straight line tracking (in closed loop speed mode) works level but not uphill

2 years 1 month ago #29534155 by JDB
SBL2360 with dual brushless motors tracks perfectly straight on level surface but unable to track straight up an incline - any ideas?

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2 years 1 month ago - 2 years 1 month ago #29534157 by Gabriel_Isko
Hmm, It is a little bit unclear what you mean by track. If you are talking about running at matching speed, let me know which operating mode you are in.

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2 years 1 month ago #29534159 by JDB
Hi Gabriel thanks so much for reply :) I am using Mix 1 - this my first vehicle and since posting i've give my question more thought. here's perhaps better description...

System behavior:
In mix-mode 1 closed-loop speed setting, on level surface vehicle faithfully tracks straight (when command 2 is neutral and command 1 is positive). Same on decline. Wheel speeds are perfectly matched. When negotiating an incline however, the slightest unevenness in surface introduces a rotation that exceeds command 2 input's ability to recover/adjust

My thinking:
I believe the controller is doing its job to maintain matching speeds but on the incline if the surface introduces minor rotation, my PID is too lazy to keep their relative speeds matching such that command 2 input can compensate. i.e. once the vehicle has started moving diagonally on the incline even the slightest bit, the downslope wheel needs to speed up faster and to a greater degree than command 2 correction (with my current PID settings) can achieve...

Does this sound like I am on the right track (no pun intended) in my thinking? Would love any guidance or pointers to references related to PID tuning for this type of challenge. I was so happy with myself that it followed commands well on level surface. Time to gain more tuning wisdom i guess.

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2 years 1 month ago #29534160 by Gabriel_Isko
Okay, I sent you a pretty lengthy email about this, but the short version is that both your motor controller and motors are undersized to handle the hill you that you are trying to go up, at least without any sort of transmission.

One of our distributors has a pretty good write up about the math you need to do to properly size motors in this condition, however we are currently working on our own application note that should be a bit more comprehensive.

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2 years 1 month ago #29534163 by JDB
Thanks so much Gabriel for the excellent insights and advice! Digesting the email and doing the math. Will keep u posted on email and upgrade as needed. Cheers

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