undergeared?

[RUSTY XL-5]

Well, I have a rusty with flightmax 3s 30c 5000mah lipos and a medusa 4800 kv. Gearing is 17/83 but the esc gets to 180ish in 20 minutes or so and I have to let it cool to prevent thermaling...motor consistently runs 150. I heard if batts are cool (they are always under 80), motor cool, and esc hot your under geared. Is this correct? Would a 19t pinion be a better choice or should I solder on a cap?


Thanks.

[SpEEdyBL]

What esc are you using? Thats a lot of power to handle if your esc isn't up to size.

[coolhandcountry]

I agree.
Some more info is required.
If the batter can handle alot of amps.
It will never heat up but the esc and motor will.
If you have an extra few pinions you could try them.

[RUSTY XL-5]

I'm running a mm but I am using an external BEC.

timing is 10...I heard that this was best for 4 pole motors
drag brake is 8
cut off V is 9.3
brake is 45%
punch control is disabled (I like it this way)
start power is medium


I was running drag brake at 15 and start power on high, but I changed that and it helped a bit with temps.

[skellyo]

What tires are you running?

[RUSTY XL-5]

masher 2k's I will add that I am running in grass but the grass isn't that thick. Since my yard is mostly weeds, they all die in the winter to leave the "thin" grass.

During my normal back yard bash, I usually top out in the upper 30's but I am geared for 45ish. I mostly do back flips and front flips. Since doing flips requires high amounts of unloaded rpm's would this be causing the unwanted heat?

[skellyo]

You're overgeared IMO. You're geared for 58mph. When you account for a small amount of ballooning, you're setup for low 60's. Running that gearing with those tires in any grass at all is going to recipe for heat. I'd drop down to something a bit lower on your pinion, like 13T or so. Or go up on your spur and drop your pinion. If you want to be in the 45mph range, you'll need something like 13:90.

Differential Ratio: 1
Transmission Ratio: 2.727272727272727
Other Ratio: 1
Spur Tooth Count: 83
Pinion Tooth Count: 17
Total Voltage: 11.1
Motor KV: 4800
Tire Diameter (inches): 4.9
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor coil Ω: 0
Spur/Pinion Ratio: 4.88 : 1
Total Ratio: 13.31551 : 1
Tire Circumference (inches): 15.39 inches (391 mm)
Total Motor Speed: 53280 RPM
Vehicle Speed: 58.33 mph (93.7 km/h)
Effective KV Value: 4800
KT constant: 0.28 oz-in/A

[RUSTY XL-5]

hmm I never got 58 when I did the speed calc. I must of did something wrong.

[skellyo]

Originally Posted by RUSTY XL-5

hmm I never got 58 when I did the speed calc. I must of did something wrong.

At least you've got an idea what might be causing the issue now though. Drop that gearing down and it should cool things down a good bit.

[RUSTY XL-5]

Originally Posted by skellyo

At least you've got an idea what might be causing the issue now though. Drop that gearing down and it should cool things down a good bit.

lol, very true. I'll go down to a 15t and if I still have temp issues, I'll either go down to a 14t pinion (smallest I have) or a 86 spur.

[Raze ST Truggy]

I have a stampede with the 5700 combo that I just put togeather the other day. It's got a 90T spur and a 14T pinion and stock talons (I think thats what they are) for tires. I'm only running 2S right now, but the temps are great. 105 motor, 95 MM, and 90 on the 2S 4000mAh maxamps pack.

I think you should try the 86 spur and see what you get for temps.

-Brian

[RUSTY XL-5]

Yal were right...over geared lol (I figured so too). I went up to a 86 spur (too lazy to change the pinion lol) and noticed a dramatic decrease in temps.

Before on 17/83 gearing after 30 mins of hard bashing:

motor was 150-160
mm esc was 180 ish


Now on 17/86 gearing afer 30 mins of hard bashing:

motor was upper 120's and lower 130's
mm esc was upper 140's and lower 150's

Much better. Thanks for the help.

[RUSTY XL-5]

Forgot to mention what I found ironic. I havn't changed my gearing really at all over the last 2-3 years. All gearing set ups provided good speed while temps were in check.

on a brushed motor on 6s nimh gearing was 15-16/86
mm 5700 on 2s lipo 17/86
and now medusa motor and 3s lipo 17/86


Interesting lol.

[skellyo]

Glad to hear it's working out better for you now. Looks like you can still stand to drop it a little bit more, but at least it's in a much safer range now.

[RUSTY XL-5]

I'll probably leave the gearing as is for now, when summer rolls around I may go a bit lower if need be. The temps I posted were off roading temps, when I drive in the street, the motor and esc drop 10-15 degrees.