Cheap & easily avalible CVT's under our nose's!!

[The-Original-T]

Right then guy's!

First things first before I go into why we can use these particular cheap and plentiful CVT's.....
You may get a little lost in my explanations but please bare with me as it will all come together at the end...

Engine power is measured in Torque, weather it be in ft/lb's or Nm.
These figures are measured across the RPM range to give a "Torque Curve".... REMEMBER THIS!!

Now.... HORSE POWER is just a calculated figure based on what TORQUE is produced at a specific RPM.... REMEMBER THIS!!!

THE ABOVE INFORMATION WILL ALL BECOME RELAVENT SOON ENOUGH!!

The CVT's I am suggesting on using are out of 50cc or 125cc scooters, bare with me before you say "THEY WONT COPE"

Torque curve for a Launtop (yanclone) 10HP single cylinder diesel

Torque Curve.jpg (30.85 KiB) Viewed 13917 times

If you look at this specific torque curve from a 10HP diesel that many of you are using or are thinking of using in your bikes you will see that its optimum RPM for both POWER and FUEL CONSUMPTION is at 3000RPM where it is producing around 8.6HP @ 26Nm (19.18 ft/lb's) of torque.

Now I agree that is a lot of torque for a scooter CVT to handle!! and No Your right it wouldn't cope..... But...
Scooter CVT's are very tuneable with Contrast springs, roller weights ect... and if it was a mildly tuned 50cc scooter engine bolted on it would be running at more like an Optimum RPM of around 9000RPM where peak power is produced! (just like my 50cc Yamaha Aerox)

50cc Mild Tune Scooter Torque Curves

As you can see a 50cc Scooter with mild modifications when tested by a reliable scooter tuning shop is capable of putting out 8.8hp @ 9000 RPM, when I back calculated the torque produced from those 2 Figures it worked out the engine was producing 6.97Nm (5.14 ft/lb's) of torque.... REMEMBER THIS!!

IMPORTANT: We have just established that our beloved diesel produces about a third of the ideal RPM for these CVT's and just over 3x the amount of Torque!!!!

Well isn't that just convenient

Easy answer then is.... Put a 1:3 gear/pulley ratio from the engine crank, to the driver side of your cheap SCOOTAY CVT!!!

e.g. A 300mm diameter V Belt pulley on your Crank and a 100mm diameter V belt pulley on the jackshaft which rotates the Driver side of the CVT, Thus increasing the CVT's RPM to 9000 and reducing the input torque from your diesel to just 8.66Nm (6.39 ft/lb's) which is just a touch (1.25ft/lb's) above the torque a 50cc scooter is producing!

But now your thinking...."well why would I want to do that, i've just reduced the power of my engine by a third!!"

WRONG!!! this is purely a "Mechanical Advantage" Remember what I said about HORSE POWER been a calculated figure, I shall walk you through it with the new figures of a higher RPM but a lower amount or torque...

When calculating HP from Torque (ft/lb's) and RPM this is the formula...

HP = Torque x RPM / 5252 (been the conversion factor, just as 25.4 is to transpose mm's into inch's)

so... 6.39 x 9000 / 5252 = 10.95HP

I know it seems strange the HP been higher than what we started with but as I said this is called "Mechanical Advantage" and is correct...

If your still confused by it all hear are some helpful links explaining in detail:

http://www.epi-eng.com/piston_engine_te ... torque.htm

http://www.1728.org/mtrtrq.htm

Now your probably wondering where you can get the 1:3 ratio pulleys and belts from for a reasonable amount....

http://www.beltingonline.com

They are so cheap! for you to buy a SPB section (19mm V Belt Section) 100mm and 300mm pulley + the Fenner couplings for both pulleys for the shaft of your specific size + a Kevlar belt at the size you will require your looking £50 DELIVERED!!!! Well Worth a Look!!!

Next thing is you will want your CVT.... just buy any blown up scooter/scooter engine off eBay for a 10er get a decent brand if you can like piaggio, aprila, Yamaha ect... to rip the CVT out of.
Or if you are wanting a higher performance CVT (they just accelerate smoother and hold a more consistent RPM but do exactly the same job) Try:

http://www.adrenalin-pedstop.co.uk/
http://www.pedparts.co.uk/

if you give them a call they are very helpful, tell them your CALCULATED Torque and RPM.... NOT WHAT THE ENGINE ACTUALY PRODUCES and they will point you in the right direction.

I hope I have helped a lot of you out on this side of the pond (England) and hopefully some of you lot in States as well!!

Remember Scooter CVT's are a hell of a lot more tuneable and customisable than those Comet TAV2's ect... and parts are a lot cheaper, better quality, and easier to get hold of...

By the way, I'm Tristan, I live Near Matlock, Derbyshire, England. This is my first post on this site, but I am an engineer....
if any of you lot live anywhere near me and fancy a meet for some fish and chips or something in Matlock Bath (Derbyshire's Home For Bikers) get in touch, cant wait to start my First diesel Build, already quite experienced with bikes and scooters but it would be great for me to see my first real life running Knocker and have a good chat over a Chippy!!!

Hope I Have Helped!! Take Care ALL!!!

[Eddy Wane]

Hi Tristan.
I found your post very interesting and I can understand the mechanics if I was driving a low weight small wheeled machine. Have you transposed any calculations to account for the weight and larger wheel size of an average motorcycle.
I did consider using a Suzuki Bergman as a base vehicle but as yet I have not measured the available engine space, this would seem to be a suitable platform to try out your ideas.

[Eddy Wane]

P.S. Welcome to the forum Tristan.

[The-Original-T]

I am looking into mounting it onto a piaggio zip 50cc frame with 10inch wheels (I have 2 scrappers at the bottom of my garden from my pedding days) and making a new swinging arm in place of the standard engine and transmission, the flat foot rest lends its self to mounting one of these engines and adding a bit of frame reinforcement, then using chain and sprockets as my final drive, thus I havn't transposed any of the calculations for a bigger bike, however as mentioned no power is lost, its just converted from torque to HP, as in the original post if the engine is at its (my) target working load at 3000RPM its producing 8.6hp and 19.18 ft/lbs of torque after it has been through the 1:3 ratio it is outputting 10.95hp but only 6.Somthing ft/lbs thus the torque has been converted into a faster rate of work (HP). I even confuse myself when thinking about it, and found myself double checking against reliable internet math sources but it all comes up trumps in the end which is a good thing, plus the job of a CVT (Torque Converter) is to always supply peak power so I am very optimistic about this, the math seems good, will just have to wait until my finances and time allow for it to be put into practise im aiming on a 12 Month build. Thanks for the Reply, Good Question and I will be interested to know the outcome once it is done

[BertTrack]

Good one.

My CV-tech Trailbloc is used for much more power when used with high rpm than it can take now. If only i had space that would have been the way to go.

[The-Original-T]

I think the thing that we all need to remember is that CVT's work on centrifugal force, against a contrast spring to keep the engine at a constant velocity.

What you are saying BertTrack is correct, as without the higher RPM's the CVT's weights/cams aren't producing sufficient Centrifugal force to push the driver and create enough friction on the belt to transfer the power!

Now this could be rectified by either the way I have stated by up gearing the initial output or...

You could have very heavy weights/cams and a extremely stiff contrast spring, which would allow the CVT to work in exactly the same way but provide much higher amounts of friction at lower RPM's of your average diesel.

The only problem being is that the parts of that calibre are either commercial un-available or the cost is huge!

I should imagine the expense is in producing a spring with enough tension that can be constantly moving and changing without being to brittle, heavy rollers and cam's would be easy to manufacture as are the light ones.

If you were to use a Scooter CVT in the manor I proposed in the original post a good starting point would be:
-The stiffest contrast spring available to your specific CVT usually around a 28KG Load (£10-£15)
- Roller weights in the region of 3.0 grams - 3.5 grams (full set of 6 £5-£8)
These parts are available from the scooter shops I mentioned and linked, that combination used together will allow the CVT to keep a steady 9000RPM (3000RPM off crank)

REMEMBER: To INCREASE the RPM's before "gear shifting" happens make your weights LIGHTER! To DECREASE the RPM's before "gear shifting" happens make your weights HEAVIER!

You do not put heaver weights in to go faster and lighter weights to get better acceleration as many people will lead you to believe! Top speed is down to your overall ratio from start to finish, the CVT just keeps your RPM's at peak power/economy! you adjust your weights to allow it to work through every one of the CVT's possible ratio's from standing still to top speed!

if anybody has any questions for me or constructive criticism that will help both me and others please post on this thread instead of PM'ing me then it will help everybody

[albertaphil]

One point to make clear is that cvts do not convert torque to horsepower. They convert horsepower at one rpm to horsepower at another rpm. If the output rpm is increased, then the output torque will decrease and vice-versa. This is true due to the fact that horsepower is simply a function of torque x rpm. If you gear up the rpm of your diesel the power output will be unchanged (minus inefficiencies in the gear/belt/chain system used).

I think the reason folks like diesel power is not so much the amount of torque produced but the fact that the torque is produced at an engine rpm that is usable. That is, my engine is in it's powerband at the rpm I'm normally riding it without shifting down several gears. Real rideability.

[BertTrack]

As we've seen with the Track's c.v.t. belt pressure is critical.

And increasing the weights would lead to the belt being gripped too early. (no centrifugal clutch!)