Rotating Axle with Varial Offset

[ancientpixel]

Hi All! Often a "reader", now a "poster", i´ve got a problem i cant fully wrap my head around.

I try to keep a steering axle straight while going through a pivoting point or turntable. The axle should rotate with the pivot (eg in the picture below the yellow bricks should always align with the grey liftarms even if the liftarms are at 90 degrees of each other) but i want to rotate it manually on one side, with the rotation + offset of the pivot on the other side. Like the axle itself would have been twisted. The furthest ive got with this is pictured below and works as long there is no friction on the left output.
I want both sides to rotate at the same time, but if you rotate the pivot/turntable then it should add just an offset "within" the axle. I dont know if this is actually possible or how to split the axle in two, add the pivot rotation to one part and then add both rotation together.

 

Spoiler

 

[steph77]

I think the only way to solve your problem is to avoid the gear solution. The best way is to use , as in real life, some link based on ball joint connector.  Look at mack set or some unimog models. This way the physical link will keep stable whatever the axle position is.

[Carsten Svendsen]

Seems to me your best option is a 3- point linkage like it appears in the Unimog set

[ancientpixel]

Thanks, I will look into that :) 

In the meantime I had the idea to flip the diff 90 degrees and let it act as an adder of both rotations, but have not yet tested it. 

[Lipko]

2 minutes ago, ancientpixel said:

Thanks, I will look into that :) 

In the meantime I had the idea to flip the diff 90 degrees and let it act as an adder of both rotations, but have not yet tested it. 

Any gear solution to that situation will introduce slack which (apart from making the steering very sluggish) will cancel out any effect.

[Leonard Goldstein]

On 2/4/2019 at 9:52 PM, ancientpixel said:

Hi All! Often a "reader", now a "poster", i´ve got a problem i cant fully wrap my head around.

I try to keep a steering axle straight while going through a pivoting point or turntable. The axle should rotate with the pivot (eg in the picture below the yellow bricks should always align with the grey liftarms even if the liftarms are at 90 degrees of each other) but i want to rotate it manually on one side, with the rotation + offset of the pivot on the other side. Like the axle itself would have been twisted. The furthest ive got with this is pictured below and works as long there is no friction on the left output.
I want both sides to rotate at the same time, but if you rotate the pivot/turntable then it should add just an offset "within" the axle. I dont know if this is actually possible or how to split the axle in two, add the pivot rotation to one part and then add both rotation together.

 

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Hi @ancientpixel,

maybe this can solve your problem:

The green differential is just used to bring two functions through the turntable:

1. Steering (red)

2. Rotation of the superstructure (green)

Both functions are added using another differential (blue).

I am not sure if this really works (I am out of LEGO now ). Maybe you have to adjust the gear ratio. I used a similar solution as a subtracter for a tracked vehicle.

Regards

Leonard Goldstein

[ancientpixel]

@Leonard GoldsteinNice stuff! Ill definitly try that, thank you :)

I came up with this horrible thing, that doesnt work as i wanted, but maybe is quite nice too and already goes in your direction:

[pleegwat]

I'm reminded of the solution used in 8837. There the steering control is on the upper structure directly above the center of the turntable, and not geared in the superstructure at all. Additionally rotating the turntable is done with a planetary gear system and the same control as steering, by lifting it.

That probably doesn't help you though.

[ancientpixel]

As usual one part is missing (another old style diff) but THANK YOU very much @Leonard Goldstein it works as i wanted! :)

[Leonard Goldstein]

11 hours ago, ancientpixel said:

As usual one part is missing (another old style diff) but THANK YOU very much @Leonard Goldstein it works as i wanted! :)

Your solution looks very smart 

One little detail you should keep in mind: driving the housing of a differential with one bevel gear fixed runs the other bevel gear with double speed. To compensate this you should have a 1:2 gear ratio on the input side. With the old style diff this is easy: 12:24=1:2. I also tried to find a solution for the new style diff, but did not succeed. The diff hat 28 teeth and there is no 14-teeth cog wheel available ... With the 12:28 configuration of your solution the subtractor will not completely compensate the two input rotations (rotating the super structure with fixed steering wheel will result in a little rotation of the steering output).

With your earlier concept you will not have this problem of course. Using the two bevel gears as input and the housing as output might be the easier way.

Now I can't wait to see the complete MOC 

Regards

Leonard Goldstein

[Captainowie]

On 2/7/2019 at 5:43 PM, Leonard Goldstein said:

 there is no 14-teeth cog wheel available

Sure there is!

http://www.peeron.com/inv/parts/4143

It's old and fragile and tricky to integrate, but such integration is certainly possible, and it does have 14 teeth.

[pleegwat]

Also the small turntable has 28 teeth, but mounting it on an axle may be tricky.