Heat In Gears On 6s Rigs

[Grumpy Old Man RC]

Here is the setup. Arrma 6s Kraton with Proline Trencher X tires, PowerHobby 3s 7600mAh/75c/150c X 2. Stock low tooth pinion gear. The electrics are fine on heat but after a good run with as much full throttle as I can handle, the spur on the center diff was HOT! Didn’t get a temp reading so I don’t know how hot.

Anyone able to tell me a temp that I should consider too hot on the center diff/motor pinion? I have a temp gun but didn’t have it with me. Will check next time.

Gear mesh is OK per my million years of experience.

 

[Primarrma]

Is the motor warm too, I'd assume the center diff would be working pretty hard, it's bound to get hot? Sorry this isn't helpful at all is it.

 

[olds97_lss]

What oil are you running in your center diff? Guessing it's what caused things to get hot which transfers to the spur, not the actual friction between the pinion/spur.

 

[Primarrma]

I run 100k center, but I have run up to 500k, it is doing a lot of work.

 

[Wmorgan]

I would expect it to get hot as it's metal on metal and only air cooled. I have the same set up except I put a 14T pinion on and running 100k in center. To be honest I've never checked the spur gear temp, but I will now with a temp gun. I've been checking motor temps frequently as I've been changing things. Before HW fan and sink the motor was getting up to 160F mid run on 50C battery before pinion gear change. Now with fan and 14T pinion it stays right at 140F. (the pinion gear would make motor work harder = higher temps which just points to the job the HW fan and sink are doing to keep the motor cool).
Next run I'll check the spur temp. You do the same and report back.

 

[Mr.Duke]

I check center diff temps along with motor and ESC temps every pack. Center diff temp really depends on what type of bashing you're doing but on average it sees mid 120's F with the highest readings in the upper 130's. No failures of any kind running those temps on a regular basis with my setup.

 

[olds97_lss]

I run 500K in mine with trencher 3.8's. They are heavier than stock tires by quite a bit. Tends to really work out that center diff. 500K is probably too much now that I'm on 6S, but I'm too lazy to change it.

Brand	Tire	Rim Size	Weight (oz)	Grams
Traxxas	Maxx AllTerrain (0 offset)	3.8	11.5	326.01925
Traxxas	Talons v1 (0 offset)	3.8	9.1	257.98045
Pro-line	Trencher 3.8 (0 offset)	3.8	13.4	379.8833
Arrma	Backflips (0 offset)	3.8	12.5	354.36875
Arrma	Minokawa Mt (Kraton v3) 1/2" offset	3.8	10.5	297.66975

I'll check the spur temp the next time I'm out if I can get at it with my temp gun. Hopefully will get some time on it tomorrow. However, the grass bmx may be a mud puddle. Been raining a ton here lately. I'm not going to run in that... Not worth the headache. Planning on taking my nitro savage as well.

 

[Primarrma]

I run 500K in mine with trencher 3.8's. They are heavier than stock tires by quite a bit. Tends to really work out that center diff. 500K is probably too much now that I'm on 6S, but I'm too lazy to change it.

Brand	Tire	Rim Size	Weight (oz)	Grams
Traxxas	Maxx AllTerrain (0 offset)	3.8	11.5	326.01925
Traxxas	Talons v1 (0 offset)	3.8	9.1	257.98045
Pro-line	Trencher 3.8 (0 offset)	3.8	13.4	379.8833
Arrma	Backflips (0 offset)	3.8	12.5	354.36875
Arrma	Minokawa Mt (Kraton v3) 1/2" offset	3.8	10.5	297.66975

I'll check the spur temp the next time I'm out if I can get at it with my temp gun. Hopefully will get some time on it tomorrow. However, the grass bmx may be a mud puddle. Been raining a ton here lately. I'm not going to run in that... Not worth the headache. Planning on taking my nitro savage as well.

Does it matter if it gets hot, what will happen? The viscosity will change a bit, even though silicon isn't meant to change with heat, it does.

 

[olds97_lss]

Does it matter if it gets hot, what will happen? The viscosity will change a bit, even though silicon isn't meant to change with heat, it does.

Probably nothing, unless it's getting hot enough to soften the plastic of the cup, then it will tear apart on you. I don't know how hot is too hot for a diff. Never really thought about it and until 6S brushless, didn't really have to. I run heavier oil because I like less front tire unloading. On 4S, I'd lose a lot to the front and not get a lot of wheelie power. With 6S, wheelies are more of a hindrance. lol! So, a lighter oil like 250k would probably be beneficial to me. If I pull the center diff for any reason, I'll likely change out the oil.

 

[Primarrma]

Probably nothing, unless it's getting hot enough to soften the plastic of the cup, then it will tear apart on you. I don't know how hot is too hot for a diff. Never really thought about it and until 6S brushless, didn't really have to. I run heavier oil because I like less front tire unloading. On 4S, I'd lose a lot to the front and not get a lot of wheelie power. With 6S, wheelies are more of a hindrance. lol! So, a lighter oil like 250k would probably be beneficial to me. If I pull the center diff for any reason, I'll likely change out the oil.

Yeah it wasn't a criticism, I just don't know?

 

[Yonic]

Check if your diff is missing oil. Hot diff is a sign of not enough oil

 

[Grumpy Old Man RC]

Is the motor warm too, I'd assume the center diff would be working pretty hard, it's bound to get hot? Sorry this isn't helpful at all is it.

All electrics are below 130 degrees and the motor was the warmest.

What oil are you running in your center diff? Guessing it's what caused things to get hot which transfers to the spur, not the actual friction between the pinion/spur.

Rear=50k
center=500k
front =100k.

I did not know what I was doing when I did this but it sounded good to me.

Next run I'll check the spur temp. You do the same and report back.

Will do.

Check if your diff is missing oil. Hot diff is a sign of not enough oil

It shouldn't be. I changed things out after only a couple of runs, cleaned factory diff fluids out and put what I wanted in. It has never shown and oils leaking from anywhere so they all should still be full.
Or not. I don't know much about this kind of power in an RC.

 

[olds97_lss]

Curious how "hot" hot is.

I run 100/500/100 in my outcast with trencher 3.8's on 6S with a 13T pinion.

Just finished a run today... but I was a bit disgusted with RC by the time I ran the outcast, then my front left bone popped out again, so I just packed it up and came home. My nitro savage fought me tooth and nail today... and it won. I meant to check the temp of my spur/center diff in my outcast, but I just was too annoyed to mess with it, especially after the bone popped out. I just threw it in the bag and came home.

Sorry about that. Would have been a good day to check too as I had a good 20 minutes of hard running on it and where I was running was pretty tall grass. Seems they don't mow the bmx track very frequently, or very short, one of the two. It had to work pretty hard in some areas to keep moving. Got some WOT big air jumps in though, so that made me feel better.

 

[Grumpy Old Man RC]

Curious how "hot" hot is.

I run 100/500/100 in my outcast with trencher 3.8's on 6S with a 13T pinion.

Just finished a run today... but I was a bit disgusted with RC by the time I ran the outcast, then my front left bone popped out again, so I just packed it up and came home. My nitro savage fought me tooth and nail today... and it won. I meant to check the temp of my spur/center diff in my outcast, but I just was too annoyed to mess with it, especially after the bone popped out. I just threw it in the bag and came home.

Sorry about that. Would have been a good day to check too as I had a good 20 minutes of hard running on it and where I was running was pretty tall grass. Seems they don't mow the bmx track very frequently, or very short, one of the two. It had to work pretty hard in some areas to keep moving. Got some WOT big air jumps in though, so that made me feel better.

Well it has rained all night and most of the morning with more on the way plus I was helping Miss Bly in her flower garden when she told me to stay away and I fell down, AGAIN on top of a 2' tall flower pot holder. Should have listened to her! If it weren't for modern chemestry, I would not have been able to get outta the bed this morning. It will be a few days before I can do much of anything RC or anything else.

Her 4s Outcast should be here tomorrow and my mini Kraton Friday. Probably be next Saturday before I can heat my 6s Kraton up again.
Hope I can remember to use the temp gun this time.

I'm surprised. It seems no one ever thought to take temp readings of the gears but I probably wouldn't have either if it had not burned me slightly.

 

[Primarrma]

130f is not very hot at all on a motor, that's happy territory.