Motobecane 50V moped EV conversion

DamnDan

1 µW
Joined
Apr 26, 2020
Messages
3
Location
Toronto, Canada
Hey gang, this is my first EV build so bear with me if I ask something stupid... I have done quite a bit of reading and research so hopefully, it's not too bad.

I've got what I believe (the VIN plate is quite faded) is a 1970 Motobecane 50V moped... well, really it's the Canadian N50 but as I understand they're basically the same. I bought it off a guy who wasn't the original owner. He had a plan to rebuild it a long time ago and instead it sat in storage. I found a lot of old vines around the drivetrain so I think he's using the term "storage" pretty loosely.

I'm building this as a city commuter for my wife and would be great to have a range of about 40kms. I'd like it to be able to cruise at 30-40kph with the ability to push it for short bursts up to 60kph or so if needed. It's mostly flat terrain with lots of stop and go at traffic lights. It will have functional pedals so it appears legal but they won't really be used. The estimated total weight including: wife, moped, battery and motor is about 220lbs.

Does this setup seem like it would be a good fit for what I'm looking to achieve?

QS 72v 3000w hub motor (205)
Sabvoton Controller 72200
72v 20ah Li-ion battery with 45A BMS

I'd like to get the EV components ordered ASAP, since I'm sure shipping will take a long time. Is there anything else I need to consider before I pull the trigger on getting them?

The one problem I'll have to solve is that the moped swingarm dropout is 125mm and the QS motor is 150mm. Are there thinner hub motors out there? I couldn't find much in the 3kw range if there is. Otherwise, I'm looking at stretching the swingarm I've got to fit. Plus I'd need to make sure there's room for a disc brake. Is that too far of a stretch do you think?

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Welcome Dan. Your list is a start, sounds like an awesome project.

My initial reaction is it looks reasonable for the lower speeds, you might be a little small on the controller and/or BMS. Full disclosure, I haven't had a chance to dive into a moped just yet. Still working through some smaller toys to learn all of the little issues that come up in these projects. But, I have seen quite a few scooter/moped conversions online and it seems like most people underestimate how much power it takes to accelerate from a dead stop.

There was a Tomos Sprint conversion that is pretty close to what you are after in the motorcycle conversions section, so it seems like you could be right on with your original expectations. Motors, batteries and controllers all can have long lead times, good to have your main powertrain ordered when you have a rough idea of performance locked in.

Good luck, post your progress. Maybe it will become an example for others if they want to do one of those classic moped conversions.
 
I've been on the fence about using a mid-drive motor. To me, the hub seems like a simpler option that would be quieter and free up real estate for the battery. Is there an advantage to going with a mid-drive over a hub?

I've been looking at this kit: http://www.qs-motor.com/product/qs205-50h-v3-max-6000w-e-bike-hub-motor-electric-moped-motorcycle-conversion-kits/ It looks like I can specify the motor winding to be either high torque, balanced or high speed. I feel like more torque is going to be useful in stop-and-go traffic with a heavy moped.

I want to make sure I understand this correctly...

The motor has a continuous current of 45a and a max current of 80a. Does that mean I can safely run it at 80a?
The sabvoton 72150 has a max current of 150a... so no danger of maxing that out.
When looking at the battery I'm considering, it has a rated discharge current of 45a and a max peak discharge of 90a. I'm assuming pushing that to 80a to match the motor wouldn't be wise? I could look at other batteries if that's the limiting factor, but might not be worth it if it would just burn the motor out in the long run.
 
I just measured the space where the old engine was... fitting a mid-drive motor wouldn't be easy. It's much wider than the ICE engine and would contact the pedals. The only way to make it work would be to mount it really far forward, which would make for a lengthy, unsightly drive chain.

Looks like it'll have to be a hub.
 
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