Suggestions needed: "one direction" conversion?

[aczkasow]

Hello,

Could anyone suggest how can such schematic be designed? It always spins the same direction no matter which direction input rotates.

Thanks in advance!

[Zerobricks]

A worm gear silding on an axle between two 8 tooth gears, which are interconnected by 2 16 tooth gears. Simple and compact.

[aczkasow]

A worm gear silding on an axle between two 8 tooth gears, which are interconnected by 2 16 tooth gears. Simple and compact.

Wow thanks! That was fast. Does all wormgears slide on axles?

[nicjasno]

Wow thanks! That was fast. Does all wormgears slide on axles?

Yes.

[chorlton]

I was struggling to picture the text description so went searching on google.

sunskytechnic

search for uni directional gearbox just over half way down.

[matias bendtsen]

if yo use this to drive a car and go downhill, it will stop, or even go uphill instead, so it is not the best solution, but it is the smallest.

[Sokratesz]

It's also a brilliant solution for using one motor to control two functions ;)

[Phoxtane]

Unless I'm mistaken, there'll be a small delay in transitioning from one direction of input to the other, since the worm gear has to slide along the axle and engage the other gear before it actually begins to turn.

[Splat]

Unless I'm mistaken, there'll be a small delay in transitioning from one direction of input to the other, since the worm gear has to slide along the axle and engage the other gear before it actually begins to turn.

This is true, but you can speed up the axle that the worm gear is on, which will make the worm slide from one gear to the other quicker.

[Hopey]

A worm gear silding on an axle between two 8 tooth gears, which are interconnected by 2 16 tooth gears. Simple and compact.

That's awesome.

As a little project, I'm trying to motorise a 7685 dozer with a single motor, such that when switched on in one direction, it goes forwards, and when reversed it turns on the spot (by driving the tracks in opposite directions).

I've figured out a drivetrain that seems to work, but (as I now realise) it's overly complicated. I've physically made a prototype, but needed to work out the right way to build the supporting structure around it, so made a model of it in MLCad.

(Apparently I can't attach .ldr files? The rear output shaft isn't really visible in the screencap, no biggie)

The drive from the motor goes in the "side" of a differential gear. Out the other side is a shaft with a worm gear. The body of the diff drives the main drivetrain, which includes a gear shifter thingy which selects one of two output shafts, front and rear. There's a 8 tooth gear on a blue friction pin attached to the drivetrain before this. The worm gear drives a clutched 24 tooth gear which rotates a gear lever.

The end result is that when the motor switches direction, the friction pin provides enough resistance that the worm gear turns instead, moving the gearbox collar to select either the front or rear output shaft. When it reaches its limit, the worm gear stops and the diff drives the drivetrain.

I've yet to do the actual drive, which will take 2 more diff. One will drive the back track sprockets in the regular way. The other will have gears between the diff and the front track sprockets, one with two gears, one with 3, so that they will rotate in opposite directions. This means that whenever it's going (one way or the other), the other diff's shafts should rotate at equal and opposite rates (driven by the track), so the other output shaft should be stationary.

I can still use the diffs concept, but with a sliding worm gear instead, and it'll be a helluva lot more compact. Might have to think about how to do it such that the two 16t gears aren't meshed; maybe put one above the worm gear and one below, or space them apart and use two worm gears. Will see...

[matias bendtsen]

thats a nice mechanism, that should work^^

[Splat]

Might have to think about how to do it such that the two 16t gears aren't meshed; maybe put one above the worm gear and one below, or space them apart and use two worm gears. Will see...

If you are working with studless, you can use two 8t gears to mesh with the worm gear. When the worm gear is at one end of the axle it turns one 8t gear, and when it slides to the opposite end of the axle it turns the other 8t gear. If you take the output from only one of the red/green axles, it will always turn the same direction (except for a brief pause while the worm slides along the axle).

You can also change the two 16t gears to get different output speeds (eg. 8t+24t, 12t+20t). So if you turn the input (yellow) clockwise, you get one speed, and if you turn the input (yellow) counter-clockwise, you get a different speed, but the output (red or green) still spins the same direction.

If you don't want the two output axles meshed together, you can remove the two 16t gears, and the red and green axles can act as separate outputs, but only one will spin at a time, and they will only spin in one direction. Also, when they aren't meshed with the worm, they will be able to free spin, which might be undesirable in some situations (eg. a crane).

If you have the pieces, build this simple mechanism and see what it does in real-life to get a better understanding. Whoever came up with this was a genius (alas, it wasn't me).

[Hopey]

If you are working with studless, you can use two 8t gears to mesh with the worm gear. When the worm gear is at one end of the axle it turns one 8t gear, and when it slides to the opposite end of the axle it turns the other 8t gear.

Yep, I discovered this through a little trial and error. Here's the new drivetrain for my dozer:

(Please excuse the quality. Do I get a bigger image quota when I've been here for a while?)

Obviously it still needs some work to add some supporting structure around it, but I think this'll be compact enough to fit inside the original structure of the dozer, with some modification. Hope to get it done this weekend...

[DLuders]

(Please excuse the quality. Do I get a bigger image quota when I've been here for a while?)

Nope, everyone on Eurobricks only gets a 150k "quota" for attachments. What you should do is get a separate account on an image-hosting service (like Flickr), and link your images from there into your Eurobricks posts.

[Burf2000]

Some brilliant ideas! Glad the question was asked!