8+6R Gearbox Design Help

[Shaglodyte]

Hi, everyone

Can someone please help me design an 8+6R gearbox for a Unimog build I am busy with? I want to be as accurate as possible since this is the actual gearbox the U5023 comes with. Unfortunately, I have no clue how to design a gearbox. I thought about maybe using a 2+2R gearbox and connecting that up to a 4-speed and a 3-speed gearbox, which would give me the 8 forward speeds and 6 reverse speeds. I have looked online but haven't been able to find a gearbox similar to this yet.

Ideally, I would like it to be as compact as possible and I thought the Chiron selectors would be best suited for this. I would also like to motorize the build and make it RC, so the gearbox would have to be sequential, which goes without saying I guess since the Chiron selectors lean toward sequential operation already.

Any help would be greatly appreciated. Thank you.

[gyenesvi]

That sounds pretty ambitious, especially if you don't have experience with gearboxes. Even if it's doable, it's going to be pretty huge I guess, with a ton of friction, so motorization is pretty much out of the question. I'd say anything beyond 4 speeds does not lend itself well to motorization in an actual RC vehicle (maybe only for showcasing a gearbox itself). I'd suggest starting with something simpler, like a high / low gearbox :) Anything more is not even practical for an RC model, as you'll see even that will not be easy if you want a meaningful speed difference and practical performance in both speeds..

[Krxlion]

I am not so great with gearboxes, but If it comes to using them I always reach out to Sariel's videos. In example below he has gearbox that you can attach to another, similar one:

You can always look for other films on his YT, he could have something that you can use. :)

[Jundis]

12 hours ago, Shaglodyte said:

I thought about maybe using a 2+2R gearbox and connecting that up to a 4-speed and a 3-speed gearbox, which would give me the 8 forward speeds and 6 reverse speeds. I have looked online but haven't been able to find a gearbox similar to this yet.

It really depends what you are aiming for. A normal 4 speed gearbox is fairly easy to realize with technic. Couple that with a Hi/Lo selector and a forward/reverse and you got 8 gears forward and 8 gears backwards.

If you really want to get close to the real model, you should check the gear ratios. For the U5023 you can find this:

So you have the standard gears AND the working gears.

In my opinion: It really doesn't make any sens to include that much gears into the system. Any advantage in the gear ratios is already lost by friction.

My advise is to stick with the option I mentioned first.

[1963maniac]

There aremany great designs here that could possibly be re-engineered for your purposes: 

 

[Shaglodyte]

On 3/23/2023 at 12:09 AM, gyenesvi said:

That sounds pretty ambitious, especially if you don't have experience with gearboxes. Even if it's doable, it's going to be pretty huge I guess, with a ton of friction, so motorization is pretty much out of the question. I'd say anything beyond 4 speeds does not lend itself well to motorization in an actual RC vehicle (maybe only for showcasing a gearbox itself). I'd suggest starting with something simpler, like a high / low gearbox :) Anything more is not even practical for an RC model, as you'll see even that will not be easy if you want a meaningful speed difference and practical performance in both speeds..

Thanks for your advice, kind sir. My biggest concerns are size and friction. I'm hoping at least that, since most of the gearing will be 'down gearing', the friction won't be too much of an issue.

I do have a backup design for a 3+R I found online that I'll use just in case the 8+6R doesn't work out.

On 3/23/2023 at 12:16 AM, Krxlion said:

I am not so great with gearboxes, but If it comes to using them I always reach out to Sariel's videos. In example below he has gearbox that you can attach to another, similar one:

You can always look for other films on his YT, he could have something that you can use. :)

Thank you very much, that's a great design and quite compact too. I especially like the idea of shifting with the motor instead of building a large stepper mechanism for it.

This is a huge help, thank you again.

[gyenesvi]

8 hours ago, Shaglodyte said:

I'm hoping at least that, since most of the gearing will be 'down gearing', the friction won't be too much of an issue.

Things are not so simple in a gearbox. Remember, that as you have gears for the different ratios, when the output shaft is spinning through the selected gear, it back-spins all the other gears for other speeds. Now as it back-spins them, that creates an up-gearing in the system. For example if you have one path with 1:1 ratio, and an other with 1:3 down-gearing, when you select the 1:1 path, the other path back-spins 3x faster than your motor output.

8 hours ago, Shaglodyte said:

I do have a backup design for a 3+R I found online that I'll use just in case the 8+6R doesn't work out.

One thing you might want to consider is that if you make an RC model, you can control the motor in reverse as well, so the reverse speed does not add much playability value, only adds to the realism of the build, which I'd find more interesting for manual models.

8 hours ago, Shaglodyte said:

Thank you very much, that's a great design and quite compact too. I especially like the idea of shifting with the motor instead of building a large stepper mechanism for it.

Indeed, if you want to RC it anyway, that is the simplest way to go, because then you'd probably need an RC switch mechanism as well. I'd say such a 4 speed gearbox would be a good compromise to start with and see how it works out for your model.