Gearboxes

[aminnich]

Hey guys,

I have been toying around with a MOC for about 2 weeks now and I have the rear end completed (ik not normally the place to start)

I have been thinking about adding a gearbox for something new to my MOCs and I think this MOC would be perfect for trying it out.  

SO I have been building other builders gearboxes today and yesterday and find one common idea, lots of gears lot of friction.  

This concept is fine, but after you are putting all that stress on the motor, the highest gear ratio you get out of most of the gearboxes is 1:1.. so what is the point of having the gearbox after all?? 

For example, a transmission in a semi truck has so many gears to get the truck going... so you could say that these gearboxes are for that, getting the MOC up to the speed of the motor.  But without a proper clutch and so much friction, the MOC would not roll when the clutch is pressed in any way. 

Do you guys get what I am saying, I am trying to put my thoughts into words and sometimes that does not always work out haha.  Let me know what you think of using gearboxes in the MOC, worth it or just a hassle?

[Sariel]

That is correct, most Lego gearboxes are primarily for gearing down. Which makes perfect sense, since LEGO motors are too weak to drive most MOCs big enough to have a transmission at 1:1 ratio. Where I live, most Lego Truck Trial models use gearboxes with at least 3 speeds, for climbing obstacles, driving on level terrain and going downhill. So, to put it shortly, I think you're missing the point of having a gearbox. It's not to gear the motor up. It's to gear the motor in such a way that it's sufficiently strong to drive the vehicle in any conditions. Make it adaptable, in other words. Balance speed against torque as needed at a given moment.

Edited May 14, 2018 by Sariel

[aminnich]

Just now, Sariel said:

That is correct, most Lego gearboxes are primarily for gearing down. Which makes perfect sense, since LEGO motors are too weak to drive most MOCs big enough to have a transmission at 1:1 ratio. Where I live, most Lego Truck Trial models use gearboxes with at least 3 speeds, for climbing obstacles, driving on level terrain and going downhill. So, to put it shortly, I think you're missing the point of having a gearbox. It's not to gear the motor up. It's to gear the motor in such a way that it's sufficiently strong to drive the vehicle in any conditions. Make it adaptable, in other words. Balance speed against torque as needed at a given moment.

First thanks for the comment, you were one of the builders that I really wanted to hear from.  

So what you are saying is that gearboxes are not meant to be used like a typical transmission in a car?  Thats a bummer.  I guess to use my semi truck example with your explanation, I would use a low gear for a heavy load, the middle gear for an empty trailer/light load and the highest gear, most likely 1:1 for just driving the truck around.  That makes sense.  

Maybe it is time to make something that works like a transmission... 

[Bublehead]

13 minutes ago, aminnich said:

Maybe it is time to make something that works like a transmission... 

You mean like an automatic transmission?

[Imanol BB]

Hi, i share the thought that using a gearbox in a Lego model should be only for gearing down, because of all the friction the parts generate, it wouldn't be worth using a gearbox to gear-up, it would make more sense to use a motor with a much higher speed and then gear it down to the needed range; of course it would be great to have a model with a fully functional gearbox for gearing up and down like in a real car, but because we cant use  or we don't have most of the things that a normal gearbox uses (efficient lubricants, parts which reduce a lot of friction, especially designed gears, etc), and also because of the small scale, we can only relay in gearing-down gearboxes, however, if you think about it, it isn't so bad, most of the electric vehicles use gears to reduce the speed and maximize torque, and because electric motors have a pretty much wider working range than a normal internal combustion engine, this allows a completely shift-less transmission, full torque availability at all times and much more efficiency, due to the reduction of the moving parts and friction-generating components, so if you apply this to a Lego model, it's no so bad.

[aminnich]

9 minutes ago, Bublehead said:

You mean like an automatic transmission?

pretty much 

4 minutes ago, Imanol BB said:

Hi, i share the thought that using a gearbox in a Lego model should be only for gearing down, because of all the friction the parts generate, it wouldn't be worth using a gearbox to gear-up, it would make more sense to use a motor with a much higher speed and then gear it down to the needed range; of course it would be great to have a model with a fully functional gearbox for gearing up and down like in a real car, but because we cant use  or we don't have most of the things that a normal gearbox uses (efficient lubricants, parts which reduce a lot of friction, especially designed gears, etc), and also because of the small scale, we can only relay in gearing-down gearboxes, however, if you think about it, it isn't so bad, most of the electric vehicles use gears to reduce the speed and maximize torque, and because electric motors have a pretty much wider working range than a normal internal combustion engine, this allows a completely shift-less transmission, full torque availability at all times and much more efficiency, due to the reduction of the moving parts and friction-generating components, so if you apply this to a Lego model, it's no so bad.

this makes a lot of sense, but I still wish there was a way to make a proper transmission.  Its LEGO... there has to be a way 

[Saberwing40k]

Most car and truck gearboxes don't gear up much at all. You have maybe one or two overdrive gears, but for the most part, gearboxes are for reduction only. Even in actual cars, overdrive is for highway driving, to keep the engine rpms low. However, with electric motors, rotation speed is not exactly proportional to power used, so you can have the motor be efficient at high speed.

Edited May 15, 2018 by Saberwing40k

[Aventador2004]

58 minutes ago, Saberwing40k said:

Most car and truck gearboxes don't gear up much at all. You have maybe one or two overdrive gears, but for the most part, gearboxes are for reduction only. Even in actual cars, overdrive is for highway driving, to keep the engine rpms low. However, with electric motors, rotation speed is not exactly proportional to speed, so you can have the motor be efficient at high speed.

Yes, if you research, you will find most cars never get 1:1. They are around 1:1.9 or so. They produce so much power, it is unessesary. If you need a gearbox, I recommend a 2 speed.

Edited May 15, 2018 by Aventador2004

[Frostbricks]

You don't want to 'gear up', the trade off is always between speed and torque (pulling power) And, if you've ever plugged in a motor for direct drive, you'll know you never get the full speed under load anyway, so how to get the best out of the motors?

Well, the different size LEGO motors have different speeds, and, importantly, different torque. An M motor is around 320rpm, and the XL is around 240rpm (from memory) but the XL does have significantly more torque. That's the first thing. Now, you can pair motors (or more) to add power, and because of how they work, give each motor it's own battery. (sharing the power between motors does roughly half their power, conversely replacing batteries inside the boxs with aluminium is a easy way to slow them down) And, speaking of pairing motors, either make sure they both run the same speed (you will see variance between even the same motor type) and there's always the option of using differentials.

So that'll give you extra power.

Then, second, is reducing as much load as you can along the way. avoid using technic pins to connect the gears, even the 'non-friction' ones give more friction that desirable, and it quickly builds up (as you've discovered) Use technic beams wherever possible, and support them on both sides so they turn smoother. And importantly, when it comes to transfering that power to drive trains, take the pressure of them by using the 'Universal Joint 3L' to connect the technic beams, and for the wheel axles, support them with 'Steering Portal Axle' or similar.

That'll let you gear down without problem, because you don't always want top speed.

And yeah, there really is an art to getting them to run smooth, and every little step along the way should be considered, but hopefully that helps a bit.

[aminnich]

Thanks for the response, lots of good information.  

I have combined 2 different type of motors together using a differential before to get a "combination" of the motor for the output shaft.  It worked pretty well.  But that is a whole different idea from what I was originally talking about.  

We all want speed out of our MOCs, most of the time.  Having a MOC with crazy torque that can pull crazy loads is awesome too.  

I have a crazy idea for an automatic transmission, I will try and build it tomorrow.  The concept is crazy, but it just might work.  

If I do not have something posted tomorrow, I either am still working it out or it failed 

[bonox]

oh generous TLG overlords. Please send us proper involute gear profiles and roller bearings such that we may appease the evils of those who oppose the practical implementation of the edict "as it is in reality"

[Pas_de_nice]

Electric cars don't need/have gearboxes because unlike internal combustion engines, electric motors have their maximum torque at low rpm. Check out Tesla cars for example: no gearbox. As @Sariel pointed out, in the case of Lego cars/trucks, a gearbox is only useful to adapt to the load on the motor depending of the driving conditions (slope, trailer, ...). Basically, an electric motor gives its maximum power at moderate rotational speed, whereas a combustion engine has it's peak power at high rpm, around 4000-6000. Basically, cars have gearboxes only to gear down the engine to get moving, because they have low torque at low speed, but once they gained enough speed, the gearing can be increased. Here are typical torque/power for both electric and combustion engine.

Torque/power for electric motor:

Torque/power for combustion engine:

 

[aminnich]

I think this conversation is going off in a tangent. 

I am not necessarily talking about the torque speed ratio, in mainly referring to the amount of friction in a gearbox just to ultimately get to a 1:1 ratio. This is great, but the gearbox does not work like n automatic transmission where the car is getting to speed where the higher gear ratio (1:1 in this case) can be achieved. 

What Sariel said about the different gear ratios in the gearbox are for different driving applications makes sense. 

[doggo]

Recently I've made a small scale MOC with a simple 2 speed gearbox, first gear actually has a higher output speed than second, despite being geared down, whereas second gear is 1:1 gear ratio but has much less speed due to motor stress.

[aminnich]

Just as a quick update:

The concept of my take on a completely RC 6 speed automatic gearbox works, 2 problems.  I do not have enough pf switches and it will be pretty big after it gets built.  

Technically it is a however many speeds you want gearbox, just gear down the motor, and you have another 2-speed selections. 

I am not sure that I will buy more switches for this project, as I never use them anyway.. but maybe I will bite the bullet for $4 a piece.  Now that I think about it, that not too bad for coming up with an automatic gearbox concept :)