Saturday, April 13, 2013

The life and death of Zoran

We got tired of not having a name for the kart so we came up with Zoran. In Norse mythology he's the god of speed and the one who built Thor's Chariot. Charles (dear leader) thought we named our car Zorak, not quite, no. (Just to clarify, Zorak is the mantis in that clip and it's from a show called Space Ghost Coast to Coast).

We put together a logo type thing and engraved it on one of the leg plates. Here's a video showing the process, I suggest you click the little gear to speed up the playback. It prints rasters just like an inkjet, but at least thirty times cooler because lasers.

According to legend, the most devout followers of Zoran would set themselves on fire and jump off of cliffs. Seems like it might have been tricky to keep up membership. We thought this was fitting enough.

With the mechanical construction essentially finished, it was time to turn to the electronics. This is a wiring diagram we made up ex post facto to actually wiring the thing. I have a decent amount of experience making connections and didn't have an issue keeping things straight. We were also super pumped about the possibility of driving the kart.

So, not super complicated, but some attention does have to be paid to good practices because of the high currents involved. The toggle switch, precharge resistor and LED are all mounted on a panel beside the large battery cutoff switch. The LED will blink out error codes if the controller thinks something has gone wrong. Rather than being mounted though the panel there is a really thin section of wood that the light shines though.

With everything wired up we threw the switch aaaaaaaand...... got an error code. Two blinks, a pause, then four blinks. There was something wrong with the throttle. Our personalities caused us to take apart the throttle to figure out what was wrong. I thought there would be a potentiometer inside but it turns out there was a hall effect sensor that puts out a voltage based on the magnetic field in the area. Twisting the throttle grip moved a magnet closer to the package and it gives a higher voltage. Turns out you aren't really supposed to take these things apart. We borked up the position of the sensor and now have another throttle on order. The error we had was fixed by reprogramming the controller. Kelly Controller makes really cool products; it interfaces with a computer using a program they provide.

That's too much text. More pictures.

Note: This is not a recommended rider position.

Shipping will take about a week, so in the mean time we have made a sketchy throttle involving rubber bands, found parts, and hot glue. It ain't pretty but it works. You don't get close up pictures because it's really not recommended.

In a short test I found out the hard way that accelerating too quickly will blow the 40A fuses on our battery. That's not okay but for now we can just go easy on the throttle. After replacing the fuse and waiting three days for the weather to hold off long enough to have dry ground we finally got a "real" test drive today. Top speed on the kart feels nice and stable in both positions and the brakes work well. I wanted my pre-frosh to take a ride but before I could get him over to where we were testing the power cut out again. Bummer. Charles thinks the batteries aren't balanced properly. They're pretty "smart" batteries and can turn themselves off if they think something is wrong. However, they're also rejects donated by the now defunct company A123. That may have something to do with it.

So, Zoran has lived three times and died three times. I really didn't expect the biggest problem with the kart to be electrical but luckily there's enough time to sort it before competition.

Here are a couple of test videos.

Until next time.