I Need some technical advice for a commuter motorcycle project

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lambokhoa   1 µW

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I Need some technical advice for a commuter motorcycle project

Post by lambokhoa » Jul 04 2018 7:20am

I’m currently planning to build an electric motorcycle for commute purposes. I’m thinking of a 48v 80ah LiFePO4 battery pack for the motorycle, but still abit torn between what drivetrain i should use-Living in Vietnam, the traffic is quite busy and there will certainly be alot of stops during my commute. I’m a bit torn between the 17inch qs motor’s hub motor and the 5kw golden motor. I don’t know what would be my donor bike yet, but it would very likely to be a 150cc motorcycle. In that case would the hub motor setup be more beneficial, taking up less frame space? I’m worried that a chain drive setup would locate the central of gravity upward, which may affect handling characteristic of the motorcycle. I really need help and advices since this is my very first ev project.

phate   10 W

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Re: I Need some technical advice for a commuter motorcycle project

Post by phate » Jul 04 2018 8:18am

I wouldn't worry too much about the difference in center of gravity between the hub motor and mid-drive setup, it will more likely than not end up quite a bit lower than it was with the gas engine. A low CG will make the bike feel lighter than it is.

Mid drives are nice because you can play around with the gearing to get closer to the performance you need/want, and can easily mess with it after the fact (for example, if you gear it to go 65mph, then ride it around for a week to find that you almost never exceed 45mph, it would make sense to gear it a bit lower for improved performance around town). Your powertrain does still take up some space in the frame, and you have to figure out the correct location for the front sprocket so the chain doesn't lose tension over the rear suspension's travel.

Hub motors make the conversion simpler. Just rip out the engine, stuff your battery/controller/charger in that space, install the new rear wheel with hub motor, and hook up the wires. That's obviously an oversimplification, but you get the idea. You'll have to do a bit more work ahead of time as far as figuring out the right balance between top speed/torque based on the voltage/current you want to run, but after that you're pretty much good to go.

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skeetab5780   10 MW

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Re: I Need some technical advice for a commuter motorcycle project

Post by skeetab5780 » Jul 04 2018 8:27am

Go mid or go home. Especially if your going to use a gas donor bike. The wheels will match already you wont need to change much the chainline and sprockets are there for you. Just need to weld a motor in the correct place.

Changing the gearing will be much easier mid

Hub motor will be quieter and slightly more effecient on flat grade

If you go hub, make sure you pick the right KV in the proper wheel size for your donor bike and check it with a online simulator or you may not be happy. Only thing you can do after the fact is raise or lower the voltage.

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spinningmagnets   100 GW

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Re: I Need some technical advice for a commuter motorcycle project

Post by spinningmagnets » Jul 04 2018 8:37am

I commuted on a small 250cc motorcycle for several years.
for example, if you gear it to go 65mph, then ride it around for a week to find that you almost never exceed 45mph, it would make sense to gear it a bit lower for improved performance around town
I strongly agree with this. Proper gearing will maximize the resulting torque-curve. Doing that will lower the peak amps across the graph, and that means the motor, controller, and battery will run cooler. All of those are good things.

As to the LiFePO4 battery pack, they are slowly falling by the wayside, but...I am still convinced that they are a very viable [and even desirable] pack to use. The life-cycle of this chemistry is typically at least double that of the NCA / NCM found in 18650 cells (if not more). The issue is that...they are normally found configured as a flat foil pouch cell, and garage builders are often drawn to the metal-encased cylindrical cells.

There are 4S packs for sale as a 12V replacement, and as an engine-starting product, they are typically available as a "high current" [high C-rate] construction. Even if you don't actually need high-current, using a high-current cell in a low current application means the battery pack will run cool, and...this is one of the protocols that will make an expensive battery pack last a very long time...heat makes battery packs die early.

lambokhoa   1 µW

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Re: I Need some technical advice for a commuter motorcycle project

Post by lambokhoa » Jul 04 2018 12:12pm

skeetab5780 wrote:
Jul 04 2018 8:27am
Go mid or go home. Especially if your going to use a gas donor bike. The wheels will match already you wont need to change much the chainline and sprockets are there for you. Just need to weld a motor in the correct place.

Changing the gearing will be much easier mid

Hub motor will be quieter and slightly more effecient on flat grade

If you go hub, make sure you pick the right KV in the proper wheel size for your donor bike and check it with a online simulator or you may not be happy. Only thing you can do after the fact is raise or lower the voltage.
I didn’t know there are simulators for this purposes

lambokhoa   1 µW

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Re: I Need some technical advice for a commuter motorcycle project

Post by lambokhoa » Jul 04 2018 11:30pm

spinningmagnets wrote:
Jul 04 2018 8:37am
I commuted on a small 250cc motorcycle for several years.
for example, if you gear it to go 65mph, then ride it around for a week to find that you almost never exceed 45mph, it would make sense to gear it a bit lower for improved performance around town
I strongly agree with this. Proper gearing will maximize the resulting torque-curve. Doing that will lower the peak amps across the graph, and that means the motor, controller, and battery will run cooler. All of those are good things.

As to the LiFePO4 battery pack, they are slowly falling by the wayside, but...I am still convinced that they are a very viable [and even desirable] pack to use. The life-cycle of this chemistry is typically at least double that of the NCA / NCM found in 18650 cells (if not more). The issue is that...they are normally found configured as a flat foil pouch cell, and garage builders are often drawn to the metal-encased cylindrical cells.

There are 4S packs for sale as a 12V replacement, and as an engine-starting product, they are typically available as a "high current" [high C-rate] construction. Even if you don't actually need high-current, using a high-current cell in a low current application means the battery pack will run cool, and...this is one of the protocols that will make an expensive battery pack last a very long time...heat makes battery packs die early.
The C rating of the pack i’m interested in is 3 C per cell
Would that be enough?

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spinningmagnets   100 GW

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Re: I Need some technical advice for a commuter motorcycle project

Post by spinningmagnets » Jul 05 2018 7:06am

3C is nice, but it also depends on how many peak amps you need and how large the battery is. There will be lots of compromises in the design phase. I think a non-hub motor with a chain will perform better, due to the higher motor RPMs, plus...you can simply change sprockets to change the top speed (instead of getting a completely different Kv of motor. However, a non-hub intrudes into the area you'll need to mount the battery.

A hubmotor (like the QS you mention) is adequate for lower speeds, but...it does make the sprung weight heavier when you hit bumps. The biggest benefit of using a fat hubbie is that it frees up the entire frame to mount the battery and controller. Much more design freedom.

John in CR has enjoyed great success with a fat hubmotor in a small diameter wheel, which has proven to be a reliable set-up. Between hub and non-hub, each has a benefit, and each has a headache. You much choose which headache you can live with.

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Re: I Need some technical advice for a commuter motorcycle project

Post by John in CR » Jul 06 2018 1:26pm

lambokhoa wrote:
Jul 04 2018 11:30pm
spinningmagnets wrote:
Jul 04 2018 8:37am
I commuted on a small 250cc motorcycle for several years.
for example, if you gear it to go 65mph, then ride it around for a week to find that you almost never exceed 45mph, it would make sense to gear it a bit lower for improved performance around town
I strongly agree with this. Proper gearing will maximize the resulting torque-curve. Doing that will lower the peak amps across the graph, and that means the motor, controller, and battery will run cooler. All of those are good things.....
As long as the gearing is just a bit lower, then that's ok, but definitely don't build something you are forced to ride around at WOT all the time. There's no fun in that, Who wants golf cart type performance. Plus into headwinds and up shallow grades it's always good to be able to maintain cruising speed. I rarely go WOT except during acceleration and I demand great acceleration all the way up to cruising speed...much better for passing. I build so my bikes are faster than me, and can't imagine riding something with weak acceleration near the top, or riding around with every puff of wind or uphill grade making me go slower than I want.
Last edited by John in CR on Jul 13 2018 3:41am, edited 1 time in total.

phate   10 W

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Re: I Need some technical advice for a commuter motorcycle project

Post by phate » Jul 07 2018 7:45am

spinningmagnets wrote:
Jul 04 2018 8:37am
I commuted on a small 250cc motorcycle for several years.
for example, if you gear it to go 65mph, then ride it around for a week to find that you almost never exceed 45mph, it would make sense to gear it a bit lower for improved performance around town
I strongly agree with this. Proper gearing will maximize the resulting torque-curve. Doing that will lower the peak amps across the graph, and that means the motor, controller, and battery will run cooler. All of those are good things.
A huge part of the reason I'm building a mid-drive with 1.5:1 primary reduction is so that I can run roughly-stock sized front and rear sprockets. I'm gearing for a top speed of 75-80mph so that I can hang with my friends on gas bikes and comfortably ride it on the highway for short distances, but if it turns out I hate riding it at those speeds I have a pile of aftermarket rear sprockets available (for the original gas bike) to adjust the top speed down a bit.

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spinningmagnets   100 GW

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Re: I Need some technical advice for a commuter motorcycle project

Post by spinningmagnets » Jul 07 2018 10:06am

I'm gearing for a top speed of 75-80mph so that I can hang with my friends on gas bikes and comfortably ride it on the highway for short distances
I’m currently planning to build an electric motorcycle for commute purposes...48v 80ah LiFePO4 battery pack for the motorcycle, but still a bit torn between what drivetrain I should use...Living in Vietnam, the traffic is quite busy and there will certainly be a lot of stops during my commute. I’m a bit torn between the 17inch QS motor’s hub motor and the 5kw golden motor....my donor bike...very likely to be a 150cc motorcycle
Experimenting is fun, and...do what you want. However...this has been tried before. It's expensive and time-consuming. If you can be happy with 45-MPH, then...a 150cc scooter frame will work. And...in spite of the poor unsprung weight being high...a QS hubmotor will work. But...even then...the system as a whole will be running at the ragged edge of viability.

You can spend a lot of time and money trying to succeed in creating something on a tight budget that will accomplish all of these goals, but...I want to let you down gently, and I say this with love...75-MPH is just never going to happen on a budget 48V build. I wish you luck with whatever you decide.

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Re: I Need some technical advice for a commuter motorcycle project

Post by John in CR » Jul 08 2018 1:09pm

spinningmagnets wrote:
Jul 05 2018 7:06am
John in CR has enjoyed great success with a fat hubmotor in a small diameter wheel, which has proven to be a reliable set-up. Between hub and non-hub, each has a benefit, and each has a headache. You much choose which headache you can live with.
No headaches here other than having to change a worn out tire, giving hubbies with bolt on rims a big advantage over integral motor and rim or spokes. I put the key in and turn it.

If going the QS hubbie route, I'd suggest going with the 13" rim instead. Hubbies run more efficient and can be run at higher power in smaller wheels. The 19"-22" diameter range of 13" tires give you some flexibility and doesn't change geometry or looks too much. Also, don't decide on a battery until you decide and simulate your drive system.

phate   10 W

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Re: I Need some technical advice for a commuter motorcycle project

Post by phate » Jul 08 2018 3:29pm

spinningmagnets wrote:
Jul 07 2018 10:06am

You can spend a lot of time and money trying to succeed in creating something on a tight budget that will accomplish all of these goals, but...I want to let you down gently, and I say this with love...75-MPH is just never going to happen on a budget 48V build. I wish you luck with whatever you decide.
You're mixing up who you're quoting dude. I was the one that was shooting for 75+mph, I just used my build as an example to illustrate how a mid-drive gives you more flexibility if your wants/needs end up changing. In my case, highway speeds or wheelies, lol.

Mine's not a budget 48v build, I have a 21s lipo pack and a pair of water cooled 120mm outrunners that are going to eat 300A each. Nothing crazily expensive (under $5k when all is said and done, unless I decide to buy expensive controller), but it'll go highway speeds just fine, although I still might end up throwing a larger rear sprocket on the bike to do hooligan things if I end up avoiding highways with it. Honestly unless my torque constants are WAY off, it would go 100mph fairly easily if I either geared it higher or ran more voltage.

I'll end up messing with hub motors if I decide to play around with one of the cheap electric grom clones in the future.
Last edited by phate on Jul 08 2018 3:37pm, edited 1 time in total.

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spinningmagnets   100 GW

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Re: I Need some technical advice for a commuter motorcycle project

Post by spinningmagnets » Jul 08 2018 3:36pm

My apologies. I'll be more careful in the future.

phate   10 W

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Re: I Need some technical advice for a commuter motorcycle project

Post by phate » Jul 08 2018 3:39pm

spinningmagnets wrote:
Jul 08 2018 3:36pm
My apologies. I'll be more careful in the future.
No worries. Multiquoting tends to get broken on most forums (it worked great back in the day, but too many people just quoted whole posts so you'd end up loading an entire thread multiple times per page).

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