View Full Version : A different conversion...I think

14 October 2011, 1358
Hi All,

I`m very, very new to this forum. I stumbled across it almost by accident. In reading some of the posts it appears that this is the place to be.

I recently came in to possession of a 2007 Honda CBR 125R that I intend to convert. While at first glance this would not be the "bike of choice", I decided on this model specifically because a) I wanted a sport bike and b) In the class I require the absolute lightest bike available to me.

The Project:

Most (actually all) projects that I`ve seen have been, generally speaking, to push the limit of speed, range and overall performance in some capacity.

I`m going after something a bit different. I`m building a bike that will take advantage of the "bicycle status" offorded by law in many areas (including mine). While there are certainly any number of offerings in this class, I don`t like any of them. Here`s why:

1) The poor quality of manufacture in so many of these bikes. The quality of the Chinese bikes that are coming into North America and Europe, make them practically disposable....Rather defeating a key philosophy of the movement...Not to mention the economic implications to us.

2) I want to change the all-to-often impression of the e-bike as a glorified electric mobility scooter for the fat and lazy...I am neither.

3) I want a bike that meets "bicycle-legal" standards, while still providing a style that is contemporary and cool. The "anti moped/scooter" if you will.

The Challenge:

Given the class in which I want to build, I have a number of restrictions that I need to follow. Some of them are simple, a couple of them I still need to explore.... I知 very open to any and all input as to how I might achieve this. Here my key issues:

**Bike must a maxium weight of 120kg (265 lbs) including batteries

OK - I have my CBR weighing in at 114kg (253 lbs). I致e not yet stripped it away and dropped the engine etc so I can weigh it in. I figure that I can lose about 45kg (100 lbs) at this point

I知 going to need to add in motor, controller, some structure for mounting etc (aluminum), and the dreaded batteries. While I知 pretty sure that I can do this with LiPol batteries, I知 not a rockefeller, so I知 hoping that I can pull this off with SLA batteries. I was thinking a series/parallel combination such as below:


Of course I知 going to have to consider if 48v will do what I need to do in the notes that follow....Or do I need to go to 72v And if so can I keep it at 500w and still meet the torque requirements? All questions I need to answer.

**Bike must be limited to a top speed of 32kmm per hour (20mph)

Easy to have a limiter sure problem I致e experienced however is that I need to be able to maintain very closely the top speed as constant on a reasonable grade. No real variation

While I need a limiter in place restricting to 32kph (20mph), I want to be able to make this fun when on a private course. Therefore, a 都witch limiter that can be removed without too much difficulty is essential....Without the limiter I would like to see in increased, but still modest (constant) speed of 45kph (28mph)

I was also told by one motor manufacturer that by introducing a limiter, I could not have regen....Don稚 know why however or if there is a work-around if actually the case.

I want to be able to get this bike up to 32kph (20mph) very, very quickly. I知 not under the impression that I can get the kind of torque I want with a brushless hob motor.....Or can I? There also the cost implication of the brushless hub motor.

Accelerating to my desired speed, approaching the rate of other vehicles however is very important to me.

**Be equipped with pedals and , is capable of being propelled by muscular power

This is an odd one. Since this bike will for all intents and purposes be a bicycle by any legal definition, I need to have these in place....

As this would be unsightly, I have a plan for a crank shaft that is telescopic. The idea here is that I値l be able to retract them in behind some fairing or housing of some kind.

More difficult This would be somewhat easy to achieve in the same way that they do on low speed electric scooters. They have hub motors and that leaves the freewheel sprocket to be mounted to a chain. Not sure how to do this with a standard brush motor.

**Be configured so that power to the motor immediately ceases when the brakes are applied

I知 going to have to introduce some sort of kill switch in to the brake levers....I知 pretty sure this is standard with many regen braking systems...I think....

I was hoping to use the bike existing braking system but I would then need to figure out the kill switch to the motor...This also means I wouldn稚 have regen, anti-lock etc...

Welcome thoughts here....


TO Joe

Ken Will
14 October 2011, 1444
There are lots of options.
Here are a few.

Brake levers with built in switches
A 48 volt 1000 watt controller
A 48 volt 1000 watt

14 October 2011, 1522
parallel the batteries first, then series them. They'll stay balanced better.

500W will not get any motorcycle up to any reasonable speed quickly, 20mph or not. 500W is.... hardly any power at all. It's going to be very sluggish, no matter what. Torque is based on current and at 48V, 500W is ~4A..... the motor side is more current than that, but lets say you're at 10% PWM (4.8V) that's still ~100A.... and with a lead acid pack, you're going to have a very difficult time making that thing move very quickly.

Pedals.....How would that even work? You'd be riding a somewhat wide moto, trying to pedal with a straddle position.....

Why aren't you doing this as a motorcycle? I mean, why the limits? Make it a street legal scooter and there's no power limits, just speed limits.

14 October 2011, 1943
Hey Joe,

Welcome to elmoto.

Personally, I'd love to have a CBR 125R to convert. It's a sportbike, but super light and could make a really fun bike. I've been looking for one, so if you give up on it let me know!

I'm not sure why you want to meet the bicycle requirements - licensing, insurance? Even if you make those written requirements, the DMV might still say it's obviously not a bicycle. Besides, if you want to change the image of electric vehicles, the way to NOT do that is to build a motorcycle with a top speed of 20 mph. There are already good quality electric bicycles (A2B, Optibike to name a couple). Or get a good bicycle and convert that.

I don't know about Toronto, but in Colorado anything under 3 kW is a moped (equivalent to a 49cc). You don't need plates or a motorcycle license. That seems like the way to go. I have a 3 kW scooter, hub motor, that does 55 mph and is decently quick for around town.

Anyway, up to you. Once you decide what you want to do, we can help you with motor/battery decisions.

14 October 2011, 2105
You might want to check that a CBR conversion can qualify as an e-bike. I took a quick look at the laws in Toronto, and it appears an e-bike needs a sticker affixed from the manufacturer stating that it is an e-bike.

14 October 2011, 2109
"I have my CBR weighing in at 114kg (253 lbs)" :eek:

I wish the US had sport bikes that light weight, I would be throwing a 96v 40ah battery with an AC-20 motor/controller haha, that thing would be a ROCKET!

my 2 cents, use lithium batteries, it makes a world of difference over SLA batteries, but if its out of your budget I can understand

Nuts & Volts
15 October 2011, 0746
Yea, 500W and pedals on a bike like that just sounds sad to me. As Noah and Tony said I would love to convert a 125 into a super fast ride. I dont want to discount your idea of a making a small conversion, but your better off just converting a bicycle with the goals you have. Cheaper, easier and less hassle with legal stuff.

Welcome to El Moto, its great to have ya!

15 October 2011, 0833
A 250lb bike with 500W is NOT going to even hit 20MPH nor will it accelerate quickly, much less have the ability to go over 20MPH "for fun". An A2B e-bike with 500W is 70lbs and it barely hits 20, and I can accelerate mine faster by pedaling unassisted, than it can accelerate itself under its own power.

You'll either want more power to work with your CBR, or start over with a bicycle if the 500W is a dead-set limitation. Either way 500W simply will not get anything over 20MPH nor will it accelerate quickly, and won't meet your desire to get a little nutty on a private track.

15 October 2011, 1054
Yep. Take a light mountain bike frame, light hobby LiPOs, and build custom fairings, so you've got something like an ENV (except with batteries instead of a hydrogen fuel cell http://www.youtube.com/watch?v=TPPuQ18Tbj8&feature=related ).
With the 20 mph and 500W limits, a chassis and wheels made for stability at 50mph+ and lead batteries are just impractically heavy.

I would expect it would be tough to convince authorities that a chassis stamped with a motorvehicle VIN, is a bicycle.

Re: why an e-bike? In many jurisdictions a person who for whatever reason can't be issued a motor vehicle license, or has had theirs suspended, is often still allowed to ride a motorized bicycle. They also typically aren't required to carry insurance or face the same, if anyregistration costs (which, if memoryserves are both pricy for motorcyclists in Ontario).