View Full Version : Derbi GP-1 Electric Conversion

09-16-2015, 08:43 AM
I have been away from the forum for a while as I dropped my Derbi GPR tuning (waiting for parts) and decided to dig in on my electric scooter project.

I currently use a gas powered scooter for going to work on, most mornings riding in stop and go traffic make you realize how stupid and wasteful gas engines are in that environment. Electric would be amazing and save fuel and reduce pollution.

For over 5 year I have wanted to build an electric scooter, something better built than the cheaply built Chinese ones often sold. The high quality ones are usually much larger, high powered and very expensive, but the styling is usually boring.

When I decided to look into the idea I wanted to choose a base that was very sporty and would convert easily. I had several bikes in mind as well as the idea to build my own complete tub chassis in carbon. In the end I chose the Derbi GP-1 as it was a naturally perfect chassis for the conversion. I started working out what I would need for the conversion and did some mockups based on images and estimation. In the end I shelved the project as I would need to obtain a Derbi GP-1 which was never sold in my location so would require expensive shipping. Also from a technical standpoint there were some challenges regarding the technology and suitability.

I kept the idea on the back of my mind and 2 years ago seeing some new progression decided to go for it and restart the project.

09-16-2015, 08:50 AM
So for those who don't know the Derbi GP-1, it was a very special project at the time. The idea was to mass centralize the scooter by moving the chassis into the center of the bike and then run a chain drive to the rear wheel. This would also reduce unsprung weight and as a bonus they used a chassis similar to the one used in the Derbi GPR. When it came out it was striking and even today I think it is the best design for a 50cc scooter out there.

This is a image of the prototype model which has some slight differences to the production version.


09-16-2015, 09:02 AM
So this was what I planned in 2008 for the conversion. The layout was to use a Perm or Brigg and Stratton DC air cooled motor with Thundersky lithium cells. I had to guess the possible layout and used my Derbi GPR as a reference. I didn't realize at the time that the GP-1 chassis was shaped differently and so would be narrower between the frame rails. I ended up shelving the idea as there were questions to whether the number of batteries needed would fit. Also at the time the bike was still a relatively new model and secondhand prices were still fairly high.


09-16-2015, 11:22 AM
What got me restarted on the project was seeing a model of electric scooter made by a company called Emoto which design wise superficially was almost identical to the Derbi, which vindicated my choice of scooter. The main advantage which did not exist before was the 13" hub motor. With this ensuring there would be enough space for batteries would be a non issue. So I started to work out what battery options I could go with and started to search Ebay in the UK for a secondhand GP-1.


09-16-2015, 11:25 AM
Since I know what's coming I'll wait for comments, but I will say this is some very cool work Scot!

And this model GP1 is by far my favorite--of course I really like the two stroke version of it. :P

09-16-2015, 01:39 PM
I've always wanted one of those

09-17-2015, 02:57 AM
that being said, i dont' think this is the correct forum for this one.

09-17-2015, 05:54 AM
Hey Matt I did ponder where best to post such a project. Technically not being an Aprilia it doesn't fit anywhere. It is a scooter, but has the chassis like that of the 2008 RS50 and is chain drive. In the end I figured I'm not a scooter guy and so don't relate so well in those forums. Anyway I'll just continue on in the project section.

It is a very cool scooter, I have 2 of them with the second still in gas mode. I have rode it a little bit and removed the restrictor washer, but still feels sluggish to me. I had to quieten it down, but took a while to figure out a hose needed to be fitted to the airbox from the exhaust. Will be interesting to weigh the two bikes to see how close the electric bike is.

09-17-2015, 07:55 AM
i tend to draw the line at clutches and transmissions vs variators, seating position, etc. lol.

09-17-2015, 08:21 AM
The search for bikes in the UK was sort of tricky. It costs a lot to deliver any sort of distance, this meant while I could find good bikes in part of the country, the shipping cost would be killer! In the end I found a place which repairs and breaks bikes fairly close to the shipping port I would been to use. It was also close to a firm that could box the bikes and deliver for me.

Originally the plan was to buy one bike, but then the guys later mentioned they has two so I figured why not! In the end it was a good decision even if I was paying more for shipping and crating the bikes. They could not guarantee the running of the second bike, but that did not matter to me. Having two bikes would be useful as there would be a surplus of parts and also on the second one I discovered some key differences on the newer one relating to additional frame support brackets. (I suspect the first ones suffered failures in the cast aluminum frame sections, something I might have to consider on the second bike)

So this is the pair, complete with oversized UK plates! :lame:



09-17-2015, 08:30 AM
One noticeable difference also was the second one which became available had non standard bits from the sister bikes. Derbi also made 3 other models with normal scooter mounted engines. They were less sporty than the racing version. You can see it with the seat being one full pad, rather than split. Also the front wheel is different with a smaller disc which was to cause some headaches as the caliper would only bite half the disc and it was difficult sourcing a bigger one with the correct bolt pattern! I did find one in the end, but then struggled centering the wheel till I found spare spacers in the seat bucket!

09-17-2015, 08:34 AM
i tend to draw the line at clutches and transmissions vs variators, seating position, etc. lol.

I hear you! At the track the racing scooters while impressive, sound irritating to me! I do ride a scooter to work everyday so am used to them. For threading traffic way easier than a geared bike, along with parking and not worrying about getting scratched etc!

09-17-2015, 09:59 AM
The bikes got shipped from UK and it took I guess 6 weeks to get here, both in their own huge box! I unpacked the pair and they spent some time under covers as I worked on getting one running! That took ages as I wasn't getting a spark. I was going through the electrics getting pissed off! At some point I sat down on the grass and was looking at it and noticed the wire harness coming off the sidestand............ F$%^ing hell! Could not believe that! :gunner:

Forgot some modern bikes have a sidestand switch, though on these bikes it is stupid as the stand kicks up automatically! So sure enough kicked the stand up and it fired straight away! At this point I worked on making it run nicely and quietly before packing it away. The second bike would be the conversion bike so started pulling off the plastics and figuring out what needed to be done.

In the photo you can see the difference between the production and prototype bikes with the rad cover. The production has slats which I never liked. I remember when I saw the production I could not figure out what changed but though it looked weird. Then I noticed the difference! I'll be making a new one without the slats in carbon when I get the chance!


09-17-2015, 02:57 PM
It's true that technically it probably doesn't fit, but Scotty does, and he probably wouldn't fit in the other section since this is where he hangs out. Plus it seems that we are all interested in this particular machine. That and well there's already a thread too. :P

09-17-2015, 06:57 PM
It's true that technically it probably doesn't fit, but Scotty does, and he probably wouldn't fit in the other section since this is where he hangs out. Plus it seems that we are all interested in this particular machine. That and well there's already a thread too. :P

Ya don't know the scooter crew, anyways will carry on bit by bit. Created a imgur account or whatever. Flickr charged with Yahoo a while back so no idea how to access my old account and files!

09-17-2015, 08:48 PM
Hey Scott, could you post some photos of the removed engine?

09-18-2015, 06:55 AM
Always liked these scooters.

They look like they will handle really well.

Wached some racing at cadwell and when it was the scooters these things were doing well in the corners.

09-18-2015, 07:52 AM
Hi Rob, I never took many photos of the engine, it's currently tucked away so would be a pain to bring back out to photograph. Still I have a photo here from when I pulled the engine out and roughly fitted the batteries to see how they would work out. It worked out perfectly, exactly the 20 cells I wanted to fit, one more and I'd have a serious problem!


09-18-2015, 07:58 AM
I wanted to figure out what the bike would look like sans engine, so bought Paintshop and went to work on some official Derbi images. I did several images playing with motor styles and using various battery configurations. In the end I think the look worked out pretty good and kept the stock look like the factory possibly would have done.



09-18-2015, 02:10 PM
Wow that totally looks like a scooter engine. I thought they had used a wanter cooled Variant/Revolution engine for this bike.

09-18-2015, 11:38 PM
yeah i'm disappointed. i thought it would be like a Start LC instead of a Start 3 or Start V

09-18-2015, 11:46 PM
What is the variant/Revolution/Start LC engine on?

09-19-2015, 12:35 AM
it's on the variant and revolution derbis haha

09-19-2015, 12:50 AM
Matt didn't you build some totally awesome Revolution at some point. Post some photos of it in this thread for Scott. I'm sure he'd love to see it. I know I would. I'd be a happy camper to have a Revolution to ride around SF. That would be super fun. :P I see why the racers change the wheels on these. Can't get good tires in that size. I don't know why they didn't just put 17's on the damn thing.


What's funny is the 2005 GP1 got subtitled the Revolution (http://moto.zombdrive.com/derbi/derbi-revolution-50/) too. :P I guess it's the engine cover that fooled me, and looking at them together it does look way longer. If I ever did get one of these GP1s I'd be figuring out a way to get a GPR engine in the damn thing. Give me that happy stick!


And I'm really bummed that Derbi didn't market the GPX1. They came out with this before the damn Grom. This with a GPR engine would have terrorized. Fucking Paiggio. (See that Japanese dude in the background? You just know that cat works for Honda. He must have gone back to Japan, and convinced Honda to build the MSX125. Even the name is almost the same.)


09-19-2015, 08:12 AM
So the variant looks dated for me, think using the scooter engine was the better option. Tons of race stuff out there for them. The could have improved by designing a lighter built design as it structurally would be in excess mounted in the chassis. But costs rule and best option was just to throw it in there. Between the two bikes there is significant changes to the plastics on the engine on the right side. The circular bit with 5 mini circles in the air intake.

Wow Rob never seen the GPX1, got to agree the GPR engine would be a better fit! Totally a Grom! Raining a little today, but hope to get more done on the scooter. Would be great to ride it today, but taking my time getting the wiring and electrics done right.

09-19-2015, 01:26 PM
Yeah I sold it to a friend thinking he would improve it and he parted it out. That made me be disappointed with derbis overall, I got really burned on the whole thing

I'll see what photos if any I can find while I'm out here in saudi, I think they are on my PC at home

09-20-2015, 12:51 PM
Scott, that's just it the Grom totally copied Derbi. This was shown like five years before Honda announced the Grom. If you compare the two Honda cheeped out on a lot of things. But most folks don't even realized that Honda got the idea from Derbi. They all think it's an upgrade to the Monkey/Z-50 bikes, but they are very different. The only think Monkey about the Grom is that stupid four stroke engine.






Matt, yeah if you have some. I remember it being something special. Revolution!

09-20-2015, 08:10 PM
Wow Rob how I ever missed that! Was probably during the point of time when I was out of bikes for a bit. Looks flipping awesome! Just looking at the bike it is a GP-1 scooter with forks and different bodywork. The interesting bit is it would not make much effort at all to convert a GP-1. What year was that bike in a show? 2009?

09-20-2015, 09:44 PM
I think it was 2007ish model year, so what 2006 introduction? It obviously didn't get much press, but it did impress Honda. I know what you mean about making one on your own, and yeah it wouldn't be that hard with the proper tooling. Making the plastics would be the most difficult.

I'm just really disappointed that they never put it into production. It is so much better than that fricken Honda it's not even funny. Honda copied so much of the styling. Even down to the tilted V on the headlight. But the Honda doesn't have the Derbi's twin spar aluminum frame, aluminum swing arm, radial brakes, and most important two stroke engine. Plus the Derbi just looks way better.

09-20-2015, 10:49 PM
Wow that is ridiculous. It looks like it was cvt based. One of the most fun things about the Grom is that it's a shifter bike.

09-20-2015, 11:38 PM
Matt--It was a CVT, but really all they did was take the GP1, and fashion it to be a mini-motard. However, they did it in a very cool way. And yeah I will agree that the happy stick is a wonderful thing. Have you seen my moped? :P

My hypothesis with this regard is they probably saw it easier to get the bikes into the market without a gear box since "moped" generally means auto trans these days. That, and well they already had the engine in that frame! :D

Ian--Honda hates 2T with a passion. They only ever made a 2T engine because they weren't able to convince everyone else of the 4T virtues. But Honda got big enough and have now changing enough racing organizations that Honda no longer has to produce a stroker. They might still make some for the Asian market, but nothing in the west.

09-21-2015, 12:37 PM
Sheesh you guys clogging up my thread! lol

Anyways I'll carry on. So got the bikes and well cost a truckload sending them overseas so kinda got bummed as no way was ready to spend money on parts for the conversion. The batteries, motor, controllers would all add up and we pay 33% tax on that stuff so was not really ready.

But someone's misfortune became my fortune! A coworker owned a E moto G5 just like the one that copied my idea and she had some issues with it. Came to find out it was a complete failure in the hub motor. She told me I could have the bike so I gladly took it. I pulled the motor apart and it was cooked. It failed as water killed the bearing causing the stator/rotor to bind and overload, burning the windings.

For me the value was in the controller, harness and most importantly batteries! The batteries are worth near $3000 so for sure they were gold! I contacted the local dealer who was no longer involved with the bikes and he gave me a second bike with dead batteries, but okayish motor and controller. So I had lots to play with, I used the good bits to make one working bike to be sure all was well. The bike worked but the motor had some issues, better than noting though!



09-22-2015, 01:32 AM
Yeah it's become the dumping ground for all scooter related stuff. Sorry about that!

Damn that's some serious burn job.

09-25-2015, 02:16 PM
Yeah it's become the dumping ground for all scooter related stuff. Sorry about that!

Damn that's some serious burn job.

no worries Rob, doesn't bother me! Yeah a serious burn job is right! Still worked out great for me as I had a parts bin to raid from!

So first thing I needed to do was remove the engine, fuel tank, radiator, rear wheel and anything related to the original gas setup. After that I did a rough mockup of the bike with batteries loosely fitted and rear hub motor fitted.

The fitment of the batteries kinda made or break the project in many ways. Until this point I had only able to guesstimate whether the 20 60AH cells would fit or not. Once I did this I was pretty excited as I knew that from here most of the other challenges would be easier to deal with!


09-25-2015, 03:52 PM
Looking good Scotty. What are you using for a throttle?

And yeah there are a bunch of aftermarket forks for scooters. I think Stage6 has something really nice. But don't these come with Piaolis?

09-25-2015, 04:21 PM
For the throttle I am using one off the donor bike. But I have just ordered a blingy Domino shorter turn throttle setup. I'll be picking it up when I go NY in two weeks. I mentioned about the forks because they are made of steel! Most forks are aluminium outers so pretty shocked at that! They look the part though! I don't know what brand mine are, in the manual both Italian fork firms are listed as suppliers. (edit.... I will go and look on the forks to read the brand on them! lol)


09-25-2015, 07:42 PM
The non-sliding tubes are steel? That's so weird. Maybe they do that because they are half forks, where as with motos using a double triple allows them to use aluminum.

That throttle is sexy!

09-25-2015, 09:21 PM
I just think after building such an expensive bike they needed to cut costs where they could and not be noticed.

So for a primer on the batteries, I am using a lithium format called LiFePO4 which is lower density than most, but also much safer. This is a kit version of them 60V / 60AH. Later on I'll go with higher spec, but for now these will do.


09-25-2015, 10:30 PM
Considering that doesn't even include the electric motor that's an insane amount of gear to have to stash somewhere on the bike. Can you tell us what all those other gadgets do?

I keep meaning to mention an electric bike that my friends here in San Francisco have been developing. Depending on the mode it's set to this bike can function as an electric bicycle--meaning no license required. Now it can be set to a faster mode that would require an M2 moped license here in CA.




09-26-2015, 09:59 AM
The Bolt bike looks pretty cool, lightweight mopedlike designs suit battery power.

So the bits are:

silver box is the charger

The black box with white label is the battery management system that gets info from the circuit boards daisy chained on the top of the cells. I shuts down the bike if voltage gets too low and some can be set to turn charger once voltage reaches a set point.

The black screen lets the user see individual cell voltage and other parameters. ( I don't have this, which is not ideal, I've ordered small cell monitors)

Finally the brass widget is a shunt which allows the current to be measured

09-28-2015, 12:26 PM
Knowing how the batteries would fit, I worked on designing a base for where the batteries would sit. I used a lightweight thin wood with a carbon wrap for added strength. Once it complete the batteries fit nice and securely. The photos show the vacuum bagging and component before trimming.




09-28-2015, 01:43 PM
Another wow that is really cool! :D A carbon battery support. I didn't pick up on that from the test ride video.

I got to see a Bolt yesterday. I can imagine a bunch of these running around on your island. The went up on an Indigogo (https://www.indiegogo.com/projects/bolt-m-1-the-ultimate-urban-transporter#/story) thing today too.


09-28-2015, 02:04 PM
That bolt is cool, would probably work well here! I like simple electrics, that one runs regular bolt on stuff, like mine really. Many small electrics are using proprietary parts which are a pain as when things go wrong you need to be a software engineer and full on tech to figure it all out! The controller on it looks like a Kelly unit.

I might be able to take part more locally as I was asked by the local Green org if I would want to head up as their EV head. Basically assist with promotion and public knowledge type stuff.

09-28-2015, 02:12 PM
With the batteries now figured out, I needed to figure out how to mount the rear wheel. The system is a bit like a bicycle setup with a slot to allow flats in the axle to locate and prevent spinning. I needed to figure out how to make it work without permanently changing the swingarms ability to use the normal mounting setup. You can see the setup on the Chinese built scooter.



10-31-2015, 02:14 AM
Scotty! How goes the GP1 action? I saw this posted, and I wondered about what you said. Maybe some mini bike plastics could be fitted, with some properly sourced forks. Then stick an EB engine in it, and you'd have a sweet bike that would make the Gromulators envy.



04-07-2016, 12:22 PM
So the project hasn't been forgotten, but I did have some issues to contend with! But finally I got it all completed so will look at where I left off and put up some photos!

04-07-2016, 09:05 PM
Looking forward to it with excitement! :)

04-08-2016, 11:02 AM
I needed to fit the hub motor to the bike, so came up with this idea below. At first I went with a solid design, but realized it would be way easier to have the mounts laser cut and use an aluminium shim to fit tightly. So I drew up in CAD and had the second set of components laser cut.

04-08-2016, 12:23 PM
Forgive a bunch of electric 'newb' questions -

How do these hub motors stand up to environmentals?
I like the look of the Bolt as well, but kind of the same question - how does that motor mounted low down, in the 'splash zone of the front wheel handle slop being sprayed up on it ?

Strikes me one of the REALLY critical factors is the balance ... having a slug of batteries mounted up high seems problematic. Granted, having an AM6 mounted in the ame location is more or less equivalent, but what is the weight like on the batts ?

04-08-2016, 01:26 PM
So the hub motors come in various degrees of "quality". Mine is a reasonable level, but not the best. They do get rusty inside over time as moisture gets drawn in when heating and cooling. One of my hubs I stripped and sealed filling with thin oil for cooling and rust prevention.

I agree with the weight so better to keep low. My finished scooter weights twenty-something kg more than the 50cc I used but is still 5 - 7 kg less than the 125cc version. I have the exact numbers somewhere. The plan in time is to replace the cells with much better ones which will shed 50lbs and place it lower, putting the bike at the same or slightly less than the 50cc original!

04-08-2016, 01:30 PM
Once I got the bits made I inserted them and fitted into the swingarm as seen below.


04-08-2016, 03:46 PM
When I was in high school we had a word to describe this sort of setup:


04-09-2016, 12:29 AM
When I was in high school we had a word to describe this sort of setup:


Cool Tora! I just searched what Sano meant and yeah totally that is the way I always try to mod my bikes....... so they look factory like! At the moment everyone who has seen the bike says it looks like it came that way which is a massive compliment!

I got two bonuses at this point of the build! One was that I scored a brand new hub motor for free! It isn't a super high quality one that I will go with later one, but it is plenty good to get the project rolling with a nice shiny new wheel!

The other big score was when I realised the 3 bolt pattern on the hub drive looked just the same as my old Japanese style NSR. I had bought 3 styles of floating disks almost 20 years ago for my NSR at the time and never used them. The bikes were long since gone so they were just collecting dust! But now they have a perfect use and the final look fitted on the bike looks sweet!

04-09-2016, 12:40 AM
The one challenge with the hub drive is it is a 13" rim, where the standard rim on the GP-1 is a 14" one. So to keep the bike from looking funny I needed to match the outside diameter of the tyres.

The 14" tyre is a 140/60 and on paper a 13" 130/70 is equal. I could have gone with a 140/70 in 13" also, looking a the photo it would look like the 140 wide 13 would be an even closer match? There is always another time! If I do this I will need to find an adjustable height shock as the bike is pretty tall as it is, so knocking 1/2" would not be a bad thing in my opinion!

10-21-2016, 05:54 AM
Been a while since the last post. The bike has been completed and just refining it for now for gradual improvements. Made a short vid some months back of an early test ride.


02-12-2019, 03:59 PM
Wow, that's really nice. Id like to convert my Aprilia SR 50 Ditech to electric but looks like a lot of work...

02-13-2019, 07:49 AM
Wow, that's really nice. Id like to convert my Aprilia SR 50 Ditech to electric but looks like a lot of work...

Hey cheers! It was for sure a lot of work, I have everything to build a second but lost enthusiasm for it so just working on my 2T bikes for now! I think the SR50 would be a nice one, but would have bigger compromises as there is less space for batteries. Means you would have to use 18650 battery packs and probably lose the helmet storage. You could get a ready to go swingarm and motor kit though which is nice would probably drop in.

As for the riding experience there is nothing like it! The low speed performance in traffic is perfect and the efficiency is really good so operating costs are low, expect to be 1/3 the cost of petrol costs. The other thing though is the insane acceleration, if you watch Tesla videos you'll get some idea of what I mean, overtaking is never an issue!