Help needed, I'm missing something....

[Finlee]

Hi, I'm after some advice. I've been working on modding a kettler pedal go kart for some time now and after putting a lot of work into it ready for my son for Xmas day, I had the motor going (24v at the time) on the workbench and all was good. We then unveiled it on xmas day, he sat on it and it went nowhere. I lifted the rear axle off the ground and it would spin away but when the tyres hit the ground it stopped dead. So back to the drawing board totally defeated. I then upped the motor to a 48v 1000w one, boom happy days, all working on the bench. I then sit him on it and again it struggled to move at all. WTF.

So I'm really scratching my head and then I think what could it be? Then I look at the gear ratio I have. I have a 12/19 =0.63 ratio going on, which must surely be the problem? What do people reckon? Please realise I an a newbie for this sort of thing lol

Also, the wood is temporary as I had a steel brace there until I cut it off trying to reduce weight as I thought that may have been the issue.

Thanks in advance.

 

[Smerft85]

I know squat about electronics, but I would say if you swapped the two sprockets you currently have it may at least let it move. On all my gas karts I have something like a 10 tooth clutch on the engine, and a 60 tooth on the axle. Not sure what is available for electric vehicles but seems to me the sprockets are set up wrong.

 

[mckutzy]

It look like he's going to have to scrap the whole rear end, cause he welded the sprocket on....

 

[ol'joe]

You can calculate this stuff with just a bit more information, but you will NEED some more information. You need to know what the RPM of the motor is, to start off.

You already know you have a bit over 1 HP, which should be good if the boy is small and the desired speed is slow.

You need to select a desired speed, though, so maybe call it 5 MPH. You can go up or down from there.

I am going to act like you know nothing about this, so if I am wrong, please understand that the next person who reads it may NOT know anything and it will be of value to him/her.

Measure the diameter (distance across) your rear wheels Top to bottom or side to side in inches.

Multiply that by 3.1416. That is the distance around your wheel, and the distance it will travel each time your wheel turns 1 revolution. Divide that number by 12 and it will be expressed in feet and/or fractions of feet.

a 6" diameter wheel is 18.84 inches or about 1.6 feet. around, or in circumference. There are 5280 feet in one mile, so if you divide that by 1.6 you will find that your wheel needs to turn 3300 times to travel a mile, and if it were turning 3300 revolutions per minute (RPM), it would be going a mile a minute or 60 miles per hour. (MPH).

If your desired speed is only 5 MPH, that is 1/12 of 60 MPH, so if you divide the 3300 RPM by 12, you will find your wheels need to rotate at 275 RPM, and you can double check that by multiplying the 275 RPM by 1.6 feet per revolution, getting 440 feet per minute, which is 1/12 of 5280, making your speed 1/12 of 60 MPH, or exactly 5 MPH.

The bad news is that if your motor speed is 5000 RPM, you will need an 18:1 gear reduction ratio. That would mean you would need a few steps with additional shafts or your axle sprocket would need to be 18 times the size of your motor sprocket. The good news is that if your motor speed is around 100 RPM, it should work just fine as it is ….Joe
Multiply

 

[Finlee]

You can calculate this stuff with just a bit more information, but you will NEED some more information. You need to know what the RPM of the motor is, to start off.

You already know you have a bit over 1 HP, which should be good if the boy is small and the desired speed is slow.

You need to select a desired speed, though, so maybe call it 5 MPH. You can go up or down from there.

I am going to act like you know nothing about this, so if I am wrong, please understand that the next person who reads it may NOT know anything and it will be of value to him/her.

Measure the diameter (distance across) your rear wheels Top to bottom or side to side in inches.

Multiply that by 3.1416. That is the distance around your wheel, and the distance it will travel each time your wheel turns 1 revolution. Divide that number by 12 and it will be expressed in feet and/or fractions of feet.

a 6" diameter wheel is 18.84 inches or about 1.6 feet. around, or in circumference. There are 5280 feet in one mile, so if you divide that by 1.6 you will find that your wheel needs to turn 3300 times to travel a mile, and if it were turning 3300 revolutions per minute (RPM), it would be going a mile a minute or 60 miles per hour. (MPH).

If your desired speed is only 5 MPH, that is 1/12 of 60 MPH, so if you divide the 3300 RPM by 12, you will find your wheels need to rotate at 275 RPM, and you can double check that by multiplying the 275 RPM by 1.6 feet per revolution, getting 440 feet per minute, which is 1/12 of 5280, making your speed 1/12 of 60 MPH, or exactly 5 MPH.

The bad news is that if your motor speed is 5000 RPM, you will need an 18:1 gear reduction ratio. That would mean you would need a few steps with additional shafts or your axle sprocket would need to be 18 times the size of your motor sprocket. The good news is that if your motor speed is around 100 RPM, it should work just fine as it is ….Joe
Multiply

Joe, I appreciate your time to write that out, that makes so much sense.

 

[ol'joe]

Not a problem. The artisan class survives by teaching one another. Without that, we are toast...Joe