First E-bike Build

General Discussion about electric bicycles.
Post Reply
User avatar
TOPdawg   1 mW

1 mW
Posts: 18
Joined: May 19 2019 11:28pm

First E-bike Build

Post by TOPdawg » May 27 2019 2:34pm

I've been doing a lot of research and have found to like the QSmotor 205 50H V3 for what I am trying to do. However, I'm lacking the information needed for the winding.

I want to push 60 mph on the flats and to be almost bulletproof up hills. My current guess-timate is that I will need to draw 80A at 72V in order to achieve those speeds. This will all be done by moped standards; 17x2.25 tires (22in=diameter). The next step I took was to understand heat shedding. Thus ferrofluid and heat fins would be applied.

What do you think of this motor? I am new to the e-bike game but am jumping right in. All information is welcome. I plan to buy Micah Toll's books but thought I should start with the community.
"Don't fake the funk on a nasty dunk." -Plato, the Republic

Vikingimike01   100 mW

100 mW
Posts: 48
Joined: Mar 31 2019 4:16am

Re: First E-bike Build

Post by Vikingimike01 » May 27 2019 2:49pm

Yeah I have this for like a month now basically does 120km/h with a 115kg rider
I have a 120 amp controller with 72v and yeah i have 2x 72v batteries in parallel. You can go up hills yeah. And still accelerate

999zip999   100 GW

100 GW
Posts: 9328
Joined: Jan 10 2010 1:40pm
Location: Dana Point So. Cal

Re: First E-bike Build

Post by 999zip999 » May 27 2019 3:24pm

How much money do you have for this project ?

User avatar
TOPdawg   1 mW

1 mW
Posts: 18
Joined: May 19 2019 11:28pm

Re: First E-bike Build

Post by TOPdawg » May 28 2019 4:55am

Vikingimike01 wrote:
May 27 2019 2:49pm
Yeah I have this for like a month now basically does 120km/h with a 115kg rider
I have a 120 amp controller with 72v and yeah i have 2x 72v batteries in parallel. You can go up hills yeah. And still accelerate
All good stuff, not the wack stuff fam. It really be like that sometimes. This dunk, thus funked.
"Don't fake the funk on a nasty dunk." -Plato, the Republic

User avatar
TOPdawg   1 mW

1 mW
Posts: 18
Joined: May 19 2019 11:28pm

Re: First E-bike Build

Post by TOPdawg » May 28 2019 5:01am

999zip999 wrote:
May 27 2019 3:24pm
How much money do you have for this project ?
We balling on a budget out here homie
"Don't fake the funk on a nasty dunk." -Plato, the Republic

Vikingimike01   100 mW

100 mW
Posts: 48
Joined: Mar 31 2019 4:16am

Re: First E-bike Build

Post by Vikingimike01 » May 28 2019 5:20am

TOPdawg wrote:
May 28 2019 4:55am
Vikingimike01 wrote:
May 27 2019 2:49pm
Yeah I have this for like a month now basically does 120km/h with a 115kg rider
I have a 120 amp controller with 72v and yeah i have 2x 72v batteries in parallel. You can go up hills yeah. And still accelerate
All good stuff, not the wack stuff fam. It really be like that sometimes. This dunk, thus funked.
are you speaking redneck? i cant understand that language

User avatar
TOPdawg   1 mW

1 mW
Posts: 18
Joined: May 19 2019 11:28pm

Re: First E-bike Build

Post by TOPdawg » May 28 2019 3:23pm

My bad. I was partying with my pals at the time and we thought it was a funny reply. But I can assure you that I am 110% committed to making E-bikes. So with that said, I will continue to keep a positive decorum towards this board and use more appropriate boards for letting, you know, me be me.

As for my current goal, I have a 1979 Free Spirit I'm converting to direct drive. I project to use 400 LG MJ1 cells in 20s20p. At 72V and 80A, I'd be pushing towards 60. However, the true speed it will reach depends on winding and what not, and that is one idea I would like to understand a little more about.

Side-note, is it possible to make a DIY motor controller?
"Don't fake the funk on a nasty dunk." -Plato, the Republic

User avatar
E-HP   100 kW

100 kW
Posts: 1217
Joined: Nov 01 2018 9:20pm

Re: First E-bike Build

Post by E-HP » May 28 2019 6:37pm

TOPdawg wrote:
May 28 2019 3:23pm
As for my current goal, I have a 1979 Free Spirit I'm converting to direct drive. I project to use 400 LG MJ1 cells in 20s20p. At 72V and 80A, I'd be pushing towards 60. However, the true speed it will reach depends on winding and what not, and that is one idea I would like to understand a little more about.
Starting with a steel frame is good, but for travelling at 60 mph with no suspension at all, the road surface better be smooth as glass. The battery pack sound like it's up to the task, but you may need to up the voltage to meet your speed goal.

PS. Welcome to the forum :thumb:

User avatar
Drunkskunk   100 GW

100 GW
Posts: 7204
Joined: Apr 14 2007 11:37am
Location: Dallas, Texas. U.S.A.

Re: First E-bike Build

Post by Drunkskunk » May 29 2019 11:15am

TOPdawg wrote:
May 28 2019 3:23pm
However, the true speed it will reach depends on winding and what not, and that is one idea I would like to understand a little more about.

Side-note, is it possible to make a DIY motor controller?
Welcome to the forum.

The true speed will be hard to calculate without a wind tunnel and some computer modeling. A good guess at true speed isn't so complicated though.

To find the motor winding you need, first you need to know the RPM needed for your wheel at the speed you want.
A motor's speed is rated in "Kv", RPM per volt. A motor with a Kv of 10 does 10 RPM at 1 volt, 20 RPM at 2 volts, 480 RPM at 48 volts, etc.
Lots of math later, and your 22" wheel will do 15.28 RPM for every 1 MPH of speed, so 917 RPM for 60mph. So at 72 volts you would need 12.7361... call it 13 RPM per volt. That means a motor with a KV of 13 will hit 60mph unloaded speed at 72 volts actual.

But that's a problem, because the motor will be under load when you ride it, and batteries don't produce constant voltage, they work over a range. your 20S Lithium pack will run from 84v peak to 60v at max discharge, though roughly 2/3 of your batteries capacity will be between 80v and 72v. 72V is a good number to calculate with, but depending on your needs, you could design around a max speed of 60mph, using 84V, or a minimum acceptable max speed, using 60v.

Figuring out how fast you'll go under load depends on your motor's efficiency and how well the bike over come rolling resistance of the drive train (Tires, bearings, etc.), and how well it can push through the wind.
If you're on flat, smooth roads, and there isn't anything wrong with your bike, then the rolling resistance is almost negligible. you can mostly ignore this.
Your wind resistance is a bigger factor. On level ground, this is where maybe 85-90% of a bike's power is used. Without a wind tunnel or accurate computer modeling of your bike, this is impossible to calculate meaningfully. However it's a problem you can overcome by throwing Amps at it. with an 80 amp controller on that motor, this becomes almost a non issue.
So the last factor is the motor's efficiency under load. The Qs 205 V3 is rated at 90.8% efficiency at no load. Under load, that falls off. For your motor and assuming a fairly conventional bike design, you're probably fall into the mid to high 80s. Call it 85%. The more wind resistance you have, or if you have to go up an incline, the more this number will drop, but a 5-6% drop is a good estimate.
This drop is also how much slower than the rated Kv the motor will turn under load. So going back to the original Kv calculations, you now need to add 6% more to the Kv rating. Take that 12.7361 we started with, and adding another 6% gives us 13.5 RPM per volt. So a motor with a Kv of 13.5 or should give you 60mph at 72 volts.


As for building your own controller, Yes you can - if you are both an electrical engineer and a software engineer. Also if you happen to have huge amounts of free time with nothing better to do and a serious shortage of girls and beer.
Buy the ticket, take the ride.
Monster Bike:http://endless-sphere.com/forums/viewto ... =6&t=38667

User avatar
amberwolf   100 GW

100 GW
Posts: 29844
Joined: Aug 17 2009 6:43am
Location: Phoenix, AZ, USA, Earth, Sol, Local Bubble, Orion Arm, Milky Way, Local Group
Contact:

Re: First E-bike Build

Post by amberwolf » May 29 2019 7:20pm

TOPdawg wrote:
May 28 2019 3:23pm
Side-note, is it possible to make a DIY motor controller?
Sure.

There's a bunch of DIY controller threads.

Most never got very far, its' pretty complex, and expensive in test equipment and destroyed components and prototypes, especially for significant power levels. You'll also need to learn a fair bit about electronics, and probably software. Unless there's simply no existing controller that does what you want, it's gonna be a lot cheaper and quicker and easier to use one of the many controllers already out there.

The main reasons for DIY are cost and unobtainability. If something already exists, then unless you just cant afford it, the only reason for DIY is just to learn how to do it. IF the reason is that you can't afford it, well, you couldn't afford to design one from scratch, either. ;) (unless you already happened to have all the bits to do it and already had a working design and circuit board).

There *are* some DIY controllers in that latter vein, where you buy the PCB(s) and parts and solder it all up, like some of the VESCs, and the various Lebowski designs. At least the Lebowski is more expensive (at least $200-300) for a basic low-to-medium power unit, than a common ebike controller of the same power level....but it can do a lot more things if you need those things.


Drunkskunk wrote:
May 29 2019 11:15am
The true speed will be hard to calculate without a wind tunnel and some computer modeling. A good guess at true speed isn't so complicated though.
You can use the http://ebikes.ca/simulator for a much simpler guesstimate.

markz   100 GW

100 GW
Posts: 9438
Joined: Jan 09 2014 11:38pm
Location: Alberta Canada

Re: First E-bike Build

Post by markz » May 30 2019 12:58am

As Amberwolf stated, it can be done but its not really worth the time involved because generic controllers are so cheap. I have looked into it, and I could totally do it following the circuit board schematics as layed out in the thread posted, but the time involved, the money, buying components. I even went so far as to buy a pcb board already laid out for a controller build. Would be simple to do, but time consuming. I understand the joys of making shiit wiff ur hands homie.
TOPdawg wrote:
May 28 2019 3:23pm
Side-note, is it possible to make a DIY motor controller?

User avatar
Chalo   100 GW

100 GW
Posts: 7961
Joined: Apr 29 2009 11:29pm
Location: Austin, Texas

Re: First E-bike Build

Post by Chalo » May 30 2019 1:35am

Free Spirit was a Sears brand of garbage bike, made from cheese grade steel with paper thin dropouts. They're not suited for 20mph, let alone motorcycle speed.

My rough calculation suggests you'll need about 8kW at the tire, so say 11kW from the battery, to hold 60mph. This assumes no streamlining and a normal upright riding position. 72V x 80A is about half that much power, but of course that gets you much more than half that much speed.

I think you should get a good bike (not a department store mockery of a bike) and make it go 20 mph. Get a better understanding of the basics before you go wasting your time and money on something unsafe, unreliable, and illegal, which will quickly become unusable for one of many likely reasons.

Keep reading the forum. Dig into the technical details. Start with something easy, like a kit, that conforms to your local regulations. That's one less thing to have to think about while you're learning the ropes. Put some miles on it, get a feel for all the practical implications-- then decide how much more performance you want, can afford, can implement, and are willing to risk.

I still have the first motor I got for my own first e-bike about 16 years ago. It was very expensive compared to anything comparable today. It's never been installed. I got carried away with a complex reduction transmission for it (I still have most of those parts too), and ultimately nothing ever came of it. This despite the fact that I had an entire machine shop and electronics bench at my disposal, and lots of manufacturing skills. I could afford the sunk costs, and eventually I moved on with simpler e-bikes. But even those first couple of bikes I finished for myself are not anything I'd want to use now. A lot of what I learned from them was what I wanted to do differently.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

User avatar
TOPdawg   1 mW

1 mW
Posts: 18
Joined: May 19 2019 11:28pm

Re: First E-bike Build

Post by TOPdawg » Jul 10 2019 4:05pm

Chalo wrote:
May 30 2019 1:35am
Free Spirit was a Sears brand of garbage bike, made from cheese grade steel with paper thin dropouts. They're not suited for 20mph, let alone motorcycle speed.
Are you thinking of the Sears Free Spirit bicycle, or the Sears Free Spirit moped? I have the moped (2 of them) and have kitted them to do 45-50 mph. I've never had any problems with the frame or any integrity issues. But the swing arm is questionable, which is why I bought a reinforced swing arm.
"Don't fake the funk on a nasty dunk." -Plato, the Republic

flat tire   1 MW

1 MW
Posts: 1905
Joined: Feb 26 2014 12:20am

Re: First E-bike Build

Post by flat tire » Jul 10 2019 6:56pm

Keep doing what you do, TOPdawg. I don't think the rest will catch on for a while and I appreciate your sense of humor.

Post Reply