sleepy23

My Feedback: (1)

just cuz someone asked....
again, test conditions using the max gearing i feel safe running

Rare

Thanks for the info! Is it possible to go higher than 26 and going with a larger spur?

Access

As far as the mamba monster max, lower KV is better, since it ultimately means more power on the electrical level (lower KV = higher voltages to get equivelent RPMs). Which translates to, more torque at any comparable RPM level. For instance, if one motor is 8000KV and another is 2000KV, to run at 80000RPM the former requires 10V and the latter requires 40V. Which means that if each motor draws the same current at 80000RPM, the latter will have roughly 4x the torque at 80000RPM since it's also consuming 4x the power (power on an electrical level is watts or voltage x current). One horsepower is a bit under 1000 watts, and you have to factor in inefficiency like heat production, so a mamba max running off 3-cells can actually approach or exceed 1 horsepower.

You see this same thing with direct drive aircraft motors, the larger the motor gets, the lower the KV rating and the higher the running voltage, the largest ones require a special 'high voltage' ESC like a CC Phoenix-HV 85 and an 8-cell or 10-cell LiPo. The guy with the 134mph touring car in the 'max speed challenge' was using that kind of setup, 8-cell LiPo and a Phoenix-HV ESC.

BitHed

...OMG Access i FINALLY understand it Nice explanation...Thanx for that [sm=thumbs_up.gif]

Reindeer

My Feedback: (25)

I know I'm joining in the discussion late. I dropped a Mamba 5700 into a Factory Team B4 this last week, thought I would give a field report.

Setup:

Factory Team RC10B4 buggy, chassis stock. Setup as per AE default.
Mamba 5700 motor/ESC. Settings: Reverse lockout, 9v cutoff. Otherwise curves and settings default.
81/21 gearing
3 cell LiPo
Futaba S3003 servo
HiTec universal FM reciever
JR XR3i radio

After I assembled the car and tweaked it out, I put it on the carpet just to check it out... I blipped the throttle, and the car immediately went nose up and wrapped itself around a chair.

Anyway, today I took it out to the local soccer field to give it it's maiden run. The power of this motor is unreal. Speedwise, it ran at least as fast as my Mayhem, and that is just shy of 50 MPH. One thing about this motor is that it is torqey as hell... I couldn't get it above half-throttle at any speed without popping a wheelie and putting it on it's back.

Runtime was about 10 minutes, and the motor/ESC was barely warm at the end of the run.

No problems with the transmission.

All I can say is very impressive. Hopefully I will be able to strap my Garmin to it sometime this week and clock some actual speeds!

jonblazed

i just droped my 7700 in my tt-01. this car flys!! i need some help with my driveshaft. i dunno why but the front of my driveshaft seems to be loose. i have already changed out the chassis. no gears look striped, all screws are tight. another thing i noticed is that the smallest curb check will effect the tt-01 even with alloy parts. I'm at 700 bucks and counting, i just started this hobby and i haven't even got into planes yet.

sleepy23

My Feedback: (1)

the secret to high speed cars is........ DONT HIT THE CURBS.
alloy means nothing when smacking a curb.

Rare

Are you talking about the Prop Shaft? Are you still using the stock plastic one? If so than you cant use the plastic one with high performance motor and esc setups...its not even strong enough. If the prop shaft is what you are talking about...buy the aluminum one.

-Inverted-

Well Id have to disagree a little there. When I was setting up my ESC I accidently programmed it wrong and It had glitched at 40 mph into the curb, if I would have had my plastic arms and shock towers im sure they would have snapped.

sleepy23

My Feedback: (1)

alloy bends and transfer the forces to much. i guess it just personal preference, but aluminum arms typically mean that hinge pins, bulkheads, hinge pins carriers, etc will need to be replaced
but the true secret to high speed driving is to stay away from the curbs...learned from experience.
basically the last thing you want is a $2k 3lb little rocket smaking into concrete.

-Inverted-

I know what you mean about aluminum transferring the force, I was lucky that time, and I also reccomend staying away from the curbs. My ESC was set up wrong so my steering inputs were recieved like 10 seconds after I put them in.

Rare

Thats just the beginning my friend. In this hobby you need deep pockets.

sleepy23

My Feedback: (1)

if you want to go fast, you defiantly do need deep pockets.

Doahh

well I'm getting a sponsorship motor from CC... the 5700k motor... it's for a mini battlebot competition but I do a writeup on it and I get to keep the ESC... can you say goodbye GTB? I keep sticking my finger in the stupid fan... I love how the mamba can run brushed motors and hello stampede? Yup... of all the people to get a pede I do

sleepy23

My Feedback: (1)

i did some prototype bench testing....results are:
with the custom foams i want to do...bench test was 81mph....

Rare

....thats ridiculously insane. What do you think it will be when its on a load?

-Inverted-

LOL, a few hours ago you were getting a mini-lst.

jonblazed

i got the alloy driveshaft, but at high speeds it kinda sounds like the plastic one but more annoying cause it's louder. i have already replaced the chassis, and have checked all gears, screws etc. i believe it's comming from the front. some where between tha driveshaft and front gearbox. how can i make it tighter so no more winding sounds. thanks in advanced [:@]

sleepy23

My Feedback: (1)

i figure around a 20% loss, so maybe about 65 if i have the room. the loss may not be that much since it is already including rotational mass, but it lacks friction, weight, and air resistance.

Access

Sleepy in all my 5700 setups I have always gotten close to the theoretical speed (based on KV rating, gearing, etc.). The theoretical speed is 65mph and the real speed ended up being 58 +/- 2mph; different gearing the theoretical speed was 60mph and the real speed 54 +/- 2mph. So it seems like a loss of 10% provided it has bearings and all that good stuff. This motor has so much torque at the high end it doesn't seem to fall off as much as other motors have in the past. And even if they're internally belted, the tires can still expand a little bit -- does the bench test take that into account?

sleepy23

My Feedback: (1)

the testing does not consider ballooning. it calculates based on rpm and steady state tire size.
what are you running your system in? truck? car?
at some point in time, aerodynamics comes in with a large effect.

Access

That's running it in both TCs (TC4), STs (MF2), even an old buggy (Bandit).
Though I did all the speed tests on flat surfaces like pavement.
Aerodynamics is like a wall pushing back against your car. The theory is complicated, but it can be approximated as the sum of a series of even powers ie.

(n[0] * (v ^ 2)) + (n[1] * (v ^ 4)) + (n[2] * (v ^ 6)) + ...

If you have enough high-RPM torque to push against that wall, it just takes away some punch / acceleration at the higher speeds. If you don't have enough high-RPM torque to push that wall, it will lessen your top speed until the wall is pushing back with equal force. The force of the wall increases exponentially, at high speeds like 100mph or faster 10 or 15 mph can mean an order of magnitude.

The only time I had problems with aerodynamics so far is with 1/18th scale that would start to 'lift off' like a plane and then start 'bouncing', basically losing traction and control at speeds around 50-60mph. Not sure when this starts to happen with 1/10th scale, I've run 60mph and never had any problems with things like that.

Tamiya Racer

A man, I just can't agree with u on that. I have been planning on buyin the mamba, and if i do i would not go anywhere near water with it.

Elmo6s

My Feedback: (1)

Is anyone else having heat problems? I can go for about 5 mins on my 7700 in a T4 before I have to stop due to ESC heat... 6 cell 4200/ 2s Li-Mns... Ridiculous speeds make it worth it though!!! On my way to Rat Shack right now to pick up a fan - I'm geared 17/87, should be fine right?

Access

Yeah, a fan on the ESC or punching holes in the body to give it some airflow will work wonders. It's typical in a decent brushless setup for the ESC to heat up more than the motor.