Mamba 6900 on ZX-5

[jefierro]

Greetings all.

Having a little problem with my new Kyosho Lazer ZX-5 SP version. in one word ... HOT!
how hot? ... is melting the body and gluing the heat shrink from the motor connectors together.

The setup:
This is a 1/10 scale 4wd buggy weights aprox 1650g.
MaxAmps 5000mAh 2s lipo on traxxas connectors.
Mamba Max 6900:

• Forward to Brake To Reverse
• Brake Amount "40%"
• Reverse Throttle "50%"
• Punch Control "80%"
• Drag Brake "disabled"
• Start Power "Low"
• Motor Timing "Low(5)"

Differential ratio 2.63.
Temps:

78/15 (Lowest pinion that can mesh)
Motor:186°F
ESC:172°F
Batts: 112°F

78/18
Motor: 189°F
ESC: 196°F
Batts: 117°F

Ambient temperature is hot 86 to 90°F
i'm not driving like a mad man, but several asphalt speed runs, off-road bashing and small jumps, nothing out of the ordinary . after 20 min in one run i had a termal shutdown ESC was ~200°F
I guess the drive line is free, as i cant find any binding, but this is my first kit build i could have done something wrong but most unlikely, feels pretty smooth.
Heck not even my HV4.5 on 4s lipos is this hot, run the same day, same torture 145°F on the esc and motor.
I'm new to the MM so I have played with some settings but other than cooler batteries I haven't fixed this problem.
I want to shorten and eliminate the motor connectors and direct solder the wires this my alleviate some resistance there, but i want to consult this before i go further.
today i've made some air vents in the body but temps still to high.

HELP PLEASE!

[GO-RIDE.com]

Wheelers are tough on temps with the bodies being so small and having poor ventilation. It also doesn't help that the batt, motor, and esc are so close together.

I run a Novak GTB with a 7.5R motor (5800 kv), in my ZX-5 SP, and it runs a bit hotter than I like geared 78/17. I'm thinking of going to a 16T because I'm still accellerating at the end of the staight and would like to keep the temps down. In general the CC motors run hotter than the Novak stuff so you may need to gear down more, due to your 6900kv motor, and see if you can get any more venting in the body.

Also check your gear mesh. The ZX-5 o-ring motor mount seems to suck the motor closer to the spur when you tighten it down. I start a bit loose and once the screws are tight the mesh seems perfect. Put your finger on the pinion and make sure the spur has some play when the pinion is held still.

[jefierro]

Well I just got a response from castle support saying that all those temps are in spec that can't be right, the motor is melting my body and they are not touching.

Thanks GO-RIDE, I'm absolutely sure the drive line is in tune, all parts moving freely gear mesh and all.

This can't be like this. Right?

6900kv seems like a lot for 1/10th 4wd. perhaps a 5700 would be better suited to the task ?

[jefierro]

Originally Posted by 83gt

6900kv seems like a lot for 1/10th 4wd. perhaps a 5700 would be better suited to the task ?

Could you elaborate further on that statement? I don't quite understand, is it out revolving the motor?

Originally Posted by jefierro

Could you elaborate further on that statement? I don't quite understand, is it out revolving the motor?

Not technically. On 2s you'd be within the motors stated limits, but I found the 6900 and 7700 CM36 motors to run very hot even in a lightweight setup. In my 1/10th 4wd buggy, I was able to move from 7700 to 5700, gear it up a a bit to compensate for the lost top end, and I ended up with a setup just as fast, but with much more manageable temps. As a bonus, the runtimes were much better as well :).

Basically i would only use the 6900 or 7700 series in lightweight onroad cars. When you start putting more load on them, they just heat up too much.

Try disabling punch control and set your start power to high. See if that helps you out some, plus cutting/soldering your wires may help out a bit as well. Is there any way of getting a fan/heatsink on the motor or a fan on the esc?

[sleebus.jones]

A bit of background from me first, I was running a 7700, and switched to a 5700. 7700 = hot hot hot, 5700 no problems at all.

Originally Posted by GO-RIDE.com

Wheelers are tough on temps with the bodies being so small and having poor ventilation. It also doesn't help that the batt, motor, and esc are so close together.

Agreed. The ZX-5 has one of the closest fitting bodies I've ever seen. I cut a hole in the front window and it helped, but it was still hot.

Originally Posted by 83gt

6900kv seems like a lot for 1/10th 4wd. perhaps a 5700 would be better suited to the task ?

Yep. 5700 is much better, 4600 better yet I think. The 7700 I had was fast as heck, but ran very hot. I can't imagine the 6900 would be much better.

Originally Posted by 83gt

Not technically. On 2s you'd be within the motors stated limits, but I found the 6900 and 7700 CM36 motors to run very hot even in a lightweight setup. In my 1/10th 4wd buggy, I was able to move from 7700 to 5700, gear it up a a bit to compensate for the lost top end, and I ended up with a setup just as fast, but with much more manageable temps. As a bonus, the runtimes were much better as well :).

I agree 100%. I had a similar experience, I just didn't gear up because the 7700 was pretty insane fast.

[jefierro]

thanks everyone.
I'll do those things, is there a better motor option in the 5700 price range? since
also i have broken a shock tower mount so it will be a wile before i can run this one (should have sticked with the plastic shock towers, CF is just to stiff).
76/20 should do on the 5700 for me, I just worry that this will have to much torque for that low kv motor, but will have to fix that some other way, this is the hole reason i went for the 6900 in the first place, never realize it would get that hot. thanks again guys.

[Mike_D]

I run a Feigao 380 8t motor with a MM and 6 cell nimh packs geared 18/78 and my temps are around 150 for the motor, 110 for ESC and about 110 for batts. I too think your motor is a litte much for a 4wd buggy.

[Mike_D]

Originally Posted by jefierro

thanks everyone.
I'll do those things, is there a better motor option in the 5700 price range? since
also i have broken a shock tower mount so it will be a wile before i can run this one (should have sticked with the plastic shock towers, CF is just to stiff).
76/20 should do on the 5700 for me, I just worry that this will have to much torque for that low kv motor, but will have to fix that some other way, this is the hole reason i went for the 6900 in the first place, never realize it would get that hot. thanks again guys.

Yeah those 6900 and 7700 motors are best for onroad cars. The 5700 is the max kv i would put in a buggy.

[DRIFT_BUGGY]

Originally Posted by 83gt

6900kv seems like a lot for 1/10th 4wd. perhaps a 5700 would be better suited to the task ?

I was running a 6900KV in my XXX4 G+ & BJ4 but that was only a 6 cell nimh. RC411/Xtreme RC ran the 6900KV motor and Peak 3200 Carbon Lipo when they did the review on the SP5 in May 08'. They had it geared at 17/78 and hit 42.0mph @ 191ft

Im usin a 6900 in my ghetto rustler. The ESC will heat up when its offroad but the motor itself stays pretty cool. I've mainly been doin on road speed runs geared high with a 3s lipo. Still playin with weight distribution and aerodynamics, have only achieved 66 mph with near stock gearing. But then again its only 2wd, but weighs in pretty hefty, 5-6 pound range.