Slash 4x4 Buggy 1717 6s

[Lizard]

Maybe it is a stupid thought of me, but if the batterys where the limiting factor, should it be accelerating more slowly, but once on speed, in will be no issue, to get that current?
I havent seen logs, and I don't know much about it, but isnt accelerating the highest draw part, and once at speed not so much, just like in 1:1 cars or horses pulling a car?
In the beginning you would have to pull hard, but once it rolls?

Yes, that is also my understanding. That's why my theory right now is that the motor must be pulling too much current at high RPMs (or maybe at all RPMs). I went 172kph with the same batteries and gearing with the TP4070. If the TP4070 can do 172 without stressing the batteries too much, why not the TP5840 then.

Your experience with the TP5640 still puzzles me, I think the difference between loaded RPM and unloaded RPM should indeed, like you said, indicate how 'loaded' the motor is, the bigger the load, the bigger the RPM drop... unless..., there's something else going on and it's not the motor that's the bottleneck, but the batteries that cannot provide the over-dimensioned amounts of juice the over-dimensioned motor needs to rev up to where it wants to go?

For me the question is, why does it draw so much current in the first place? Gearing was the same, the car is only about 100g heavier with that motor compared to the TP4070 and traction is limited so it shouldn't draw alot more power if I understand the underlying principles right.

Also I have read on boating forums, that the big 6-poles have much lower RPM drop under high load when compared to 40mm 4-poles. But maybe that comparison doesn't hold true for my case, because of the big length difference (5840s = shortest 58mm motor, 4070=longest 40mm motor).

Re the braking we talked about earlier, I think the difference in acceleration and braking distance can be explained from the fact that all the forces (drag, rolling resistance, driveline friction) the motor has to battle during acceleration, are helping it during braking. Not sure how well it holds in practise

I think in reality, rolling resistance and driveline friction is negligible, and drag becomes negligible below somewhere around 80kph :)

My XL2 does not seem to log negative Currents, but my EagleTree does, and I've never seen my braking Currents go much past 40A in the 8ight-T set-up that pulls 200+A at acceleration. Now, I don't exactly understand how braking works, as I think braking Current can be divided between a regenerative part, sent back to the batteries (that part is measured by my logger), and a part that is just dissipated in the motor by the ESC shorting the motor windings (that part cannot be measured by my set-up). I think you and Vedder talked about that once, but I did not pay enough attention then to recall exactly :).

Like you say, the current is either not being logged or not being sent back to the batteries. But it is there (and the torque proportional to it).
Vedder said as far as he knows, hobby ESCs just sort of short the windings and have zero percent regen, but maybe that's only true for really simple/cheap hobby ESCs.

Regarding logging with the Monster X: No, I'll use it in the Kyosho buggy first, want to make sure it works reliably with a "normal" setup before I take it to the extremes. And I think logging won't help much, I have no baseline to compare with anyway. If everything get's hot and the batteries are drained very fast, I know without logging that it must be high currents. If the performance is not accordingly, it must be low efficiency :)

[Dr_T]

Originally Posted by Lizard

If everything get's hot and the batteries are drained very fast, I know without logging that it must be high currents. If the performance is not accordingly, it must be low efficiency :)

Yeah, crap... seems you guys are right and I'm trying too hard not to have to accept bigger might not always be better. There goes my theory of everything RC... did I say crap already?