Hrafn's small builds

[Hrafn]

Every so often I put together a proof of concept or small creation that doesn't need its own topic; this is a place for such things.

First off, a proof of concept for a brake/neutral/drive gearbox.  Input is via the green axle connector.  With the 20z gear selected, the differential has half the angular velocity of the input, so the output is braked and the motor is not strained by the braking. 

Off the top of my head I could only come up with the 14z/28z mesh to get the brake to work properly - is there another gear combo (using any of the differential housings) that works?

This thing is way too large to use in my current project but let me know if it is useful to you.

[pleegwat]

28z/12z should mesh here, given that 20z/20z meshes on the same axle pair (sum of teeth count is the same)

[Hrafn]

15 hours ago, pleegwat said:

28z/12z should mesh here, given that 20z/20z meshes on the same axle pair (sum of teeth count is the same)

It does, but 12:28 does not give the right ratio of 1/2.  14z meshes with double bevel gears as if it were 12z, but gives the right ratio, which is why this works.  14z gears are kind of a pain to use and somewhat fragile (not to mention long out of production) so I don't really like using them, though.

12:12 and 8:16 (using the 16z side of the old 4L differential) would work but the 12z gears aren't clutch gears.  There may be another solution using chains.

Edited September 14, 2021 by Hrafn

[2GodBDGlory]

Clever! I always enjoy seeing uses for the 14T gears, though I understand your desire to eliminate them.

[Hrafn]

Here is another way to do it that should be more robust.  In Drive gear, the output turns in the opposite direction to the motor input.

Or a long skinny variant

 

Edited September 14, 2021 by Hrafn

[Void_S]

The variants with RC heavy duty differential should work even for relativelly big and heavy models. 

[Hrafn]

Here is another use of the 4L differential: an automatic R-N-D gearbox.  The yellow connector blocks the differential from rotating, so the output is the same speed (but opposite rotation direction) as the input.  When there is no input, the output can spin freely.

The yellow axle joiner is the input, the red is the output.  The clutch gear does result in a non-trivial amount of wasted energy in D and R gears.  And R is not geared down from D, unlike in my previous prototype below; but this design is much more compact.

 

 

 

 

[Hrafn]

Here is a steered, driven hub for 49.5x20 tires, using a CV joint.  

[Jurss]

Interesting.

Just not shure, if it would be better in some way than standard. Distance from steering axle to wheel may be shorter, it seems?

And I think, that steering lever can be made shorter, if some other parts are used.

[Jurss]

Would look like this. Main issue, that this won't be rigid. It should rely on some bracing between suspension arms

[Hrafn]

5 hours ago, Jurss said:

Interesting.

Just not shure, if it would be better in some way than standard. Distance from steering axle to wheel may be shorter, it seems?

Yes, my goal was to get the pivot point as close to the wheel as possible.  This design might be a dead end for my current project since there are other designs that will probably work better, but I wanted to share it in case it was of use to anyone else.

Your design is nice and compact, though you are probably right about its rigidity.

Edited February 16, 2022 by Hrafn

[Hrafn]

Can anyone improve my bi-directional freewheel? It works ok (though only with the old, un-reinforced 8t gears). Input is yellow.

 

[Zerobricks]

I recommend you check Nicjasno's one - way clutches:

 

[Hrafn]

On 7/12/2024 at 3:39 PM, Zerobricks said:

I recommend you check Nicjasno's one - way clutches:

I need a two-way freewheel, not one-way. Piterx’s solution, while elegant, is also slightly too large for my application - three studs is the limit.

The initial design I posted works except that it sometimes binds when the input is stopped and the output is free wheeling.  A rubber band would help the parallelogram linkage stay in a square when the input is not turning, so that might be one direction to go.

 

 

Edited August 26, 2024 by Hrafn

[Hrafn]

Here is a two-way centrifugal clutch, based on the classic one by @piterx and using the “minions goggle” piece (https://www.bricklink.com/v2/catalog/catalogitem.page?P=68325#T=C)

It isn’t 100% reliable with a PF-M motor run from a Lego LiPO battery, but at higher speeds (buggy driven by a BuWizz 2) it definitely is.

Adding one of these helps a bit with reliability: https://www.bricklink.com/v2/catalog/catalogitem.page?P=11833#T=C

Edited August 26, 2024 by Hrafn

[2GodBDGlory]

10 hours ago, Hrafn said:

Here is a two-way centrifugal clutch, based on the classic one by @piterx and using the “minions goggle” piece (https://www.bricklink.com/v2/catalog/catalogitem.page?P=68325#T=C)

 

It isn’t 100% reliable with a PF-M motor run from a Lego LiPO battery, but at higher speeds (buggy driven by a BuWizz 2) it definitely is.

Adding one of these helps a bit with reliability: https://www.bricklink.com/v2/catalog/catalogitem.page?P=11833#T=C

Cool! I don't recall any situations where I needed a centrifugal clutch, but if I did, something like this would work well! Maybe with LPEs?

Edited August 26, 2024 by 2GodBDGlory