View Full Version : Shift on the fly LEGO gearbox

07-13-2003, 08:05 AM
After seeing the Shift-on-the-fly TechnoKat Gearbox I was inspired to see if it was possible to create one using LEGO. And of coarse it turns out that you can! (What can't be built with LEGO? :))

Below are two pictures of the gearbox. The first one shows the shifter in high gear and the second in low.


Please note that the gearbox can and will be built much more compact. I wanted to keep it spread out so I could easily show everyone how it worked.

Please post any questions or comments.

Tytus Gerrish
07-13-2003, 09:28 AM
tharts cool, i built a lego 4-speed w-reverse gearbox W/o The fancy parts. I wish lego made Dog-Geers and coaxial gears

07-13-2003, 09:50 AM
i wish i had legos to play with :-(

07-13-2003, 10:02 AM
Originally posted by piotrm
i wish i had legos to play with :-(

ditto :'(

07-13-2003, 10:07 AM
I wish i had Lego Leaque when i was in Middle School. The Gearbox is possibly one of the coolest Lego creations i have seen yet.....Maybe i should go get mine and try the same thing.....

07-13-2003, 10:19 AM
i wish i had legos to play with :-(
ditto :'(

http://shop.lego.com/product.asp?prod_id=K3800&CatID=%7BBABF5D45%2D663E%2D40AF%2D8D83%2D897F51A3A 6A9%7D

If you guys are really serious about starting with LEGOS the above link is the best set to start with.

I would love to see what some of you could come up with!

This is not related but if you want to see other Lego creations take a look at http://www.brickshelf.com/ Must of the stuff on here is junk (Bionical stuff) but if you click on the technic link there is some pretty amazing stuff in there.

You can also check out my website where I am working on posting all of my creations. http://www.boomspeed.com/rlowerr/

07-13-2003, 10:47 AM
I'm not quite sure I understand exactly how this would work with spinning metal gears and the such. I understand that this is designed to be able to shift on the fly.

However, I dont understand how the gears are supposed to be meshing. From the way it looks, the two main drive gears are always spinning, and they continue to spin as the main shaft shifts over. Now from what I've learned, as well as from first-hand experience, "shoving" a spinning gear into a non-spinning gear can't be healthy. Sure, it will eventually mesh together and start to drive -- but what is happening in that time before they mesh? I, personally would not want to trust something like this b/c I would be afraid of gear teeth breaking.

Is this how 45's gearbox works? I'm not really sure... I looked at it VERY briefly LATE last night while I was falling asleep, and I just couldn't figure out how that shifts. If that is the case, I would like to find out how those gears held up to grinding and/or breaking teeth...

Tytus Gerrish
07-13-2003, 11:19 AM
As far as i know LEGO does not make Dog gears or Coax Gears so the gearboxes we end up making shift by switching the gear combo (Not selecting it with dogs) so The lego ones are never perfect

07-13-2003, 11:20 AM
This is not exactly how the technokats works. On the technokats the two output gears are not attached to the shaft. As far as I can tell they rotate freely around the shaft until the dog is shifted inside the gear thus spinning the output shaft at that gear ratio.

I would assume that my Lego version works because of the size, number, and spacing of the teeth. If you had gears with more teeth it would seem that it would have a harder time at meshing the gears.

I’m no expert at mechanics… just LEGO! My strong point is more on the initial concept and design, not the final product.

07-13-2003, 12:13 PM
as rlowerr just said, no it's now how the technokat transmission works. If this were to be a 'real' gearbox, shifting on the fly would be a bad situation at high speeds.

rlowerr's box works, the motor facing leftward drives the main shaft, which has a 2 halves. The ingenius method is to have the second motor (facing up) attatched to a fast moving worm gear (see white gear to small gear to worm). The worm engages the Lego Stop (Small spacer with a groove), which then follows the worm teeth up and down to shift the 2nd half of the main shaft (via connection by the black arms). See that clog of stuff on the main shaft? That is what allows the shaft to spin and move too. (Awesome thought). Then, depending on if the shaft is up or down, the gears engage with the drive shaft gears.

Lego Pro:
Because of the low torque and RPM that the Lego motors provide, the Lego gears can withstand the "shock force" (I don't know if thats a real term, but thats what I'll call it), of forcing the spinning gear into the non-spinning (motor spinning, not engaged to either) or different speed gear (Shift on the fly).

Real World Con:
FIRST and other motors usually provide enough torque to rip the teeth of a steel gear if not properly built. Involute gears don't "force mesh" to happily because of how little play there is. Force meshing will put a high load on the edges of the teeth which can and probably will weaken and damage at least one of the gears.

While this is a really cool concept, using this as a shift-on-the-fly in the real world could have painful reprocussions. However, using this as a "stop-and-shift" would work beautifully if done correctly, (short push of the gears so they force-mesh slower.

rlowerr: Awesome idea, really cool and original movement methods (I've never seen a worm used like a reverse rack and pinion), but this just wouldn't work as well with metal and high power motors. Please, don't take that as an insult, thats my personal opinion and I've been known to be wrong. I like your gearbox. :)

07-13-2003, 12:23 PM
116's posted gearbox uses this method of meshing the gears. If you use light gears and take the time to file down the teeth a bit where they mesh, it works fine.

If you don't take the time to file down the teeth, when the gears do not mesh, they'll end up flattening their teeth by rubbing against one another. After a bit of this, they won't ever mesh. Then you'll need to go in and file like you should've done in the first place.

07-13-2003, 12:49 PM

Thanks for the reply! I wish I could take credit for the lead screw made from a worm gear but I did learn that from another LEGO builder. But I am happy to say that the shaft extender (off the main shaft that allows it to be extended and rotated) was all mine. It only came to be after much aggravation and cartoon watching.

M. Krass:

Do you know where a picture of 166's gearbox is? Id love to take a look at it.

07-13-2003, 01:11 PM
Here (http://www.chiefdelphi.com/forums/papers.php?s=&action=single&paperid=104) is the white paper.

07-13-2003, 01:18 PM
Ahhh, yes. After I took the time this morning to examine the whitepaper of 45's transmission, I now understand exactly how it works :P

No more confusion here :cool:

07-13-2003, 03:29 PM
Ok, I’m back after working on the shifter for a while and I was able to get it down to quite a small size.


It is basically all still the same. The only difference is that the worm gear now only actuating one shaft instead of two. (For sake of space saving)

All I need to now is figure out the motor mountings and then I will be ready to actually implement it into a robot!

07-14-2003, 09:45 AM
would it be possible to gt a small video or animated gif of this thing moving? I think i get the principle, but im not exactly sure how and where it moves (shifting and such)

07-14-2003, 04:01 PM
would it be possible to gt a small video or animated gif of this thing moving? I think i get the principle, but im not exactly sure how and where it moves (shifting and such)

A video of the shifter can now be found here:


I am sorry for the quality, I took it with my Lego vision command camera. Also the file size is quite large.

I hope this clears things up for you.

07-14-2003, 10:33 PM
Beautiful. Nice work.