Lambretta University Project

General Discussion about large electric scooters and motorcycles and other things with no pedals.
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bjreadings   1 µW

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Lambretta University Project

Post by bjreadings » Jan 14 2020 10:33am

Hello all, I'm a final year product design student studying in London.
For my final project of my degree I am trying to convert a vintage Lambretta to electric.
There are already companies that are converting these scooters, but they simply remove the original engine and replace it with a hub motor.

I want to do something different, I believe that if I can replace the crank of the original engine with a suitable motor I can power the original engine,(a similar concept to what EVwest and Electric Classic Cars are doing) this way the scooter will remain geared and not demoted to an automatic :lol: . I have found that the original output of the crank is around 10hp/7.5kw at 6000rpm at its peak power.

I've been trying to find a motor that will match (or improve) these figures. I've been brought up on petrol and pistons and have done a fair amount of research into ev motors but have realised that I really don't know a lot.

The motor that I have found that seems to be what I want is the 5kw offering by goldenmotors(https://www.goldenmotor.com/frame-bldcmotor.htm). I'm not sure if this is a suitable motor, and what variation would be best, 48v,72v or 96v. The site offers a controller and battery pack, but once again, I'm not sure this is actually what I want.

Any help from you wonderful people will be massively appreciated,
Thank you in advance Ben.

SRFirefox   10 mW

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Re: Lambretta University Project

Post by SRFirefox » Jan 14 2020 3:41pm

Step one is to lose the gearbox. Seriously. It's only going to take up volume and mass, cause headaches, and offer no real benefit over a single-speed reduction from motor to axle. If you can put the shaft of your motor where the transmission outputs to the final drive, you don't even have to worry about changing the geometry of the original vehicle. Or the output of a primary reduction if your final drive doesn't offer a large enough ratio for the electric motor.

As for motor, the QS 138 70H is a mid-drive motor capable of 10kW+ peaks with the suggested EM150S controller. Silent Enduro have used it successfully on their Husqvarna high-power dirt bike build. viewtopic.php?f=10&t=102858 There is also a thread on it here. viewtopic.php?f=30&t=93627

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mistercrash   10 kW

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Re: Lambretta University Project

Post by mistercrash » Jan 18 2020 8:26pm

There is a good reason why scooter conversions are often done with a hub motor. It is easy, and no sprockets and chain to deal with. Much quieter and leaves a lot more room in the belly of the scoot for a larger battery that will give more power and range. You can get peaks of 40+ hp with a 5kw 12'' hub motor and a proper controller. Exhilarating accelerations I tell ya.
Send $10 at paypal.me/Ray1964 and you will be in my thoughts and prayers.

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grindz145   100 MW

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Re: Lambretta University Project

Post by grindz145 » Jan 21 2020 1:43pm

An e-lambretta would be dope. I imagine you're interested in the non-hub motor setup because the whole swingarm is essentially the motor/gearbox assembly. I think there are some swingarm conversion kits out there that would allow you to drop all the deadweight of the gearbox. That being said keeping the weirdo twist shift handebar thing might be a fun novelty (although woefully unreliable in my experience with my Bajaj Chetak)

pics or it didn't happen

CONSIDERABLE SHOUTING   1 mW

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Re: Lambretta University Project

Post by CONSIDERABLE SHOUTING » Jan 22 2020 10:47am

Yeah, we're gonna need some pics.

Hi there- I'm also a newbie here, but I've been learning a lot and I think I can help a little. First, I've been reading this website intended for Audio electronics that I've found is an excellent primer: http://www.bcae1.com/ It was linked to me from an Air Force mechanic and it's done a great job forming a "bedrock" of sorts. I don't know what your knowledge base, skill level or resources are so I'll assume we're starting from square 1 with very little money.

You should hold onto the gearbox until you have made your motor decision. Not only will it provide mounting hardware and a good blank- depending on the motor you use it can still be needed. Transmissions for combustion engines work to keep the motor within a "range" where it produces the most power and amplifies torque, and motors like that Brushless DC unit you posted still have a "range" where they produce the most of it- 2000 to 6000RPM in this case. I also wouldn't jump at a hub motor just yet. Hubs are great and serve many purposes- but they also have difficulties with heat control, load mass onto the rear wheel, and slow on inclines due to their lack of gearing. The ebike blog has a great piece on why the smallest hub motor that should be considered is a 750w unit, and it's simply because those can reasonably make it up a hill.

First off, you should take a honest look at what goals you want to achieve, making a list of needs and wants and contrast it to your skills. Are you building out of a tarp garage from harbor freight bout on sale for $160 or are you in a a full machine shop where laser cutting is down the hall? You mentioned this is a project for school- do they want you to salvage motors, try to build a usable kit or start over from scratch as a proof of concept? And how much money do you have to spend on this? Ecetra.

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grindz145   100 MW

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Re: Lambretta University Project

Post by grindz145 » Jan 22 2020 12:41pm

By comparison electric motors have a huge efficiency range compared to a gasoline engine, and the losses due to to all the extra rotating bullshit further skews the need of a transmission. hence why not commercial EVS have transmissions.

The torque of even a small electric motor can destroy the dogs of a manual transmission if not shifted carefully under load, so another reason to be careful.

Would be a cool novelty though, doesn't technically do anything useful though.

bjreadings   1 µW

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Re: Lambretta University Project

Post by bjreadings » Jan 22 2020 3:33pm

First of all, I really appreciate the replies.

I am from a purely mechanical background, having to built Lambrettas and Vespas for 6 years since I was 15.

The aim of this project is to retain the gears and clutch, so that it offers an experience that is closer to the original than that of a direct drive that would reduce it to an auto. It will also allow the setting of cables and the maintainece of these scooters. The community around vintage Lambrettas and Vespas are very passionate about not riding an automatic :lol: :lol:

I have plenty of machinery and knowledge at my disposal at my university, laser cutters, water jet cutters, cnc lathes.
I have also secured funding for this project, so while being reasonable budget isnt a real concern.

I was just after some advice from people who have more experience in this field, as I'm not 100% sure on the required power and therefore what motor will be required.

I have attached a diagram that I drew of the Lambretta engine, I am looking to simply replace the crank with an electric motor via some kind of conversion coupling.


Thanks again all.
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Lambretta Diagram.jpg
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amberwolf   100 GW

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Re: Lambretta University Project

Post by amberwolf » Jan 22 2020 5:33pm

bjreadings wrote:
Jan 22 2020 3:33pm

The aim of this project is to retain the gears and clutch,
<snip>
I was just after some advice from people who have more experience in this field, as I'm not 100% sure on the required power and therefore what motor will be required.

I have attached a diagram that I drew of the Lambretta engine, I am looking to simply replace the crank with an electric motor via some kind of conversion coupling.
the coupling should be easy enough, depending on how the crankcase and transmission case are designed.

if they have a common oil bath, you will need to come up with an enclosure for the motor-to-crank coupling (probably chain drive) that prevents oil loss or contamination.

or seal the crankcase off from the transmission, so there's no oil in the crankcase, and then remove all the bits of the case you don't need/want, leaving just enough of the crankshaft to support with a bearing and drive from the new motor.

you could also use gears (helical would be quietest but will require side-loading support bearings), but chains are probably a lot easier to deal with sprockets and adapters to fit onto crankshaft and mtoro, as well as to easily find the right sizes to give the right motor-to-crankshaft speed ratio.



the required power is dependent on the usage, speed, weight, terrain, wind, etc.

since you're going to use the crank input to the transmission, you'll want to start with a motor whose shaft speed is the same range as the crank speed of the original engine (i don't know if thats the same as the engine rpm, but i'm sure you do). or one that will be easy enough to gear up or down with whatever gearing ratios you can fit into the space you have.

then the torque the motor creates at that speed needs to be similar to that of the original engine.

so the first two things you need to know (probably already do) are the speed and torque of the original engine, at the input to the transmission.

speed x torque = power, so once you know what those two numbers are, you have a first basis for how much power the motor must be able to produce, and at what speed it must produce how much torque.


now the question is, do you want just the same performance it originally had, but just in electric, or do you want better performance?

if you just want more speed, you can use a faster motor; it'll also need to be more powerful to overcome the extra air resistance at the higher speed.

if you want quicker takeoffs or better hill climbing, you can use a motor with more torque, keeping in mind that more torque applied to the input of the transmission risks breaking things inside it that can't handle that, if you go above the limits it's designed around--you've probably dealt with that sort of thing before, so may have some idea of what those limits are.

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