Hi,

Before starting on this project I tried searching the net to see if anybody had made anything like this before, but I've come up empty handed. I needed to make a mechanism that would allow me to have one motor run two functions in sequence, where one action was executed first, then the second, and when you reverse the motor, the sequence reverses as well. That is, in reverse the second action will happen first.

This would be useful for any two function that are supposed to be in sequence, like: The forks and the extendable mast on a forklift, the feet of a mobile crane, sections of the boom on a mobile crane, and so on...

Detailed description:

I've made a two action mechanical sequencer that first will execute one function til it stops, then the second til it stops. When you reverse the single motor running it, it will reverse first the second function til it stops, then the first function. It you change direction of the motor anywhere, it will reverse the functions from that point, but will keep the same sequence. To explain my self better; if the first function has not reached its stop, and you reverse the motor, the first function will reverse, while the second function will not activate.

I've included a couple of pictures, and a movie will be coming soon.

I would really appreciate if anybody could help me make it more compact, or come up with a simpler solution to my problem.

Pictures: The gray axle into the black 12 tooth gear is the input (from medium or large motor. XL is to slow to engage this direction sensitive gearbox), and the green and pink(?) axle is output 1 and 2. A unintended benefit to this design is that when both outputs reach their stop, the whole construction functions as a clutch and saves the motor from locking up. (The whole setup might however be a bit tough on a medium motor...)

Finally the video is ready!

And of course, the .lxf file. The file also contains a few older/alternate versions.

-ED-

EDIT: Added video.

Edited February 5, 201312 yr by Nazgarot

This is already a clever solution.

Another possible solution is something with a gear rack passing multiple gears (look in the technic idea book 891 for two implementations of this idea). You use one input to slide the gear rack forward. It will then first engage the first gear, when you continue it will disengage and engage the second gear. When moving backwards the sequence is reversed.

Thanks!

That is actually a very clever idea, even though it has limited uses. I have mainly been focusing on a solution that allows infinite number of rotations before locking (LA's primerly), and didn't think about that at all. It would be a great, and simple, solution in some cases. By adjusting it slightly you could even make the functions overlap...

The main problem with my solution is that it takes a lot of room. I would love to make it more compact, but not necessarily change the components. A different "direction sensor" might do the trick, and allow the diffs to be placed differently...

Anyway, thanks for the input!

-ED-

I've successfully made a version of this gearbox, and I've made some changes. The ratcheting gearbox has been switched out for a crawling worm gear, allowing the use of an XL motor for power. It's a great design, and I've managed to make it fairly compact, and eliminate some of the 8 tooth gears.

@ Saberwing40k: Can you share your gearbox design?

@ Saberwing40k: Can you share your gearbox design?

Yes, please share pictures/.lxf!

This is probably just what I was hoping for; someone picking up the idea and improving it further! I like the idea of using a "crawling worm gear". I've done that several times before, but didn't think of it for this application as I needed greater speed, but i would still love to see it. I didn't especially like the solution with the 8 tooth gears, so finding a way to get rid of them is definitively a step in the right direction. I have cooked up a version where the diffs are turned around, and the axle from the direction sensor ends in a "Pin long with stop bush". Can't wait to see your solution...

I'm curious how this responds when the torque on the first output suddenly drops off. Does it revert back to the first stage, or stay on the second stage?

Your design looks like it is relying upon the resistance of the axle-pins with friction to route the power of the motor between different functions. This can work, however you will be adding extra resistance that the motor then has to overcome, and you may need to play around with different amounts of resistance to get it working just right. I have a proof-of-concept video that also uses resistance to achieve this (a rubber band/belt), but I have never used it in a finished MOC, and it might not be in the correct sequence for your needs.

As you can see in the video, I didn't get the resistance just right, so it would have to be tweaked further, especially when a load is put on the linear actuators as the resistance would change.

This recent video by Philip Verbeek also shows a system that you might be able to modify for your purposes (jump to about 15 seconds in):

It relies upon the motor switching the position of the driving ring, and therefore routing power through a different drive-train.

Using a differential, you could route the power of the motor to one output, and when the resistance is too great, it then switches a driving ring to route the motors power to a second output.

Your design looks like it is relying upon the resistance of the axle-pins with friction to route the power of the motor between different functions. This can work, however you will be adding extra resistance that the motor then has to overcome, and you may need to play around with different amounts of resistance to get it working just right. I have a proof-of-concept video that also uses resistance to achieve this (a rubber band/belt), but I have never used it in a finished MOC, and it might not be in the correct sequence for your needs.

"Video"

As you can see in the video, I didn't get the resistance just right, so it would have to be tweaked further, especially when a load is put on the linear actuators as the resistance would change.

This will be way to flimsy for my use, and it will have the wrong sequence. I need the following sequence: action 1 til it stops, then action 2 til it stops. And when reversed, action 2 reversed til it stops, then action 1 til it stops. If it is reversed anywhere in between it should reverse the sequence from that point.

This recent video by Philip Verbeek also shows a system that you might be able to modify for your purposes (jump to about 15 seconds in):

"Video"

It relies upon the motor switching the position of the driving ring, and therefore routing power through a different drive-train.

Using a differential, you could route the power of the motor to one output, and when the resistance is too great, it then switches a driving ring to route the motors power to a second output.

This is a good way to sequence two actions, if they are equal in lenght, repeting and quite short. It will not be a good solution for longer sequences, and sequences of different length.

It is how ever a good idea, for it's uses.

-ED-

Well, I've uploaded my version to my Brickshelf Gallery, including the .lxf file. Should be moderated fairly soon.

Pics:

I love these challenges! Here is a very reliable solution that does not rely on friction. (Bracing and compactness could certainly be improved).

The basic mechanism is:

motor -> one side of differential

other side of differential -> selector gearbox with changeover catch

differential housing -> spring-loaded axle with two stable positions -> "clutch" with large amount of slack -> changeover catch

Here is a very reliable solution that does not rely on friction.

Incidentally, this can also be modified to give an "auto-reverse" mechanism (e.g. to make a LA continually expand and contract): connect the two outputs of the gearbox so that they turn in opposite directions, and put the differential _after_ the gearbox in the drivetrain.