LEGO CVT (Continuously Variable Transmission)

Greetings with my next post: a very special transmission. This is a CVT (continuously variable transmission), and it can switch smoothly to any gear ratio possible. So essentially, it has infinite gear ratios. This particular transmission is actually an IVT (infinitely variable transmission), which means that the gear ratio range is from 1:- infinity to 1: infinity. I know that many builders have made CVTs with two cones and a rubber band, but they are no good because they easily slip. Other CVTs and IVTs use ridiculous numbers of moving parts, resulting in a huge, impractical design with tons of friction. But mine only has 15 gears and 2 differentials, and that includes the control mechanism and everything from the motor to the wheels.

This transmission splits the motor speed into two parts with a differential. One part is geared up and the other is geared down before a second differential combines them again. The final gear ratio depends on the split in the first differential. The control motor sets the split and therefore the gear ratio. However, it is possible for the split to be beyond the normal, for example -50% on one side and 150% on the other. This is why this CVT can use any possible gear ratio – not just any ratio within a certain range. The control motor can be used to set either the lower or higher ratio split, but since the motor will add a little extra power, I chose the higher split to give the transmission a boost in high gears.

Feel free to use it (giving credit) in a vehicle or other application. For a better explanation, see my Youtube video.

R3CORD BR3AK3R

Greetings with my next vehicle: a record breaker, in more ways than one! As a challenge, I have decided to create the narrowest possible car with supercar specs. I used 68.8×36 wheels, which are commonly used on large LEGO cars. I have incorporated a differential, full independent suspension, drive, steering and a 2-speed transmission, yet the car is just 14 studs wide, 9 studs of which is wheel. This is why it might be an unofficial record-breaker – I highly doubt anyone can improve on the width while using the same wheels and the same specs.

I found that the trick with the suspensions was that the wheels are partially hollow, so some of the suspension could fit inside the wheel, vastly reducing the width. Driven independent suspensions are often very wide, because the conventional double-wishbone type needs four universal joints, which add a lot of width. So I invented a new suspension type, similar to the one used on front of my CUTLASS model (sorry – built before the blog, see at http://www.us.lego.com/en-gb/mindstorms/community/robot?projectid=2d839ede-fc8a-410e-8ab7-1501be06c6a2). It works by mounting each wheel on a lever, which turns to allow the wheel to move up or down. For a driven suspension, the lever has gears inside, like a portal axle gear hub. The front suspension is a normal double-wishbone type, but made as narrow as possible.

As for the transmission, it is loosely based on Sariel’s 2-speed ratchet transmission. It shifts by changing the direction of the motor. The main downside to this transmission is that the vehicle cannot reverse. However, it doesn’t need an extra motor to shift.

I am planning an incredible transmission to show you, so keep your eyes peeled! Hopefully ready in a week, two tops!

To read more, go to:

http://www.us.lego.com/en-gb/mindstorms/community/robot?projectid=bee0e29a-00c3-440c-8f5e-a99b0283e4cf