Minibot climb rate

[JesseK]

Originally Posted by Gary Dillard

So you can see that for a robot less than 5 pounds, even including some inefficiencies 3 seconds is absolutely feasible.

Check your math. The short story is -- equations only tell us where to start with MINIBOT prototyping, yet only real prototypes will tell us if the theory is sound.

The problem with such simple Power->Torque conversion in this case is that it does not account for the increased time the MINIBOT will take to get to its max speed under a higher torque load. Kinematic equations are non-linear with that respect when combined with the inverse relationship of an electric motor's speed-versus-torque relationship, thus analyzing a distance-versus-time chart between the two options may surprise you.

The problem is, distance-versus-time isn't quite as straight forward as it seems. In my analysis, I have to piecewise the graphs into acceleration sections and max-speed sections based upon the calculated time it take to accelerate to max speed under load.

So while I don't claim to have my calculations be 100% precise to real-world conditions, they do show that MINIBOTS with a 0.5:1 ratio with 4" wheels and a 5-lbs of weight will spend over 75% of their climb time in the acceleration phase, resulting in a 6+ second climb. 0.5:1 ratios with 3" wheels have 4-4.5 second climbs (50% of which is acceleration). Direct-drive 4" wheels have about the same times due to greater efficiency motor-to-pole coupled with less mass due to no gearing (all else equal), even though its max speed is technically slower than 0.5:1x3" wheels on a flat field.

...or they are direct driving but with that said you direct drive the motors get really close to stalling after only a few pounds

Actually, putting a 0.5:1 ratio on the MINIBOT puts it's torque load twice as close (ish) to stall as direct drive does.