Torque and gearing revelations on a 4000 kv

[Jeb]

https://www.facebook.com/video.php?v=1309445889111259

I played with upping the pinion gear to a 22 tooth thinking it would ease some torque and push it to the top end. It did give the truck a ridiculous top end speed, which you would never be able to control on a short course, but I immediately started stripping spur gears. I stripped my third in 2 weeks today and after further inspection realized it had bent all the teeth over on the pinion gear. The spur wasn't totally trashed so I put the original 18 tooth pinion back on. It was noisy, but it ran free of any binding. It also dramatically reduced the motor temperature. I was able to limit the torque by backing off the slipper clutch and it actually was much more drive-able on the course we race on. Seems the big pinion was an unnecessary upgrade for my needs and put un-needed stress on the motor and drivetrain. Here's a short clip of running it back with the 18 T pinion. Yes you can still hear the spur, but I might as well just milk it.

 

[xlDooM]

Looks like it's about right for this course!

 

[Jeb]

I rebuilt the motor and transmission again after the race Saturday. I had gone back up to a 20t pinion. The Tamiya pinion gears do not seem to mesh well with the ECX spur gear. I had bent the teeth on the pinion, thrown a slipper pad out of the clutch (the slipper pad was on it's 4th spur gear and the adhesive was weak) and trashed another spur gear. Tamiya pinions are still a 48 pitch, but they don't mesh like the stock dynamite ones. I ordered a set of the Dynamite ones to experiment with. There was obviously excessive heat in the drive train. I replaced the bearings in my Kinnexsis 4000 kv motor for the second time and cleaned the motor with electrical contact cleaner. I also had to put my second metal differential set in. The diff case had worn out where the axle shafts come out adding tremendous play on the axles. The bearing play in the motor surely contributed to stripping another spur. This is my fifth spur in 4 months. I put a new set of slipper pads on this time. I have been running a relatively loose slipper to gain better traction on to stop the wheelies on the track. I have been paying much closer attention to motor temps and it seems to top out at 156 after a 10 lap race which should be acceptable. I have my suspension set way softer which has helped a lot. I'm using the green associated t4 springs in the front with 35w oil with stop collars removed and silver rear t4 springs on the rear with 40w oil and added additional stop collars from my sons amp to achieve a level ride height. The improved performance on our loose track was dramatic. I managed to place 3rd in the finals and was in the lead most of the race until a couple crashes. Still had some fun aerial and inside corner passes before the finish. The truck is running smooth and quiet again and tops out at about 37mph even with the stock 18t pinion. Woohoo ready to go break it again! On another note, multiple racers commented on me running the stock plastic axles. They are plenty tough and I have had no problems. We have no pavement up where I live and seem plenty strong for our dirt and gravel conditions. I keep a spare set in the tool box, but at this point, they are the only thing in the drivetrain that hasn't failed.

 

[sc302]

Oil or different metal with higher melting points (then you would have to worry about plastics melting). Heavier teeth for more metal composition per tooth, maybe mod1

 

[Jeb]

Oil or different metal with higher melting points (then you would have to worry about plastics melting). Heavier teeth for more metal composition per tooth, maybe mod1

I repacked the diff with grease once when I noticed the play starting and that gave it another month of life. The differential was still working, but I had changed the outer carrier bearings 3 times. The problem is that there are no inner carrier bearings. The axle shaft just rides in the case with no bushing or bearings. I tried to find a nylon sleeve bushing to fit in the case, but was unable to match the diameter of the axle shaft. A metal axle riding in a non serviceable plastic sleeve is going to fail much earlier than the metal gear set. Seems like a design flaw. The one that's in there is brand new, but when I repack it, I'll try a silicone grease. Because of the axle seal (or lack of one), I think the oil would just shoot out and collect grit.

 

[sc302]

The only other thing you can do is try to make a inner lip to put a seal in.

 

[Jeb]

The only other thing you can do is try to make a inner lip to put a seal in.

Yep, I'll keep searching the hardware stores till I find something that works. I'm in and out of them all the time. Home with a sick kid today

 

[Jeb]

So after a lot of reading and forum searches I learned something new about gear pitch. Gears listed as 48p do not necessarily mesh perfectly because depending on manufacturers they can be metric or imperial. A metric 48p is actually closer to 42.5 per inch with a imperial conversion. The Tamiya pinions I've been playing with are 48p metric and ecx spurs are 48p imperial. This has contributed to my stack of shredded spur gears and bent pinions as well as the bearings I've cooked in a motor that's only 4 months old. I even questioned the pitch of the Tamiya pinions at the shop and he looked them up and of course they are listed as 48p. They wood work fine with a 48p metric spur, but not with imperial American spur manufacturers. Go figure. At least that's sorted out now. Got a Dynamite pinion set and more spur gears coming.

 

[Jeb]

These are the alluminum Tamiya pinions that were bending and shredding on a plastic spur. Don't use them.

 

[sc302]

I would use hardened steel, not aluminum.

 

[i_r_beej]

Interesting about the metric vs. imperial "pitch." I had always assumed that metric meant "modulus." That would explain why the Robinson pinions I use always mesh perfectly.