Gearboxes and clutch gears and bracing (oh my!)

[Captainowie]

I just had a "Eureka" moment.

I have recently been spending a fair bit of time re-designing the power transmissions for some of my GBC modules. I made sure that everything was properly braced, all the axles were supported in at least two places, etc. I also took the opportunity to include one of the torque-limiting clutch gears, in case something goes wrong and the mechanism binds.

My realisation was that if I'm going to put in the clutch gear, I don't need to go overboard re-inforcing the structure - I only need it to be strong enough to withstand the amount of torque that the clutch gear can provide, rather than being able to withstand the torque of the driving motor. The clutch gear will slip before the bricks come apart.

I guess my point is that bracing and structural soundness is all well and good, but it is certainly possible to make it far sturdier than you need.

Owen.

[Alasdair Ryan]

It's fine saying something might work but until you post a picture of it in real life then we 'will not believe you'.

Even with a clutch gear you will still require bracing just not as complex.

[Captainowie]

Pictures or it didn't happen

(I may have paraphrased a bit there!)

Ok, so here's the general idea. (sorry about the crappy picture)

In the above pics, the connector block hitting the pin represents a large load on a drivetrain.

In the image on the left, if you turn the liftarm, the load is engaged, and because there's no bracing, the bricks separate.

In the image on the right, however, if you turn the liftarm, the load is engaged, and the clutch begins to slip. The gripping power of the studs is sufficient, and no further bracing is needed - any bracing you put there is just going to add weight and complexity to your model without serving any function.

I guess the lesson I've learned is to design your supporting structure for the load it has to take. If it's going to have to handle a lot of torque, then you need to make sure it's properly braced. If it's only going to have a light load, then just the gripping power of the bricks might be sufficient (there's bound to be some equivalent for studless building, but it escapes me at the moment).

Actually, when I put it like that, it seems kind of obvious really :-)

Owen.

[Alasdair Ryan]

Well I only build studless...

I would still add a beam linking both bricks together (in your photo).

[gti180]

Thats something I learnt a long time ago the picture below shows the drive train for a mobile crane i was building. at the time Lego parts didn't include shorter uv joints and stronger diffs. i struggled with this problem for ages then I changed the gears to suit the clutch gear and eureka!!

something else that's worth thinking about is sharing the load between more than one motor and reducing the distance between the motor and its application - the shorter the distance the less resistance the motor will have to compensate for