Grinhilia - my Aprilia RS125 Conversion

Grinhill

10 kW
Joined
Jan 22, 2009
Messages
555
Location
Newcastle, Australia
It's been a few years since I've documented a build on ES, but I think this one will be interesting.

Back in 2012, I got a learners permit for motorcycles. Its been an exciting step up from e-bikes which I have embraced enthusiastically. I have found that there is a wealth of knowledge in the ICE-powered motorcycle world, and I have been eagerly taking in as much as I could. I've also hung out with some of the electric motorcycle racing crowd in Australia, including a bit of part-time work at Catavolt. I now feel confident to take on my own motorcycle conversion.

Presently there are five motorcycles in my shed. One of them is an Enertrac-powered Kawasaki Ninja GPX250. I commenced that conversion around two years ago, I learnt a lot in that process but I've decided against getting it registered for road use. It will be used occasionally for demos and local EV gatherings.

View attachment 1

The Project
Donor: 2008 Aprilia RS125 – 2-stroke, 21 kW, 140 kg (308 lbs) wet weight.

Desired Outcome: Increased power, say 60 kW, weight only marginally higher than original say 145 kg, range not crucial, all equipment enclosed within original fairing, bolt-on only conversion as much as practicable.

Drive Train: Emrax Medium Voltage Combined air/liquid Cooling http://www.enstroj.si/Electric-products/emrax-228-motorsgen.html
Rinehart PM100DX Inverter
LiPo Battery Pack approx. 4.5 kWh

Apr_12-rs-125-8_600x0sm.jpg
 
Thanks guys.
izeman said:
4.5kWh is a lot for an ebike,
- but for a motorbike, I look at it as less than half the size of a Zero pack, so range would be way less than a Zero also.
izeman said:
but how long do you plan to ride with a 60kW motor?
- it would only get the chance to hit that sort of power for a few seconds at a time, unless riding on a track. :twisted:
izeman said:
even at 10kW constant power the pack will be empty in under 30min.
- that's a pretty good estimate, I guess the average power usage on the highway would be close to that. Most of my trips would be less than 20 min at present.

Here's some more about my "Search For A Donor":

As a background to the types of bikes I have ridden previously, here's a little list of the bikes I have owned since 2012:
Honda CBF250 2007 – my first learner-approved bike. Sold.
Kawasaki Ninja 250 1991 – now electric
Suzuki GS500F 2009 – still learner legal in Australia. Sold.
Kawasaki ZX-6R 2005 – first bike on unrestricted licence. Sold.
Suzuki GSX-R600 1997 – track bike only, will sell soon.
Triumph Street Triple 2010 – daily ride
Honda CBR600RR 2007 – weekend ride
Aprilia RS125 2008 – project!

So you'll notice a lot of 600 sportsbikes in there, no cruisers and no offroad bikes. I started doing some advanced rider training courses, and found that track days were the best way to improve my riding skills. It also helped with confidence on the road. I still don't feel quite ready for a litre bike.

When I bought my CBR600, I did have the idea in the back of my mind that it would make a great conversion donor (I'm not the only one to think this - see teddillard's thread http://endless-sphere.com/forums/viewtopic.php?f=12&t=65641&hilit=teddillard). I even considered building a race bike. However, after riding my CBR for a few months, including a track day at Eastern Creek, I decided that I love it as is. I would be disappointed if I ended up with something that wasn't as exciting to ride as it is at present.

I also have test-ridden a Zero SR and a Brammo Empulse. These were both great bikes, but after jumping off a 600 sportsbike they just seem to be missing a few killer-watts, particularly when the price is taken into account.

So the search began for something else – I wanted a sportsbike-style bike, preferably low starting weight, reasonable suspension and brakes, low km recent model so that not too much work needs doing. The Aprilia RS125 seemed to fit the bill, and I prefer the look of the later iteration (from 2006 to 2012). The downside is the narrow chassis, meaning a lack of room to mount stuff.

I found one very cheap with 7000km on the clock which wasn't running and was missing the RH fairing. I had to get a battery, fairing, indicators, straighten the brake pedal, clean the spark plug, fire it up and get it registered. I rode it around for about a month. Loved the light weight, the riding position was good too, not so much fun was revving the bejesus out of it to get off the line at traffic lights!
 
:mrgreen:
motoguzzi_mgs01_corsa_02.jpg

Yeah! A shaft drive conversion would be pretty cool, not quite as easy to adjust the gear ratio though.
 
In order to reach my performance goals, I need something optimised for light weight. This is something in common with my earlier e-bike builds, using RC outrunner motors. A dual- Colossus was a potential candidate that I considered. Still going with the outrunner theme, I've decided on the Emrax 228. It's an awesome motor, but on the downside the cost is high.

To drive this motor I need a sinusoidal controller. Probably only three or four options, but I have gone with Rinehart since my mate Sutho down the road sells them and has a couple of EVs using them. The 100kW model should do just fine.

I'll post some battery calcs soon, but since I'm going with a short-range low-weight pack the C-rate will need to be quite high.

OK so now the $$$ are getting in to Zero/Brammo territory. So why am I building this bike? I think its more about the design and build process, and the challenge to improve performance. I hope the plan works out!
 
I to am looking forward to this build and I agree with you about why we build these things. The thrill of the chase and building something unique and personal. I will be interested in your battery choice.

Good luck

Bernel
 
Thanks Bernel.

The next question is how will everything fit?

I've scratched around on paper quite a lot looking at motor mount locations. The motor has a diameter of 228mm and a width of 86mm, and is mounted from one side only. There are three configurations which I considered:

1. Outboard mounting a la Buckeye Current (http://current.osu.edu/) – motor would not be clear of frame, also not within original fairing.

2. Mount low in belly pan and use additional chain via jackshaft – good chain line but increased mechanical complexity.

3. And the winner is - the most commonly used approach for conversions, which is to mount the motor pretty much where the original ICE was. However, it needs to be moved forward to clear the swingarm, requiring a slightly longer chain. Downside – a single rectangular battery box won't fit, must use L-shape or split pack into two parts.
Apr_08_skeletonM_ES.jpg
It's now getting more difficult to make measurements with everything still intact, so time to pull the engine!
 
subscribed!
 
Before pulling the engine, I weighed both ends - 69 kg rear, 71kg front. This info will be essential for the engineer who inspects and certifies the changes. I also made a rough measurement of the Centre of Gravity by lifting the front end with a sling and engine crane until the balance point was reached.

I then measured the height/angle of the bike, giving the front axle 1570mm above ground, and the front axle about 500mm ahead of the rear axle (measured along the ground).

Although not super-precise, I then used these measurements on a scale drawing. So the front-rear weights tell us that the CofG lies on a vertical line half way between the two axles (a few mm closer to the front for the perfectionists). Now I tip the drawing like I did to the bike, and add a triangle using the balance point measurements, and this results in another vertical line drawn upwards from the rear tyre contact point. The intersection of these two lines is the CofG, and it's pretty much at the bottom of the flange where the carby attaches to the cylinder. On the line drawing above, this would be the top centre of the orange circle.

I did have one unforeseen minor problem with this little process - some of the 2-stroke oil leaked out of the top of the tank (located under the seat) and ran all over the swingarm and rear wheel. :?
 
I bought myself a motorcycle lift table, which is awesome for working on bikes. It was a pretty straightforward engine removal, as usual there were heaps of pipes, brackets and wires. The trickiest part about it was the fact that the main swingarm pivot bolt runs throught the rear of the gearbox case, so this bolt had to be removed to drop the motor, then returned into place.

For the impatient, here's the abridged version:
View attachment 6
And here's a few more detailed photos.
249.jpg
263.jpg
268.jpg
281.jpg
295.jpg
308.jpg
 
Here's an estimate of weights of various components before and after conversion.
Code:
Before:                        After:
Rolling Chassis    87 kg       Rolling Chassis   87 kg
Engine/Gearbox   22.5 kg       Motor             12 kg
Exhaust           6.5 kg       Controller       7.5 kg
Airbox/Tanks        7 kg       Brackets           5 kg
Fuel               11 kg       Batteries         34 kg	
Cooling/Oil/Cables  7 kg       Cooling            2 kg
                               Wiring             1 kg
Total ICE         140 kg       Total EV         147 kg
This is how I arrived at the battery size for this project - any larger and the weight would start to be significantly higher than the original bike.

So the next order of business is the motor mounting plate. I like to use the tried and tested progression from paper template to cardboard template to plywood template. I've also added an extra step before progressing to aluminium (U.S. Readers please ignore the extra i in that last word :wink: ). It's a 12mm white acrylic, leftover from a kitchen renovation a few years ago. It machines really nicely and is very light and very rigid. This will allow me to make a few adjustments (mistakes!) before committing to the final plate.

1466s.jpg
I think 12mm is a good thickness for the motor plate also, provided I do a bit of lightening. It will look a bit like swiss cheese anyway with all the bolt holes and ventilation holes.

Now to locate the motor axis. It will be forward by about 50mm from the original gearbox output shaft, also up a little higher. You may notice that the chain drive is on the RHS of the bike, which is not very common. I'm sticking with the stock 16T sprocket to begin with, I can make some adjustment to the rear sprocket size.
313s.jpg
 
Nice work mate. I'm going to sit back and let you make all the mistakes / discoveries that I'll need to apply to my own conversion :p
Your comments on the engineer wanting to know about weight distribution are interesting. So they frown on fitting a stonking great hub motor in the back wheel ?

Your motor and controller combo sounds interesting. I was vaguely considering the 207 motor but was coming up blank for a cheap/easy controller solution. Dare I ask what they cost ? I'm guessing much more than I have to spend if you're comparing them to zero prices...
 
Hyena said:
So they frown on fitting a stonking great hub motor in the back wheel ?
Not necessarily, if it's balanced by a stonking great battery pack! Remember also the weight of an exhaust and chain/sprockets would offset the hub motor a bit. There's still a get-out-of-jail card if required, just make it restricted to single-seat use only.

Hyena said:
Dare I ask what they cost ? I'm guessing much more than I have to spend if you're comparing them to zero prices...
Yeah north of 5K for motor, north of 7K for controller, not helped by crappy AUD$. Funny thing is the list price of the 207 was the same as the 228 when I last looked, seems crazy.
 
My motor arrived, packaged very nicely in a small wooden box. While 12 kg doesn't sound like a lot of weight, when you pick it up the immediate thought is - wow that's heavy! It is a work of art, really well made.

The mounting bolts are eight M8 on a 78mm PCD (pitch circle diameter). The spacing is a little odd to allow for cooling tubes. I ordered the brass right-angle hose connections. In hindsight, maybe the straight ones would have been better. It is necessary to have a slot for these to pass through in the motor plate, as the resolver prevents them from being screwed in after mounting the motor. The spec for inlet pressure in the cooling system seems very high at 1.2 bar, yet the fittings are just barbed which I'm a bit concerned about.
View attachment 1

Note also there are two temp sensors (thin black wires between phase wires). I added a PT100 to my order as well as Emrax's standard Phillips temp sensor. Maybe unecessary, I thought it was required by the Rinehart but have since found that it would have probably worked OK with the standard one. I might be able to hook something up to the stock dash temp gauge.

A sprocket carrier is required on the front of the motor, using six M8 bolts on a 76mm PCD. I'm going to fabricate my own when I find the correct chain offset. The stock Aprilia chain is a 520, which is good because this is a type readily available as a weight-saving upgrade for sportsbikes running 525 chain, so is suitable for higher power applications. I've started with an acrylic one to test fit with.

I tried mounting the motor on the acrylic plate to check clearances, looking good so far. The main area of concern is around the swingarm bolt, and I'll also allow for a tubular spacer there, say 30mm diameter with a 14mm bore. Now I'll find the right location left/right for the motor plate, which will be locked in by the spacers.
910s.jpg

You can also see my plywood Rinehart, which seems to fit neatly in the belly pan. I'll try hanging it from the motor plate.
 
The motor is beautiful! I have been reading a little on these after you mentioned them, stunning power to weight. Am I correct in thinking these are the most power dense thing available right now? I especially like the availability of the low voltage options, it's very feasible to assemble a bike with similar performance without resorting to HV.

Grinhill said:
The spec for inlet pressure in the cooling system seems very high at 1.2 bar, yet the fittings are just barbed which I'm a bit concerned about

I would not be concerned. I have run high pressure fuel line at 60+psi on barbed fittings with simple hose clamps for 100k km without issue. The cooling loops in most ICE vehicles operate at the same pressure with rudimentary clamps on plastic barbs for 15 plus years without major problems.
 
Ohbse said:
Am I correct in thinking these are the most power dense thing available right now?
Hmmm, is the Plettenberg Nova 150 actually available? Its specs would exceed the Emrax. So would the cost. :cry:

Ohbse said:
I have run high pressure fuel line at 60+psi on barbed fittings with simple hose clamps for 100k km without issue.
Cool, thanks for the reassurance.
 
Grinhill said:
There's still a get-out-of-jail card if required, just make it restricted to single-seat use only.
Good tip! I'll just keep my 48kg wife off the back and fit the baddest hub known to man :p
north of 5K for motor, north of 7K for controller, not helped by crappy AUD$.
Ouch. Looks like I'll be playing in the e-moto kiddy pool for this build.

And yeah our AUD exchange rate is terrible at the moment. I bought $4000 USD worth of stuff the other day and it ended up costing $5200 in our money :(


That IS a pretty motor - almost a shame to hide it behind the fairings.
The Rinehart is a big chunky unit. Must be named after Gina :lol:
What voltage are you going to run ?
 
Probably around 360V.

Hey speaking of big chunky hub motors, have you seen Ripperton's Posty Bike (on DIYelectriccar) - he's joined two of the big QS motors together. That would be a pretty good bang/buck ratio.
 
I just made some swingarm bracket / Vario mounts for Any Marsh's RS 125.
You could do with a set of these to get the Emrax further back





 
Nice work Rip. So the plates are only attached in the centre, and just lean against the upper and lower frame tubes to prevent rotation?

My main reason for hesitating to cut the swingarm bolt is the large increase over stock power which I will have, so I don't want to make any structural changes to the frame.
 
Grinhill said:
Hey speaking of big chunky hub motors, have you seen Ripperton's Posty Bike (on DIYelectriccar) - he's joined two of the big QS motors together. That would be a pretty good bang/buck ratio.
I haven't but I'll go check it out. I remember years ago he was talking about a postie conversion when he picked up a few X5400 motors from my last group buy. QS are actually selling dual stator motors now and I looked into getting one for this purpose but they were mega pricey - well over double the cost of 2 regular motors. I'm thinking now I'll see how far I can push one of their new "8kw" 273mm 50mm stator motors. I reckon they'll take more burst power than I can throw at them with cheapish controllers.

Ripperton, are these cracks or just cast marks ?

 
Hyena said:
... are these cracks or just cast marks ?


Apply some oil, wait a while and wipe it off completely. Check again for oil a few minutes later with a paper kitchen towel or such like. If there is a crack, oil will seep out. No oil, no crack.
 
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