First post on here, but been reading on this board for the past couple weeks. I'm here to build my own eboard, I've been thinking about it for about 6 months, and with how incredibly dry and warm this winter was, I've been a bit more motivated to finally get this project going.
A little about myself: I'm a 28 year old EE student at Portland State University(only a few terms left), I've had some involvement with a student club building electric formula style race cars for an annual engineering/design competition, prior to/during my earlier years in school I spent 6-7 years working at ski resorts doing all sorts of jobs and am still pretty passionate about snow.
When it's not raining, I've been commuting 10-15 miles round trip everyday on my longboard(currently a drop-through Madrid carving deck, bear trucks, wheels that I've had for so long I can no longer identify them). It's a pretty mild commute, mostly slight downhill with a couple flat/slightly up hill on my way to campus, and the reverse heading back. Skating back during the day when I still have energy isn't so bad, I do a little more walking with it, takes probably 20% longer than going the other way.
Anyways, to the technical stuff...
I'm starting this thread to not only to introduce myself, gain insight from others, but also to help serve as a log for this project as it progresses. I've found the longer I keep things in my head before writing things down, the longer it takes for me to ever get around to actually building anything.
In a perfect world, I'd be building a deck with 2x 2.5kW sensed motors, a dual channel roboteq controller, and a 10s2p battery pack with some of Dow Kokams 7.5Ah LiNMC cells. but figure I should do as basic of a build as possible before I find a way to drop $2k on shiny stuff. So, I've decided on a single motor, single belt driven wheel and a 6s battery pack.
I haven't selected a motor yet, but have narrowed it down to one of the 63mm Turnigy motors. Looking for something in the low 200kv, I weigh around 180lbs and often carry a fully loaded backpack. I have considering messing around with the cheaper NKM motors, hard to beat 35$ if it can work good enough for a prototype, but from reading others experiences I'm not sure I want to take that risk, if I get it and break it I see a good chance being out the same amount of money(and more time) than if I had just went with a higher quality motor. Will post more on this later.
So many options, I'm not even close to selecting a unit... so will also come back to this. I feel like I want to go a little more robust with this since there's a good chance it'll probably see future use as I go on to a more advanced setup, but cost is also a huge factor. It would be nice to have a way to record data, such as current/power, motor speed, distance, etc.
Right now I'm looking at Headway LiFePO4 cells. They are heavy and clunky, but they are still small enough to be used, somewhat safe, can take a little abuse, and are cheap($15-17 per cell). The shape of the cells also leaves me with a few ideas to build a pack that spans the length of the deck, but also leaves the deck with a mostly natural flex. The 3 cells I'm debating between:
10Ah, 3C continuous(10C max), $16/ea:
http://www.evassemble.com/index.php?mai ... ucts_id=18
12Ah, 3C continuous(10C max), $19/ea:
http://www.evassemble.com/index.php?mai ... ucts_id=21
8Ah, 10C continous(25C max), $17/ea:
http://www.evassemble.com/index.php?mai ... ucts_id=20
I only recently discovered the 8Ah HP cell, and I think that'll probably be the ticket. However, the 10Ah cell is cheapest, and it seems most of the motors I look at are only rated for around 50-60 amps continuous, and I'm not sure how often it'd ever have to be pushed to the 10C discharge. 12Ah cell is a 3cm longer version of the 10Ah cell, with similar charge/discharge characteristics.
Anyone have experience working with these cells?
Haven't put much thought into this yet. Probably go with a wireless one eventually, but for simplicity when first building and testing, may start with wired.
I'm not entirely sure what LiFePO4 require for a 6s arrangement. I need to read up more on this, but cheap, easy basic is the primary requirement here. I plan to have 1 solid state relay on the DC side of things that can be opened in the event of a cell being over/under voltage, and probably have current limited by the ESC. If I can't find a solution for this, I was thinking of using the analog inputs of an atmega328p to monitor voltage at each node between the cells. I've read some on this and seen that some people have stated that all the inputs reference the same ground is an issue, but really just makes it very simple--solve it in software by taking deference between each node. Ideally though, I'd like to build a prototype where I need to apply as little of my EE skills as possible... still have a few terms of classes and other projects to complete.
Working on some of my connections through the ski/snowboard world to see if I can find anyone willing to donate gear. I'm not sure I could ride anything other than a drop through deck after having been doing that for a while(I had a sector 9 board setup for LDP that I tried to ride the other day, first time in a long while, road rash=bad). Anyways, once I get a motor and trucks, I'll be drawing up a bracket in Solidworks to weld on to the truck, I have free access to a machine shop with CNC/laser cutting capabilities.
I have contemplated designing a truck that uses a solid through axles that drives both wheels, but doing that is a matter of time(busy student). Have many people tried a setup like this? Run it as RWD or FWD? I think one important benefit is the additional braking traction, but not sure how it affects steering. My initial thought is a RWD setup would want to oversteer in a sense, back end slide out more easily, and vice versa for FWD, would want to understeer/push through turns. I feel like a FWD setup would be better for optimal braking. My gut feeling is a 2 motor setup would be easier for me to setup, than designing a mechanical system to do the same thing, and then that'd open up some options for torque vectoring later down the road... but sticking to 1 motor right now.
And I think that is all for now...
Looking forward to talking shop with you guys!
P.S. Anyone on here from around the Portland area? I have yet to see anyone riding an electric skateboard around town(though see all sorts of other weird things all the time).