Help with low speed gearing

[Steve_s]

Hello.
Could someone please give me some gearing advice.

I'm building a mini tractor (it was originally going to be a kart!)
and I don't want it to go very fast as it's for my 4 year old son.

I'm using a 5.5hp B&S horizontal shaft engine that will be connected to a Peerless 700 gearbox so that it can have a reverse gear.
I only want to use 1st gear and reverse.
and I will be using a live axel and limiting the throttle cable.

This is the Centrifugal Clutch I'll be using.

http://www.ebay.co.uk/itm/361769833648?_trksid=p2055119.m1438.l2649&ssPageName=STRK:MEBIDX:IT

I will be copying this great guys set up.
https://youtu.be/58M3rdzKFbM?t=5m12s

Could someone please tell me what size sprocket to use on the input of the Peerless and what size to use on the live axel so that it can have a nice slow pull away and about 10mph top speed?

It will be driven in fields and woodlands and will be towing a small trailer.

Thank for any advice.

Steve.

 

[itsid]

Hi Steve.. DO NOT limit the throttle cable!
there is very little to play with anyways, and the clutch must fully engage to not burn out due to slippage.
it engages at ~2000-2200 rpm and the engine has only 3600 max roughly anyways (idles at around 1200-1400)

so limit the throttle and more pedal movement will be needed to actually engage the clutch relative to adjusting the speed .. which is counter intuitive really...
and in the end will ruin the clutch

talking about the clutch, that one is a BAAD decision IMHO!
first it's 1" shaft.. small Briggs come with a 3/4" shaft 99% of all cases,
so please check that it's the correct bore.
second and almost even more importantly.
You want the SMALLEST Possible toothcount! (for a 3/4" that's 10 teeth, for a 1" that should be 14 indeed except...)
in case you indeed have a 1" shaft, find clutch with a step down sprocket
like this:
http://www.gopowersports.com/10t-1-bore-centrifugal-clutch/
ten teeth! (also available on ebay from different sellers)

ten teeth is the way to go instead of 14.. since that will make your kart/tractor 30% slower compared to a 14T clutch (and 30% more torquey )

And to slow down you want the BIGGEST rear sprocket you could find that matches your chain,
the lower the ratio (bigger number!) the slower and more powerfull the vehicle will move.

And since frankly you -must not- limit the throttle cable (you really really shouldn't )
that's the only way to reduce max speed really.

you could use a Series 30 Torque Converter instead with a limiting weight,
that way the clutch will fully engage but the TC will not shift much
http://www.ebay.com/itm/COMET-TORQU...-CLUTCH-3-4-30-75-12T-35-10T-41-/361364618504
(10tooth #41 again )
plus the speed limiter:
http://www.gokartsupply.com/speedr.htm

that's imho the best way (since it can be adjusted easily.. removing the speed limit is as easy as installing the original weights)

Now that being said: without the internal ratio for the peerless and the Size of the driven wheels (outer diameter)
we cannot tell you what sprocket //gearing you will need in the end.

also depends on wether or not your going to use the TC or a CC.

OH one thing.. slow pull away is NOT going to happen!
the more you reduce the speed with gearing the more you increase the torque.
and since that both of these contraptions will engage at around 2k rpm (the max torque of the engine) this will be a powerfull jerk when the vehicle starts moving.
There is no way around that (no way that's not destroying the clutch/tc-belt that is)

frankly.. 4yo that should be going slow... much smaller engine or small electric motor is imho a much nicer idea.
especially since IMHO a 4yo should not get anywhere near driving a kart (helmet weight vs spine musculature on impacts thing)

Your kid, not mine.

Now, tell us about the ratio of your peerless and the size of your wheels and we drop in the numbers

'sid

 

[Steve_s]

Hi Sid.
Thanks for such a detailed response..
The shaft size is correct at 1". The engine came from a MTD LAWN HOOVER (http://www.mtd-eu.com/index.php?id=22295)

Thanks for the heads up about the throttle cable!
I think the internal ratio for the peerless is "Gear ratio (1st) 9.2:1" I got that info from here http://www.peerlessgear.com/node5380.aspx?pid=300905

The rear wheels will be 16" tyres on 8" hubs.

The reason I'm using this engine is because this build is a test for me to learn about mechanics and also how to weld, and I managed to get that engine locally as a non runner.

My children already have an electric quad but it just can't handle the terrain where we live, so I thought I'd go petrol.

It's going to be towing a trailer made from 1" box steel that should hopefully weigh it down a bit and It will only be driven under strict supervision.

Thanks again for helping me out, I really appreciate it.

Danke schön

Steve.

 

[itsid]

You're very welcome, we're here (mainly) to help each other out with questions like these

Now, 9+:1 and 16" tyres is already a nice number, even if you'd run 1:1 ratio from clutch to gearbox that thing would move just nicely (assuming it doesn't weigh a metric ton LOL)

Now that being said, the cent clutch should also work just nicely even with that "high" toothcount.

14 clutch to 26 teeth on the gearbox input sprocket would put you at 10.03 mph in first gear
(input speed on the gearbox then would be ~1940 rpm so well below what it can handle)
and assuming a 1:1 ratio on the gearbox to axle side of things

it might be difficult to find a big enough peerless OUT sprocket (or small enough axle sprocket for that matter)
So try to match those first and get as close to 1:1 as possible,
if you have those;
the math is rather simple.. for a 16" wheel and 10mph top speed you'd need a 17.1:1 overall ratio (+/- a few )
divide by 9.2 (the gearbox) and you have 1.86 roughly left to work with 26/14 is 1.858...
so that'd work just fine.
divide again by the output side ratio (axleteeth / gearout teeth) and see what you're left with
multiply that number by 14 and you know what gearbox IN sprocket you're going to need

'sid

 

[Steve_s]

Thanks again Sid!

Would you mind just idiot proofing this for me please?

I understand everything you've said up until the Peerless out sprocket and axel sprocket size.
Does 1:1 mean that both sprockets are to be same size?
I'm lost with that math! Is there an ideal size that both sprockets should be? Could going to big or to small drastically alter the 10mph speed?


Kind regards.

Steve.

 

[itsid]

You got that right...
1:1 means both sprockets (output shaft peerless and axle) are to be the exact same size
No matter what size that is (both ten teeth, both 100.. doesn't matter)

Now, it does make a difference what size sprockets you use though,
but only on the extremes and it has nothing to do with the top speed
the more teeth are actually engaged on the chain, the longer the chain and sprocket will last.
so say 8teeth or less is never a good number for a sprocket
(since at best 4 teeth would need to transfer all of the power)

But in your case since one is the axle sprocket and the other needs to fit onto a peerless700;
it really doesn't matter much;
whatever toothcount fits both will do just nicely!

This is in fact really easy once you wrapped your ehad around it.
Allow me to explain that in more detail again.

[LONG EXPLANATION AHEAD -skip if you like-]

1:1 means both ends will turn at the exact same speed with the exact same torque.
in fact the X:1 notation only means
how many turns do I need on the driver to make the driven turn exactly once

if the sprocket on the peerless OUT is larger than the axle sprocket
(unlikely but let's just assume that for a second)
then your axle (and thus the wheels) will turn FASTER than the peerless out shaft
(more speed)
if the Sprocket on the peerless OUT is smaller than the axle sprocket (very well possible)
then your axle and wheels will turn SLOWER than the peerles out shaft.
(less speed)

by how much is determined by the ratio of the two 2:1 for example means the DRIVEN
is twice as large as the DRIVER and thus will turn at half the speed. (with twice the torque)
(two rotations needed to make the axle turn once remember)

Driver and Driven just means what is actively turning and what will get turned over by it..
Driver is the engine (clutch) Driven is the INPUT-shaft of your peerless gearbox.
Skipping the gearbox internals for simplicity...
in the next step
the Driver will be the peerless OUTPUT shaft and Driven is your axle.

each of these steps has a ratio (Driven / Driver [simple division])
talking toothcounts
that could be 26/14 (from clutch to peerless as above ) or simplified 1.86:1
the internal ratio of the peerless' first gear is 9.2:1 (given I don't know what toothcounts they use LOL)
and the final ratio (peerless out to axle) let's just assume 20/20 teeth which means 1:1

all of these ratios multiply together to give you the overall ratio.
1.86 * 9.2 * 1 = 17.112
(overall ratio 17.1 : 1 )
that's the ratio you want to hit to peak at around 10mph with your wheelsize

and whatever you need to do to get there is basically fine.
Say for example your axle sprocket for some reason is half the size of your peerless out sprocket (again unlikely but to make an extreme example)
said ratio would be 0.5:1 (10/20 or so)
to compensate just do some math
9.2 * 0.5 will result in 4.6
4.6 times clutch->peerless ratio must be 17.1 (to hit your 10mph)
thus 17.1/4.6 will let you know the your clutch->peerless ratio (3.72 in this case)
which not coincidentally is twice the ratio we determined earlier (1.86:1 remember?)

as simple as that

'sid

 

[kenworth85]

 

[itsid]

and .... where have I lost you?

'sid

 

[Steve_s]

Perfect!
You're the man!
Whilst researching this project I've come across lots of you're posts so thank you very much.

I'll post some pics if it turns out anything like it does in my head!