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Discussion Starter · #1 ·
I am building a Kart for my kids from scratch and purchased several separate kits online and spliced them all together. I took a welding course and this is my first project, however in hindsight I should have taken an electronics course instead because I am having issues. The kart has large tires and was built for two small girls to drive around in the back yard with their neighborhood friends (all under 10yoa). There is no incline, just flat surface. Not looking for speed, just torque to move them around. I went with an 1800w 48volt kit, and while on jack stands it screams like a banshee, with a load (cart (125lbs) on the ground and me (175lbs) in it) it barely moves. I tested the load weight volts and it barely dropped so I know the packs are good. If I mash the accelerator and "Fred Flintstone" it I can get it rolling. I have come to the realization that it is just under powered. So my question is, which of the below is my best option going forward? Back sprocket is 41t and front is 10t, which I would like to keep.

1. get a second identical motor and controller and attach them to the one battery pack and throttle. I can easily have both chains running to the same solid axle. I have heard a lot of issues with syncing, and one motor leading due to factory quality control so they are not exactly the same motors.

2. upgrade to a single 3000 watt 72 volt motor and controller (will this have enough torque to move 500 lbs comfortably)

3. while less desirable due to noise, switch to a gas engine. This would be the last resort as I really want an electric motor, but if that is what is recommended then so be it.

4. A suggestion that I haven't thought of that is within reason for a weekend warrior.
 

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You should try a larger axle sprocket. Try using the largest that will fit and adjusting the ratio with different motor sprockets. It is probably very convenient to use the 10T, but it is too small for durability and excess noise. You may be able to weld larger motor sprockets onto the 10T sprocket, if you can't find ones that fit your motor shaft.
 

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Discussion Starter · #3 ·
You should try a larger axle sprocket. Try using the largest that will fit and adjusting the ratio with different motor sprockets. It is probably very convenient to use the 10T, but it is too small for durability and excess noise. You may be able to weld larger motor sprockets onto the 10T sprocket, if you can't find ones that fit your motor shaft.
If I go with larger sprockets, how much more torque will I get, that is, will it be enough to move the cart comfortable under load of say 500 lbs? Or should I get a bigger sprocket AND think about more power? Thank you for the reply by the way.
 

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Try the larger sprocket first. Bicycle chain and sprockets, because of their wide size range and availability, might be a good choice for ratio and speed testing. Ultimately,
you may need to use a stronger chain.
 

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Discussion Starter · #6 ·
I ended up getting a much larger rear sprocket, a 3000 watt motor and will create a jackshaft (if needed). If this doesn't work i will probably throw in the towel. Thank you for the responses, They are really appreciated.
 

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Gearing! Motors can rotate at high RPMs for sustained periods of time, and it sounds like your issue is the torque required to get moving initially. What you want is a reduction gearbox, say 5:1 ratio. This will give you 5x the torque but 1/5th the RPMs. Which shouldn't be an issue unless you want to be really dangerous and take a go kart above 60mph.

This is what everyone does. Tesla has a gear reduction of around 10:1 in their differentials.

True direct drive (no transmission OR differential) almost never makes sense since having a wheel spin at 10,000+ RPM is not ever necessary, so you can convert that rotational power into torsional power.
 

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Rather than expecting anyone to advise on a specific gearing solution, it would make more sense to me to just go back to the basics - this is really a very basic problem.

  1. What is the tire overall diameter? If don't know that, no rational calculations are possible.
  2. What is the desired top speed for the kart? If you don't know that, you can't choose a suitable compromise between low-speed acceleration and top speed capability.
  3. What are the maximum speed of the motor, and the motor speed for maximum power? You can't choose gearing to suit the motor if you don't consider the motor.

Given those three bits of information, you can calculate the maximum overall gearing reduction ratio (ratio of motor shaft speed to axle shaft speed). You have 4:1 now; you need more to get moving, but still less than that maximum to avoid excessive motor speed. If you do the basic calculations and try suitable gearing with the original motor first, you might not need to switch to the larger motor.
 
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