At this point we only have a couple of days left to finish this project. We’re working hard to pull all the parts together.
Haydn and I have made a couple of prototypes of the motor and gear housing on solidworks and then in cardboard.
Currently, Nick is machining alloy wheel rims, with John the workshop technician running the CNC Haas machine to produce the Urethane wheels.
James is currently working on redesigning the hand controller.
Jason has designed a packing spacer to fit under the front trucks, to make the board level. Just waiting on access to a Modela to machine it.
Damien has bought some larger trucks from Australia, and bought a new board deck from trademe. We’re still waiting for both to arrive.
Hubless Wheel Material and Components
The components and materials for the hubless wheels are all sorted.
We had three options for the bearing sizes which are:
Bore - OD - Width
90 - 98 - 30mm $125.00ea
95 - 103 - 30mm $95.50ea
100 - 108 - 30mm $75.15ea
The prices for the bearings are quite expensive, mainly because it’s not that common to use these bearings for large applications, they’re mainly used for smaller applications but we’ve decided to go for the middle sized bearing.
The materials we decided on is Urethane and Aluminium. We chose the Aluminium because it’s got a excellent strength to weight ratio, helping to keep the overall weight of the board down. It’s going to be for the inside ring, it’ll be cut out on the modela and then finished on the manual lathe. Most common skateboard wheels are made out of Urethane with a hardness rating of between 75a and 100a typically. It’s a hard rubber type material, although not too soft so we can’t use it on the CNC lathe. The Urethane we have obtained is 125mm OD x 250mm length with a hardness of 90A so it’ll be perfect for our wheels.
We need 36V worth of batteries to power our board.
We want a good weight to power balance. NiMH batteries could be the solution to this problem. Sourcing these batteries is not a problem, finding a 36V charger for these batteries is. Ideally, each individual cell should be charged equally and separately. A 36V charger could damage the cells.
For the purposes of demonstrating our board we think we may make a bank of 30 1.2V AA NiMH cells, totalling 36V, and charge each cell on a charger before each use. This means we can have a very discrete, small, battery pack. This is also a very cheap option. At 3000mAh we can still get almost a third of the power and distance of a commercial off-road board.
Nigel Vining, founder of Greenskate
Greenskate.co.nz has, so far, been our point of reference for electric skateboards in NZ. They almost exclusively are the only online retailers of electric skateboards, outside TradeMe.
I bought a motor controller from Greenskate. Nigel Vining, founder of Greenskate, agreed to meet up with us in Wellington City to give it to us and talk skateboards.
Nick, Damien, Jason and I met Nigel in town. He told us about how Greenskate started. At Christmas in 2007 Nigel saw an electric skateboard and really wanted one. He said he began experimenting in a similar way to us. He even had the same electric scooter at one stage. Electric skateboard retailers in NZ were too expensive and he soon found that it was more cost effective to buy a batch of ten from China and keep one for himself. The other 9 sold quickly, and later people were demanding parts for them. When Nigel developed a Li-Poly battery pack, other people wanted that too. Now Nigel runs Greenskate with two friends supplying the NZ market with electric skateboards and parts.
Our skateboard requires a pretty decent output power, and a motor will draw a lot of current.
We need some decent, compact batteries that are high capacity and have a high energy density.
At the lowest level are SLA, Sealed Lead Acid, batteries like your car battery. They’re cheap, low maintenance and high capacity, but are heavy and very bulky.
At the top of the range are LiFePo4, Lithium Iron Phosphate, batteries. They’re very high capacity and very small and compact. They have a great amount of energy for such a small package. They require a special charger to charge each individual cell equally.
Ranking in between SLA and LiFePo4 batteries are NiCd, NiMh, Li-Ion & Li-Po. Any one of these could be an adequate compromise.
The price different in these is huge. A set of SLA batteries (at the lowest level) for our board would be about $250. A set of LiFePo4 batteries (at the best level) would be about $700.