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Old 03-15-2019, 07:45 PM
scorn001 scorn001 is offline
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Default Kart Conversion issues

So I'm converting a Carter Brother's Lightening LX go kart to electric using a MY1020 48V 1800W motor & controller and I've encountered 2 issues:

1. The cart previously used a #40 chain so I'm planning to put an 11T #40 sprocket on the MY1020 shaft. I got the part from electricscooterparts.com. The sprocket itself didn't seem to fit the bore on the shaft quite right, it had a little bit of slop when mounting one way, mounting the other way (flipped), there wasn't as much slop, but the rotation had a little bit of wobble to it, enough to cause the chain to want to jump occasionally. Had anyone else tried this sprocket from this company? I'm working on getting a replacement, but I'm concerned there is something else wrong I guess.

2. The top speed seems too high when I do the math. The motor is rated for between 4500 and 5200 RPM. 11 teeth on the shaft sprocket, 60 teeth on the axle sprocket. I have a ratio of 1:.183. Giving me a range of 825 to 953.3 RPM at the wheel. The wheels have a circumference of 51 inches....giving me a top speed of 39.5 to 46.5 mph? I know the motor won't have the power to take me that high - but the gearing seems a bit too high and I fear it won't have the takeoff power. Is my math right?

Thank you.
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Old 03-16-2019, 06:29 AM
voided voided is offline
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I’m thinking if my math is right you have a off-road gokart and that maybe to tall of a tire.
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Old 03-16-2019, 06:33 AM
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Kool! I love electric conversions.

IMO #40 chain is some pretty "heavy" duty stuff
From my experience, #35 chain is adequate for a 48V 1,800W set up.

Sprockets MUST fit tightly & true (perpendicular to the shaft)
...or you WILL have problems

Here is some info on sprockets for these little electric motors.
http://www.diygokarts.com/vb/showthread.php?t=38425


Motors are usually rated unloaded (not connected to a load)
...when loaded the max RPM will drop considerably (how much depends on the load)

* IIRC, a 11T drive sprocket & a 60 tooth driven sprocket = a 5.45:1 ratio 60/11= 5.4545454


So, using the "Ball Park Equation" with lets say a 3,000 max (motor) RPM

MS/GR=ASxTC=IM/FT=FMxHR=FHxMM= MPH
http://www.diygokarts.com/vb/showthread.php?t=38785


Motor Speed 3,000 RPM's / Gear Ratio 5.4 = 555 RPM (Axle Speed)

Axle Speed 555 RPM x (Tire Size) 51" = 28,305" (Inches per Minute Traveled)

(IPMT) 28,305" / (Foot) 12" = 2,358.75" (Feet per Minute Traveled)

(FPMT) 2,358.75' x (Hour) 60 = 141,525 (Feet per Hour Traveled)

(FPHT) 141,525 x (Multiplier) 000189 = 26.74 MPH

If my math is correct, it looks like your top speed should be ~26 MPH
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Old 03-16-2019, 07:29 AM
scorn001 scorn001 is offline
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Understood. That 3000 RPM number is what I was looking for. The gokart has a roll cage and a solid rear axle, and is an offroad cart. I wasn't sure if the #40 chain was more of a necessity because of that? I went with the 1800W because it seems heavier than most of the electric karts I'd seen online, I expect that even with 1800W it won't be super fast, maybe not as fast as it was with the 6.5hp gas engine, but should still be quick enough and fun - and easier to keep running.

I'd prefer to go with the smaller chain, I'm thinking maybe less drag? I'm just not sure if it'll be strong enough for the heavier kart with the solid rear axle? Does that even matter?
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Old 03-16-2019, 07:36 AM
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well.. with a kart that bulky and heavy,
45mph is out of reach for sure

Ideally you want to gear for a top speed the motor is actually capable of reaching,
or lower.
and 45mph would require ~5400 Watts of mechanical power I'd say.

So let's see..
frontal area times coefficient of drag (frontal area: 1.5 m Cw : 0.75)
I assume around 1.125 combined
that times half of air density (1.2 kg/m) gives us a factor of 0.675

to find the maximum speed we further assume the motor is actually capable of delivering 1800W of mechanical power (w/o the specsheet even this is guesswork)
And divide that by the 0.675 from above to end up with 2666.67
now taking the third root and get 13.867 (m/s) as your top speed
nice that's round about 31 mph

that is the physical limit of air drag (based on our made assumptions about your kart )
and it's certainly a lot of guesswork but it sounds about right I'd say.

Okay.. w/o the specsheet for the motor I don't know where the kink in the torquecurve is
and what rpm the motor will actually provide under 'ideal' load..
I wouldn't go as far down as FA.. but 3500 rpm sounds about right to me as well..
And with a 16" rear wheel that's indeed a 5.45:1 gear ratio (11 -> 60 teeth sprockets)


that gear ratio is at least not too far off the ideal
again.. we made lots of assumptions on the way down here,
and maybe you can improve on the performance a bit by adjusting the ratio up or down a hair;
but at least you are in the correct ballpark of ratios.

If however the motor is indeed rated for 4500-5200 rpm under load
you will need to gear much lower ( like 8:1 ) that'd be 88 Teth on the axle
and since that's a large sprocket
you might want a 10T motor sprocket to shave 8 off that axle sprocket
to end up with a 80T on the axle

'sid

for chain: get 420 chain.. way stronger than #35 and #41, not as heavy as #40
and best of all: it fits #41 sprockets nicely (which likely are the ones you already use )
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Old 03-16-2019, 08:02 AM
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What kind of axle sprocket are you running? Can you post a pic? You might want to go to ebay or bmikarts and grab the biggest one you can fit. With your setup I would want at least a 90T or bigger. Or go with an industrial motor. Imperial 3.6HP motors are cheap and easy to come by on ebay.
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Old 03-16-2019, 08:50 AM
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In case any of you are interested, here are some pics of what I've got right now, just to give an idea of scale if nothing else.

Click image for larger version

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Old 03-16-2019, 08:53 AM
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So I guess I need to maybe figure out which chain(s) I can use on that axle sprocket and go with the lightest I can get away with, and then find a matching shaft sprocket.

Also, for the record I have no interest in the cart ever doing 30 or even 25 mph. This is a dirt cart to ride around the back yard, for my kids. My thought is that 15 mph is plenty fast, MAYBE 20. I just want to be sure it can handle the gradual inclines at more than a snail's pace.
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Old 03-17-2019, 03:55 AM
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Electric scooter parts sells a #35 double d conversion sprocket for that motor in a 10 tooth.. that allows for you to find the more common sprockets in what ever size you want..

My motor setup like that has 3 speeds. Instead of a switch set the speed and leave the others as a possible solution when they are ready for more speed.
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Old 03-17-2019, 06:15 AM
scorn001 scorn001 is offline
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Thank you, after yours and other comments about going to #35, I looked at the store again and saw that. I think that is my plan. I've got a ticket created for this #40 sprocket. When they call I'm just going to ask if I can swap out for #35 and then get the axle sprocket too, along with the chain.

Thanks for all of the help.
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Old 03-17-2019, 09:05 AM
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Quote:
Originally Posted by scorn001 View Post
Thank you, after yours and other comments about going to #35, I looked at the store again and saw that. I think that is my plan. I've got a ticket created for this #40 sprocket. When they call I'm just going to ask if I can swap out for #35 and then get the axle sprocket too, along with the chain.

Thanks for all of the help.
Buy the biggest axle sprocket you can fit on your cart. That little motor is going to need all the help it can get to move that beast.
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Old 03-17-2019, 10:34 AM
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Quote:
Originally Posted by Quinc View Post
Buy the biggest axle sprocket you can fit on your cart. That little motor is going to need all the help it can get to move that beast.
Do you guys think this is going to be an issue with an 1800W motor? I know it's not the biggest, but it's not the smallest either. Did I under-buy?
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Old 03-17-2019, 11:13 AM
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You should be fine

For more info, here is a full size Dingo with the 48V 1,800W Boma motor

http://www.diygokarts.com/vb/showthread.php?t=37062

& here is a video of it in action

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Old 03-17-2019, 02:30 PM
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Quote:
Originally Posted by Functional Artist View Post
You should be fine

For more info, here is a full size Dingo with the 48V 1,800W Boma motor

http://www.diygokarts.com/vb/showthread.php?t=37062

& here is a video of it in action

The dingo axle sprocket looks much bigger then 60T.

the 1800w motor will be fine but you need to gear it properly. Also sprockets are cheap..
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Old 03-17-2019, 03:44 PM
scorn001 scorn001 is offline
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Looks like a 72T to me? I can get one of those made of steel, but to go any higher I'd have to go with aluminum @ double the cost and not nearly as strong or forgiving I'd think. Not sure aluminum is a good place to start.

Maybe I'll start with the 72T. I may remove the roll cage to shed some weight too.

My main concern now, is all of these videos show it being driven primarily on roads, with some driving in nice level grass. My yard is on somewhat of a slope. With a gas engine the kart could go up the hills just fine - of course you'd have to put your foot in it a little more and the engine would have to work a little harder for a bit, but it could do it without issue. I'm a little concerned this little motor will have real struggles with that. I guess I'll just try it and find out. If it turns out I need more motor then I'll address it then.

Excuse the red neck swimming pool and my burn pile.
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Old 03-17-2019, 06:20 PM
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A nice 90+ tooth axle sprocket with your 10 tooth motor sprocket will take you up hills in grass for sure. It probably won't be terribly fast, though.
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Old 03-17-2019, 06:33 PM
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More Boma info

Here is a thread where I tested & compared several different motors on a simple yard kart.
The motor sprocket is 10T & the axle sprocket is 84T, for a 8.4:1 ratio

http://www.diygokarts.com/vb/showthread.php?t=37442

The Boma test starts at post #35


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Old 03-17-2019, 09:26 PM
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Quote:
Originally Posted by Functional Artist View Post
More Boma info

Here is a thread where I tested & compared several different motors on a simple yard kart.
The motor sprocket is 10T & the axle sprocket is 84T, for a 8.4:1 ratio

http://www.diygokarts.com/vb/showthread.php?t=37442

The Boma test starts at post #35




Seriously, you post a ton of helpful stuff. Thank you
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Old 03-18-2019, 10:52 AM
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Agreed. I've been scouring many threads where both Functional Artist and itsid (and others) provide a ton of useful information. Thank you so much.
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Old 05-14-2019, 12:51 PM
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Quote:
Originally Posted by scorn001 View Post
In case any of you are interested, here are some pics of what I've got right now, just to give an idea of scale if nothing else.

Attachment 105809

Attachment 105810

Attachment 105811

Attachment 105812
An 1800w motor can move around easily move around a kart that big at 20mph?
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