Lego Cvt

[garson]

A cvt is a type of transmission that can produce an infinite amount of ratios between 2 set number such as 1 to 1 and 5 to 1 utilizing a cvt instead of those to set ratios you can have any in between such as 2 to 1 2.5 to 1 and so on I want to know if there are any types that are 1 not zblj design knock offs, 2 dont overuse differentials and 3 they have to be able to transmit real torque as in driving a moc and cant be some micro style belt design(i already tried and they rip themselves apart)

[DLuders]

317070 posted this

of "A continuous variable transmission in lego, this is an automatic transmission which uses no motor or other mechanism to change gear ratio, but changes this automatically by the gears themselves.

Forward: automatically switches gear ratio from 1:1 up to 5:1

Backward: gear ratio exactly 5:1

2 Power XL motors, one for the left side, one for the right side.

The gear ratio is changed automatically by the gears themselves by detecting the power which they exert on their surroundings, which happens separately for the left and the right side. The force at which this happens can be controlled by a lego spring.

This mechanism normally uses 2 differentials per motor, but then when the wheeles are blocked while in reverse, the motor still keeps spinning, and the maximum torque on the wheels is equal to the torque caused by friction inside the differentials.

This is no good, but by adding a third differential this problem is solved. Now in reverse the gears act just the same as a regular 5:1 gear set.

This robot can drive fairly well, however, the small gears inside the ouput differentials can't handle the torque from a power XL motor and break in 2 pieces when the robot is pushing against an object.

The clicking sound is caused by an oscillating part in the gears, which is perfectly normal ;-) it isn't a bad gear connection or something breaking down. It is caused by the robot lying upside down, otherwise gravity prevents it from oscillating."

[garson]

317070 posted this

of "A continuous variable transmission in lego, this is an automatic transmission which uses no motor or other mechanism to change gear ratio, but changes this automatically by the gears themselves.

Forward: automatically switches gear ratio from 1:1 up to 5:1

Backward: gear ratio exactly 5:1

2 Power XL motors, one for the left side, one for the right side.

The gear ratio is changed automatically by the gears themselves by detecting the power which they exert on their surroundings, which happens separately for the left and the right side. The force at which this happens can be controlled by a lego spring.

This mechanism normally uses 2 differentials per motor, but then when the wheeles are blocked while in reverse, the motor still keeps spinning, and the maximum torque on the wheels is equal to the torque caused by friction inside the differentials.

This is no good, but by adding a third differential this problem is solved. Now in reverse the gears act just the same as a regular 5:1 gear set.

This robot can drive fairly well, however, the small gears inside the ouput differentials can't handle the torque from a power XL motor and break in 2 pieces when the robot is pushing against an object.

The clicking sound is caused by an oscillating part in the gears, which is perfectly normal ;-) it isn't a bad gear connection or something breaking down. It is caused by the robot lying upside down, otherwise gravity prevents it from oscillating."

unfortunantely that uses like 5 differentials and i dont have that many 0_0

[DLuders]

unfortunantely that uses like 5 differentials and i dont have that many 0_0

Well then, get some more differentials from Bricklink!

[allanp]

To me, those diffenecial transmissions are more like crude automatic 2 speed transmissions as they can only change between two fixed ratios or worse, waste power by forcing a clutch to slip. Unfortunately your only option for a true CVT would be something like this which probably can't take much torque if built any smaller. Even one this size probably won't take much torque.

[dhc6twinotter]

I agree with allanp. The best way to build a CVT is to use two cones like shown in his illustration. You could use a wheel in the center or build a chain/belt to go around them.

As far as I know, the CVTs put in real cars use two cones with a belt or chain wrapped around them.

[garson]

http://www.google.com/imgres?imgurl=http://static.howstuffworks.com/gif/cvt-17.gif&imgrefurl=http://auto.howstuffworks.com/cvt3.htm&h=300&w=400&sz=329&tbnid=rgmT-xjF1FbwYM:&tbnh=93&tbnw=124&prev=/search%3Fq%3Dtoroidal%2Bcvt%26tbm%3Disch%26tbo%3Du&zoom=1&q=toroidal+cvt&usg=__SPso7zoyu9C8OjzwmcJzYPRTJxI=&sa=X&ei=SroXTrTqCM7egQe99pQW&ved=0CCMQ9QEwAQ

is something like this possible? it certainly seems the most able of the designs, unless someone can figure out a ratcheting cvt

[dhc6twinotter]

Well, that's pretty cool. I hadn't seen that kind of CVT before. I like it.

[garson]

http://www.youtube.com/watch?v=DbS27qDb2eE&feature=related

the first and last transmission designs are both cvts alas the first works the best but obviously is super parts intensive, the last is an intresting design but a bit impractical

[parda]

Last week I have developed a gearbox like this, with a third differential to control the 1:5 gear ratio "switcher" and a reverse blocker for the 1:1

Best see the video:

Soon new versions in my blog!

Edited July 14, 2011 by parda

[garson]

Last week I have developed a gearbox like this, with a third differential to control the 1:5 gear ratio "switcher" and a reverse blocker for the 1:1

Best see the video:

Soon new versions in my blog!

wow this is quite good, one question is it a cvt? it looks like some automatic transmissions ive seen

[Nazgarot]

There is a lot of great ideas for automatic transmissions around, both CVT and traditional stepped automatic gearboxes. Should we start a thread to collect them? A Automatic gearbox index, or even an gearbox index with all kinds of gearboxes?

@garson: The absolutely most interesting design I've seen of a CVT?. It seems to have speeds between the 5:1 and 1:1. Could you elaborate a bit?

-ED-

[parda]

Should we start a thread to collect them? A Automatic gearbox index, or even an gearbox index with all kinds of gearboxes?

One of the last entries of my blog is a little recopilation of automatic gearboxes, hope it can help a bit

Automatic gearboxes post at Technic Delicatessen

[DLuders]

[bUMP]

Nico71 made this

of a Lego Technic Continuously-Variable Transmission (CVT). He wrote that there is "More at http://www.nico71.fr . [it is] Based on modified version of Zblj's Transmission. This CVT enables a variation of the speed (and the torque) from 40rpm to 200 (1/5, 1,1) with constant speed for the motor (200rpm). This device is on the way to be included in a lego car. The two mechanical tachometers show respectively the speed of the motor and the speed of the output."

[dhc6twinotter]

Nico71 is da bomb.

[nico71]

Hello,

Thanks David for the feature !

The CVT I create is a modified version of zblj's one (slightly). But the functionning is the same of misha's one : based on friction.

A interesting way to get a CVT is to work with resistive torque but not by friction, resistive torque by gyroscopic effect, like this :

The main advantage is the loss : less than a friction. The other advantage is that you can recover the kinetic energy.

For my CVT, I will put in the first mass-produced car which had a CVT : DAF Variomatic (mine will be a 55 model, not the 33).

[matias bendtsen]

For my CVT, I will put in the first mass-produced car which had a CVT : DAF Variomatic (mine will be a 55 model, not the 33).

I know that car, it goes just as fast forward as backwards.

[nico71]

Exactly ! Some backward races have been organized in the Netherlands and they always have finished with some crashes.

Some new :

http://www.nico71.fr/continuously-variable-transmission/

Some pictures to rebuild it are included :)