motor help

In Over My Head

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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 428 chain and front is 10t 428 welded onto a smaller T8F sprocket, 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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JTSpeedDemon

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Sounds like you got a gearing problem. You've got a 4.1/1 final drive, and it looks like at least 20" tires, you need to get a bigger axle sprocket, smaller motor sprocket, install a jackshaft reducing setup, or get smaller tires, which doesn't look like an option.
You'd be really surprised what a small motor can do, what people call "underpowered", 95% of the time it's just bad gearing.
 

In Over My Head

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Thank you, I picked out a 56T rear sprocket online. (Still in my cart ) I did not see any that were bigger that would fit my setup. I am still thinking about upping the power to be safe and am not sure if I would be better off running two motors with two controllers and two battery packs- hooked up to one throttle and a solid axle, or just upgrading to a 3000w 72v motor. Either way, i have to buy another motor and two batteries. So the cost is pretty close in the end since another 1800w motor is cheaper than a 3000w. Any thoughts on my logic? Will another/bigger motor be needed after i get a bigger sprocket?
 

JTSpeedDemon

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I recommend doing one big motor, dual motors can certainly work and it can be very cool, but it's so much more complex so I would recommend just doing one big one. 56T should get you going a lot better. If it doesn't then you'll need a jackshaft.
 

In Over My Head

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I ended up getting a much, much larger rear sprocket, a 3000 watt motor and will create a jackshaft (if needed). I researched them online and am pretty sure i can fabricate one if required. If this doesn't work i will probably throw in the towel. Thank you for the responses, They are really appreciated.
 

madprofessor

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Greater gearing ratio should definitely be your first step, the "much larger" rear sprocket is the way to go. For those little kids, less top end with more starting torque acquired in trade is optimum answer for minimum effort and cost.
If "much larger" means 72-tooth, you're there. If you make a habit of swapping axle sprockets to find what works best, I heartily recommend getting a hub to put on your axle just the one time, and do your experimenting with split sprockets that you can buy for less than $15 all day long. 6 bolts to the hub and done, maybe 5 minutes.
 

In Over My Head

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Thank you for the info. Unfortunately, I could not get a 72 T sprocket to fit within my frame as I had built it around the stock 41T sprocket. I was able to measure out a 56T sprocket. I also thought that was "much bigger" but now I am not so sure. Anything larger would mean cutting a lot of welds and refabricating the back end. Not a deal breaker, but also not on the top of my list. I am not an engineer, nor an artist, so please forgive both when you look at the picture below. In my head, this works and will give me more torque. If the kart tops out at 5-10mph, that is fine with me. I am looking for a kart that can hall 6-7 kids around, while dragging a couple more behind it. Will the set up shown below work? Will it drain too much power from the motor? Am I over thinking it and will a 3k watt motor and a 56t sprocket be enough?
 

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madprofessor

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If motor sprocket is 10-tooth with that 41-tooth axle sprocket, that's still only a 4.1:1 ratio. Need your 3K watts motor's rated rpm's to use the calculator mckutzy linked above.
I just ran it as 1k rpm's on 20" tall tires, got a top end speed of 14.56 mph., straight up, no jackshaft reduction.
The 10-tooth jackshaft sprocket to the 56-tooth axle sprocket is 5.6:1 ratio. Multiply that out with the 4.1:1 ratio above driving the jackshaft and you get a 22.96:1 ratio at a whopping 2.6 mph.
If that were to be the 20" tires, the 1k rpm's, and the gearing above, that thing should be able to pull a dump truck out of a ditch.
 
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