Current draw question, using eagle tree....

[Over_revO]

Hi guys,

Me and my friend bought a RC8T and we did a first test yesterday,

we didnt had the tires in time so we used other.

I used savage tires with a 14T pinion (16t was in kit)
2200kv cc combo

my friend:
MMM esc Neu 1515 1.5d 14t pinion with badland fitted on rulux half-up(like LPR)


we tested with Eagle tree, on brutal wheelies thats where we had the highest peak, neu 1515 1.5d= 181 amp

and for me with 2200kv 178 amp

my friend did a couples wheelies then ran very slowly climbing a hill and the esc smoked.


i stopped mine, we later went out, i used his badland tires (smaller diameter)
i pulled 173amp peak on wheelies on asphalt now., but normal driving is ok, mix like 150 amp max.
tested top speed, 54mph and may be 56mph was possible.

thats a bit too fast for bashing anyway,

so we installed a12T pinion,

peak of 170amp on WOT from standing wheelies, but other peak were 150 and less, normal driving under 100 and some small peak in the 120s.

estimated speed around 50mph....


We tested braking, low speed load etc and the highest peak came with brutal take-off. or mid to WOT instantly....

my question is, how can my friend smoke the esc at low speed?
most esc that i seen smoke was at low rpm, but at low rpm our current draw was always under 80 amp....

Is there anything that affect the esc at lower speed?


Im really trying to figure out what is happening....

The highest watt was 3800 i think with the Neu 1515 1.5d


We also tried the Neu 2.5d 1650KV on 14T and it also pulled 178 amp!
but had only 1860 watt!

on the 12t with 2200kv it produce 4.25 hp
and the 1650kv it produced 2.5hp but peak amp was higher than the 2200kv...


thx for reading all of this, im trying to not smoke my esc

It just seem like even geared for 35mph it will pull those amp.
On low speed it really seemed good.


I will try to get a eagle tree log data today and post it here so you will guys have a better idea of what im trying to explain....


Shortened question:

Low speed climbing is ok? if no why
high peak but normal current draw on normal driving ok?

Thx!

[E-Revonut]

What voltage are you running? I also have an RC8T, FT kit and I'm running the RC-Monster full chassis conversion. MMM/ Tekno Neu 2.5D 5s lipo. Here is my Eagle tree graph.

[Over_revO]

I dont have the graph here, but i think it started at 25 volt, and the lowest when we tested speed was like 20 volt, then it came back to 25volt when i let off the throttle.

Using Thunder power 40C 2X3S and Lipoly 30C 6S

Im going bashing in a sand pit today we will try again on 12T pinion ill post the graph tonight.

Thx for your graph, what pinion are you running?

[E-Revonut]

That was a 15T pinion 50T spur and proline BowTie LPR tires

[Over_revO]

Heres some eagle tree log!


My setup:

-MMM cc 2200 combo
-12t pinion
-Badland tires stretched on rulux half-up
-top speed on 6S 51 mph
Test on 4S:


^^ you can see the first part is gradual acceleration to WOT, the highest peak are
standing still wheelies at WOT.


test on 5S:


^^ i tried to let spaces between test so you can see what i did...
you can see 2 gradual accel, then a WOT wheelie from standing still then so drifting mid throttle, then a top speed WOT from standing still(quickest i could go whitout wheelies..)
then 4 brutal WOT wheelies from a roll.


6S:

^^^Basicaly the same thing... you can see where it was WOT wheelies and gradual accel...


Now top speed test on asphalt 51mph:

I did 2 runs, the first one i accelerate as fast as i could at edge of wheelies...


Now my friend's RC8T
-EZrun esc 150a
-Neu 1515 2.5D 1650kv
-14t pinion
-savage tires
-top speed on 6S 48mph going a little side way...too much balloning...

On 6S:

The highest peak is from a standing still doing a wheelie... you can see gradual acceleration too up to top speed.... in dirt.

top speed on asphalt 48mph:

the high peak at the end are 3 wheelies...

And a my friend savage flux stock everything on 6S:

while bashing normaly:



So from what i can see even the savage have high current draw when doing wheelies...

What i seen is that the watts produced on the savage were a lot lower, under 2000 watts, and mine peaked at 3500 watts today if i remember right....

the 1515 2.5d was about 3200watts for bashing.

That make me think i have to watch the watts? more than current draw?

if that make sense.... next time i will add the watts on the graph... i dont have the data here so i dont remember all the watts...just approximation...

We are bashing in fine sand...


if anyone have a good explanation of what i should watch let me know. :)

[BrianG]

Watts is simply voltage X current, so other than saying your setup has X amount of HP, it's really not that useful IMO. Current draw is more useful because it can help show the effects of gearing, battery quality, etc. Voltage will dip more the higher the current is, that's to be expected.

[Over_revO]

Ok, so may be my friend just had a defect esc?

Thx!

[J57ltr]

The slower the motor turns the less impedance it has (closer to a dead short). As the rpms increase the power delivered to the motor decreases. So when going slow the on vs off time of the fets is longer than when the the motor is running faster.

Jeff

[Over_revO]

Ok, i think i partially understand that, lol

Can you explain me what is fets. and what is the "on and off" time of the fets?

sorry for all the question i really try to understand how they work.

And is it what fail when the esc smoke?

[J57ltr]

Fets is short for MOSFET (Although there are JFET's as well, but that's a different animal). The way a brushless speed control is setup to control the motor the fets are like switches. When going slow the fets are on longer than when the the motor is turning faster. It shouldn't really hurt them going slow, but since your friend did a couple of hard starts then started crawling maybe it was just too hot you didn't really say how long he did that but I'm just guessing it overheated, who knows. I guess just send it in and get it repaired, then ask Castle what they think happened.

Jeff

[BrianG]

Oh boy. This can get really technical, but here is a simple explanation:

FETs are Field Effect Transistors, and there are many of them paralleled in an ESC. There will always be a multiple of 6 (one for the + rail, one for the - rail, for each phase). The on/off cycles refer to the pulse-width modulation signals fed to the ESC. Longer on pulses results in the motor seeing more average voltage, shorter pulses results in less average voltage getting to the motor.

ESCs smoke from over voltage, being forced to pass excessive current (like when overgeared), or excessive current ripple is present (from low quality batteries), and several other reasons.

[J57ltr]

[QUOTE=BrianG;318998]Oh boy. This can get really technical QUOTE]


Ya I totally didn't want to get into sinking and sourcing, H bridge and all that

The battery stuff, I am not so convinced it's not an engineering issue, it should have been forseen.

Jeff

[Over_revO]

Thx a lot!


yeah no need to go very technical! lol haha
He used Thunder power 5000mah 40C 2X3S

He was climbing a 2 feet hill at very low speed trying to climb as slow as possible, then got partialy stuck (wheelspin...), he just did 2-3 quick WOT burst and it climbed it,

then he just climbing anoher one slightly uphill, may be 25 degree... then the esc partialy cut-out, then he appied throttle and POOF... smoke, burst of fire ...lol

So even if the amp is very low when going low speed, it can smoke the esc if geared too
wide?

if the savage have peak of 189 amp, , how can i know if it is not overgeared?
the motor never get hot...

On my truggy the motor is between 145-155F all the time, with spikes at 170 amp.

I know the savage will wheelie when too much throttle is applied and the truggy will have more constant load , but isi it teh main reason it overheat?

thx for any tips, appreciated :)

Mike