any idea what I can do to get traction strength closer to 160 / 200 lbs?