I'm just getting started, but here's what I have. An electric trail bike based on a '99 YZ125. Everything is assembled, wired, and running. It needs a lot more work to get it into a useful state. I don't have much to show right now, but I'll get some pictures of the components and go into what it took to get to where it is now. Until I figure out embedding vimeo videos; http://www.vimeo.com/26986399
Right at the bottom of the post. It embeds perfectly in the 'test your embed video' thread, but not here. Go figure. Here, I'll try again: <iframe src="http://player.vimeo.com/video/26986399?title=0&byline=0&portrait=0" frameborder="0" height="300" width="400"></iframe> Edit again: One message to the mods and it works! Embedding wasn't turned on for this forum yet. Thanks Johnjen!
I hope you get it worked out right! I would love to have an electric dirtbike capable of a couple hours of medium riding. Would be amazing to tear through some woods w/o bothering the houses that are near.
Cool project! Just out of curiosity, exactly which city in Oregon is idiotville? I think there's more than one possibility. My vote is for Springfield.
So I have a few goals for this bike. They may be modest, but they're goals. 1: Built like a real woods bike. I'm basing this on a full sized bike's chassis, and it needs to not weigh much more than the original bike. The YZ has a claimed weight of around 210 pounds, I didn't check the actual weight before stripping it and I'd like it to end up the same after conversion, but I figure if I keep the weight under 250# that'll be good enough. That's the weight of a modern 250 4 stroke. I'd prefer lighter (sub 225#) but we'll see what I get. 2: Good performance. It needs nice smooth power delivery, especially since there is no clutch to mask any thottle issues. It also needs to wheeley. Top speed should be good enough for local trails, which is around 25 mph. 3: 10 miles of range. That's not much, but if it can be recharged quickly and/or have swappable battery packs then that's good enough for around here. My trials bike has about a 20 mile range and that's enough for a good multi-hour trail ride.
Thanks! No, it's not Springfield. With all respect due our beloved Springfield ADVer's, that's a pretty good guess though. I actually live in Beaverton; Idiotville is an old logging camp in the coast range where I usually go trail riding. http://en.wikipedia.org/wiki/Idiotville,_Oregon. Surprise, it's a real place.
Anyway, since I have some pictures of them, let's start with the batteries. There are a zillion different kinds available. It turns out, though, that only one type will deliver the sort of power* that I want. They are a lithium cell made by A123. They're the same one used in the electric drag race bikes, and in the lightweight replacement starter batteries. The bad news is that they are only made in a long-C cell size, not a big rectangular pack. So I would have to build a big pack out of a lot of little cells. *Batteries are usually rated by how much energy they hold, which translates into the range of the bike. Almost as important is the amount of power they can deliver, which translates into the power of the bike. The cells are expensive, and would be hard to pack into the available space. A little math showed that 100 cells would make a pack that would deliver most of the power that the motor could use. So I paypalled $800 to some guy on ebay and crossed my fingers. He delivered. And one pack is filled. It isn't wired yet. The two packs are different sizes due to the way everything mounts on the bike. This one is smaller, a grid of 9 cells in series, 5 parallel. The other is 11 series, 5 parallel. Lithium cells require management, and I couldn't find anything off-the-shelf that I liked, so I built these: They limit the voltage to each cell to prevent overcharging, tell the charger when each cell is nearly charged to get the charger to slow down, and tell the bike if the cell voltage gets to low so it doesn't discharge them too much.
Sweeeet!!!! What an amazing project, and the bike rides really nice already. I can't wait to see how it feels after some of your power delivery tweaks! Luke, you are an inspiration. Majorly impressive accomplishment!
It's an Agni brushed DC motor. Among the motors I could find that had the right amount of power it was the lightest. As a bonus, it's a lot easier to control than the brushless types, which makes things much simpler. The Agni is rated for around 38 ft-lbs of torque for 5 seconds, which is similar to a 600cc 4 stroke. The continuous rating is half that, which will hopefully be fine in real use. The bigger problem is that there's no transmission, so I have to pick one gear ratio and stick with it.
I need to mention that Earwig has graciously allowed me to work in his shop, which in addition to having much more space than my garage, has much more understanding neighbors. Thank You.
Awesome project! What motor controller will you be using? I (and lots of others here I'm sure) would love more technical details and pictures. This really is a cool project, best of luck.
Cool thread. I've only mucked with electric on a much smaller scale for RC Helicopters years ago (before Lith) but am able to follow you. I thought building up an 18v pack of Nicads was a PIA ;-)
I got a little more work done on it today, and took a bunch of pictures. The motor. As mentioned before, it's made by Agni. It's a Permanent Magnet DC brushed motor. It's rated for 72V and 400 amps maximium. The output is up to 6000rpm and 38 foot pounds of torque. Since 6000rpm is faster than I want to turn the countershaft sprocket, there is a jackshaft in between the motor and the wheel. The stock gearing is 13/47, I am using 11/48. Even then, the motor needs to be geared down so there is a primary reduction between the motor and jackshaft. I have a range of sprockets that can be used, currently it is 12/23. There are a pair of parallel steel plates that hold the motor and jackshaft. They are welded together with spacers and attach to the stock motor mounts. The motor is bolted to another plate, which can slide a little on the main plate to adjust the tension on the primary chain. Pardon the welds. Thin wall tubing and 1/8" stick aren't a great combination. On to the electronics. The throttle is an off-the shelf part made by Magura. It even comes with a matching left side grip. It can plug directly into the controller, but that makes things too easy. The controller is made by Alltrax. It's good for 450 amps and a nominal 72V battery pack. There's a relay and a fuse for safety. You could probably run the entire Touratech catalog off them. Battery mounts without batteries: It may look skinny, but it's not skinny enough. I'm still puzzling over how to fit twice as many batteries on this bike. I'd really like 2.5x. And with batteries: And of course, rider distractions. At the moment, they show motor and battery current and voltage. And the battery charger. It's a bench power supply that's really nice for running the bike on a stand to test the electronics. Unfortunately it doesn't produce enough voltage to charge both batteries together, so I have to charge each separately. It takes about half an hour to charge each pack. With the best possible charger the batteries can be charged in 15 minutes.