CVT (constant variable transmission) in R/C?

[poup00]

Hi R/C enthousiast,

I work in a company that make CVT for a great variaty of vehicules types.

I was asked to look if people who are racing R/C car and trucks would like to have a CVT inside there machines. Our company would be interested to build them if there is an interest. I looked on the web and didn't found any company that made CVT for R/C vehicules. So I decided to ask you what you think about it but first, let me explain what is a CVT.

Our CVT is normaly made of 2 pulleys and a rubber belt. Both pulleys can change diameter to vary from a 4:1 ratio to a 0.75:1 ratio. The change in ratio is driven by the engine RPM. There is normaly a gearbox after the CVT.

The good side of a CVT is very good acceleration. At full throttle, the engine raise to peak HP RPM and stay there. The CVT will change ratio to maintain peak RPM shifting all the way to top speed. All showmobile and now most of the ATV use CVT. With a CVT you don't need a centrifugal cluth to engage, the CVT do it also. The CVT is fully adjustable. so you can set the RPM you want it to shift, among other things.

The down side is that you loose about 10 to 15% of power out of the CVT.

So, what do you guys think about it?

I have not mentioned the name of the company I work with as my intention is not to make publicity.

Pierre Poulin

P.S. Please excuse my poor english. It is not my native language.

[pauster]

Bonjour Pierre,

I thing this is a splendid idea with great potential ! We need innovation !
It would probably mostly (only ?) apply to nitro/gas engines because
on the electric sides brushless motors already have a nice flat
torque graph and excellent efficieny.

I believe one challenge will be how to set the CVT's "gear".

Cars use fancy electronics that detect the driver's intention
and gear accordingly. How would a R/C car do this ?

A for the transmission loss - I think a regular gear pair
already looses 5-10% power, and you could replace several gear
pairs in a 2/3 speed transmission with a CVT.

Patrick

P.S. I think you might want to consider a different userid - the one you chose resembles an English word you don't want to be associated with

[poup00]

Hi Patrick,

Yes, the CVT would be only interesting on nitro R/C cars/trucks.

As for your question about "shifting the gear" Modern cars have an electric motors that do the shifting. This method is very effective but cost many $$$. On smaller vehicules like ATVs there is 2 parameters that do the shifting: engine RPM and torque. The driver pulley (the one on the engine) is sensitive to the RPM by using calibrated weight and transforming centrifugal force into lateral force. And it will always try to shift the driver pulley into higher ratio. The driven pulley (the one on the gearbox) react to the amount of torque it receive from the belt. So when you release the throttle, the driven pulley will up shift into higher gear (or if you want, it will let the driver pulley shift) into "higher" gear ratio. As soon as you increase throttle (torque) the driven pulley will open and lower the ratio. The engine RPM raise and try to reach peak HP RPM. The engine then loose torque and upshift. All this mecanics is done really quick! So there is always a balance between the 2 pulleys and the engine RPM is always between peak torque and peak HP for maximum acceleration. When we do a calibration here we can easyly set a given RPM *like 8000 RPM for a snowmobile) and the engine will stay at that RPM during all the acceleration whle the pulleys will do the work. It is very effective!

Pierre

P.S. Thanks for the userid warning. It appear I can't change it :( Oh well, I'll survived it I guess...

[pauster]

Pierre

this sounds pretty cool ! The larger scale (1/8 - 1/4 scale) might
be your best target market for a technology that has been proven
in real full scale vehicles ...

If a servo could be used to "tune" the ratio on the fly, for example
to get more torque or more rpm - the driver could adjust the
transmission while driving using a channel on the transmitter.

Good luck !

Patrick

[awnelson]

Pierre, could you tell me what kind of weight would the transmission be and what the rotating intertia amount is of the CVT? One other thing is that the transmission would need covers so that it doesn't get dirt or water into it and cause slipping and premature wear. One of the biggest drawbacks to any transmission is the amount of rotating mass that must be moved even before the tires start to turn. That is the main reason for using small, lightweight plastic gears. Also, if this is a true CVT then are the ramps adjustable either by moving them or being able to change the weight on the cones? I'm still interested, tell me more.

[nitrohead5300]

Whats up , Pierre?? I am glad to hear someone is thinking about re-introducing the CVT to rc car again. The first rc car manufactor that I first hear of doing this was a after market parts manufactor name John Thorp. Mr. Thorp was around in the early days of rc in the 70's. I believe that his CVT car placed 2nd or 3rd in the nationals one year during the 70's. A couple of guys in our local rc club during the 70's had Thorp cars and they were blazing fast if you got the tranny adjusted just right. If they lost any power I could not detect where. The acceleration of these cars was very linear !! Faster and faster you did'nt hear the tranny shift just the cars speed would continue to increase. The adjustments were made on the pulley on the motor that was attached to the flywheel by 2 springs the tighter the springs the more rpms it would take for the pulley to move and change diameter = gear ratio change. The pulley was cone shaped on one side and was larger towards it backside when it would come out it would push it self into the belt changing the gear ratio simple but effective below is a picture of a Thorp car.. I hope you guys come out with one good luck.

[poup00]

That is a great idea Patrick, using a third channel for clutch tuning...

Awnelson, there is at least 4 parts that can be changed to properly tune a CVT: the driver clutch weight (to set shift RPM), the driver clutch spring (to set RPM engagement), the driven clutch spring (to set backshift speed) and the driven clutch cam (to set the pressure on the belt to prevent slippage). The ramp are normaly pre-set and molded directly into the flange itself. The ramp are determined by the engine power curve so it normaly don't need to be adjusted and don't have that much of an impact once properly calculated.

Yes, we try to maintain rotating weight as low as possible. I can't tell you the amount of weight that would be needed as we are just looking if there is an interest in that kind of R/C product. But to give you an idea, on a 600cc, 8,000RPM, 100HP snowmobile we use six 18grams weights. The faster the engine turn, less weight it need. I belive that nitro engine in R/C goes into the 10,000 RPM? Am I right?

You are also right about the dust cover. It is a standard use on ATV and UTV. We built also cooling fins and air duct when needed.

Pierre

[poup00]

Wow Nitrohead5300!!!

That is exactly what I was looking for!!! Nice picture. Thank you very much! If you have a link or others, please let me know!

Yes, CVT are very effective. And I think that it could be done in a scale down version.

Thanks again!

Pierre

[nitrohead5300]

.21 size motor capable of reving up to 40,000 rpms without load under load appox 35,000 - 38,000. These are high end motors. Thorp cars are collectors idems now if you check the classifieds or E-bay every once in a while you find one for sale. Here is another picture. The rectangle shaped box you see on the rear axle is a early rear gear diff design you could also adjust you castor by rotating the front axle.

[NotWalkinBlind]

poup00, maybe you could contact John Thorp through MIP... they collaborate with him on their hex driver wrenches....

MIP Thorp Hex Driver Wrenches

MIP is bringing back the legend of the world famous Thorp wrenches. As the exclusive manufacturer, MIP has worked very closely with John Thorp to produce the best wrenches the R/C industry has ever seen.
http://www.rchobbies.org/car_mip-accessories.htm

MIP's website: http://www.miponline.com/mip_race_table.html

Mailing address and phone number:
Moore's Ideal Products
830 W. Golden Grove Way
Covina, CA 91722

626-339-9008

[pleaseletmeon34]

Kyosho offered something at one time, but I don't think it functioned the same as what your describing. Would be interesting to see.

http://forums.radiocontrolzone.com/showthread.php?t=227907

[nitrohead5300]

Yeah Thorp's was belt drive and had a low part count.

[RrR]

I don't like CVT type trannys on ATVs but they might be cool on an RC(?)

[nitrohead5300]

The Thorp car I had back in the 70's was very fast after you got the tranny adjusted just right which was alot of trail and error. But once you got it right it was a missle. :D

[NotWalkinBlind]

NH5300, was there a ball diff in that setup?

**** Nevermind... I just saw what you said about the gear diff in that box.

When did ball diffs begin to appear, and who pioneered them?

[Smib]

While I only run electric and therefore would probably never use one of these, I think it would be very cool if they were introduced to the rc world, well, re-introduced.

[nitrohead5300]

Not Walking Blind, I think associated introduced ball diffs in the late 70's

[ElectricThunder]

This is a cool idea. Actually, I think there may be some merit to CVTs in relation to electric motors. If you can keep the electric motor RPM where's it's most efficient....that'd be great!

[rccardude04]

I think it would be very cool to see a CVT in the world of R/C but only if it is EXTREMELY reliable.
I'll be a test dummy :p
-Eric

[poup00]

Thank you very much for all the input guys. It is very helpfull.

Now, the question that kill...

How much would you pay for one? For a complete transmission that would give you a ratio rate going from 4:1 to 1:1.

Pierre

[pauster]

If I was running a 1/8 scale car with a Nitro Engine (which I am not) I'd be willing to pay about $100 - $200 for a high quality transmission.

You might want to consider a hopped-up version with more metal parts (titanium pulleys ? may some carbon ?). The bling factor is worth $$$.

[nitrohead5300]

IF it really proved to be compeitive and gives a racer the edge about $200.00 But you better check with the ruling bodies to make sure that this type of tranny would be considered legal and allowed in races. And if you produced it good complete detailed instructions would be needed on how to properly set it up. When my Throp car was not setup right and it shifted too soon because my spring tension was too loose it would bog down the engine you could see the car loose speed and hear the motor labor. So really good setup instructions would be a must.

[rccardude04]

I think bigger vehicles should expect a higher price tag - like the owners of 1/5 scale cars that already cost them upwards of 5,000 bucks would be willing to pay more than billy bob joe who just bought his t-maxx and wants it to go faster.
I find it very difficult to answer the question of "What would you pay?" because it depends ENTIRELY on the quality of the product and its actual functionality.
For example, the superchargers. Is it 200 dollars worth of bling bling? On a show truck, hell yeah! On anything I own/race/fly, there's not a chance in heck. I think if you avoid the bling bling market, as well as the hardcore racing segment and stay within the MUCH larger range of sport bashers and weekend racers, you'll have a lot more success.
-Eric

[ducati777]

That thorp car is perfect. I've had that design in my head for a while. Anyone who's tuned their clutch for a higher engagement rpm knows how much power you can gain here. Our motors turn 30,000 rpm, but have a very peaky powerband, a CVT would change everything.

Monster trucks would be an excellent market. Its a huge market, and those trucks need grunt, meaning a low gear to get those big wheels turning, but then top speed is a big bragging right too, that why you see so many multi-gear trannies in that crowd. Plus with their large chasis you'll have the much needed room to fit a pulley/belt setup.

I agree with 200.00 for a good price. While being adjustable by a servo is a neat idea, don't forget KISS! Fewer parts, no additional channel required, just give me a preload set screw to adjust the motor rpm up and down.

[rccardude04]

With the CVT, you could actually get rid of the giant transmission that currently resides in the likes of t-maxxes, revos, LSTs, MGTs, and savages and just replace the whole entire thing with one of the CVT setups. I think that would indeed be an awesome starting place.
Good call, ducati
-Eric

[ducati777]

One more quick point, 1:4 to 1:1 is a HUGE range. You could cut that in half and still have an excellent product. Most 2 speeds only have a 20-25% difference between the gears. This would give crazy launches, and the car would continue to accelerate until you ran out of room, not gearing.

[awnelson]

It will replace the normal reduction gears. The only car that you can calculate the 20-25% reduction on is direct drive vehicles. BTW, normal gearing design recommends only reducing by 4:1 each gear set. If the output of this system was set up correctly, it would be great on crawlers as well as 1/8th on and off road cars.

[NotWalkinBlind]

ducati, I know you ride bikes, do you remember the Rokon automatics with the CVT?

[poup00]

The beauty of a CVT system is that on a full acceleration, you want the engine to reach it's peak HP RPM as quickly as possible and then the CVT do all the work all the way to top speed. That is why you want as much ratio range as possible. Normaly about 5.

I also think it would be great in R/C cars and trucks.

Thanks for all the inputs! I'll keep you updated on the projects.

Pierre

[ducati777]

ducati, I know you ride bikes, do you remember the Rokon automatics with the CVT?

Not familiar with those. But I've seen and used CVT's on scooters, snowmobiles, and the ford hybrid escape. I'm a huge fan of the technology and hope these guys are serious. Just like the car pictured, only could just make 1 adjusting pulley for simplicity, they don't both have to adjust.

It would be like your car launching with a 12 tooth pinion, and as it accelerated the pinion magically grew to 24 teeth. These guys want to do a factor of 4, so that 12 tooth could grow to 48 teeth, but I think R&D will show that big of a range isn't needed.

[Speedtester]

For all those who want to learn more about the CVT system, go here.

http://auto.howstuffworks.com/cvt.htm

[awnelson]

ducati, how much reduction is in your car currently? Or bike for that matter. From the input shaft to the axle, how many times is it reduced?

Also, the one pulley thing; are you going to make the motor or the axle move when the pulley changes diameter? Or are you just going to have it not engage at idle to about half throttle?

[guver]

http://forums.radiocontrolzone.com/showthread.php?t=219998&highlight=variable

I'm definately on board. lol.

[ducati777]

I used to know all the gear ratios but to make it simple, first gear is good for 70 mph, which is as low as it needs to be since you can loft a wheelie just by using full throttle. Makes me giggle every time. Top speed is 150, and I think top gear is theoretically good for 160, so you're looking at about a ...... 2:1 ratio between low and high gear, just like I was saying earlier.

I think the overall reduction in first is about 12:1, meaning top gear is reduced something like 6:1. I could look up the exacts but this is close nuff.

And neither the motor or axle moves, the belt has a tensioner on it. Go look at a ten speed bike and see how it keeps the chain tensioned even when shifting gears. Same sort of deal, different ratios but neither the pedals or axel move in relation to each other.

Now on snowmobiles and golf carts the belt goes slack at idle, and as the motor gains rpm, the pinion grows and takes up the slack, engaging the belt. I doubt they would use that here, when they could just mount the bell on a normal clutch. It would save a lot of wear on the belts to do it that way too.

I wonder if these guys want to hire me yet...

[pleaseletmeon34]

Now on snowmobiles and golf carts the belt goes slack at idle, and as the motor gains rpm, the pinion grows and takes up the slack, engaging the belt. I doubt they would use that here, when they could just mount the bell on a normal clutch. It would save a lot of wear on the belts to do it that way too.


That looks like what is happening here. But only the drive pulley is getting larger (so it needs the tensioner). Most of the torque converters (mini bike, go-carts, golf carts, Malibu Grand Prix cars), the driven pulley expands and gets smaller at the same time the drive pulley compresses and gets larger. So it doesn't need a tensioner.

Most of the 1/1 autos have a 2-3:1 reduction for first gear. Top gear being 1:1 (without OD)

[nitrohead5300]

http://www.youtube.com/watch?v=x3UpBKXMRto check out this link about CVT Trannies being banned from F-1 unfair advantage.

[skylineTT]

it would be a big thing in the truggy crowd i believe. there is a lot of room on the flat chassis to run things like that.

[GearheadXNT2]

this would be cool for off-road racing. especialy if these things came in close ratio...
and great for all those bl and lipo guys who want the most vroom out of their setup

[guver]

The beauty of it is it is variable ratio so that is as "close ratio" as you can get. Just have to worry about the bottom and top ends. If the starting ratio is low enough and the top ratio is tall enough then it is real nice to build a very pipey high rpm engine and not worry at all about bogging, low-end power, power range, ect. Just worry about building MAX power engines .

[poup00]

Update!

Well, not much new but still wanna give you guys some news.

I am currently talking with the marketing director and the R&D director to see if our company want to go into the R/C market. Since I'm a mechanical designer, not a vendor and/or marketing specialist, I have to wait to see what will be there decision about the project.

Meanwhile, I have started to develop some basic idea based on the input I got here from you and the knowledge I use in my day to day work. I have started to design a simple yet effective clutch system that would go into an R/C vehicule.

I'll keep you informed on the development! And thanks again for the help you gave me :)

Pierre

[nitrohead5300]

PoupOO The Thorp car used only one variable pulley one on the motor. Would your system use 2? One on the motor one on the axle?

[poup00]

Yes, it would use 2 "activated" pulleys. You double the ratio range you get and you can control the slipage way better. You also got a very nice backshift (moving back to mini ratio) when you let go of the throttle. And on idle, you have no drag compared to the tentioner that always pull on the belt.

Pierre

[nitrohead5300]

Man that sounds good even better than Thorps original.

[poup00]

Hi again,

Does anybody know of a good article that talk about R/C market. Numbers of vehicules sold per years... That kind of stuff?

Also, what vehicule should we concentrate first? I thought about the Traxxas T-maxx. It looks like a popular model. What do you guys think?

[nitrohead5300]

That or a Savage

[poup00]

Savage is made by HPI right?

[nitrohead5300]

That is correct. Hey PoupOO check out my post have you hear of this engineer??

[poup00]

What post? Where?

[poup00]

Nope, I don't know the guy. But he is much more brave (fool) then me!!!

:)

[ajlovering12345]

Hi

poup00. I sent you an email regarding this. I need a CVT for my speed car. At the moment kits only have 2 speeds and trying to get an IC car to do 150mph with 2 speed is not an option, it either burns the clutch out or stalls when changing into 2nd.

I need the gear ratio to be able to drive the car to 40mph at 33,000 rpm then adjust the gear ratio to go from 40mph to 150mph. Is that possible? I calculate if your using a 22/45 gear ratio and the rear tyres are 65mm you can use a 10mm x 30mm pulley system and that would give you around 40mph then if the 10mm went to 22mm and the 30mm went to 18mm the speed would be 151mph.

Would you keep the pulley centres the same and adjust both pulley widths or adjust one pulley and then adjust either the belt tension or the pulley centres? (just read your post above.. ok got it now!)

[chewie]

Hi again,

Does anybody know of a good article that talk about R/C market. Numbers of vehicules sold per years... That kind of stuff?

Also, what vehicule should we concentrate first? I thought about the Traxxas T-maxx. It looks like a popular model. What do you guys think?


i dont know exact number but just remember this..
no matter how bad the economy is people will always find a way to play with their toys..