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Discussion Starter · #1 ·
It pains me a bit to convert a vehicle in perfect working order, but it’s free and exactly the style of e-motorcycle I want for commuting to work. And I’ll help save the planet.
120359

I am a mechanical engineer with tons of experience in electromechanical product design and fair automotive/mechanic skills. I also have a 3D printer at home. It turns out that my exact bike was on HUM3D and I already downloaded the 3D CAD model so I can start to figure out what motor and batteries that I can fit in my chassis.
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The problem I’m having is trying to figure out what type of motor to use, what voltage and how many/type of batteries to get. I can’t make heads or tails of the motor performance curves.

My ideal goals:
  • Get back and forth to work (30 miles round trip) in Florida (flat as a pancake) with city type driving and an average speed of 40-50 mph (if I take the back roads).
  • Be able to take the highway route if I choose (75mph for about 9 miles of trip). For this bike 80mph or faster is a bit rough since I have no windshield and the you need the wind to deal with the heat 9 months of the year.
  • Be able to accelerate as fast as I can today. Moderately aggressive acceleration if I want, but tires will NEVER squeal on dry pavement. I get 51 ft-lb of torque at 3400 rpm today.
  • I’d like to be able to use the existing belt drive on the bike which has a 2.0625 gear ratio. I know this is low for most ev builds. 72 mph requires just over 2000 rpm on motor.
  • I do have a radiator and fan on this bike that I can use if I need to water cool the motor.
  • Keep the conversion cost below $5k
  • Style the bike so it looks like an EV. (I love the look of the 2013 Voxan Wattman motorcycle)
I’ve looked at the HPEVS AC-20 motor (which is in the rendering) and that allows me to get 12X 40 Ah SLA batteries. But that setup doesn’t seem to produce enough continuous torque.

I’ve looked at a ME1616, but that is a monster and I get much fewer batteries. It looks like my cost goes pretty nuts if I have to go Lithium, but maybe I could charge the bike at work which drops my range to 15 miles.

I’m at a loss and I don’t really want to develop this EV with trial and error. Any advice or guidance would be greatly appreciated.

Thanks,
Derek
 

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It pains me a bit to convert a vehicle in perfect working order, but it’s free and exactly the style of e-motorcycle I want for commuting to work.
Motorcycles are so simple (compared to cars) that it seems to me that the obvious alternative to sacrifice a vehicle in perfect working order is to buy just the fork assembly and rear suspension, wheels, tires, brakes, etc from a salvage yard, then build your own frame which is better suited to the electric motor and battery, and build a custom bike. Of course there can be legal issues with that (registration, licensing, and insurance for a home-built), and perhaps the parts you would need are exactly the ones which are wrecked on bikes being torn down for salvage. Why not just start with a bike with a dead engine?
 

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... 12X 40 Ah SLA batteries.

... It looks like my cost goes pretty nuts if I have to go Lithium...
Do you really want to start an EV project in 2020 using lead-acid batteries? The cost of lithium-ion cells and modules depends on the type and source - what are you considering?
 

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Discussion Starter · #4 ·
Motorcycles are so simple (compared to cars) that it seems to me that the obvious alternative to sacrifice a vehicle in perfect working order is to buy just the fork assembly and rear suspension, wheels, tires, brakes, etc from a salvage yard, then build your own frame which is better suited to the electric motor and battery, and build a custom bike. Of course there can be legal issues with that (registration, licensing, and insurance for a home-built), and perhaps the parts you would need are exactly the ones which are wrecked on bikes being torn down for salvage. Why not just start with a bike with a dead engine?
Brian,
I admittedly have not spent a tremendous amount of time looking for bikes with dead engines, but my area does not seem to have many options in this area that don't cost almost as much as I can sell my working bike for. I don't live in a major metropolitan area. My thinking was that if I can sell the ICE then I'd probably be really close to the same net cost. Also, I know 100% that all of the road/safety systems work perfectly and I don't have to mess with them.

Thanks for the comment.
Derek
 

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Discussion Starter · #5 ·
Do you really want to start an EV project in 2020 using lead-acid batteries? The cost of lithium-ion cells and modules depends on the type and source - what are you considering?
Maybe I'm working backwards, but I've been trying to figure out the motor and voltage with my range before figuring out the batteries. I have a potentially good source for 12V 40 Ah batteries, but I'm not married to this. I understand the tradeoffs between chemistries and think it is a distinct possibility I may have no choice but to go lithium. I'm trying to get help to get me to that decision point.
 

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Do lots & lots of research, before spending any money.

Most folks change their minds, as they learn more (as they should)

SAM_5998.JPG
Here is my El Moto

Here is where I upgraded to lithium
 

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Discussion Starter · #7 ·
Most folks change their minds, as they learn more (as they should)
Thanks "Functional Artist". You left me a few breadcrumbs. I went back to some of your old posts and found I may overthinking my torque requirements. My current motorcycle generates about 50 ft-lbf of torque and a top speed of 102 mph at around 2800rpm. So with aerodynamic drag being several factor times velocity squared I figured that the torque required for me to get 75mph was around 13 ft-lbf. Does that sound about right?
 

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Maybe, it depends (everyone's "favorite" answer)
...aerodynamic drag (like you mentioned) is important
...rolling resistance
...& the over all weight (including rider) too

Plus, there are many differences to "keep in mind" when converting to electric propulsion

Like, with electric propulsion, the torque is available right from 0 RPM's
...where as, in an ICE, you have to wait for the torque to "show up" (so, the first ~1,000 RPM's are basically wasted)
&
The top speed of 102MPH @ 2,800 RPM's would probably be in when in high gear (maybe an OD even)
...but, when converting to electric, most don't use a transmission
(their usually not beneficial/helpful & take up/waste valuable space, that's better used for more batteries)

That's why I always suggest to do lots of research
...to see what others have done
...how they did it
...what worked
...& also, what didn't :)
 

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Thanks "Functional Artist". You left me a few breadcrumbs. I went back to some of your old posts and found I may overthinking my torque requirements. My current motorcycle generates about 50 ft-lbf of torque and a top speed of 102 mph at around 2800rpm. So with aerodynamic drag being several factor times velocity squared I figured that the torque required for me to get 75mph was around 13 ft-lbf. Does that sound about right?
What gear are you in at that speed?

Is that the peak torque of the engine or the torque it puts out at a 1:1 final drive ratio to the rear wheel at highway speed?

I wouldn't put 13 ftlb in a kid's Big Wheel, lol.

Think torque wrench...
 

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Discussion Starter · #10 ·
What gear are you in at that speed?

Is that the peak torque of the engine or the torque it puts out at a 1:1 final drive ratio to the rear wheel at highway speed?

I wouldn't put 13 ftlb in a kid's Big Wheel, lol.

Think torque wrench...
So the published dyno reading for my ICE moto gives me 50.1 ft-lb max torque on rear wheel for between 2700 to 4000 rpm on motor. They publish the top speed at 102mph, which seems about right since I've been in the mid ninetys without topping out. I'm assuming that at max speed the motor torque is maxed. A 102 mph my wheel is going 1377 rpm so with a 2.0625 belt drive ratio and .963 5th gear ratio of .963 the torque on the drive pulley of the belt is 24.3 ft-lb and at the motor 25.7 ft-lb @ 2733 rpm. So belt can handle 25 ft-lb. I come up with 13 ft-lb by calculating the total drag force (Fd = Drag Constants * V^2 ) of the bike at top speed and dropping that down to 75mph.

Unless this is wrong it is looking like I am getting into continuous torque range of an AC-20 motor running at 48V and around 2000rpm.
 

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So the published dyno reading for my ICE moto gives me 50.1 ft-lb max torque on rear wheel for between 2700 to 4000 rpm on motor.
That doesn't seem likely. Published dynamometer results are normally scaled to match the gearing, rather than reporting the actual torque at the wheels. A roller dyno doesn't even know the torque to the wheels, only the force on the roller surface. If that is 50.1 ft-lb max torque at the engine output, then with the engine turning between 2700 and 4000 RPM that would be 26 to 38 horsepower, and actual engine output is higher (because the dyno is measuring after losses to gearing, the belt drive, and the tire), which is plausible for a 900 cc air-cooled twin.

The first published spec that I found for this bike is
Maximum Torque: 60.8 lb.-ft. @ 3,700 rpm
which corresponds to 43 horsepower (peak power would be more, at a higher speed). The lower 50 lb-ft value over a wider range seems consistent.

Another online source confirms the torque specs and adds
Power:50.31 HP (37 kW) @ 5700 rpm
That implies that all the way up at 5700 the engine can put out 62 Nm or 46 lb-ft. This suggests an engine with a very broad usable power range; once significantly above idle, this thing runs like an electric motor. ;)

I'm assuming that at max speed the motor torque is maxed.
That's not likely, either. Almost any vehicle hits its top speed in something lower than the top gear, with the engine speed near the peak power level, well above the engine speed for peak torque. If the vehicle can hit a given speed with the engine at the torque peak, it could go faster by shifting down a gear for more power. The top gear is just for better fuel economy, less noise, and less engine wear.

A 102 mph my wheel is going 1377 rpm so with a 2.0625 belt drive ratio and .963 5th gear ratio of .963 the torque on the drive pulley of the belt is 24.3 ft-lb and at the motor 25.7 ft-lb @ 2733 rpm. So belt can handle 25 ft-lb.
If you want to know what the belt can handle at least briefly, just multiply the engine's peak torque output by the first gear ratio - that's the torque at the drive pulley.
 

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Discussion Starter · #12 ·
120427


Here are the dyno curves I found for my Vulcan (green curves). So if its not torque on the wheel the belt drive has a 2.063 ratio, 5th gear is .963 ratio, 4th gear is 1.1
 

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Here are the dyno curves I found for my Vulcan (green curves) View attachment 120427
Excellent :)
It's engine speed. Logically, anything going to about 7000 RPM is obviously not a plausible wheel speed, but it is what you see on the tachometer (which of course is engine speed).

The numbers are lower than the published specs, because the power (and the corresponding torque) is measured at the rear wheel, after drivetrain losses, while the manufacturer's published values are for the engine.

That Vulcan certainly achieves its goal of a broad power band. (y)
 

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This chart is for engine torque and HP. Between the engine output shaft and the transmission input shaft is a set of primary reduction gears(or sometimes a chain drive) inside the engine, with a reduction ratio of ~2-4:1. You need to figure this into your calculations.
In real world apps for the AC-20 motor typically a 5-6:1 reduction ratio is used in the final drive. Also, some people noted they could use more HP than what the motor produced. Enter AC-20 in the search bar above. Or, google AC-20 motorcycle conversions.
 

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Discussion Starter · #15 ·
So I found that the Vulcan has the following. Primary drive:2.184, 4th gear 1.107, 5th gear .963 and a final reduction of 2.063 (belt).
 

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Discussion Starter · #16 ·
Thanks guys. So I went back to my original calculations on drag force and matched that up with the torque at the wheel at 102 mph (236 ft-lb). With max ICE torque and the total drive ratio in 4th or 5th gear the max wheel torque calculated to about 220 ft-lb. This is pretty close and if I drop drag force down to 75mph sustained I get 117 ft-lb at the wheel. With a 2.063 belt drive ratio this is not going to cut it.
In real world apps for the AC-20 motor typically a 5-6:1 reduction ratio is used in the final drive.
A 6:1 gets me a into the continuous 10 ft-lb and 6000 rpm range of the AC-20. So it looks like I'll be working on the gear reduction
 

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Those numbers at the wheel feel a lot better.

Now you can also go back and calculate the acceleration in g's you get from your ratios, cuz a bike is not just about top speed....
 

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My bike has a 8,000W brushed PM motor
...powered by a 2kWh section of a Chevy Volt battery - 45V (nominal) 49.5V (max)
...running @ 5.4:1 (10 tooth on motor & 54 tooth on axle)

My top speed was ~35MPH
...but, it got there really really quick (like 0 to top speed in ~3 seconds) Super Fun! :)


This spring I wanted to try lowering the ratio, just a bit
...so, I changed the rear sprocket from a 54T to a 50T

Which increased my top speed up to ~ 40MPH
...but, @ the expense of some acceleration (like 0 to top speed in ~4 seconds)


You have a bigger/heavier bike
...& want to go faster

So, yup you'll need a more powerful motor
...& to run 'er @ a higher voltage

Just some info, kinda as a base to go off of :cool:
 

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I think you should go with the Vulcan bike. A conversion is never nicer then the donor bike :)
My first conversion was a beaten up Cagiva Mito 125cc and unless you fix and paint everything it will always look "old".

My next was a Harley Street Rod in perfect condition. Sold the drivetrain easily!
Also uses the AC-20 motor with a gear ration of 1:6. Less will make the current very high (heat) and there will be broblem with hills and staring at redlights. And the bike will not be as fun!

If you use Curtis controller you can downlod a RPi software that we developed -> github -> Curtis-dashboard.

There is also a AC-23 with higher torque.

/Marcus
 
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