Scooter Project Help

cchurchill · Mar 15, 2016

Background:
Recently, I finished my mobility scooter project. It was an electric mobility scooter that I remade a frame for to fit a predator 212 on it. I used the existing tires and made a new axle for it. The axle diameter is 5/8".

I upgraded the predator with:
Bored carb
ARC Connecting Rod
Cam
Valves
Springs
Header
Governor Removal
Billet Flywheel

THE PROBLEM:
Since, I wanted to leave the original cover on to hide the engine and make it look factory, I don't have much room to do much. I am using a centrifugal clutch setup with 10 tooth #40 chain. There isn't much clearance around the axle, so I went with a 12 tooth rear sprocket, making my gear ratio around 1:1. I knew it would be very slow on take off, but I was hoping the upgraded motor would help improve this.

First test run proved this, it barely wanted to move on take off but once it got going it had the speed. Any suggestions on how to improve this?

The biggest sprocket I could get for the axle that would still fit (barely) is a 36 tooth, making the gear ratio around 3:1?

OR Upgrading the clutch to a better centrifugal clutch, I just bought a cheap one? I choose a centrifugal clutch because I am using it for my brake by using a band brake to stop the clutch.

Poboy kartman · Mar 15, 2016

Ain't gonna happen.....you're going to have to have a jackshaft...

cchurchill · Mar 15, 2016

To get it up to 6:1?

If I put a TC on and still kept the 12 tooth on rear tooth would it take off quicker? Or will the TC still need a lower gear ratio?

itsid · Mar 15, 2016

the clutch (nor a TC) will be able to do anything around that ratio..
they both will just burn in a matter of seconds ...

what's the wheel diameter?
that's still part of the gear ratio and thus it'd be good to know to give you a reasonable advice on the ratio.

'sid

landuse · Mar 15, 2016

A 3:1 ratio is just not going to cut it. I would suggest nothing smaller than a 50T sprocket to give you at least a 5:1 ratio. You say you have no space, so you will need a jackshaft. There is no way around it. The 5:1 ratio is a good place to start, but you might need to gear even lower. The only reason I am saying 5:1 and not lower, is because your wheels are so small. You might just get away with it. Otherwise you are going to be smoking clutches at a rapid rate

Poboy kartman · Mar 15, 2016

Well ....those tires look pretty small....(it would help to know their height) ...you might get by with a higher gear ratio....but that's with the larger axle sprocket....

An 8 tooth clutch....( good one with the 36 axle sprocket) might work....but probably nothing is gonna work with a 12 tooth axle sprocket....certainly adding a TC without a gearing change is just going to change the part that fails.

---------- Post added at 02:00 PM ---------- Previous post was at 01:47 PM ----------

landuse said:
A 3:1 ratio is just not going to cut it. I would suggest nothing smaller than a 50T sprocket to give you at least a 5:1 ratio. You say you have no space, so you will need a jackshaft. There is no way around it. The 5:1 ratio is a good place to start, but you might need to gear even lower. The only reason I am saying 5:1 and not lower, is because your wheels are so small. You might just get away with it. Otherwise you are going to be smoking clutches at a rapid rate

Yeah that's why I said 8/36 ....that's 4.5:1.... and with the modded engine AND the best clutch money can buy and the small tires.....it's possible I would think....

---------- Post added at 02:00 PM ---------- Previous post was at 02:00 PM ----------

landuse said:
A 3:1 ratio is just not going to cut it. I would suggest nothing smaller than a 50T sprocket to give you at least a 5:1 ratio. You say you have no space, so you will need a jackshaft. There is no way around it. The 5:1 ratio is a good place to start, but you might need to gear even lower. The only reason I am saying 5:1 and not lower, is because your wheels are so small. You might just get away with it. Otherwise you are going to be smoking clutches at a rapid rate

Yeah that's why I said 8/36 ....that's 4.5:1.... and with the modded engine AND the best clutch money can buy and the small tires.....it's possible I would think....

cchurchill · Mar 15, 2016

My tire size is around 6 inch diameter. I don't have much clearance to put a big sprocket on axle. I think trying to fit a jack shaft will be my best option.

Poboy kartman · Mar 15, 2016

cchurchill said:
My tire size is around 6. I don't have much clearance to put a big sprocket on axle. I think trying to fit a jack shaft will be my best option.

Poboy kartman said:
Ain't gonna happen.....you're going to have to have a jackshaft...

Probably so....

One other thing...that kinda always is in the background of these "will it work?" gear ratio questions is this: I have a 6 cylinder pick-up....Now...I guarantee you...I can pull at least one if not two spark plig wires off....and it will still "work"....
I'll tell you though...this one is close...

Edit: I thought so for a minute...but...we need to know the total height of the tires from ground to top...using the Predator for scale...hard to believe they're 6"...more like 6" rims....(which is useless information) ...

cchurchill · Mar 16, 2016

Measured the tires last night, tire diameter is 8". There is no room to add a jack shaft, so another option would be to switch to a #35 chain (instead of #40 chain I'm using now) and put a 60 tooth sprocket and get a new clutch (12 tooth). A 60 tooth sprocket OD is around 7 1/4", so I'm hoping I will have enough room (won't be much ground clearance but I'm only riding on flat roads).

How well do you think a 5:1 ratio will be?

itsid · Mar 16, 2016

5:1 seems to be good enough (for up to ~360lbs total weight)

'sid

ezcome-ezgo · Mar 16, 2016

This is pretty cool. Can you post a pic of the axle/drive-train set up?

cchurchill · Mar 16, 2016

Definitely, ill take some more pictures tonight.

cchurchill · Mar 17, 2016

Here's some more pictures of the set up. The reason I went with such a small rear gear was I had it already and was hoping the increase motor HP would be fine...

Tomorrow my new 12 tooth clutch and 60 tooth sprocket will be here. Switching to a #35 chain to have more room for a bigger rear sprocket.

ezcome-ezgo · Mar 17, 2016

Your axle sprocket is going to hit the frame before it reaches the ground, isn't it?. Can you cut off that rear frame cross-member and put on an extension?

cchurchill · Mar 17, 2016

ezcome-ezgo said:
Your axle sprocket is going to hit the frame before it reaches the ground, isn't it?. Can you cut off that rear frame cross-member and put on an extension?

Yes, I will have to cut that part out.

chancer · Mar 17, 2016

Ok this is gonna cause arguement but.
I have 2 standard size typical yard karts. one with 13" tall tires and on with 15" tires. both are geared 6:1. 2 stock 6hp with cent clutch drive. But both will spin the tires from a dead stop in hard dirt.
I want to gear them 5:1, In my opinion they will work just fine.
So I think with your tiny tires. (you say 6") and your engine mods. You will be fine at 4:1.
Possibly even 3.5:1.
Wait for it....Go

itsid · Mar 17, 2016

chancer said:
...
So I think with your tiny tires. (you say 6") and your engine mods. You will be fine at 4:1.
Possibly even 3.5:1.
Wait for it....Go

eight, not six...
see?

cchurchill said:
Measured the tires last night, tire diameter is 8". ...
How well do you think a 5:1 ratio will be?

but let's just ask my calc, shall we?

KartInfo by kartcalc.net:

Code:

[FONT="Verdana"]
[B][U]KART[/U][/B]
[INDENT][I]RW diameter[/I]: [B] 20.32 cm | 8 in[/B]
[I]Total weight[/I]: [B] 164 kg | 361.56 lbs[/B]
[/INDENT]
[B][U]ENGINE[/U][/B]
[INDENT][I]Original HP[/I]: [B] 6.5[/B]
[I]Asummed HP[/I]: [B] ~6.5[/B]
[I]Torque[/I]: [B] 12.86 Nm | 9.48 ft lbf[/B]
[I]RPM[/I]: [B] 3600[/B]
[/INDENT]
[B][U]TRANSMISSION[/U][/B]
[INDENT][I]Final ratio[/I]: [B] 3.5:1[/B]
[/INDENT]
[B][U]PERFORMANCE[/U][/B]
[INDENT][I]Max Wheel Torque[/I]: [B] 45.01 Nm | 33.2 ft lbf[/B]
[I]Acceleration[/I]: [B] 2.7 m/s² | 8.86 ft/s²[/B]
[I]Top Speed[/I]: [B] 39.4 km/h | 24.48 mph[/B]
[/INDENT]
[B][U]PROBLEMS[/U][/B]
[INDENT][B]You might burn your clutch/belt![/B]
[B]Gear ratio too high![/B]
[I]Suggested final ratio[/I]: [B] at least 5:1[/B]
[/INDENT]
[/FONT]

And that's why I said:

itsid said:
5:1 seems to be good enough (for up to ~360lbs total weight)

'sid

Yes, reducing the weight will most certainly allow for a higher ratio;
so will a high quality clutch... a better performance engine also helps (how much will have to be tested)
but the fool and fail proof answer remains to be 5:1 IYAM

'sid

chancer · Mar 17, 2016

OK Cool. The fool and fail proof answer is 5:1
But I mean, for a few bucks (15 dollar axle gear.)
I say think out of the box and try 4:1 with a quality clutch.

There is nothing fool and fail proof about a granny scooter with a juiced up predator gas engine on it.

Flyinhillbilly · Mar 17, 2016

Can you mount a jack shaft directly above the axle?

Also, have you seen The one Colin Furze built?
http://youtu.be/w7gWMgN1NGM

chancer · Mar 17, 2016

I have another question.
Will this Brake band actually work to stop the Kart with it on the clutch bell?

I guess in theory it would work. But too much heat would be generated and negatively effect the clutch's life span.

Particulary on this build due to the High Gear ration being possibly attempted.

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