This happened a little while ago, but there you go. Besides the kart, a good chunk of the costs are the motor, motor controller some related components like diodes/fuses/contactors/relays etc. In my case, this ended up being a total of about $1200. Not an easy expense to get through, but it has to be done. Most of the parts involved are fairly rugger and I’m not really worried about … break-age. Apart from the motor controller and the pot box, the rest of these parts were bought from evdrives.com. Talking to them over email a few times showed that they are very responsive (responses in a few hours to a day each). After I did make a purchase, the parts arrived in about 5 days. I was actually somewhat surprised. I was expecting a few weeks of lead time, but the package shipped the next day. Yes, you can go with a random Chinese website, but buying from inside the country is heavily recommended since the stock is here and the people are based here. Things get very complicated (if you read stuff on the forums) if you bought something from China and you don’t get your stuff. EV Drives came through though. Very happy with my purchase.

Same goes for the DIY Electric Car forums where I bought the motor controller and the pot box used from a member. I can’t stress enough the awesomeness of being able to talk to people to get opinions/suggestions and sometimes cheap (and good) parts!

I’ve been maintaining this Bill of Materials for a while, but well, here it is. As you can see, most of it is a nice bright green. The only thing I’m still missing are batteries.

Sparkplug 1.0 Bill Of Materials

I wonder what my next post will be about? Hmmm……

With the motor picked out, the next big component of the system is the motor controller. The motor controller controls the current drawn by the motor based on throttle inputs and a few other configuration settings. For my particular motor, the ME1003, I had the following requirements:

• Cheap-ish (as always)
• 72V @ ~400A
• Easily programmable

Looking through the forums, I happened to come across a pretty good deal for an AXE7245 on the DIY Electric Car forums (another great resource both for used parts and information). This one met all my needs. And to make the deal sweeter, the used item I found was about $250 less than retail!

The AXE7245 controller supports anywhere up to 72V at 200A continuously. It also supports 450A for about 2 minutes. This is in line with what the ME1003 can handle. Another big advantage with these Alltrax controllers is that they are programmed using a simple RS232 cable. You don’t have to buy something custom. More importantly, since it’s just RS232, at some point some sort of embedded programming could occur if I felt like it was needed.

I’ve already connected to the controller using the software, so at least I know the used part works. Yay.

Besides the frame, the next most important component of an electric kart has to be the motor. In order to compete with some of the faster karts out there, I was looking for something in the 15HP-30HP range. Setting aside procurement options, there are two basic types of motors to choose from – Permanent Magnet and Series Wound. Yes. There are also brushless DC motors. But these were expensive and work with AC voltages and multiple phases. I did not want to deal with any of these things (especially the cost).

Permanent Magnet

Permanent magnets are the simpler of the two designs. Permanent magnet motors have fixed permanent magnets as the outer set of magnets. Only the inner set of magnets are electromagnets and are continuously switched in orientation to keep the shaft rotating. (Instead of me explaining in useless detail how a motor actually works, you can look at the wiki article. That should get you a fairly good understanding of how these things work.)

Permanent Magnet motors tend to be smaller and cheaper. Most of the permanent motors today use Neodymium magnets, which are apparently much better than previously used materials. BUT, even with better materials being used today, permanent magnet motors have a problem with heat build-up. Since these motors use permanent magnets, their outer set of magnets suffer from demagnetization. This happens as the magnets reach their Curie temperature. And when the outer magnets lose their magnetic strength, the motor effectively loses power. A further concern is that this magnetization isn’t always reversible to the full extent, so you could do some real damage to the motor if you don’t watch the temperature.

Series Wound

Series wound motors are slightly different in that their outer set of magnets are also electromagnets, instead of permanent magnets. These outer electromagnets are kept configured in a fixed configuration, so logically, they are the same as permanent magnets. However, since these outer magnets are just coils, they can overheat and still not lose magnetic strength. Obviously, there is a point where the temperature is hot enough that it starts fusing the coils of wire, but these temperatures are much higher than the ones that will cause damage to the Permanent Magnet motors. This allows the Series Wound motors to be abused a lot more without permanent damage. The disadvantage of these Series wound motors though is that they tend to be about 20LB heavier. They are also usually more expensive. On a kart, the continuous abuse these motors can handle could possibly outweigh (hah) the weight and price disadvantage, but in my case, I went with the permanent magnet motor – the ME1003 to be specific. I don’t see myself doing full throttle long enough to get the motor too hot. Additionally, a fan might be a cheap / light alternative to paying the weight and money costs with a series wound motor. The permanent magnet motor (ME1003) is also smaller in dimensions compared to the ES-33 motor that I was also considering.

The ES-33 is actually a very good option and has recently also come down in price (annoyingly). But the theoretical power output is still about 10HP less. If it was $625 when I bought the ME1003, I think I might have considered the ES33 more.

Oh well, too late now.

ME1003 Motor Specs

• Power: 11.5KW continuous, 23KW Peak for 1 minute @ 72V
• Voltage: 12-72V
• Speed: 3050RPM @ 72V
• Size: 8″ OD, 7.42″ long (w/o shaft)
• Shaft: 7/8″x 1-5/8″, 3/16″ key

As the power section above says, the motor is capable of doing 23kW (or about 30HP) for a minute. This seems somewhat short, but on a typical autocross track, turns come often. According to the manufacturer of the motor, “The 1 minute rating is caused by heat in the armature and brush holder.  Once it cools down, then you can do it again.” So hopefully, I can abuse the motor right after a turn and let it cool down while braking / during the turn. With the given specs, and using an online calculator, the theoretical top speed of this kart is about 80MPH …

Heh

When I was first shopping around for parts and options for Sparkplug, I was set on spending about $100-$200 on a simple frame – or better yet, building my own.

Given that I have no welding skills, the building-my-own idea was quickly thrown out. There are however, lots of people who have done this and made their kart specifically to be able to easily mount their motor/batteries etc. One example that I liked was the Neurotikart. I am not entirely sure what his numbers are as far as weight goes or how well the kart actually handles, but he says he goes up to 60mph. Fun stuff.

The $100-$200 option also slowly came to a painful crawling death. Mostly because of this:

This is what you usually see for $100-$200. Well actually, I lie. You actually see much shittier, older versions of these. After another month or so of periodically searching online, I finally decided to spend up to $500 or so. After a very random lucky visit to eKartingNews (awesome resource for kart parts / help), I found something like this:

As you can see, you definitely get what you pay for. Instead of an old ass kart, this one is a fairly new shifter kart rolling chassis (wheels not shown here). I was lucky to some extent. These frames usually go for about $700-$1000, but I got this one for $550. So moral of story is look again and again, look local if you can and bargain (the seller initially said $650). It’s even better if you can find someone just trying to get rid of their stuff (like this guy was). Usually they will have other stuff on them that they will give you for very little more. I got 2 free front tires from this guy (yay).

Yes, if you look closely, you will see “CUPCAKE” on the front of the kart. That will obviously change…

The seat unfortunately is too small for me. Even if I lose more weight, I think I’ll be happier with a slightly larger seat. The one in here is actually a REALLY good one. Hoping to get about $200 for it. In it’s place something simple/cheaper (around $80-$100) should do the job.

So frame sorted, now to find me a motor.

Hmm… wonder what this could be. Perhaps a battery powered go-kart?

This idea of building an electric go-kart started with a very random thought during the 2011 Solar Decathlon process as I was helping the UMD team. I felt like a small motorized bed would be helpful when moving underneath the house (working on wiring and plumbing). Inevitably, my mind wandered into the territory of “wait, what if it was faster?”

Initially, this was going to be a very simple project, with the end result being something that would be a 10-15mph kart. This eventually also went in the direction of “What if it was faster?” The end result is Sparkplug.

As the picture shows above, I already have a frame and some other parts. There will be more posts soon about these things and how to get them/use them etc.

But for now, you can enjoy the plethora of kart porn.