Knex differential

I created the differentials a while ago. Larger versions are possible without any modifications of the basic pieces. This version is designed to be smaller in diameter than the main drive gear, requiring a modification to that gear.

Picture of Knex differential
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Hyshinara2 years ago

I tried this design, as it was the smallest I could find without the special snap-on gears GWorks' used in theirs (

I don't really get why you placed the cross braces (orange connector with 2 white rods) diagonally instead of just straight over? I found they created too much friction when compared to the straight-over configuration.
I do think the yellow gear mod is a good idea! As you said, the giant gear also has such a feature and it doesn't obstruct in operations. It's also a sturdier solution than using wire. It is now my first-ever modified Knex or Lego piece :P

In the end, for the differential, I eventually went with a hybrid of yours and Forsterimages' V2 ( :)

Speed8ump (author)  Hyshinara2 years ago

I found that without a little inward pressure on the flywheel gears (the two grey gears) they pretty easily jumped teeth under any kind of load. Thus the diagonal arrangement. It also avoided the need for any extra pieces to stabilize the two white end caps,

Aha! I was indeed experiencing gear skipping when I increased the load. :)
Then again, my intended load is a stunt kite, and I've come to realise Knex connections probably won't be able to handle the forces that the kite can create.

My complete plan was to make an automatic stunt kite reel. Stunt kites have 2 reels and it's rather difficult to reel them in, especially if you are flying high, because you have to reel them in simultaneously to keep the kite upright instead of crashing to the ground. Using a differential and a cordless drill, I would be able to reel in both reels at the same speed, while also being able to make adjustments by slightly slowing down one reel by hand. Or by just stopping the drill and turning one reel by hand.
I think the idea is OK, but that it just can't be functionally built with Knex. :)

May I ask where you are going to use the differential for? ^^

For a stunt kite reel :) (see my other comment above)
I might revisit the project one day, but then I'll just use 2 cordless drills and attach the reels directly to them. :P

Aha! like that. Sounds cool!
That cordless drill idea sounds mean >:)

MI69 years ago
Wow fantastic work, really good going. shame about the holes but amazingly good.
Speed8ump (author)  MI69 years ago
Thanks. I don't know why they didn't put the holes in the original mold. The same hole position is in the large gear, and having the holes there doesn't interfere with any other operation of the gear (at least not that I've seen). It's also an easy modification so i figured it's not a big deal (a fine point felt tip, clamp, cordless drill, bit, and 5 minutes did all of mine). Anyway, I've had some people ask about how I did it so I figured it belonged here. I realize I am at risk of bringing the "gun" to "not gun" ratio down into the double digits but hopefully I'll be forgiven ;)

Heck yeah you be forgiven! Variety is always a great thing about this site and always will be. The best ideas are always the ones no one has tried before and succeeded.

I hope to see many more projects from you in the future. I'd love to see an automatic transmission if you got any ideas on how that can be done.

Speed8ump (author)  JonnyBGood2 years ago

I have no idea how to create a synchronizer which you would need for a geared transmission. I'll think about it though and see what I can come up with. :)

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