Robustness in gearboxes

[HectorMB]

Hi everyone,

I'm working in a MOC in which I would like to put a gearbox. Now, my option is Sariel's 4 sequential gearbox. Nerveless, because it's handling some torque (4 xl PU motors), some gears are slipering. So, I'm wondering about how can I increase the robustness of the gearbox or, if not possible, which are the most robust gear combinations.

 

Many thanks for the advice! 

[marcus2388]

If you are looking for a solution to handle the “too much torque” situation… there might be three ways… I guess.

1. You could simply speed up the gearbox… and reduce the speed after the gearbox in the same amount. This should reduce the torque stressing the gearbox internals… but it would also increase friction (a lot!). So, the result would be a mixture of loosing power and still stressing the material. This could be optimized with a lubricant for the gears.

2. You could multiply gears… so instead of using two gears, use 4 and so on. This might not necessarily help with slipping clutch problems. You could multiply them as well.. meaning: if you use two synchronized gearboxes, you’d half the torque for each one of them. Like… build two of Sariels gearboxes and use them simultaneously in the same drivetrain. Obviously, this consumes a lot of space… and adds more friction.

3. You could try to find ways of building a sturdier structure through making the whole gearbox bigger… with adding in crossbeams, bars and so on internally… maybe even adding in gears (and gear switchers) which only do one thing: support the existing gears, by surrounding them. This solution would put a lot more stress on the gears. So… while having a solution for your slipping gears you might end up breaking them.

Since you are utilizing 4 XL motors in your MOC… I am guessing that movement is a high priority. I would consider going for a radical solution: not having a gearbox at all. I know it is somewhat of a sacrilege in this forum… but honestly:

- From an engineering point of view – it does not make sense, to force the power of 4 electric motors through one mechanical bottleneck. This is neither elegant nor efficient.

- From a scale-modelling point of view: having a gearbox which takes up to 30% of your total space is super unrealistic.

I hope this helps… or at least draws the attention of gearbox enthusiasts towards your thread :D

*runs away

[HectorMB]

Many thanks, the advice is indeed quite helpful! 

I already speeded up the gearbox, but with the same result. I am more thinking about trying to secure the gears by using companion gears. 

At the end, if I don't have any solution, I may end up removing the gearbox, yes. But the idea of the model was to put a bunch of functions together: a robust axle, a gearbox, independent suspension, Ackerman geometry, and high potency... But let's see what I can do. At the end, is my first MOC! ;)

[Gray Gear]

Honestly I doubt that shooting 4 motors through a gearbox is a good idea. You already encountered the torque problem, and if your gear up the entire system you'll see pieces wearing out quite fast due to increased heat development.

[amorti]

The sturdiest 4 speed gearbox out there is in brunojj1's red supercar. You can get the instructions free in the CaDA Facebook group.

It's basically a pair of identical/mirrored gearboxes, one each for the two CaDA Pro L Motors, which are easily stronger than Lego XL Motors. Even so, that starts to get unhappy and make plastic dust when you put 4* CaDA Pro Motors in it, although it may have been the differential clicking.

[HectorMB]

Thanks again for the comments and suggestions. Indeed, besides the possible functionality (which I think is very limited), it is just kind of a proof-of-concept. So, I will try the gearbox suggested (brunojj1's) and see how it performs :)

 

 

[MinusAndy]

Why not do something clever with the outputs of four motors using differentials instead of a gearbox that will probably soak up more power than it delivers?

 

[2GodBDGlory]

As others have suggested, I would say that the key is to reduce torque (increase speed) at the input as much as possible, without slowing the drive motors down too much from the stress. Alternativly, you could try a sliding gear based design, which could be very durable, but introduces many design headaches.