Filling Ar44 With oil?

[SteveB1]

I can't overstate how important it is to get the gears shimmed properly. In my opinion, the excessive levels of heat are not coming from the gears in contact under speed, but more so they are due to the gears incorrectly contacting at speed.

From the 1/8 scale buggy world, my Tekno grass racer pulls 80mph with no problems, and the gears are not melting the plastic housings. From skimming this post, you're pushing a bit more than 1/3 the speed. My point is it's not the speed, it's the gear setup.

There are a number of videos on youtube about shimming diffs in the 1/8 buggy world, and they will give you a good idea as to what you need to be looking for. That pinion absolutely cannot be floating in or out against the diff gear ring, and that diff can't be floating around either. Shims will fix those in place.

I run Timken high-pressure grease in my rock racer's diff housing and bearings, and it rips around the track with massive tires for hours per practice session. Now there is no question the diff oil inside the diff gets cooked and I replace it every few races, but I've never felt anything even remotely warm around the plastic bulkheads or gearboxes. I've also never seen heat damage except for one time when the pinion bearing blew and sized, and the heat from the spinning pinion melted the area around the bearing and ruined the bulkhead.

I don't have any high-speed solid rear axle platforms (yet), but I've raced against a few Traxxas UDR's hauling butt on 6s, and they seem to run relatively cool at the rear axle. Might want to review those schematics and see how they have shimmed the pinion and diff.

I'm sure it's also been mentioned, but use good bearings, and keep them clean and greased. I run AVID bearings on everything.

Let us know how it works out.

And a photo just for fun...

 

[TITANIUM94010]

Thanks for the reply, I think properly shimming the diffs will definitely offer a noticeable improvement, and I’ll do some tests to find out what the I best configuration is. But a big problem with scx10ii gears is that they are helical, which does make them stronger, but also causes the gears to rub together much more as compared to standard rc gears (or less helical, most gears are helical to some degree, but the scx10ii gears are extremely helical)
It’s kind of like a worm gear, for every rotation the gears have to rub against each other rather than touch and move on.

 

[SteveB1]

I have run helical gears on my Nomad DB-8 and that's outfitted with a 2050 Kv motor on 6s, turning a 30 tooth pinion gear. It's not the necessarily gear design that's giving you a problem, but for sure it's not ideal for speed. Now if your gears have a heavy angle, then you are going to need to change them out to a different design. I have a worm drive crawler, so I understand what you are getting at. Grease, lube, snake oil ain't gonna solve the problem if you're chasing wheel speed. I would also venture your bearings might also be undersized and not up to the task.

 

[SteveB1]

I just thought of two things to check:

1. Make sure the pinion gear is not pushing too deep into the housing. I would remove any internal shims against the inside of the pinion gear, move it out as far as possible, reducing gear mesh.

2. Make sure you have a small shim between the drive shaft coupling and the pinion bearing. A shim less than half the diameter of the bearing. This way the bearing can spin completely free without the drive shaft coupling pressing on both the inner and outer diameter of the bearing ( thus turning it into a bushing ).

See what you find with that. A pinion too deep will deflect and run off center, and that will for sure cause heat. If you find play, thats when you add in shims to move the pinion deeper into the housing until it snugs up against the diff ring gear. You'll need to experiment with these shims, as well as shims to adjust the position of the diff from right to left.



s

 

[TexasSP]

Yes, good point on the pinion pushing in too deep. Had that issue years back on my e-maxx based off some bad shimming advice.

I am also wondering about the shaft angle and the shafts going to the pinion. You could also easily be binding in that area and creating deflection inside the diff case between the ring and pinion.

Going back to the grease things, always use light coatings. Using too much can cause problems too.

 

[meatmonkey]

I tried sealing up the original AX10 axles back in 07. Ran rtv between the case halves, and on the ID and OD of the bearings. Drilled a 3MM hole for filling with a syringe, capped it with a 3mmr grub screw. It sealed until driven. Everything just flexes too much. That thing oozed gear oil for about a year. I will say that running oil as opposed to grease at higher speeds will improve lubrication and reduce heat buildup, until you run it out of oil. If your not opposed to the inevitable mess, I say try it and let us know your results.

 

[Almighty Malach]

High pinion or low pinion? Running it high pinion will always try to pull the pinion gear into the ring gear and is harder to shim correctly. Flipping the drop out to low pinion will push the pinion away from the ring gear and utilizes the bigger inner bearing to brace against those forces.

I run AR44 diffs in my Scale Ultra bomber and they have 60-70 hard miles on them so far with minimal wear. I run with this car, so its capable of 25-30 mph and gets beaten hard in the rocks.

 

[TITANIUM94010]

I tried sealing up the original AX10 axles back in 07. Ran rtv between the case halves, and on the ID and OD of the bearings. Drilled a 3MM hole for filling with a syringe, capped it with a 3mmr grub screw. It sealed until driven. Everything just flexes too much. That thing oozed gear oil for about a year. I will say that running oil as opposed to grease at higher speeds will improve lubrication and reduce heat buildup, until you run it out of oil. If your not opposed to the inevitable mess, I say try it and let us know your results.

Hmm, now im having some doubts.

But the SSD axles are mostly metal, with only the diff pumpkin being plastic, and ive got those sealed up pretty good. I doubt they'll leak around metal parts, but maybe the diff case itself will leak a little. If it does, I think an extra thin layer on the outside should do.

Syringe arrives tomorrow, I guess we won't know till then

 

[meatmonkey]

Your off to a way better start than I was. I suspect it will still wick through the shaft to bearing fitment, since nothing on these axles are press fit.

At this point I'm genuinely interested in your findings, so you should try it in the name of "research".

 

[TITANIUM94010]

I just checked, axle mounts arrive on Friday so I wont be able to actually drive until then

But I mount it on a drill and test it that way, only it won't be able to flex.

 

[TITANIUM94010]

Update:

Syringe arrived today, filled it with Valvoline 80wt-90 (Which has a weird smell of garlic thats gone bad) And did 5 min of continous running with driveshaft attached to drill (hex side driveshaft for more speed) It's a good seal, with only a little leaking from the link mount holes because I haven't installed them yet.

It's really smooth and pretty quiet, so thats a plus. I'll have to see how it holds up on the actual car once the axle mounts arrive on friday.

 

[MAGNUMB]

Hudy Graphite grease and add HBN(hex boron nitride)

https://onlinelibrary.wiley.com/doi/full/10.1002/eng2.12216

 

[TITANIUM94010]

Suspension arm mounts are here, and I am happy to report that they seal 100%!

Woo!

Well, ive only driven it for 5 minutes on asphalt until the battery died. I'll do a much heavier test tomorrow with a full 3s 5k pack.

 

[TITANIUM94010]

Did some extensive testing today, and unfortunately oil started leaking out of the bearings. The RTV sealant sealed completely, but even with grease-packed bearings, the oil leaked out. However, it did run pretty quiet and cooler than with grease.

I cleaned the axle out and refilled with some grease, it was noticeably louder and also noticeably warmer (The diff had cooled by the time I was done switching to grease), but even after some hard runs, they held up fine. I think the Axial sintered gears are just really weak. These SSDs can handle full throttle at launch on gritty asphalt. If I did that with the axials they would strip.

So I guess thats the end of that. The oil hole I made is still good for filling grease in, you just have to jam the grease in the syringe as opposed to sucking it in before filling/adding.

RTF makes a really good seal, if the bearings can be completely sealed, then filling an axle with oil would work, and well too. It's a pretty cool concept, and definitely decreases wear. So if anyone wants to give it a try, it won't hurt.

 

[TexasSP]

Grease should be put on by hand thinly, you don't want to 8nject gobs of grease as it can actually create a lot of resistance. This can work inside spider gears to create a positrack type setup but it's bad on the ring and pinion.

 

[borlo]

Don't mean to threadjack, but do you have more pictures of this rig? Loving that rear cage!

The red cap is to fill up the diff and it works I don't take it off as I use udder budder in my F9 Currie axles but that would be an axle option if your using liquid lubricants as opposed to solid lubricants.....