Power drop at WOT on 6s with MMM geared for 90mph...
 

Hi guys,

Me and my friend are doing speed runs, and we kind of encounter a problem ,
we got his revo to 91.2mph a month or 2 ago and we decided to give another try today with similar setup, but with a different MMM, (in fact we tried 2)

And once speed climed , the truck could reach about 85 then speed would begin to decrease to 78-79 on that same run...

The wires were a little warm, same for battery. may be 120-130f
motor and esc at 150f after one run...


But on the 91mph run with the MMM we used it had plenty of power no problem like that...

only difference is we used different batteries,

for 91.2mph : thunder power 40c 4200mah


today : Thunder power 40c 5000mah
and SMC 5000mah 25c

it was about the same power wise.... 84-85 then speed decrease at WOT.


any idea of what can cause that?
can there be difference in MMM efficiency from one to another?

we use traxxas plug, my friend will install CC 6.5mm plug soon.

Thx for any info/help!

Did you calibrate the new MMM to the receiver? It may just not be seeing quite full throttle. After I do this, I usually bump up the throttle EPA a few % points. It doesn't make it go any faster, but will compensate for any value drift in the throttle potentiometer.

Take a look at your battery connections. After repeated plugging/unplugging, the contacts can get pitted from the initial arc. After a while this, and any "soot", results in higher contact resistance, and more voltage drop at higher currents.

As far as the decreasing speed: Motor speed is a function of battery voltage, so if the battery voltage falls after several seconds, the total RPM will drop as well.

After doing a number of speed runs, I would look at things like tire balance, bearings, etc. Those things can affect speed at the levels you are running.

So if i understand right we experienced a voltage drop that also bring a current draw? more amp draw..?

(still learning hehe :))

The bearing are fine, might be a good thing to inspect the balance, i balanced them about 2 months ago.

I know there was a connector that was damaged, the part that keep the plug from falling, there was a dent in the little metal part (not what make contact, but what seem to keep it plugged...if you see what i mean..)

Ill tell him to redo his wiring and change the plug,

can the cc 6.5mm make a difference over the traxxas plug?
i have no idea if the traxxas plug are up to the task for what we do...

Thx for your help BrianG!
appreciated :)
Mike

Umm, balance the pinion gear? Some sort of resonance at speed causing high load on the motor?

We will look at that too, seemed from what i remember ok but we never know. :)

If possible, hook an Eagletree up to the vehicle. That may give you a hint at what might be causing issues.

I told my friend to get one, i hope he will, can also be useful to see what happen on his MGM 10S esc... an other problem.. lol

Good luck. I expect a 95mph run when you get the bugs worked out. :whistle:

Thx!!

Thats what we expect too!

100mph if we can get the MGM esc to work like it is supposed to...
no news from MGM after 2 weeks and 3 emails... :(

You should check out the phoenix 110 HV if MGM doesn't pan out for you.

We thought about it, but theres no mechanical brake on the e-revo :(

you dont need them, just set up the drag brake to stop the truck

I didnt know we could setup drag brake on them...

thx :)

I wouldn't recommend using drag brakes for those kinds of speeds... If you have it set too high, it's flip it over... And if you have it set too low, you may not be able to stop in time... You "NEED" proportional brakes for what you are trying to do... just my 2 cents...

Test them at a slower speed to dial them in FIRST...:whistle: Then work your way up...