Friday, June 28, 2013

More Progress on the Electric Skateboard

After quite a long hiatus, I've finally got some time to add a post updating the electric longboard build. This past semester was my last in undergrad. I graduated from UH and have a temporary job that will give me some money to add to my savings. The plan is to try to get into law school and see how that route goes. Looks like I'm actually gonna study law.

Anyways back to the longboard - Thanks to the recommendation of a reader, I picked up an Alien Drive Systems motor mount kit for the skateboard, and my work on the electric longboard has progressed immensely. I've already been through many versions of the longboard, each with improvements on the previous.

The biggest decision to make was whether to give up all the work and money I had put into my previously planned drivetrain and pick up an Alien Drive kit, which comes from the UK and is about $175. You'll get the mount, pulleys, screws and a belt. You need to bring your own motor, motor controller, battery, board, trucks, and wheels. While you have freedom over the motor, motor controller, battery and board, you must use Holey Trucks and ABEC 11 Flywheels. You can get the trucks here for about $60 and the wheels pretty much anywhere for about $50-$60.

As much of a waste as it was, I pretty much scrapped my previous plans for a motor mount and drivetrain and went with the Alien drive mount because it would be more simple and quick. I'll try to use the leftover metal for scrap and melt it down or something. After trying the kit out on my S9 board, I realized that at speed, the ride would be pretty unstable due to 2 factors: the board is really flexy and the wheelbase is short. I still wanted a light board with a relatively small wheelbase, but it would still have to be able to keep stability at speed. I ended up going with a Never Summer Motive and haven't been disappointed. Never Summer was originally a snowboard company that now produces longboards as well. The Motive is as long as the S9 (33 in.) but with a wider wheelbase. The Motive is also thin and light but doesn't flex as much as the S9, being built for freeriding and higher speeds. Some miscellaneous things: I also used a 1/4 inch riser to make sure that the motor and mount would clear the bottom of the board. You may be able to get away with a 1/8 in riser depending on which motor you use and the flex of your board, but I think the riser is necessary. Also, a top-mount board seems to be the only way to go. Any other mount style won't leave enough clearance for the motor and motor mount, and you'll most likely end up with board bite.

I'm using a 5065 270KV brushless outrunner on my board, and you should be able to find one for about $50-$60 on ebay. After about a week's worth of testing, I'm debating over whether to use a stronger motor. I would probably go with a 6364 270KV motor - a little bigger physically, same speeds, more torque. Most, if not all, Ebay brushless motors come from China, and most sellers offer free shipping, but you'll probably wait at least a week before you receive the motor. You can also try Hobbyking, but shipping to US is also long and is pretty expensive. I'm using a Hobbywing XERUN 150A brushless ESC but am thinking of changing to a Castle Creations Mamba Monster 2. I'm researching it and am actually only considering it because I can get a good deal on it. Redrock Board Shop actually uses the Mamba Monster ESC in their electric skateboard truck. I got the XERUN for $80 on ebay. I picked up 2 lipo batteries from Hobbyking, and when deciding on a battery you may want to try LiFePO4 if you don't want the risks of lipos. My lipos have een treating me well, and it seems that as long as you take care of them, they won't puff up or spit fire. I got a 6S battery to maximize the power I could get out of the board. The max voltage for the XERUN and the Mamba is 6S too, so that's pretty much the limit.

For the first version, I already had my Arduino code mostly refined and ready to go, so I mounted everything to the board and duct taped anything that didn't seem stable. A good temporary solution, but I needed to find something better for the long run. Seeing how others managed about 6 miles on a 5Ah battery, and my battery is 2.25Ah, I calculated about 2.5 miles per battery depending on the incline. I took the board out on the road and tested it out. With a small push to get it going, the motor took off pretty good, but the speed increments were a little to punchy. I refined the code more and configured the interface for less jumpy acceleration.

I had been testing the board and riding around with everything duct taped to the board for quite some time, so I looked for a way to secure everything and found PureTech. They sell all types of velcro battery straps, and the double PSA straps work pretty well at keeping the battery and electronics secured to the bottom of the board. I wanted to avoid bolting or screwing everything to the board in case I wanted to make changes or have to quickly strip the board. If I ever want to sell the board and get a different one, I would be able to sell an unblemished board as well.

At first, the arduino with the wireless Wii nunchuck wouldn't keep a solid connection, so I made a DIY antenna out of copper magnet wire I had lying around. The antenna works pretty well, and I have a reliable connection between the board and controller now. I got a plastic waterproof case from a friend and used it to house the arduino and nunchuck receiver. The goal is to keep the board as light as possible, and with the setup I have now, the board is about 10.5 pounds. The setup is:

Never Summer Motive
Holey Trucks
ABEC 11 76mm Flywheels
Zealous bearings
Trakpower 6S 3400 mAh hard case lipo
Hobbywing XERUN 150A ESC
5065 270KV Brushless outrunner
Arduino Uno
Memorex nunchuck

The majority of the weight comes from the battery, motor and motor mount, which I don't really have any control over other than getting lighter hardware, which would mean shorter runtimes and or lower power. Most of the other people building electric boards are using 5000 mAh and up, but 3400 mAh seems like a good middle range amount, and I specifically looked for a hard case 6s lipo so that I wouldn't need to add any additional protection. If the battery falls off, or I don't have enough clearance going over a bump, the battery will be safer than just hanging bare underneath the board.

I did some research into battery connectors and decided to go with Anderson Powerpole connectors. They don't require soldering, but there is the very rare possibility that you can short 2 batteries if you plug them into each other since powerpole connector pairs are identical as opposed to connectors like the xt60 (what I used before changing to powerpoles) or the deans plug, etc. This scenario would probably only happen if you did it on purpose.

Here's a video of me testing the board:

The video quality isn't that good, but it shows the board in action. I got to the top speed in the video and was going up a hill near the end. I used my phone GPS, and assuming it's accurate, the top speed is around 22 MPH. I keep on making changes to the board, so I don't really have any up-to-date pictures, but I'll put them up here when I make time. The board is too fun to play with, so I'm mostly riding it around everywhere testing the speed and interface.

Here are a couple pictures of the latest setup: