CVT Tranny?

[BrianG]

I did some googling, but couldn't find anything about a miniature CVT transmission design. Sounds like a good idea to take advantage of a BL motor's torque, while eliminating that shifting hiccup (and possible loss of control), allow us to use smaller motors, and be able to use the motor for brake and reverse...

IIRC, most CVD designs in 1:1 cars are kinda limited in the amount of torque they can handle. Just wondering if it would be a good idea for R/C use.

[Arct1k]

I think you mean Continuously variable transmission - I'm not sure it would work as the motor RPM is kept pretty constant over a broad range of vehicle speed. Speed is determined by moving the pulleys which would be hard...

In a brushless motor RPMs are driven by voltage...

http://en.wikipedia.org/wiki/Continu...e_transmission

[BrianG]

Yup, that's what I mean.

The motor would be driven to it's sweet rpm spot where it's at its max efficiency. The CVT would just work to keep the motor rpm at that spot (other than initial take-off from a dead stop).

[Arct1k]

I didn't think that constant RPM is a motors sweet spot IIRC motors didn't like being run unloaded...

[BrianG]

No, not unloaded. But each motor does have an rpm where it is the most efficient (see Griffin's motorcalc proggy). The motor would still be loaded. The vehicle would just go faster and faster up to the CVT limit. So, the motor load would increase slowly, but rpms would be kept fairly constant.

Would eliminate setup problems where people gear too high to attain a high speed, while allowing enough rpms at low speed for proper ESC commutation.

[Arct1k]

You'd have to have a funky mixing radio to increase revs over first 30% say of throttle input and then hold max and then over say 10-100% of throttle movement move the pulleys apart. You also need to shrink the cones to 1/8 scale and have a servo that will take the force of moving the pulleys...

[TexasSP]

So does this work some what like a torque converter?

[BrianG]

I guess I don't follow. The way I see it, the CVT would start out in a "low gear". Once the motor hits the preset rpm (via an rpm sensor), the CVD starts to increase the ratio slowly.

[E-Revonut]

Think snowmobile clutch! That is a cv setup, it uses two seperate clutches connected by a belt. There are different helix, spring, and weight combos for different snowmobiles depending on the weight of the sled and the power being produced as well as what your riding style is and how hard you want it to engage as well as what RPM for it to start engaging. This is pretty much the only way a snowmobile can have a transmission, if you had to let off and shift and hammer on it again it would most likely get you stuck!

There could be potential in designing a system like this for RC but I think it would be better suited to a nitro rather than a BL truck. BL has no problem supplying torque on take off and that is pretty much the whole point of any transmission. The weight that you would save by being able to run a smaller motor would be offset by the weight of the system. Not to mention another tuning aspect, and if you think tuning a nitro motor is hard just try getting one of these set up perfectly! There are all kinds of books on tuning a snowmobile clutch that go way further in d!epth that tuning a nitro motor(if it's hot richen it, if its cold or lacking power lean it out) These clutch setups would be a major PITA!

[lincpimp]

I think that I will try to design and proto this, but will include an electric cooling fan in the core design, so to prevent Brian from using it.

I am surised that you are posting this here Brian, when you have access to the super secret area 51 section of the forum. Surely there is more knowledge in one of the allowed users there than all of us cretins combined?

[shizzon]

check out the NuVinci continuously Variable planetary transmission, kinda the same idea but a little more high tek. This one is made for a bike, but i would assume that it could be made smaller for rc-applications. would be expensive though.

http://www.youtube.com/watch?v=kVPjhmTThPo

[What's_nitro?]

I've thought about designing one of these for a while. It is "CVT", BTW. The problem would still be how to make it handle all the power since CVTs have quite a few moving parts other that the two main pulleys/cogs.

[What's_nitro?]

Originally Posted by shizzon

check out the NuVinci continuously Variable planetary transmission, kinda the same idea but a little more high tek. This one is made for a bike, but i would assume that it could be made smaller for rc-applications. would be expensive though.

http://www.youtube.com/watch?v=kVPjhmTThPo

Seen that. Love it. Wish I had thought of it...

[plettenbergs]

wow ..that is sweet!...cvt?

[shizzon]

the concept is pretty cool actually. orrigionally thought up by davinci himself, so you know its legit! ;)