[HELP] Gear Grind at Differential

[nicjasno]

From the driveshaft to the gear on the differential. The place where the grinding occurs.

[Gonkius]

Well, perhaps you're right if you use this in a conventional way where the driveshaft must be perpendicular with the outgoing axles. That's not the case in my application. I apply the force on the turntable wheel using a worm drive: Slow speed, high torque and low friction were the important keywords during my design. If you can place the motor close to the differential you don't have to introduce the problematic 90-degree angle at all. Difficult to achieve this in a suspended 4WD of course...

As a sidenote I even tried a planetary design of the differential using the inside gear of the large turntable that precisely fits five 8T gears. Difficult to make a robust design this way and the friction due to the small gears and the turntable itself caused issues. Not a useful design other than for demonstration purposes.

[nicjasno]

The problem with your design is, that the diff will fall apart in the middle. Very quickly. The structure doesn't support any torque.

[Milan]

I apply the force on the turntable wheel using a worm drive: Slow speed, high torque and low friction were the important keywords during my design.

Worm gears have highest friction than any other gear types

Edited December 27, 2014 by Milan

[Leif]

Same topic but new angle..

I recently destroyed my first (yeay.. ) gear.. Bewel gear in center diff when I had center diff locked so rear and front axle both had to work.

Have you thought about it? when you build a center diff, lockable, you actually only lock one of the axles strongly with the diff. the other axle has to be driven through the three tiny little weak bewel gears inside the diff..

The solution should be something like pic below. naturally diff suffers from bracing and however you brace it, it will not be near the gear. Driven from both sides is a recommendation.

Thoughts? experiences?

[DrJB]

That is absolutely true. A normal diff lock (in real life) would lock both left and right gears (in your picture). Otherwise, the middle diff gear would transmit twice the load.

[Nazgarot]

Gents,

I have build some strong machines, powerful, geared down, lots of motors coupled together.

But the weakest link, and it is pretty weak, is always the perpendicular gear at the diff.

Even though it is most of the time a 1:3 gear down in a portal hub after the diff, you will get gear grind..

"Funny" thing is I have noticed several times that the gear grind will appear even on only 1 XL PF motor, so the second motor really cannot do any good. Before we can use its power, perpendicular gear have given up...

Any advices? Not happening to you...? revert to old style Diff? More complex gearing but sometimes that may be the best solution.

see pic, Bracing is what it is so to speak..

I would suggest a custom diff if you have the necessary space...

Have a look at my heavy duty diff. This can handle any torque generated by lany number of Lego motors...

-ED-

Edited December 28, 2014 by Nazgarot

[Leif]

I would suggest a custom diff if you have the necessary space...

Have a look at my heavy duty diff. This can handle any torque generated by lany number of Lego motors...

-ED-

Thanks, neat idea! I will certainly look into this, space consuming though..

[Gonkius]

Worm gears have highest friction than any other gear types

Absolutely right. But in my application the friction from the driving shaft was not important, only friction between the two outgoing axles... Perhaps not very useful in vehicles but a perfect fit for my usage.

I like the design by Nazgarot, very similar to mine, but uses smaller gears. I did one design with this frame a while ago, but it didn't fit my application. It is possible to use the larger 20T 45-degree gears in this frame. I used the frame the other way to make it shorter.