[MOC] Super-Diff

[Hrafn]

Somehow I find it quite difficult to explain simply, but I try:

Try to put the fourth gear (no third gear!) on the side of the differential housing without a pin. It just falls out even at negligible torques.

This is no different when there is a third wheel (the fourth wheel doesn't "know" that there is a third wheel since it's not in contact with it), so the fourth wheel would still fall out under any load.

The only reason it doesn't fall out is the fact that the third gear on the pin bares the all the load.

Or:

Build the four gear setup and put load on the whole differential (don't let either wheels turn). All the gears will be held in place (no slack) but the fourth wheel will still have some slack. A good sign that it doesn't bear any load, so does nothing at all.

Thank you, that makes sense.

[Lipko]

For bonus points, can anyone guess why LEGO didn't just make two spider gear guide pins in their original differential? There is a good reason!

Um..... I guess because it's much harder to assemble, because you have to insert both output gears at the same time but from the opposite sides (while the spider gears are already inserted)?

Or more likely the molds would have cost a lot more....

Edited February 18, 2014 by Lipko

[Blakbird]

Um..... I guess because it's harder to assemble, because you have to insert both output gears at the same time but from the opposite sides?

Right! It is theoretically impossible to assemble. However, allanp's design can be assembled because the spider axis is inserted externally after the gears are in place.

[allanp]

I guess because the protruding teeth of the crown wheel in the original diff would have got in the way of sliding the two remaining gears into place.

Right! It is theoretically impossible to assemble. However, allanp's design can be assembled because the spider axis is inserted externally after the gears are in place.

Just like a real diff

[Lipko]

Right! It is theoretically impossible to assemble. However, allanp's design can be assembled because the spider axis is inserted externally after the gears are in place.

Why would it be impossible to assemble? It wold require some manual skills but not impossible at all. As I said, you have to insert both output gears at the same time but from opposite sides (because inserting one gear would try to rotate bot spider gears in the same direction which is locked by the already inserted other gear), then slide the output axles into the output gears.

I guess what Zblj was trying to say that it could make a limited slip differential?

Edited February 18, 2014 by Lipko

[DrJB]

Um..... I guess because it's much harder to assemble, because you have to insert both output gears at the same time but from the opposite sides (while the spider gears are already inserted)?

Or more likely the molds would have cost a lot more....

It is not impossible, but a bit trickier .. though not much so. You can assemble them as per the following sequence:

1. Put the two gears on the spider first

2. slide the 2 gears (that connect to the wheels) in, from each side, symmetrically.

Why would it be impossible to assemble? It wold require some manual skills but not impossible at all. As I said, you have to insert both output gears at the same time but from opposite sides ...

You beat me to it... but I agree fully.

Edited February 18, 2014 by DrJB

[allanp]

Why would it be impossible to assemble? It wold require some manual skills but not impossible at all. As I said, you have to insert both output gears at the same time but from opposite sides (because inserting one gear would try to rotate bot spider gears in the same direction which is locked by the already inserted other gear), then slide the output axles into the output gears.

Do you not think the teeth of the crown wheel would get in the way of being able to slide them in? I haven't tried putting 4 into the original style diff myself and i'm not near my Technic to try it .

Edited February 18, 2014 by allanp

[Junpei]

What DrJB said actually is impossible-the gears won't slide in. You would have to insert two of them at 90 degrees and the other two while they are lined up- this would be made impossible by the 2nd pin sticking out.

Would love to see allanp's differential 3D printed!

TLH

[Lipko]

@Allanp: you are probably right, but I was saying that it's theoretically perfectly possible.

@TwentyLeggedHen: Just try the method DrJB and I said. You don't even need a differential.

[DrJB]

What DrJB said actually is impossible-the gears won't slide in ...

I'm tempted to send you a free differential + 4x 12-teeth bevel gears ... just for you to try it out ...

Edited February 18, 2014 by DrJB

[Blakbird]

Why would it be impossible to assemble? It wold require some manual skills but not impossible at all. As I said, you have to insert both output gears at the same time but from opposite sides (because inserting one gear would try to rotate bot spider gears in the same direction which is locked by the already inserted other gear), then slide the output axles into the output gears.

Try it and you will see. The only way to assemble it is to bend the parts. Read your sentence again and think about it carefully. You can't insert both output gears at the same time because they require the spider gears to rotate in opposite directions.

It is not impossible, but a bit trickier .. though not much so. You can assemble them as per the following sequence:

1. Put the two gears on the spider first

2. slide the 2 gears (that connect to the wheels) in, from each side, symmetrically.

That doesn't work. You can't do step 2 because to slide the side gears in, the spider gears need to turn the same direction even though they normally spin opposite directions. The direction they need to rotate to put the gear on the right is the opposite direction they need to rotate to put the gear on the left. It can't be done unless you push so hard that the teeth skip. It can be done with only one spider gear because you can rotate the output gears while you translate them. With two spider gears, this is impossible.

@Allanp: you are probably right, but I was saying that it's theoretically perfectly possible.

@TwentyLeggedHen: Just try the method DrJB and I said. You don't even need a differential.

You DO need a differential. The pins on the diff housing which hold the spider gears are what make it impossible.

I'm tempted to send you a free differential + 4x 12-teeth bevel gears ... just for you to try it out ...

I've already tried it lots of times in the past. You can force the 4th gear in on a Technic diff only because there is no guide pin. With 2 guide pins, it can't be done.

[DrJB]

Try it and you will see. The only way to assemble it is to bend the parts. Read your sentence again and think about it carefully. You can't insert both output gears at the same time because they require the spider gears to rotate in opposite directions.

Not quite sure where the disconnect is here ... both Lipko and I are saying you insert the output gears from OPPOSITE sides of the differential cage, yet at the SAME time ... That is why a good coordination is needed ... or maybe a third hand/fingers if one can afford.

What are we missing???

Edited February 18, 2014 by DrJB

[Blakbird]

I see the disconnect now. The illustration below shows why you can't put them in from the same side (the red arrows require rotation one direction and the green arrows require rotation in the other direction at the same time). But you are suggesting installing the output gears from opposite sides of the cage. This would be possible with the old diffs but the new diff only allows insertion of the output gears from one side. Allanp's thought about the interference of the crown gear teeth might also be a problem with the oldest diff.

The following picture from Dikkie Klijn's tow truck instructions is why I was so adamant about the impossibility, since it is physically the same as a differential. What you see here cannot be assembled because both black gears need to be installed from the top. The only way to put it together is to take all the Technic bricks off, align all the gears, and then lower the whole assembly onto the chassis.

[Alasdair Ryan]

Maybe if we ask Efferman or Alasdair Ryan gently they want to help......

I do not want to start making a whole lot of custom parts,it will not be cheap to make Allanp's design ( roughly 50 uk pounds).

I will leave it up to Efferman to come up with a cad file.

Edited February 18, 2014 by Alasdair Ryan

[jesse66058]

@Zbjl Just realised a 4l bar is too long to work. 3 studs long is the maximum length. Otherwise there is no safe space for the bevel-gear to turn. (Maybe 3.5 studs is acceptable to prevent dismounting under high stress)

Allanp's thought about the interference of the crown gear teeth might also be a problem with the oldest diff.

I don't see any problem here. When you want to put 4 (working) bevel gears in it, you have to add a bar. When you add a bar, you mount it as last, which means you can install the bevels a the outer sides of the diff first, then add the other 2 and then mount the bar. Excactly the opposite pair to begin than in your drawings

Next to that i came up with some new ideas to make the old diff fully compatible with the lego system. Just have to prove it's possible.

Edited February 18, 2014 by jesse66058

[Lipko]

I didn't think about the new differential, since it's impossible to insert a fourth wheel anyway, because there is that box thing (I'm not sure why...)

[efferman]

based on blakbirds picture i have made a simple modification of the 3 wide diff

the distant block is removed, a second bar is added and the cavity at the bevel gear side shows now in the opposit direction. theoretical a standard dif can modded to this

Edited February 19, 2014 by efferman

[jesse66058]

Well, realised that edge a little bit too late

With that edge there my idea is not going to work properly.

I found out i can print very cheap.

Printing with Ultimaker 2: Starup costs: 6 euro + (PLA-PHA BLEND) 0,40 per cm³. I can print in many colors.

Printing with Ultimaker 1: Startup costs: 5 euro + (PLA-PHA BLEND) 0,30 per cm³. Again i can print in many colors

Is the material and resolution of these printers okay? I have seriously zero knowledge about this

[allanp]

@Zbjl Just realised a 4l bar is too long to work. 3 studs long is the maximum length. Otherwise there is no safe space for the bevel-gear to turn. (Maybe 3.5 studs is acceptable to prevent dismounting under high stress)

A 4M axle should fit with clearance. The frame has a 5M hole (plus a little bit for tolerances) and the bevel used to drive this diff would be half an M. Plus the 4M axle isn't quite 4M long, the bevel need not be quite half an M thick and to ensure clearance there is an indent in the bevel. The 1M bushing should help prevent the axle from sliding. But I guess if it is still too close then a version using a 3M axle and all 12t bevels (with 1M think centre sections, two with + hole, two with O hole) would still be much better than what we have now.

Edited February 19, 2014 by allanp

[DrJB]

I see the disconnect now. The illustration below shows why you can't put them in from the same side (the red arrows require rotation one direction and the green arrows require rotation in the other direction at the same time). But you are suggesting installing the output gears from opposite sides of the cage. This would be possible with the old diffs but the new diff only allows insertion of the output gears from one side. Allanp's thought about the interference of the crown gear teeth might also be a problem with the oldest diff.

Glad we got that resolved. I should have been more specific that we were discussing the old (not oldest) diff all the way, though on the new diff, one cannot add a fourth gear anyway, because of the square obstruction in the way ...

Edited February 19, 2014 by DrJB

[jesse66058]

I tried this:

It doesn't need any bushings to hold the bar in place, however it was a difficult job to insert. You're not so happy when you snap a gear inside The bar itself also gives a significant amount of friction so i think you can call it in a certain way a LSD. For whom to want stronger half bevels. You can always divide an 1L bevelgear like nicjasno did here: https://www.dropbox....s2/DSC_7414.JPG

@AllenP

I don't understand where the 5M distance comes from, but as you can see in the first picture a 4 bar should be already tricky.

Edit: i finally see it. we're talking both about different subjects. Bar and axle.

@ efferman

Could you share the file of your diff? I'm going to take a look in the 3D printer world :P

Edited February 20, 2014 by jesse66058

[allanp]

The 5M distance is the size of the hole in the 5x7 frame. To drive a 36t gear (used as the crown wheel) in the frame you need a half M bevel, not a 1M bevel.

[jesse66058]

The 5M distance is the size of the hole in the 5x7 frame. To drive a 36t gear (used as the crown wheel) in the frame you need a half M bevel, not a 1M bevel.

I think we're misreading each other. But yes, you're right. :)

Edited February 20, 2014 by jesse66058

[efferman]

if someone want print my diff mod

https://www.dropbox.com/sh/bbmy7hygu568iz6/IJpfzv2Zx7

[markus53]

we did also enforce a differential because it was not skip proof under heavy load. The main advantage is that the forces on the axle bearings are symmetrized and so they vanish. Also the bearing play is much better and prevents skipping.

Additionally differential lock function found earlier in this forum.

markus and jakob