Help with a school project?

[toasterbike]

Hi everyone!

So I'm a new guy here coming from DAAP's Transportation Design program at the University of Cincinnati and for my capstone, I want to design an electric moped. BUT I NEED YOUR HELP!

I've already been doing tons of research, and I'm at the stage where I need to figure out the package for this moped (battery, controller, motor, etc.) this way I can take the next step and start to build my sketches around an actual package.

I want this electric moped to compete with the Stealth Fighter and the BOLT M1. However, I want to have the frame 3D printed using a printer similar to how Local Motors printed Strati.
I feel that the car, while impressive, is not the right application for this material or manufacturing process. Its strength and lightness better lends itself towards a moped frame. Smaller parts yield faster build times, frames could be customizable per the rider, potentially on-demand? (I wouldn't want to cheapen it by doing the Lens Crafters' product in 1 hour thing, I would like to keep the waiting list at a minimum though). I also feel that the current rise of new battery/motor technology deserves new frame technology to really make a breakthrough in that market.

Anywho, I need some help deciding on which batteries and which motor to use.

I want it to have:
-about a 35mph top speed (little lower or high is ok, it could have a "competition mode" like Stealth does to save itself from the law)
-charge in a few hours
-25 to 50mile range
-as lightweight as possible

I don't want to directly copy Stealth's or Bolt's setup, I think my electric moped could hit better numbers since its frame would be lighter. But I don't know which size LiFePO4 battery to use, or which rear hub motor would be better suited for the numbers I want to hit. I have been also been entertaining Panasonic's “B” cell (3400-mAh Panasonic NCR18650B), and Samsung's 30Q cells (3000-mAh per cell, so a 5P string provides 15-Ah) BUT i'll be honest, math isn't my number 1 subject (I've taken up to Business Calc 3 with an A) and when I present these to my professor, I want to be bulletproof. Recently, VW seems to have retracted their offer of an internship to me, so there's a little bit of spite involved too. Get better, not bitter right guys?

Long winded message, BUT I NEED YOUR HELP. I mayyyy have a shot at building a running model of this thing too. Thanks!!!

 

[amberwolf]

I want it to have:
-about a 35mph top speed (little lower or high is ok, it could have a "competition mode" like Stealth does to save itself from the law)
-charge in a few hours
-25 to 50mile range
-as lightweight as possible

I'd recommend looking at builds here on ES that actually already do what you want yours to do, and then using what they used. Then it will be "bulletproof" as you can show that it does what it needs to by direct example.

If you don't want to use exactly what they used, then you will have to figure out how much of what you want to use will make up the difference between your choices and theirs.

If you read around, you'll find there are quite a few "noob" threads about deciding what to build that show how to figure out things like range at speed vs terrain, torque vs speed, etc., whcih you'll need to know to determine exactly what you need if you're not going to use known-working combinations.

Recently, VW seems to have retracted their offer of an internship to me, so there's a little bit of spite involved too.

I doubt they can afford anyone new. You might wanna read this thread if you haven't heard the news about VW:
https://endless-sphere.com/forums/viewtopic.php?f=1&t=72870

 

[toasterbike]

Any good commuter builds you could recommend? Thaks for the reply!

Yup, I've been keeping up to date with VW, they seem to have made offers to some other students in my class but that whole thing is a different story

 

[Punx0r]

Design for a pack of 18650 LiCo cells IMO. They very justifiable in that they're safe, reliable, long-lived and energy dense and can be arranged in whatever shape fits your frame. They're not that expensive (for a manufactured bike), either.

Your maths is correct in that 5 parallel strings of 3000mAh gives you 15Ah capacity (then add the series voltage of 3.7V per cell nominal). Total pack capacity is then the product of the two to give watt-hours.

 

[toasterbike]

Thanks Punx0r!

How do I calculate the ohms of resistance for a custom battery?

If I were to have 90 cells of Samsung's 30Q 18650 INR battery, I should be getting 270Ah. Electricbike.com said this kind of setup in an 18 Serial (I'm not quite sure what that means) should yield 72V.

So I took this information and went to use the Motor Simulator from ebikes.ca, plugging in this custom battery setup but its asking for the ohms of resistance. They explain it as, "Any respectable supplier would know or be able to get this detail. Lacking that, you can get the data by observing the voltage of your system under load. For instance, if a battery is showing 49V at rest, and 44V when you draw 25A at full throttle, then the battery resistance is approximated by ΔV/ΔA = (V49-44V)/(25A) = 0.2 Ω." But since this battery is purely theoretical, I'm looking for another way to calulate the ohms of resistance. ANY HELP APPRECIATED!

So far here's the setup I'm working with:

Nine Continent M3006RC rear hub motor (would be paired with 17" moped rims)

72V 270Ah Custom INR battery (from Samsung 30Q 18650)

36-72V, 40A Controller C7240-NC

 

[Drunkskunk]

Your project sounds interesting so far. Do you have a design in mind? Will this be a step-through scooter type moped, or were you thinking more like they 70's style pedal mopeds?

If the manufacturer can't give you the specs on the battery resistance, the only way to calculate it is by testing.

A 270AH battery would be larger than most electric car batteries. It would probably need a small pickup truck to haul it around. That's probably far more than a 500lbs battery. you would have a hard time fitting a battery 10 times smaller than this on a scooter, it would still be huge.

 

[toasterbike]

Maybe my math is wrong?

So if I had 90 cells at 3000mAh per cell, that should yield 270,000mAh or 270Ah.

If each Samsung 30Q 18650 battery is roughly 18mm wide and 65mm long, and if I stacked them in 18 rows with 5 cells to each row; then I should have a battery pack thats (18mm x 5 = 90mm) around 3.5in long, (18mm x 18 = 324mm) around 12.8inches tall, and (65mm) wide. If each battery weighs 48 grams, then the battery pack (48g x 90 = 4320g) would weigh around 9.5 pounds. Probably about a pound more accounting for the thin strips of nickel, wires, and battery meter.

This size battery pack should be able to fit into something around the size of a Puch Maxi. I'm leaning towards a step thru style frame with pedals as well, something approachable/comfortable for the general population. Kinda like a more nimble version of the Gogoro Electric Scooter. I don't think the frame would weigh very much since it would be designed to use as little material as possible to make it structurally sound (I'm thinking bird-bone like structure). But so much of the form is going to come from the drivetrain so I really need some help to nail the battery/motor/controller combination!

 

[SlowCo]

Maybe my math is wrong?
So if I had 90 cells at 3000mAh per cell, that should yield 270,000mAh or 270Ah.

If all 90 cells would be used parallel than you'd have a 3.7V 270Ah battery pack. All strings put in series keep the 3Ah capacity...

 

[Drunkskunk]

90 (3.7V, 3000mAh) cells arranged in a 18S(series) x 5P(parallel) configuration would give you a 66.6V, 15AH battery of 999 watt hours.

You add the Voltages in series, you add the Amps in parallel.

That's actualy a good size for a small scooter. at 20mph, it would be good for a minimum of 27 miles or so, and under ideal conditions, probably double that. At 30mph, it would probably do a reliable minimum 10 miles.

 

[markz]

Simple

Voltage in series, is added, and Ah is disregarded.
Amp Hour in parallel, is added, and V is disregarded.

10 series non in parallel = 37V 2Ah
10 series + 10 in parallel = 37V 4Ah
20 series + 20 parallel = 74V 4Ah

so on so forth.

 

[toasterbike]

Ahhhhh there's the maths. Thanks guys! Back to the drawing boards for now. Will be back soon with some sketches!