gear ratio preference

[dcastillo]

trying to pick out what size gear to buy for my jackshaft, and at $20 a piece, i dont want to buy multiple ...
Gokart is powered with a 2kW 36V motor and runs 16" rear tires...

Ive heard 6:1 is a good ratio, but is that for electric too, or just gas? With my current gear available I can get either 12.6:1 or 3.4:1, both I *think* are a little outside the desired window...

Top end doesnt really concern me... Ive had it doing 25+ already on a previous gearing... and can always limit the topend with the controller for the kids if needed...

thanx
Danny

 

[Half-breeder]

IMO... Electrical is bout the same(asfar as gearing), just depending on how long youll wanna take, to reach top speed. N evidently the more powerful the motor... (theorietically)... The less time itll take to get there... IMO.

Ill take it your running a cent clutch? What gear #'s you runnin now(teeth).

 

[dcastillo]

no clutch...

current setup
motor-12
JS in- 19 (was a 15 and 12 at one point)
JS out-10
axle- 64


so currently im at 10.1:1, but i have ran it at 6.4:1 and I dont remember having issues..

The motor side is on a #35 chain and my brother just gave me a new #40 motor sprocket with 10t and a JS sprocket with 19t

so once I make the switch I only have two options
10-19-10-64 which gives me a 12.6:1 ratio
or
10-10-19-64 which give me a 3.4:1 ratio

neither of which I *think* will work well.
I dont want to mess with the motor or the axle sprockets, so just trying to figure out what to do with the JS area, currently I have a 10t and 19t, so I was messing with the numbers trying to figure what to buy in order to have 3 JS sprockets, giving me multiple setups for gear ratios...

Just thought I would see what others recommend
-Danny

 

[xXPhasemanXx]

I don't know much about go karts, but from what I've gathered from this forum there is nothing wrong with 6:1

 

[exenos]

2kw is ~2.7 hp. What is the operating rpm of the motor? Thats the most important thing to know.

The common 6:1 ratio is for a 6.5hp kart with 10-12" wheels, not really applicable to your situation.

 

[itsid]

hehe...

Well it's an electric motor, not a gasoline engine;
and funny enough it behaves differently when it comes to gearing ratios.

So you need to find out what max rpm your motor provides first

(I think it'll be something between 1400 and 2000 rpm)
and you need to go from there.

A 2kW motor is (whom do I tell ) enough for some serious fun; and thanks to a wider torquecurve than it's gasoline powered friends, you can gear MUCH lower with the same amount of fun.

So, for a good idea of where to start with your ratio..

just assume the 6:1 is for 3.6k rpm that's 1/6 (exactly the opposite) per 100 rpm of the motor you have.

So, let's say it turns 1200 rpm, thats a 2:1 ratio 1800rpm 3:1 ratio
and so on and so forth and everything in between.

Keep in mind that this is just a starting point 2kW should get you up in the 20s mph-wise,
I'd say without checking the math.

Since you say you can set up a 3.4:1 ratio with the parts you have,
do so and see how it turns out.
should be good torque and a little low on the top speed.
(assuming something in the 10"-12" tire range)
you can always play around with the calculator to set up your actual wheel size and rpms..
just target ~20-21 mph and you'll end up with the gear ratio to start.

'sid

 

[dcastillo]

Thanx most of that made sense till I got to this part

"Since you say you can set up a 3.4:1 ratio with the parts you have,
do so and see how it turns out.
should be good torque and a little low on the top speed."

wouldnt the smaller the first number then higher the top end speed?
as in a 3:1 would go twice as fast as a 6:1?
(translated, 3 engine turns equals 1 axle turn or 6 engine turns equals 1 axle turn)

 

[dcastillo]

Also, the highest its been geared is 6.4:1 and it did about 25mph
So if I gear it at 3.4:1 it would in theory (if it had enough power) do about 45mph, right?

 

[itsid]

yes.. 3.4:1 is faster than 6:1...

But remember: that is assumed the motor is turning no more than just 1800 rpm
(instead of a 3600 rpm of a stock predator or clone for example with 6:1)

If your motor reaches the same rpm as a gas engine, you need to gear the same
(about 1/6 per 100 rpm of your motor)

Most dc motors I've seen so far, don't (2000 is about the highest rpm I can remember)

That's why I started with

you need to find out what max rpm your motor provides first

It did 25mph on a 6.4:1 ratio??

So it turns 3400 rpm (with your 16" wheels) that is insanely high for an ev motor..
but if you say so I'll believe that of course.

So, 3400.. your gear ratio should be 5.67:1 or precisely 17:3
to have the same starting point as you would have on a clone motor.

'sid

 

[dcastillo]

Technically it's a series golf cart motor that's 36v and i run it at 48v giving it the higher rpm

 

[dcastillo]

quick update, I got it setup with the 3.4:1 ratio...
to my surprise, the motor had enough torque to actually take off, not to quick of an acceleration... but I did clock myself approaching 30mph which was kinda scary

unfortunately there was barely enough torque to climb inclines and grass, not to mention the increase in current required to take off killed my batteries twice as fast it seemed...

Looks like Im going to need to buy a 15t sprocket to get the following possibilities:

motor - JS in - JS out- axle -ratio
10 - 19 - 10 - 64 -12.16
10 - 15 - 10 - 64 -9.60
10 - 19 - 15 - 64 -8.11
10 - 15 - 19 - 64 -5.05
10 - 10 - 15 - 64 -4.27
10 - 10 - 19 - 64 -3.37

Im thinking 5.05 or 8.11 will be my best bets
thanx
Danny

 

[itsid]

5.05:1 seems to be a good idea;

maybe another 10 or 15T sprocket, just in case you want to nullify the jackshaft
to try a 10 -(15-15-) 64 setup with a 6.4:1 ratio.

'sid