Sliding worm 3-speed automatic gearbox

[2GodBDGlory]

This gearbox design just came to me last night while fiddling with gears. It uses a worm gear's tendency to slide along axles to create a compact 3-speed automatic gearbox. There is essentially a long axle with a worm gear and several springs from Lego shocks (two soft and one hard). On each side of this axle are longitudinal beams with 8T gears sandwiched between them, which mesh with the worm gear. If the worm is to the motor side of the axle, it directly drives the output through an 8T gear, if the worm is in the middle, it runs a different 8T gear, which drives a 16T gear, which drives a 28T gear, which drives the output, and if the worm is on the far side of the axle, it drives the output through two stages of 16:28 gearing. Half of the 8T gears are actually idlers, and only function to press the worm into the 8T on the opposite side. The shifting happens when the worm gear "decides" that it is easier to not run the output (because it is stressed), and instead inches down the axle against the springs, causing it to mesh with a different gear, at a slower ratio.

The video may help you understand how it works.

The gearbox is fully functional, but somewhat clunky. It could be expanded to have more speeds, but this would require an axle longer than a 12 (I have ordered a 16L and a 32L, but they aren't here yet), but there might not be much practical benefit, since gears get exponentially lower, and complexity and size increase. It would be interesting to try this relatively compact gearbox in a car, but its space efficiency might be annulled by its mechanical inefficiency, what with the worm gear and all.

Please let me know what you think of this gearbox!

 

 

 

Edited August 16, 2020 by 2GodBDGlory

[Metagross555]

Is there any significant issues caused by torsion on the worm gear axle?

 

Edited August 19, 2020 by Metagross555

[All_About_Lego]

‘Clunky’ or not. It’s still a very clever idea! - I would love to see this concept improved upon over time as it looks like a great solution

[amorti]

Clever idea, maybe try fitting it into a basic chassis to see if it works?

I think you could maybe use two different rate springs, a soft and a hard, to give it a more defined step between gears.

[Nazgarot]

Hi.

I've been playing around with a similar concept, and tried to integrate it in your gearbox to make it more compact (not by much) as well as making the shifting more consistent. 

I've swapped the gears for a lower gear range (because I don't have the new gears), and at the same time placed them so that the gears easily can be doubled to increase the durability and torque capability of the gearbox. To do this you simply add another set of gears on the upper 9L liftarms and connect them to the lower set of gears with 3x8t or 2x 12t gears.

The link shows the gearbox in it's simplest form, combining rubber bands and a hard spring to give consistent gear shifts. Shifting from 3th to 2nd gear is controlled by the rubber band, while 1st to 2nd is controlled by spring and rubber band. The rubber band is placed between the yellow bushes and the black pin with ball. I've also hidden one 9L liftarm to show the construction better.

https://drive.google.com/file/d/1-CUxJWzRz7z-6s4rut3gRrWuGwNmiqei/view?usp=sharing (unfortunately I don't have a uploaded image ready for sharing. waiting for brickshelf to approve it).

This is both shorter and narrower though much more burly being 9 studs long, 5 wide and 3 high (4 of you count the gears), and filling that volume. The smaller gears also require less space, and makes it easier to integrate this into a model. It can be built with less bracing, but will not be fit for high torque application if one removes the 5x3 liftarms.

Thanks to 2GodBDGlory for the great idea! I've simply built upon that.

Edited August 17, 2020 by Nazgarot
added picture

[MangaNOID]

Great idea/concept! 

 It will be interesting to see how much load it can take. 
 

would using the bigger 1L worm gears take more load perhaps? ... is that a stupid question   Of course it would be  bigger in size but for a big crawler maybe??

[Nazgarot]

You could avoid the frail 8t gears by going to the 1L worm, but I think the worm itself is a lot weaker.

It is also posible to avoid the 8t gears by doing a half stud offset and using the 12t black gears, but it would be very hard to brace such a construction...

Would be nice to see more ideas to avoid the 8t gears as they are the weak link here.

-ED-

[SNIPE]

@sariel this is what I was talking about before re your automatic gearbox idea.

 you might wanna put a half bush or full bush at the end of the spring instead of a 1x1 beam because the spring coils have a tendancy to get stuck in the groove or an axle hole and then unwind their coils which obvioustly damages them.

Since axle holes don't have this groove, it fixes that, (eg: a half bush.)

Regards, S

Edited August 17, 2020 by SNIPE

[pleegwat]

3 hours ago, Nazgarot said:

It is also posible to avoid the 8t gears by doing a half stud offset and using the 12t black gears, but it would be very hard to brace such a construction...

Wouldn't that also require a 1.5 stud long worm gear?

[2GodBDGlory]

13 hours ago, Metagross555 said:

Is there any significant issues caused by torsion on the worm gear axle?

 

 

You may wanna fix that lisp if English is your main language

No, I have not noticed any problems with torsion. If you did expand it, using a 16L or 32L axle, that could become a problem though, I suppose.

 

12 hours ago, amorti said:

Clever idea, maybe try fitting it into a basic chassis to see if it works?

I think you could maybe use two different rate springs, a soft and a hard, to give it a more defined step between gears.

I should try that soon. I did use a few different springs, two soft, and one hard, to get the right rate, but perhaps it could be more sophisticated.

13 hours ago, Metagross555 said:

 

 

 

You may wanna fix that lisp if English is your main language

^I want to get rid of that box, but I don't know how...

9 hours ago, Nazgarot said:

Hi.

I've been playing around with a similar concept, and tried to integrate it in your gearbox to make it more compact (not by much) as well as making the shifting more consistent. 

I've swapped the gears for a lower gear range (because I don't have the new gears), and at the same time placed them so that the gears easily can be doubled to increase the durability and torque capability of the gearbox. To do this you simply add another set of gears on the upper 9L liftarms and connect them to the lower set of gears with 3x8t or 2x 12t gears.

The link shows the gearbox in it's simplest form, combining rubber bands and a hard spring to give consistent gear shifts. Shifting from 3th to 2nd gear is controlled by the rubber band, while 1st to 2nd is controlled by spring and rubber band. The rubber band is placed between the yellow bushes and the black pin with ball. I've also hidden one 9L liftarm to show the construction better.

https://drive.google.com/file/d/1-CUxJWzRz7z-6s4rut3gRrWuGwNmiqei/view?usp=sharing (unfortunately I don't have a uploaded image ready for sharing. waiting for brickshelf to approve it).

This is both shorter and narrower though much more burly being 9 studs long, 5 wide and 3 high (4 of you count the gears), and filling that volume. The smaller gears also require less space, and makes it easier to integrate this into a model. It can be built with less bracing, but will not be fit for high torque application if one removes the 5x3 liftarms.

Thanks to 2GodBDGlory for the great idea! I've simply built upon that.

I can't see the whole setup clearly, but I did try something similar initially. If I see correctly, this gearbox would cause every other gear to be the reverse of the other ones, because the 8T gears are stuck in different directions by the 12 and 20T gears

6 hours ago, MangaNOID said:

Great idea/concept! 

 It will be interesting to see how much load it can take. 
 

would using the bigger 1L worm gears take more load perhaps? ... is that a stupid question   Of course it would be  bigger in size but for a big crawler maybe??

The 1L worm gears probably would take more load, but they would have a hard time grabbing on the next gear, because they aren't long enough, and they don't slide nicely on axles, which would make shifting less smooth.

6 hours ago, SNIPE said:

@sariel this is what I was talking about before re your automatic gearbox idea.

 you might wanna put a half bush or full bush at the end of the spring instead of a 1x1 beam because the spring coils have a tendancy to get stuck in the groove or an axle hole and then unwind their coils which obvioustly damages them.

Since axle holes don't have this groove, it fixes that, (eg: a half bush.)

Regards, S

I agree that it can get stuck in those bushes, but my reckoning was that the one end of the spring setup would get stuck in the worm, but it wouldn't push very hard, because it could just rotate the 1L beam along with the axle. Though on further thought, I guess the bush and worm would always rotate at the same speed, so that wouldn't cause a problem either, and would probably be better, even if only because the axle would be less likely to slide out of the motor.

[2GodBDGlory]

I just built a little mock-up car, and it revealed some flaws in the gearbox. The tuning was off, so it would only get into third on downhills, but more worryingly, it would often skip, with the worm between the 8T gears. I think I will try to upgrade to 12T gears, which would add strength, and keep the worm firmly seated on a gear more of the time.

[TechnicBrickPower]

Great idea - I like it!!!

[piterx]

that is awesome :) i thought of something like that a while ago but never had the chance to actually try it out! ill give yours a try when i can, im pretty sure that it could solve multiple problems related to auto shifting cars :)

[2GodBDGlory]

I have been experimenting with several different designs, which I will list here:

1. 2L worm with 12T gears, 3-speed. This gearbox has very weird spacing, and friction issues

2. 2L worm with 24T gears, 4-speed. This gearbox is way too big

3. 1L worm with 12T gears, 9-speed. Probably too ambitious, the worm skips against the gears sometimes, it requires grease to work well, and it has slightly weird spacing

Probably I will go back to the original, simple design, and try to refine it more.