Tuesday, October 14, 2014

Electric Surfboard (extreme sports in slow motion)

After my last post, the surfboard got a brief water test in the Charles and there was evidence of a very slow leak in the tail. To remedy this, the board got two more hot coats to (hopefully) seal things off. (Spoiler: it worked)

Fins and fin mounts (compatible with commercially available fins) were hastily 3D printed from ABS. Fins were reinforced with aluminum rods but the fins were actually very strong without them. The weakest point of the fin is by far the point where it is held by the mount. The fin mounts were attached to the board with epoxy/microballoon slurry, where balloons were added until the mixture had the consistency of yogurt.

Fin mount

The aluminum bits are where the screws contact the fin and push inward/up to hold it in place.

The lab's resident Hawaiian and surfing expert noted that these fins are WAY too thick.  Next came the 'waterproof' battery. I built a 22Ah 13.2V pack and submerged it in epoxy. When you do this, you prevent the cells from being able to vent, which is bad. I tried to remedy this by attaching pieces of foam to the pack to allow for some displacement but the foam just soaked up the epoxy and by then it was too late. The pack is completely sealed and will not be happy if it ever needs to vent.

Attempt at foam with kitchen sponges. This did not work.
After the epoxy had set fully, I put on a plastic cover and cut a section out of a smoothie bottle to allow for sealing off the battery while still allowing access to power and balance leads. This was done in a rush. Adrian, don't do this again. Bad. It still worked fine in the water, but we must remember that the Charles is freshwater. No sea legs for this setup.

Sealed up
Another precaution I took was a 'deadman' switch. This is so if I fall off the board, it doesn't keep going. There are controls on the motor itself, but they don't require the user to give continuous input and it will stay on if it isn't turned off. The monstrosity below is a springy 3D printed frame with aluminum contact pads that come together when pressed to complete the circuit. When released, the circuit is opened and the motor will turn off. Umm. The glove makes it waterproof. Yeah.

Next was the motor mount, which involved very very drippy microballoon epoxy and an aluminum plate with holes for 80/20 to be attached. It looks like crap and I know it.

It's a surfboard?
The motor was attached next and damn was it heavy. Not pictured: the battery on the nose of the board for counterweight.

Sometime in October, a few friends and I headed out to test. It wasn't a sunny day but the weather wasn't bad. I had a wetsuit so I stayed pretty warm throughout the trip. Huge thanks to Tommy, Calvin, Dan, Rodrigo, and Andrew for helping out!

Everything was tied down with twine, especially the motor and GoPro.

By the way, the battery is in my backpack along with a whole bunch of foam for buoyancy in case it falls off.

It floats!
It floats... but lower

Here goes...

I went about 1/3 of the way across before turning back.

There is footage of the trip but it's 30 minutes long and I haven't edited it yet. Overall, the trip was a success. The motor didn't push me nearly fast enough to stand up. This was partially due to the motor's power being fairly lacking (it is the smallest of its class) and also because when I was just sitting or laying on the board, I was mostly underwater, providing more resistance and making it more difficult to gain speed. I topped out at about 5 mph, which was still quite a lot of fun. Also I haven't grown any extra limbs since being in the river, so I've got that going for me, which is nice.