Braking Problem With 9918

[Qball76]

When I first got my brushless setup hooked up I noticed I would lose the braking function once my batteries started to wear down. Tonight the brakes werent working halfway through two packs, has anyone had this problem before, could this possibly be a programming error?

[RC-Monster Mike]

Another user on these forums had a similar problem. I am not sure if he figured it out though. What gearing are you running? Also, what are the settings on your controller? Do the brakes slowly fade or are they there one minute and gone the next?

[Qball76]

I'm running the 51 turn ofna spur with a 15 turn pinion. The brakes will work great when I'm running a fresh set of batteries. Before the brakes only got worse towards the very end of a pack, but tonight they just quit completely halfway through the packs.

[RC-Monster Mike]

The gearing is a little on the high side and lower gearing may help this problem, although it shouldn't be happening. Try to reprogram it and see if it helps (guessing here, but it doesn't hurt to try).

[Dafni]

Okay, I just saw this thread.
I have the same problem on my TwinForce, I know exactly what you are talking about. But I think it has nothing to do with the state of the batts. Could you please try this: When your brakes are gone, drive slowly for a moment, or even let it sit, so the controller can cool down a bit, and then the brakes should be back.
I figured the braking mosfet is at its limits, what with our MT's and all 4 wheels digging in. If I put a one-way up front, the problem is gone!
They call this brake fade, and I talked to german users about this. They say we have to live with this. Lower gearing should take care of the problem. Actually it should work on a Maxx (which is what you have, I assume) without problems.
The gearing on my TF is also on the high side, but I already got used to it. Altough I must say I drove it into some ditch with water once, because of this. Controller got drenched, but is still alive!

Btw: maybe a fan solves this, too. But I would try lower gearing.

Sorry for not getting back earlier, or updating my other thread about this (look for "9918 only brakes when it wants) but my Revoxx distracted me;)

[phildogg]

thats exactly what I said about your problem ( brake fade )dafni. glad you got yours fixed.
phil

[Dafni]

Nah, it´s not really fixed. I still have to gear it down. I removed the oneway again, because of different reasons. First of all I don´t like the maintenance of this bugger, it get´s dirty really quick and looses its bite. This leads to stress on the front diff (when the oneway suddenly grabs at high rpm, I think) and since the TF is my basher and not a racer, I don´t really need the added cornering capability. Plus I like doing wheelies in reverse with this truck.

I just have to think ahead and avoid ditches

However, Phil, sorry for not posting earlier about my experiences, but the bad luck with my other BL overtowered this.

[Qball76]

I'm going to attempt to reprogram it and see if it changes anything, somehow I doubt it will since they work great part of the time. I've noticed that sometimes when the brakes start to fade if I downshift into first that will buy a little time with the brakes but towards the end of the packs they go out completely. As far as gearing goes I would love to drop down a tooth on the pinion, the only problem is no one that I know of currently has any 13-14 Mod 1 5mm pinions in stock. Hopefully Mike or Jamie over at Starluck will get some in soon, I'm actually very suprised someone doesn't carry a large stock of them with as many brushless systems are being sold.

[Serum]

a transistor or a FETT drops in current handling when it gets hotter (when it can handle 60A at 20 degree it can drop to 15A or less at 70 degree.)

When you brake, the motor stores the energy back into the cells. It brakes on the internal resistance of the cells. Get it?

You could also have got a bad cell in one of the packs. Did you tried another set of batteries?

When the problem stays,
I would try a fan first.