Haphazard lipo dirt bike build

flat tire

100 kW
Joined
Feb 25, 2014
Messages
1,970
I have a 2005 CR125 motocross race bike that I decided will be electric. No more 2 stroke. That powerband sucks anyway! So far I have only ridden this bike at the track, but when it is electric I can probably sneak it around a fair few other places. Don't worry, I'll exercise the utmost discretion!

Here's what I'm thinking:

Golden motor 10KW water cooled, 25KW maximum output (air cooled might be too vulnerable to debris while riding)
Kelly controller, 120v maximum
Battery...RC lipo, probably run 24s around 3-5KWh. I only ride for short periods at low intensity due to low skill and fitness so this may be an acceptable capacity for 20 minute motos and the bike can be fast charged.
Motor mounts: steel, fabricated by me
Reduction: whatever, just really monkey with the sprockets direct output from the motor
Charger: 2KW of ichargers, want 20+KW bulk charger in future.

Pic of the bike with combustion motor: http://imgur.com/nfgiZIl
 
OK ladies here is an update:

I've been riding the bike for a year on the stock motor (well, modded ofc) and finally decided it was time to get this build underway. The intended use is no longer motocross, local stealth trailriding instead so some changes have been made. Here are the spec changes since the op:

Motor: QS205 V3 50H in MID DRIVE configuration
Controller: Powervelocity 24F 150V
Battery: 30S Turnigy Graphene 2.1KWh usable capacity
Gearing: 55MPH top speed
POWER: ~18KVA peak draw from battery
All up weight: <210lbs, or in other words slightly less than the stock weight once you add gearbox oil coolant and a tank of gas.

Roughly speaking this setup will give the bike slightly greater than 300lb of thrust from 0-20 which should make it a lot of fun on the trails. I chose a small high discharge battery so the weight remains low while allowing still allowing full power from the 24F controller.

Here's a pic of the bike stripped down, waiting for the electrons to come.

PSjTd6K.jpg
 
flat tire said:
OK ladies here is an update:

I've been riding the bike for a year on the stock motor (well, modded ofc) and finally decided it was time to get this build underway. The intended use is no longer motocross, local stealth trailriding instead so some changes have been made. Here are the spec changes since the op:

Roughly speaking this setup will give the bike slightly greater than 300lb of thrust from 0-20 which should make it a lot of fun on the trails. I chose a small high discharge battery so the weight remains low while allowing still allowing full power from the 24F controller.

Here's a pic of the bike stripped down, waiting for the electrons to come.

Stealth trail riding was one of the things that I originally wanted when I started planning my motorcycle build. Couldn't find an enduro bike with paperwork that wasn't stupidly expensive, so I ended up going with a small streetbike instead. I still want one, lol.

Also: 250-300lbs of thrust is right around my performance target as well, I figured that should be enough to be solidly "not slow". I'm using salvaged 200A rated lipo's for a similar small-but-powerful pack. It weighs 50lbs and only has 2.6kWh, but it's capable of happily supplying 800A, so I figure I should be pretty much good to beat on just about any motors I put in the bike.
 
I'm hoping the bike will be real fast off the line and on the trails. It only has half the stock power but for the intended use it should be faster and easier to ride than the stock 125 motor.

Currently trying to figure out how I will cover where the gas tank used to be. I'd like to maybe keep the top part of the tank with a J1772 concealed under the lid.
 
Awesome project, subscribed. I have a street legal dirt bike that I would love to convert but I’m a total noob to all this stuff so I will follow your build with great attention.

210 lbs will be a super light trail bike!
 
flat tire said:
I'm hoping the bike will be real fast off the line and on the trails. It only has half the stock power but for the intended use it should be faster and easier to ride than the stock 125 motor.

Currently trying to figure out how I will cover where the gas tank used to be. I'd like to maybe keep the top part of the tank with a J1772 concealed under the lid.

I have some similar ideas for the tank. I'm going to dremel the bottom of the tank out, keeping just the top outer sheetmetal and anything that attaches to the frame or fairings, then stash any of the lighter components up there.

If you can find a dyno chart from the original engine, you can combine that with the gear ratios and tire diameter to graph out how hard the original bike will pull at different speeds/gears. You'll probably find that the original bike might pull a lot harder in first and/or second once you get near the peak, but at most speeds the electric will outrun it until the gasser hits its powerband, then once you get into 3rd or 4th the electric is pulling harder again.
 
Ya this will be cool, at first i saw hub motor and got scared but mid mount will be sick!
 
Which graphene bricks did you use for this build? They have different graphene ones for sale at HobbyKing, I’m trying to wrap my mind around which ones will attain this powerband, I understand it’s 5 6s bricks correct?
 
I finally bought 15x 6s 8Ah 15C graphene from hobbyking for the pack. They went up $300 between the time I found them and buying. Should be here before the motor and sprocket are mounted.
 
so for the battery we are talking 30s 3p configuration? 37#? Charger?
https://hobbyking.com/en_us/turnigy-graphene-professional-8000mah-6s-15c-lipo-pack-w-xt90.html

Perimeter-framed goodness going on here
 
thoroughbred said:
so for the battery we are talking 30s 3p configuration? 37#? Charger?
https://hobbyking.com/en_us/turnigy-graphene-professional-8000mah-6s-15c-lipo-pack-w-xt90.html

Perimeter-framed goodness going on here

Right.

I'll be first charging with a iCharger 3010b but have a bulk charger in the works too.
 
OK, small update on this project. My friend owns a motocross track in central texas and we've decided the CR125 will be better off being rented out at the track since the bike is mint. In return I'm getting a crappy YZ125 with a shit engine, which is perfect for the conversion instead of wasting a good CR125 (it's modded, rebuilt and has a lot of power). Plus the YZ has a steel frame, which means any frame modifications will be way easier. I can TIG aluminum but you have to post process it to make it resilient, so I don't mess with structural stuff in Al.

To sweeten the deal I'm also getting a CRF250R under loan, which I'll be riding at the track after I rebuild the motor. That bike is a lot easier to ride than the 125 and should be fun.

I'll post pics of the two new bikes once I pick them up.
 
Good deal on the bike trade.

Don't know if you already bought all of the electric parts but if not, this is a pretty sweet deal and would probably make more power than your current plan. I actually have a CR125 frame sitting in my garage but I can't afford to build it or I would have snatched up this deal myself already.

https://endless-sphere.com/forums/viewtopic.php?f=9&t=94250

Either way, cool build plan and I can't wait to see another converted dirt bike.
 
DanGT86 said:
Good deal on the bike trade.

Don't know if you already bought all of the electric parts but if not, this is a pretty sweet deal and would probably make more power than your current plan. I actually have a CR125 frame sitting in my garage but I can't afford to build it or I would have snatched up this deal myself already.

https://endless-sphere.com/forums/viewtopic.php?f=9&t=94250

Either way, cool build plan and I can't wait to see another converted dirt bike.

Good stuff. I may buy just the motor to use with me PV controller. Right now this project is still on hold. We reassembled the 125 as a combustion bike and I have the 250, but don't currently have the YZ. I may go up again this weekend or next to grab that thing.

Stuff is moving along tho, I have a full rebuild for the 250 coming in next week.
 
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