Torque Converter on a Motorized Bicycle

[augidog]

imo, a legal on-road motorized bicycle is 50cc or under, single-speed or auto, and completely pedal'able. since i travel extensively on this rig, political correctness is my middle name. those are my willing choices, so that's what we have to work with here...who wants to help?

at the moment, i use a Golden Eagle system...belt-drive single-speed, with quick change drivegears ranging from 25:1 to 20:1. the Tanaka 47 Type-R (brand new! what a lucky find) makes 2.8hp and is rated to 11,000rpm. it hauls butt on the top-end, and it hauls many butts on the low end...but i need a way way way lower option still. the bike & trailer are both very heavy-duty, plus i carry a lot of stuff.

i've already ruled out a 4-stroke 50cc/converter setup as just too doggone wide for a pedal-bicycle, so i want to insert a TAV2 30-75 into a diy (centered/inline) drivetrain.



as you see, i have plenty of room for the t/c under the seat.

sprocket on engine's centrifugal clutch.
sprocket on top of the t/c's drive pulley.
idler-hub bolted to t/c's backing plate where it would normally mount to an engine.
jackshaft on that hub, for the drive pulley and sprocket.
(when assembled, this would kinda look like the jackshaft at the driven end)
driven pulley feeds a freewheel sprocket on my pedal-jackshaft.
pedal-jackshaft feeds moped freewheel hub.



the t/c will sit vertically, just like in the above thumbnail, and slotted brackets will let me independantly adjust tension at each end. can you picture the physical assembly i'm trying to describe, and are there any obvious flaws?

so far, it looks like buying a whole t/c kit gives me a lot more parts for the money. if this still gets too wide, i'll make my own double-sided mount & 'shafts, and put a single bearing on each side.

a final ratio of 20:1 is my target top-end, with the torque converter in the 1:1 position...this ought to give me a low-end (when i need it) that's out of this world, and i may even see some bonus over-drive under the right conditions. if you wanna play around with your speed calculator, my engine likes 6-9k for cruising & my tire circumference is 82".

now the tricky stuff, for me anyway...

i have 3 places to make my reduction, actually way easy...but how much of it during step-1, from the engine to the drive-pulley? i "think" the larger portion should be at the beginning. the centrifugal clutch engages at 3000 and the engine is definitely pulling by 5000...so...how easy is it to drop the converter's engagement point to 1000-1200 so i can use a 4:1 & take advantage of the Tanaka's rpms? or should i consider 3:1? etc? etc?

and this is why i'm here...i needs me a converter guru. any help will be mucho-appreciado'd.

 

[fowler]

woud it not be easier to mount the engine and tc inside the bike frame

 

[augidog]

personally, i've made my choices, and i'm happy with them...and now i'd like very much to find someone willing to help me with my math and torque-converter questions, which apply regardless of where the components are located..

 

[fowler]

i can help u with what u want i was just offering surgestions

u can get differant springs or weaken those ones u have
that will make the convertor engage earlier

 

[augidog]

fire away, my friend...i need to address the ratio from the engine to the converter, and how to modify the engagement point to make the t/c compatible with the engine's parameters.

edit: i saw your edit above...so i can *slightly* stretch the existing garters to lower the engagement? that is what i thought, but i needed a pro to confirm it. thank-you. truth be told, i wouldn't care if the t/c engaged immediately, as it will be isolated by the centri-clutch at the input & a freewheel at the output. so it looks like i can use a 4:1...double thank-you...that makes the rest of my reduction-math way easy.

based on your experience, does my hub/backplate/drive-pulley/sprocket jackshaft idea hold water, or should i definitely go for a bearing on each side? i.e. will that alloy backing plate be strong enough?

 

[fowler]

to my knowledge if u weaken the springs it will engage at a lower rmp

but i wouldnt go chopping just yet

as for the ratio
u will have to play around with it ill u find one that work
http://www.diygokarts.com/speed-calculator.html

but from what i got u are trying to drive the bike though the pedals
why not drive straight to the rear wheel

fit anouther sprocket to the rear wheel
like the ones u get with the profressional kits
it will save alot of time and money
it may be a little fiddlier to make but why not

 

[augidog]

fowler...i'm the new guy here, and i do not wish to offend...but you should know i'm an extremely experienced motorized bicyclist. i created and ran the leading MB forum until the commercialism took all the fun out of it, and i retired in disgust. the main reason i chose to register here is that y'all are ad-free. i've raced at the bonneville salt flats, organized rallies, and have used every style of assist kit out there, including helping to develop prototypes that are now leading domestic choices. i've used the Golden Eagle system exclusively for 4 years (for an "assist" kit there's none better) and they are personal friends of mine...they were my professional sponsor for the landspeed racing. but, with all the traveling i do, and the extreme payload i carry, i need overkill when it comes to strength & durability, and that's the only reason i'm giving up my Golden Eagle...i've far-exceeded it's "kit-on-bicycle" capabilities. and that's why i'm here picking your brain, the components you guys use offer me what i need.

i don't think the admin will mind...this is my personal ad-free website: www.mb-rambler.mysite.com

 

[fowler]

ok sorry ill probs keep making surgestions thats just a habit espesically when i dont fully understand what u are trying to create but ill try stop

from further study of your diagram
i think (if i read it right) u can make the tc engage at a lower rpm my altering the gear ration that connects the two

what gear is on the engine its self?


also as i said dont go chopping yet
im no pro, i deal with motorcycle powerd buggies
but i know the basic working of them from reading stuff on here and basic services on our ag bike

 

[oldbikerarlo]

I like where your going with this, I do have to question the torque applied to your last drive chain. Do you think it will be up to the tensil forces that will be appiled? Will you break your chain?

 

[augidog]

fowler, i didn't take offense, i just wanted to clue you in about my qualifications without offending you.

'arlo, my wheels are based on 1982 amf moped hubs, drum brakes, 10G spokes front, 9G rear w/freewheel. converted from loose ball-bearings to sealed cartridges. with a real go-kart chain, i'm positive it will handle the load.

so...pedal to the jackshaft using bicycle chain, converter feeds freewheel on jackshaft with #40, jackshaft feeds rear hub with #40.

4:1 (for sure, for best take-off rpm's) from engine to converter, 3.5:1 from converter to jackshaft, 1.5:1 from jackshaft to rear hub. the last two are approximations right now, but you get the idea.

the clutch spindle has a 5/16-28 stud, i can adapt whatever i want to it. i'm considering cogged belt from engine to converter, but haven't made that decision yet.

btw, speaking of torque-converters, here's a cross-link that matters: http://www.diygokarts.com/vb/showthread.php?t=13579

 

[fowler]

could u go 1:1 engine to tc then u dont have to mess with the tc
also u would have to make the tc engage at effectivly 750rpm with that much reduction

 

[augidog]

nope, and here's why i ruled that out early on...1:1 from the engine to converter leaves me too much (still 20:1) reduction to deal with after the converter. in that case, i would just use a huge lefthand sprocket like you suggested, but i ruled that out early. i like having only one drive to the wheel, with assist inserted at the proper point.

like i said, the t/c will be isolated with freewheels so i don't really care how low it hooks up...remember, this basic t/c is designed for low-rpm 4-strokes utilizing an approximate 1000-4000 range. using some reduction lets' me take advantage of the Tanaka's strong point, which is its 4000-9000 usable powerband. based on a 3-4k clutch engagement, and a (modified) 1k converter engagement, the math says 3-4:1 is what i want for decent synchronization of the two engagement points, and proper operation of the t/c within its intended range.

i think.

does anyone have an opinion on whether the backing plate can handle my drive-pulley jackshaft idea? should i just build me a custom 2-sided assembly, with a bearing on each end instead of 2 on one end?

 

[fowler]

by those numbers true

but i got 2.2k as the engagement i dont know enought to work out how to 1/2 the engagement and if at those speeds there is enough force to grab the belt

its 12 am over here im going to leave it for someone with more experance and see the result in the morning

 

[augidog]

k'...thanks for the input & interest...cya tomorrow.

btw-you playing devil's advocate is helping...i'm now considering a 2:1 from engine to (un-modified) t/c, but i have to figure out how to cram a 4.5:1 between the t/c and the jackshaft...that could get messy.

i think it's time to go shopping for cogged-belts & gears...any recommendations?

 

[Bluethunder3320]

what about just using this engine? youd have enough power for pretty much any load and still great speed.

im making a frame with schwinn wheels and a 13.5 HP engine and it doesnt look too ridiculous... lol. i use 6.5 clones on almost everything else i build though.

http://www.harborfreight.com/predat...d-for-all-states-except-california-68120.html


for the TC, you cant get just any belt because they have special angles. the 30 series has an asymmetrical belt and (i think) 26* or something on the other side.

check out http://www.surpluscenter.com/ for sprockets and everything else... theyre really good.

 

[augidog]

i'm not getting a new engine, especially one that's considered way illegal for an on-road motorized bicycle in 'most every state but ca...and they're gonna crack down soon due to widespread abuse...some ca cities are already advocating outright bans. and the east coast isn't exempt either...in ma on-road mb's are illegal, and boston went so far as to enact a definitive ban on all small un-registered motorized 2-wheelers.

legal mb'ing is my area of expertise, and this is more than hobby to me...please see my personal site...it's a lifestyle. if i needed or wanted something more than 50cc/30mph for on-road use, or i didn't like pedaling, i'd just buy a motorcycle and be done with it. but, i happen to LOVE the challenge of getting more from less, and life is wonderful at 30mph on America's secondary roads. that's my story and i'm sticking to it.

i am aware that the t/c uses a proprietary belt. i'm considering using cogged belts for the input and output.

thanks for the surpluscenter link, i'll go check 'em out.

recent research: a genuine GTC "made in USA" t/c is available thru only a couple outlets, and costs a lot more than the chinese knockoffs. guess i'm eating a lot of ramen-noodles next month.

 

[r_chez_08]

I would not advise using belt drive. When wet, belts slip excessively.
I would buy the tav2 system. The torque converter pictured looks like either a tav30 or a chineese converter. The tav2's have a stronger cast aluminium backplate. I would only use the steel backplate if you have restricted room.

As for the engagement, you can buy new "garter" springs for the driver. I do not know if you could get your low engagement required though.

Another option could be to heat up the springs to weaken them, but I could see this shortening the spring life and being terribly inaccurate.

A final method that may be worth trying is going to a hardwear store and finding some springs with the same diameter that are weaker in strength, and trying those. The problem with having too weak springs however, is that the driven will go into high gear really quickly, meaning your "torque gear" wont last for very long.

Have you looked at pocket bike torque converters like this one? http://scooterparts4less.com/web_gas/x2_Pocketbike_gearbox.htm
They may suit your application better.

 

[augidog]

ah, but i'm talking about a cogged belt, like the Golden Eagle system uses, but heavier...NO slippage ever. if i find something suitable, i'll post it.

and yuppers i'm well aware of that chintzy pocketbike cvt. horrible construction, and noisy as heck to boot.

i agree, r_chez_08...i'm choosing a genuine GTC "TAV2" over the knockoff...and i'll first try a 2:1 reduction and use the original garters as-is. that puts the engine at 4400r's & that should be fine.

i'd like the "cast" backing plate, alright...but does anyone actually have one and know if it would withstand my upper-jackshaft idea? how about the blue-anodized "extruded" one?

 

[r_chez_08]

Ah I see what you mean by a cogged belt. I thought you meant a cogged v belt!

I have never used a chineese pocket bike ctv, so I dont know.

What do you mean by the blue anodized one? Pics? Is this the one that bullet lines sell?

 

[augidog]

bulletlines and gokartsusa are the only 2 sellers of GTC i could find. same prices, but there's a $12 difference in shipping. no cover is included with any GTC kit i've seen.

nothing on ebay but knockoffs, and 2 leftover genuine Comet TAV's on amazon, complete 1" kits with cover, but too pricey for me.

GTC offers the cast plate on the 1" versions,
and this extruded one on the 3/4" versions:



(it looks extruded to me, i seriously doubt it's billet)