[HELP] Controlling 3 driving rings at once

[TheMindGarage]

I'm building a 6-speed sequential gearbox for use in a future MOC and I've come across an issue. Basically, I need to control three driving rings with a single input, but I can't figure out how to do it. I'm familiar with the standard method of controlling two rings by using eccentric mechanisms 90 degrees out of phase, but this doesn't work with 3.

I need six positions that can be selected with a single axle. I don't need a paddle-shifter - I can do that bit myself. The positions must be in order like this:

[The three changeover catches are in a line, F means flipped forwards, R means flipped backwards, O means in the middle/neutral]

1. FOO
2. ROO
3. OFO
4. ORO
5. OOF
6. OOR

This is all to do with the way the gears are arranged (I needed the ratios to be close; difference between each gear is around 1.3x). I can't change this. The crucial thing is that the mechanism must be compact. I can't give exact dimensions, but I'm quite pushed for space in this MOC.

Thanks in advance for any help!

[Jeroen Ottens]

I really hope you find a solution for this. In my experience this is nearly impossible to make with a single input, unless you go for a linear system like Sheepo's. I have tried a lot of variants with the pulleywheel as drivingwheel (since that has 6 positions), but never succeeded.
I have tried schemes where you always have two drivingrings engaged and use differentials to combine the outputs (I think I wanted to have reverse in as well, that was mathematically impossible), but also without succes.

It actually might be easier to go for an eight-speed gearbox with three driving rings. You can check my DB11 thread for an explanation of how to make such a gearbox. But I must say, even though it is quite compact for what it does, it only fits in a 1:8 scale car...

[TheMindGarage]

Just now, Jeroen Ottens said:

I really hope you find a solution for this. In my experience this is nearly impossible to make with a single input, unless you go for a linear system like Sheepo's. I have tried a lot of variants with the pulleywheel as drivingwheel (since that has 6 positions), but never succeeded.
I have tried schemes where you always have two drivingrings engaged and use differentials to combine the outputs (I think I wanted to have reverse in as well, that was mathematically impossible), but also without succes.

It actually might be easier to go for an eight-speed gearbox with three driving rings. You can check my DB11 thread for an explanation of how to make such a gearbox. But I must say, even though it is quite compact for what it does, it only fits in a 1:8 scale car...

I know how to do the 8-speed with 3 driving rings, but I want it to be a 6-speed since the real car has 6 speeds. Also, the 8-speed has quite a lot of friction and might be too big for this - I'm building a car in what is usually 1:10 scale (using 68.8mm wheels - it's 1:10 for normal cars, but it's probably closer to 1:8 for this particular car).

[aeh5040]

I would not be optimistic about a compact solution to this, unfortunately.  I think you might be better off redesigning the gearbox so that the gears come in a different order, such as:

FOO, OFO, OOF, DOO, ODO, OOD

[brunojj1]

It´s not impossible, even if this is a very delicate task though. You need 2 driving rings changing position F-O-R-O-F each and a third driving ring which has a F-R-F sequence. This way it can be shifted by 1 input only.

Good luck with it and keep the topic updated with any progress  !

Edited December 31, 2016 by brunojj1

[aeh5040]

3 minutes ago, brunojj1 said:

It´s not impossible, even if this is a very delicate task though. You need 2 driving rings changing position F-O-R-O-F each and a third driving ring which has a F-R-F sequence. This way it can be shifted by 1 input only.

Good luck with it and keep the topic updated with any progress  !

That would be much easier.  What he is asking for is for each driving ring to execute the sequence FROOOO.

[brunojj1]

17 minutes ago, aeh5040 said:

That would be much easier.  What he is asking for is for each driving ring to execute the sequence FROOOO.

I think it´s impossible. IMO the only way to shift by one input only by the following scheme:

1. FOR - 2. FOF - 3. ORR - 4. ORF - 5. ROR - 6. ROF

Edited December 31, 2016 by brunojj1

[aeh5040]

Just now, brunojj1 said:

I think it´s impossible.

It's certainly not impossible!  One way would be a groove cam like akiyuky's controlling each driving ring, but with three positions.  However, a compact reliable solution seems unlikely, whereas redesigning the gearbox itself is relatively straightforward.

 

[Myers Lego Technic]

@TheMindGarage

The solution is relatively easy. 

While I am not entirely sure what you want, you can create a device that works off a very similar mechanism to Sariels unwieldy servo six speed with one reliable input. The way it works is heavily based on timing, but using the right gear pairings it can be surprisingly reliable. You simply need to connect the two mechanisms, the mechanism that slides the selector, and the switch. 

   The axle which the switch rotates on should be connected on one  end with a large lever, connected by a lift arm type connection between that lever and a smaller driving lever, allowing continual rotation of the input (small lever) for a back and forth movement (preferable 90*. Though governed by the lever sizes) of the large lever (output). The input axle rotating the small lever will be directly connected to appropriate down gearing depending on your previous lever sizes, connected then to a 90* limiter to the rotating lever connected by a steering link (like in sariels) to the Gear selector (selector switch). This will have the same three settings as sariels, but is of course attached to the 90* limiter which would allow for fast and reliable gear changes in selector position, timed to be taking place when the red selector is in the neutral position. This is a different version of the cam shown above. 

I hope this helps. 

Edited December 31, 2016 by Myers Lego Technic

[Burko-uk]

Not just the Mustang. There's one in the Defender (which I've built). The only issue I had was that the tension of the elastic bands was critical to operation. I struggled to get that right, and Sheepo admits in the instructions and supporting notes that the shifter is not 100% reliable. I'm not sure if there has been further development in later models.

[TheMindGarage]

17 hours ago, aeh5040 said:

I would not be optimistic about a compact solution to this, unfortunately.  I think you might be better off redesigning the gearbox so that the gears come in a different order, such as:

FOO, OFO, OOF, DOO, ODO, OOD

I was thinking about that, but it would lead to having gear ratios way too far apart.

[Technic Jim]

On 12/31/2016 at 5:16 PM, aeh5040 said:

[...] One way would be a groove cam like akiyuky's controlling each driving ring, but with three positions. [...]

Now that would be clever!

[aeh5040]

On ‎1‎/‎1‎/‎2017 at 1:49 AM, TheMindGarage said:

I was thinking about that, but it would lead to having gear ratios way too far apart.

Can you explain why?  Surely the gear ratios depend on the gear combinations used, not how they are distributed between axles...

[TheMindGarage]

56 minutes ago, aeh5040 said:

Can you explain why?  Surely the gear ratios depend on the gear combinations used, not how they are distributed between axles...

The 6-speed design has gearing to connect driving rings 1, 2 and 3, then the front and rear "halves" are connected with a different ratio. I used 20:12 gearing (that's 1.67x difference) between each driving ring and 16:12 (that's 1.33x difference) between the halves. If I were to do it the other way, the difference in gearing connecting the halves must be greater than the difference between the rings squared (the difference between ring 1 and ring 3), so I'd have to use 24:8 (3x) or higher. There is no way to reduce the difference between the driving rings since they have to be 2 studs apart.