pic: Concentric Shifting Transmission Concept

[Madison]

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[Kevin Sevcik]

That's a neat idea, and actually rather similar to the ball-lock trannies that started showing up a few years ago.

Example here

The main difference obviously being your use spring loaded pins. While the pins would probably cary more torque, I'd be worried that the would bind and wouldn't release when you wanted them to. You could solve that with a tapered hole and tapered pin such that the pin would get forced downwards without something pushing it up from underneath, though. Which would basically make it like the ball-lock trannies.

[Simon Strauss]

I'm a bit confused as to how the pins are being forced down away from the gears when they are not engaged. I assume that the whole system is modeled after the tumbler of a key and lock, but what is to prevent the springs from getting caught or damaged while a gear is not engaged, if the spring is in the gear and rotating around the shaft with it. It may not be an issue but i think you may want to consider A)shorter springs and a second pin attached to it that stays in the gear, like that of a lock with your pins that are already there taking the place of what would be the teeth on the key. This might prevent gears from getting jammed. Also B) I'm assuming that you are curving the top of the pins so that they are flush with the outside of the tube that they are in and because of this I'm worried that the round pins you have in it now might rotate and cause themselves to no longer be flush. Because of this i think that square pins might be more advantageous in that they will only go in directions you want them to.

-Simon

P.S Ive never built a shifting transmission so these issues maybe completely irrelevant or nonexistent, you and others here know much more about this than i do.

[Al Skierkiewicz]

Maddie,
Interesting concept. First thing that came to mind was that the ends of the springs meant to keep the pins in place, are actually moving around the shaft for the gear that is not engaged, correct? Assuming that the pink is the input drive shaft. There will be some significant centrifical force driving the pins to the outside, so the springs need to be pretty strong and the ends need to be protected from the abrasion as they pass over each of the holes and pins. I remember seeing a segmented collar that had a spring wrapped around it that might be better. Sort of like the shoes on a centrifical clutch. A little lubricant and you should be good to go.

[gburlison]

Lets first analyze what is going to happen to the gear that is engaged by the pins. Looking at your at your diagram the biggest problem that I can think of would be the binding of the pin when you try to shift gears. Assume that the inner rod is shifted to the right and the pins are engaging the green gear to the red shaft. When a load is placed on the transmission, the pin will be bound very tight. Moving the shift rod to the left will not be enough to disengage the pins from the green gear. I can not imagine springs strong enough to disengage the pins. The transmission will have to be unloaded long enough to unbind the pins so that the springs can then move them.

Next lets analyze what is going to happen to the gear that is not engaged. Once again assume that the shift rod is shifted to the right and the pins are engaging the green gear. The blue gear is turning at a different speed than the red shaft. The springs in the blue gear are pushing down on the red shaft with some force. This will cause some friction and a loss of power. Ever half revolution, the springs will press down on the pin and possibly push it in a little depending on how good you machined the pin. This means that the spring might enter the hole in the red shaft a small amount and will either bind up the transmission or cut off the end of the spring.

Like Kevin has mentioned, the solution to the problem of using pins is to round them off until they are balls,

[Gabe]

The solution could be to have not one, but two pins per spring. When you use one pin to lock you are essentially putting a shearing force on the pins. The problem arises when the pins retract and, as the pins wear down, they retract too far and shearing forces are applied to the springs which will damage them. By adding a very short pin segment with rounded ends in between the locking pin and the spring (shortened a bit), the transmission will unlock by splitting at the union between the pins. This concept is the same as the pin tumbler lock.
Notice that the ends of the pins are rounded to make the pins separate easily. When the lock is "locked", the inner cylinder can't turn because the pins aren't shearing. Study the image and apply the mechanism design to the shifting transmission. The simplest solution to the current design on the drawing board is to insert a ball bearing in between the locking pins and the springs, after having rounded over the end of the pin.

[Kevin Sevcik]

Gabe,

That would solve the issue of wear on the end of the springs, but you're left with the more serious issue of the pin binding when it's transmitting torque to the gear. If you want to continue with your lock tumbler analogy, this is similar to how you pick a lock. You use something to turn the cylinder till one of the pins binds, then you force it up till it releases. But you need a decent amount of force to move it, and that's just a little lock with a light amount of torque. This is a tranny with a lot of torque, and only a spring to overcome it. So I think your best bet is to use the torque it's trying to transmit to shift the pin by slanting the side of it or turning it into a ball.

[Dick Linn]

Just FYI, the ball shifting type of transmissions were used in Hodaka motorcycles back in the 70's. If you don't have the resources to make all the parts, you might cannibalize an old Hodaka tranny. I saw a few old motors and parts bikes on eBay.

[team222badbrad]

It appears to me that the transparent yellow is a free floating collar to hold the springs in place.

I'm also assuming that the red is the output shaft and the two gears which are driven are either locked or unlocked from the shaft. Like our Ball-Lock transmissions.

You can't really tell from the drawing, but it appears to me that there are six pins per gear?

I too would be concerned about the wear on the springs on both ends.

The springs may also catch on the small gap.

It looks pretty good, but can you give us some more information?

Hodaka, which is long out of business, used five speeds in their motorcycles.

[Madison]

I posted some CAD drawings to stir the pot a bit around here and, of course, I've been too busy to reply.

The design was inspired by the lock and tumbler mechanism, NYCPunk. Good catch.

I agree with pretty well all of the criticism leveled here. There ought to be a second 'pin' so as to refrain from sliding the spring end around the shaft and getting it caught on the holes. The pins should be beveled to better handle misalignment between the red output shaft and the gears. Also, as a matter of reference, there are six pins per gear on the model for no reason in particular other than to increase the chance of one pin grabbing a hole.

Best of all, since it'll give me something more to think about, I have no good answer for a method to ensure that the pins will release from one gear when the mechanism shifts.