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May 11, 2020, 08:52 AM
Wake up, feel pulse, be happy!
Piece's Avatar
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Discussion

BLHeli ESC + Tamiya buggy + 6S lipo


I originally bought my DT-03 for FPV, with no plans to do any crazy modifications.



Except I couldn't just ignore the combination of BLHeli's extraordinary low-RPM sync and torque, and the "bidirectional" setting that lets any random quad ESC run forward/neutral/reverse. Plus, quad ESCs are incredibly good at what they do. Active freewheeling bypasses the old part-throttle heating issues, resulting in a very tiny, lightweight ESC, and the "brake" is always active, slowing the motor down by force as soon as the throttle is reduced.



So long story short, I installed a cheap 3100Kv 3650 size motor, with the test ESC being some 30A BLHeli-S unit rated for 2S-6S that weighs about 4 grams. Initial tests rolling around my apartment showed it gives just a small jerk to get moving, but once the rotor is turning, the ESC will slow it down to a bare crawl and keep it there without effort. It makes the stock brushed setup seem like an uncontrollable rocket by comparison... and the torque is there, baby. I started shoving various objects and finally got the knobby tires to slip pushing a gallon jug of water, although the buggy was still able to move it around.



The braking is scary. It doesn't coast - you increase throttle, the motor speeds up. You decrease throttle, the motor slows down, by force. Backing off the throttle too quick can send the car skidding even more easily than punching it too hard (because the front has no brakes, duh), which is tricky to control (at least on rough, sandy asphalt with worn-out tires).

I ran it outdoors on a 2S li-ion, and then a 3S lipo, and the ESC barely got above ambient temperature. Power is pretty nutty on 3S - the top half of the range was basically unusable. I decided to try the 6S lipo anyway, which proved to work just as well as 2S at low speeds (smooth, controllable, no noticeable temp increase), but it caught fire when I started trying to do speed runs. It was only a 30A ESC, remember, so the fact that I was able to drive it around and make several fast passes on 6S in the first place is pretty neat.

Anyway. Looks like the fire started at the caps, not the FETs, so I'm guessing motor inductance is a problem here. I've already ordered a beefier ESC (80A, 8S, BLHeli32) and some big caps to go with it. Should be interesting.

And oh yeah, I haven't forgotten about FPV
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May 17, 2020, 09:19 PM
Wake up, feel pulse, be happy!
Piece's Avatar
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Box arrived. Got everything soldered up, then spent all night wrestling with firmware and downloading stuff before I was able to program the ESC... but it does work. In fact, it works a lot better than even the BLHeli-S version. The 32-bit controller starts more smoothly and consistently, and the "non-damped" setting solves the harsh braking that made it so hard to control on the last attempt.

I'll need to get outside to test it at higher speeds (and gather realistic current data) but here it is showing off its low-RPM performance.

First test runs with the BLHeli32 buggy! (3 min 4 sec)




May 17, 2020, 10:23 PM
If it flies, I can crash it.
rocketsled666's Avatar
Hmm. I have a Tamiya Wild Willy, which came brushed, but was built brushless. I was thinking of swapping in one of my old sensored brushless motors because the low speed performance was poor. Impossible to get the car moving without popping a wheelie. But I have plenty of Quad ESCs with BL_Heli and you're right about low speed performance with props. Worth a shot with a gearbox! I'm gonna give this a try.


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