Mamba Max 7700v

[pthunell]

I just recently aquired a Mamba Max esc and 7700v motor. I'm going to build a rustler mainly for high speed runs. I keep reading that the 7700v runs too hot and it's better to get the 5700v and gear it higher. The 7700v that I have is brand new. Do you guys think I should just sell it and get the 5700v? I plan on using A123 batts, but may do big lipo down the road after some experimentation.

Any recommendations would be great since I'm new to electric rc and there is so much info to learn.

Pete

[sleebus.jones]

I'd get the 4600kv and run 4S :)

[snellemin]

I've ran the 7700 on 4s A123 before. It will cook pretty quick if you don't pay attention.

[neweuser]

I have a rusty with VXL Shocks, tranny, bearings, and tie rods with a 4600/Sidewinder. :)

[DRIFT_BUGGY]

In internal and beta testing, we were unable to find gearing options that would actually thermal the controller when used within spec:
Max input voltage for ESC: 3s lipo or 12 cell NiMH/NiCah
5700Kv motor max voltage: 3s
7700Kv motor max voltage: 2s

The Kv of a motor is the number of rpm’s it will turn per volt of input. So the 4600Kv motor will turn 4,600 rpm per volt of battery. On a 6 cell pack we can presume good cells are holding around 1v per cell, so 6v x 4600Kv = 27,600 motor rpm.

On the other hand, if we take a 3 cell lipo pack with the 7700Kv motor, that gives us 10.5v x 7700Kv = 80,850 motor rpm which is safe for the ESC, but well over the safe motor rpm limit so it cannot be used either.

So how can you get the most speed? You might think the 7700Kv motor having the highest Kv would automatically allow you to have the fastest setup right? Let’s find out:

7700Kv x 2 cell lipo voltage (max with this motor) = 53,900 motor rpm.
5700Kv x 3 cell lipo voltage (max for the motor and ESC) = 59,800 motor rpm

So the fastest 5700Kv motor setup is actually 6,000 motor rpm faster than the fastest allowable 7700Kv motor setup!

Now if you are racing with 6 cell packs only, then obviously the 7700Kv motor will be the fastest option for you, but we are routinely asked “what is the absolute fastest setup for my car/truck?” The answer in this case, is the 5700Kv motor with a high quality and high output 3 cell lipo pack made for 10th scale cars.

[BrianG]

I'll take the 4600 on 4s anyday.

And no need to quote the spec... 4s lipo=12 NiMH cells nominal and fresh-off-the-charger. So, technically, 4s is within spec...

[mkrusedc]

I thermalled my MM in an RC10 with stock gearing and 3s all the time. Definatly get the 5700 or lower and then gear up.

[pthunell]

Thank you all for the replies. I will be selling the 7700v and getting a lower kv motor. The knowledge and advice is much appreciated.

Pete

The 7700 is not so bad if you don't mind running 2s. I ran that setup in my T3 and was very happy with it. The speed was pretty ridiculous and it didn't get too hot.

[neweuser]

I may have a 4600 with a sidewinder esc for sale. :)

[vassmar]

My friend run a 7700kv @ 3s almost all summer long last year. It was no problem. Sure it got hot, but it still works ;) But it's not recommended if you want to keep it safe. I'm planing on running the same setup in my 1/10 pan car.