woodkart – it works!!

Oops, we finished this over a year ago, but I never got around to blogging. Better late than never, right?

The title glosses over some details: since the last post, we added the seat, breaks, motors, batteries, and motor controllers.

surplus pan seat ftw. The seat bolts to a piece of wood that is screwed to the kart.

surplus pan seat ftw. The seat bolts to a piece of wood that is screwed to the kart.

the mounting holes in the wood needed to be counterbored so the nuts would not stick out

the mounting holes in the wood needed to be counterbored so the nuts would not stick out

adding motor mounting plates

adding motor mounting plates

To mount to motor we first assembled the chain, then pulled the motor back as far as we could and marked the hole locations. However, when actually drilling the pilot hole for the screw, I drilled the hole even further back. That way when we drove the screw in, the chain would be even further tightened. If this approach failed to tension the chain enough, my contingency plan was to add washers under the motor. Thankfully, we didn’t have to resort to this.

motor is mounted by some beefy wood screws

motor is mounted by some beefy wood screws

we used standard bike brake levers

we used standard bike brake levers

I sawed open the clamp on the brake lever so that it would fit over our steering wheel. Although not ideal, if you tighten the screw, this actually does tighten the lever enough

I sawed open the clamp on the brake lever so that it would fit over our steering wheel. Although not ideal, if you tighten the screw, this actually does tighten the lever enough

brake cables run from the levers to each rear wheel

brake cables run from the levers to each rear wheel

the wooden kart frame also serves as the cable stop

the wooden kart frame also serves as the cable stop

Next we built up the battery packs using A123 cells. We built two packs, each one 4s 6p. The packs are wired in series, which provides 24-28V to the motor controllers.  We stared by hot gluing the parallel cells together.

A123 cells soldered together

A123 cells hot glued together

To connect the cells we used flat braided copper wire, commonly used for shielding or as a ground strap. 3/8″ or 10mm wide is plenty for this application. Because the braid and the cells are huge heat sinks, it is essential to have a soldering iron that can provide lots of heat and has a large enough tip to spread it over a large enough area. I ended up buying something like the Weller 80L soldering iron, although I’m pretty sure mine is only 60W and not a real Weller – but it works fine for this application.

soldering cells

soldering the hot-glued rows of cells together

heat shrink tubing for insulating the battery terminals

heat shrink tubing for insulating the battery terminals

soldered packs: with the main wires and the balancing wires

soldered packs: with the main wires and the balancing wires (careful not to set these things on anything metal!!!)

One of my favorite battery pack tricks is to heat shrink pack them with 2 liter bottles. These bottles are blow molded, so when you heat them, they shrink to return to a state of lower stress. You can think of them as balloons that were blown up and then frozen. When you heat them up, they will want to shrink down again. With some careful heat gunning, they will fit very nicely around your battery pack. and provide a semi-hard protective shell.

heat shrinking the entire pack

heat shrinking the entire pack

whoa! it looks like a go kart

whoa! it looks like a go kart

For the motor controllers, I bought the cheapest option when searching ebay for “250W 24V scooter motor controller”. They are basically cheap replacements for controllers on Razor scooters or ebikes. Most of these controllers have connectors for battery, motor, charger, on/off switch, brake, battery charge indicator, tail lamp, and throttle.

We only made use of battery, motor, and throttle. The on/off switch is permanently set to ‘on’ by jamming a U-shaped wire in the connector. For the throttle, we just used a normal push button. So in fact, there aren’t really multiple speeds – just on and off. This makes for a slightly choppier ride, but since usually people just want to go as fast as possible, you don’t notice it too much. Besides, variable speeds sounds like a beta model feature…

a look at the wiry guts

a look at the wiry guts

And…finally! Here’s the proof that it works:

yay, happy people!

yay, happy people!

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s