Electric go kart

[Chuechco]

Hi kart-builders,
I'm a student from germany. Half a year ago, I watched a video on youtube about an gokart moved by an electric forklift motor. Since then, I want to build an go kart. I am also interested in electronics and want to ride smoothly and with little noise comming from an powerful motor. I already bought the motor for this purpose. It weights nearly 40 pounds and is advised to run on 24v. I will overvolt it to either 48v or 72v which is not critical if it only drives little weight. I attached some pictures of the design I made. All parts' dimensions are real. Except for the seat which I didn't want to design correctly. http://imageshack.us/photo/my-images/51/23467625.jpg/

The kart is 160cm (63") long and roughly 120cm (47") wide. The black boxes on the sides are the lead acid batteries of course. They weight 66kg(145lbs) together. Yeah, they are heavy.
http://imageshack.us/content_round.php?page=done&l=img405/8467/42365460.jpg&via=mupload&newlp=1
I haven't designed the rear axle yet. I'm not quite sure which gear-ratio to take and I haven't yet thought about brakes. Just to give you an idea of the motor:
http://imageshack.us/content_round.php?page=done&l=img189/9080/61792706.jpg&via=mupload&newlp=1[/
Does somebody have an idea how to attach these pillow-blocks to the frame?

Here's the layout of the frame:
http://imageshack.us/photo/my-images/215/53919248.jpg/

I also kept in mind to include some steering geometry.
Camber-angle is 11° and caster-angle is 10°. I also took care of the ackermann-angle which you cannot see from this picture
http://imageshack.us/photo/my-images/202/37749406.jpg/
As you can see I want to attach the spindle-assembly not in center so that the front wheels are in line with the back wheels. Will it break when driving?

The kart will probably weight more than usual street karts. Using this motor, top speed will be more than 30mph. I'm not sure which pipe to use in this case. Any suggestions? The pipe in my design is 1" in diameter. But how thick?

 

[landuse]

Keep the pics coming. This should be an interesting build. I would probably go with 1.8mm or 2mm wall thickness. That should be more than enough.

 

[wingnut]

Have any specs on the motor? Do you have a speed controller picked out? I'm skeptical that a motor wound for 24V with any significant power is going to work with 48v. I think that the current draw will be too high for the controller. To get to 35mph with any kind of acceleration then you're talking about a 2 KW motor at least.

 

[Chuechco]

Motor is a series wound forklift traction motor.
http://imageshack.us/photo/my-images/59/dsc07755g.jpg/
http://imageshack.us/photo/my-images/94/dsc07756iw.jpg/
http://imageshack.us/photo/my-images/835/dsc07759z.jpg/
The shaft gives me headaches. Thats the only problem with this motor I think...

Some facts:
U = 24V
I = 140A
n = 1800rpm
P = 2.4kW

So it's meant to be powered at 24v which gives 2.4kW of power. But while reading about some similar motors, I found out that these electric motors will have a higher peak power.
Many electric go karts use forklift motors and overvolt them. http://www.evalbum.com/1205
Ok, the motor used in this kart blew at 140V and 900A. 72V is the maximum I want to run mine.
I did some experiments on motor controller in the past. I've already bought 7 power MOSFETs rated for 120A and some flyback diodes which may be a bit underpowerd (15A continuous each). Is there anyone who's built an motor controller rated for something like 300A?

 

[wingnut]

Yup. Tons of amps. The controller used in the project you linked was a $2k controller (made for a car?). Another thing to consider is the battery life and how deeply you can cycle them. A regular 12V car battery is going to give you around 100 Amp hours but if you cycle them below 50%, they don't last very long. If you want to pull 300Amps, that works out to run times of around 10 min before you have to recharge.

 

[Chuechco]

I chose 4 deep cycle 34Ah batteries. I'm going to add 2 more when I can afford them

 

[baer]

Hi looks like an interesting project
You may want to consider these points -
- wiring for 300A current should be close to seens in EV's
- front wheel shaft: the shaft should be as short as possible, the longer it gets the thicker the shaft and spindle should be. Are you planning diy spindles?
- i built diy controller (for 300w) with 120A mosfets, for details you can see my thread

 

[wingnut]

34Ah isn't going to give you much run time with that kind of current. Even deep cycle batteries can't cycle down to zero without damaging the battery. Come to think of it, if you're building your own controller, I think you'll want to be careful with the batteries. A commercial controller will cut off the power when the voltage gets too low to protect the battery. If your circuit doesn't do that then it will be really easy to kill the battery.

Have you considered just running it at the rated 24V? 2.4KW is the range that standard golf carts run at and they're reasonably quick plus you'll be running with lower weight. That way, you're current draw is reasonable and you can run your 4 batteries in a 2x2 configuration doubling your Amp hours.

 

[r97]

looks like a fun project! i wanted to make something just like this but got turned away by the costs.....

unless i'm looking at it weird, it looks like your camber is 0*, and you have confused king pin inclination (KPI) with camber,

 

[Chuechco]

Hey guys,
thank you for your help.
300Amps should be the total amount of current the controller will handle. When driving along I expect an average current of far less than that. But ok you convinced me. 24v should be fine to start off. I've connected a 12v battery to the motor and it spinned like hell. Then I go for the 68Ah 24v battery system which should give me a total runtime of more than half an hour I think. And thanks baer, I will read your thread about the controller.
@r97: Yes sorry, dealing with all these english technical terms is sometimes a bit hard. My KPI is 11°.

 

[r97]

don't worry about it! i can't wait to see this thing finished, please tell me there will be a video!?

 

[wingnut]

I always like the idea of electric power. Quiet, simple, easy to fix. I converted a go cart to electric for my kids using electric scooter parts. Worked pretty well and the performance was appropriate for their age. When you start looking at higher performance applications though, the price gets kind of ridiculous for motors and controllers beyond the 4Kw range and battery technology just isn't there yet.

 

[Chuechco]

I'm going to upload some videos as soon as the kart is finished. But it will take some time. My welding skills are limited. A friend of mine is a metalworker and will help me building the kart together. We will order the pipes next wednesday. Meanwhile I will work on my controller. Here's a video of a small controller I built. I added some information if anyone's interested:

http://www.youtube.com/watch?v=m2jFqllNWOU

 

[baer]

Liked that oscilloscpoe.
Note that the mosfets needs good colling otherwise they will burn at relatlely low power.

 

[Chuechco]

The controller for the big motor will have a big heatsink for both the mosfets and diodes. But with my current setup the mosfet doesnt even get hot. I felt so confident that I went stupid and connected the big motor to this tiny controller. I turned the potentiometer just a little bit so that the amperemeter read 1Amps. I'm not sure why, but the mosfet suddenly got extremely hot. i think I would've destroyed it by going just a bit further. Do you have an answer for that? One reason might be, that the mosfet is not controlled by an mosfet-driver. The PWM signal of the microcontroller goes right to the gate of the mosfet. I've heard about a certain capacity between gate and source which has to be charged until the mosfet becomes conductive. The microcontroller probably draws too a little current.

 

[baer]

Yup they get hot very fast also with 1A and even with a heat sink not well connected (now I use cpu thermal grease). They can also be destroyed by too long soldering.
The one I am using (link) was burnt before the heat sink was good enough.
I read somewhere that it is good to put a serial resistor between pwm and mosfet gate, I used 100 ohms which creates a small throttle delay, therefore I recommend 10 ohms.