Mamba Max Question

[evaderst69]

I know everyone say that the 5700 is faster than the 7700 beacause you can run the 5700 on 3s lipos.. Now according to towers site you can run the 6900 on 3s lipos so wouldnt that be the fastest of the bunch

[JakeE]

According to Castle Creation's website, the 6900 is limited to 2S.

CM36-6900 Product Page (http://www.castlecreations.com/products/cms36-6900.html)

6900kV * 7.4 = 51060 RPM
5700kV * 11.1 = 63270 RPM

Now, if you don't mind operating outside of the warranty then hook the 3S pack up to the 6900 and go to town.

[evaderst69]

oh i didnt check the site oh well im prolly just gonna get the 6900 anyway i was just wonderng since towers site said that

[guver]

I find it easier to figure it backwards (to find the max voltage) and then use the appropriate number of cells.

[chilledoutuk]

hmm well everyone knows the 6900 will work on 3s lipo as will the 7700

But the question is how long will it last?

[GSMnow]

Running high KV motors on huigh voltage is just going to make a ton of heat and shorten the life. You are much better off with the lower KV and the highest rated voltage for that motor. A 3S LiPo has a nominal 11.1 volts, but right off of the charger it is actually 4.2 x 3 = 12.6 volts. The bearings in the Mamba Max motors are rated to 80,000 rpm. No load (wheels in the air) you could potentailly hit 12.6 x 6900 = 86940. Sure the voltage will drop a bit and there will be some load drawing it down, but that is certainly skirting a fine line. Even at the nominal 11.1 you are at 76590 rpm which is scary high.

What are you running this in? How fast are you trying to go? And WHERE can you reach those speeds without crashing?

The 5700 on 3S is 63270 nominal and 71820 peak rpm no load. Within the 80,000 limit, but still scary fast. The 7700 on 3S is just plain going to fail in a short time. The rotor may over heat and de-mag, or it could just fly apart and trash the windings. Between the 5700 and 6900 on 3S, they will both make 1HP at just under 80 amps, just at slightly different rpm's. The 5700 will turn slower but be making more torque so it will pull the higher gear to make the SAME wheel speed and torque. Choose the motor KV to fit a reasonable gear ratio in the car. Work back from the wheel rpm needed to hit the desired road speed. Ideally (if you choose a realistic road speed) you want a motor KV that will put you in the middle of the ratio range that will fit your car. That way you can go up or down in gearing to adjust for real world differences like aero drag, foam tire wear, rubber tire ballooning, etc. In my case I am running the 5700 on just 6 cell NiMh and I am on just the second smallest pinion. I should be running a 4600 since I run a tight course with a stadium truck (tall tires that really balloon).

[vashon10]

Send Tower a note and ask them if they will warrantee it running on 3s since the manuf won't. You'll see how fast they correct their errors.

[kufman]

I wouldn't recommend 3s onthe 6900, it runs hot enough on 6-NiMH's.

[Big House]

I ran my 7700 on 6 cell for about 20 minutes, both slow and full throttle at times and I didn't notice any of this heat everyone speaks of.

[kufman]

I ran my 7700 on 6 cell for about 20 minutes, both slow and full throttle at times and I didn't notice any of this heat everyone speaks of.

Were you driving on a real track with race conditions?

[SpEEdyBL]

20 minutes of runtime on a 6 cell means you weren't pushing it that hard.

[Dagger Thrasher]

GSMNow, excellent point on most of that :) ...but the Mamba motors are rated to 65,000RPM, not 80,000 unfortunately. Above 65,000 you're most at risk of fracturing/exploding the rotor from the insane centrifugal G-forces, so you'll want to stay below that. 3S on the 5700 is close to the limit, but will run fine. IF you don't mind living a bit on the edge, then a 4600 on 4S is utterly crazy (a few people have tried this setup); although this does exceed the RPM limit at WOT, you're very rarely going to hit WOT with that sort of power. Even when you do, it'd be momentary and would probably be fine...but of course, it depends if you wish to risk it.

However, that's all if you want a ridiculously fast "speed" setup. For normal bashing/racing, a much more sensible setup (5700/6900/7700 on 6 NiMH cells /2S LiPo) would be what you want.

[evaderst69]

i wasnt really planing on running 3s lipos i just say that and wanted to meke sure what i thought was right which it was but really shouldnt be done whenever i do get my mamba whether it be the 5700 or the 6900 i was gonna run 8cells or 2s lipos

[guver]

I'll try to work on a spreadsheet or chart/graph that easily displays the max rpm for each motor at various voltages.

I'll use the velineon 3500, mamba 4600, 5700, 6900, and 7700 motors.

Maybe I can shade in or highlight typical voltages for certain cell counts on NI , LIPO and a-123 batts. It would be up to the user to determine the voltage under load at a specific speed.

[guver]

Here's a start (using 65,000 rpm for a max)

7700 8.4 volt max 7 cells
6900 9.4 volt max 8 cells
5700 11.4 volt max 10 cells
4600 14.1 volt max 12 cells
3500 18.6 volt max 16 cells

I was thiking of running the chart from 20,000 - 80,000 and the voltage from 4 - 20 volts. In fact if someone who is proficient with computer programs can probably do what may take me hours in 15 minutes or so?

[Big House]

I would have to disagree with you there. It is honestly a mute point in that I cannot prove my statement other than what I have said, with my experience, in both my cars, the 7700 on 6 cells got me about 20 minutes all out bashing and throttle asisted braking. ESC remained cool and the motor and heat sink both were cool to the touch. Gearing and wheel size does make a difference.

20 minutes of runtime on a 6 cell means you weren't pushing it that hard.

[SpEEdyBL]

You are using a 6 cell battery which has a certain amount of capacity. Simply put, the longer it takes to use it, the less power that (energy per second) that it is supplying on average.

[GSMnow]

I would have to disagree with you there. It is honestly a mute point in that I cannot prove my statement other than what I have said, with my experience, in both my cars, the 7700 on 6 cells got me about 20 minutes all out bashing and throttle asisted braking. ESC remained cool and the motor and heat sink both were cool to the touch. Gearing and wheel size does make a difference.

Of course the gearing and wheel size makes a huge difference. but in any case, if you are getting a 20 minute run on just IB4200 NiMh cells, you are only using an average of 93 watts. My 12 minute run times come out to 150watts. There are other variables, but that gives you an idea how much power you are using.

[SpEEdyBL]

It's even less than that. A ni-mh pack does not deliver nearly as much as its rated. You'll notice that if you run the same capacity lipo, you'll get a lot more runtime.