Some questions on a theoretical Motorcycle build

[jackie_black]

Good Day ES.

I'm curious about this but not building this (yet). I have a motorcycle licence and have recently got into e-bikes. This is fast developing into a full on need to explore things further.

I can easily get hold of a 125cc motorcycle with a wrecked motor as a donor vehicle.
So

What size motor/battery/controller combo would I need to go 70mph (max) for 20 miles. The bike plus me will weigh about 250kg.

Is this possible? Using Lipo or whatever tech is available. The reason i'm interested is a 20 mile range electric motorbike would mean i'd never need to pay for petrol (gas) to travel to work again.

I literally can't wait to hear what you know about this,

cheers.

[Kingfish]

Where to begin?

Four basic problems to overcome: Weight, Power, Charging, Drag.

Weight: Biggest weight issues can be broken down as Frame, Batteries, Drive system (see Power). The best that money can buy is to invest in good mass-produced battery technology, and for that I suggest LiPo. Bang for buck, it has the highest power density per gram in the smallest package possibly. Keep your weight down and you’ll need less power and can travel farther!

Power: To keep it simple, purchase a well-matched motor and controller, then link this to the driven wheel(s) how you please (chain, belt, shaft). There is enough information on this forum and in other technical areas to sort out a good reliable power system to get you started. Understand that to go from 0-20 mph will require nearly double to go from 20-30, and 30-40, etc. This makes the calculation for power required to reach and to hold 70 mph difficult because much depends upon weight and drag. I could provide a theoretical value of the amount you could need, but then it’s my opinion and worth about that much. I would survey the thoughts of fellow members on their power consumption at velocity to build a profile, then figure your needs to be in the upper end on your first attempt.

The second part of the Power requirement is to determine the type of terrain: For 20 miles, is it hilly, flat, blustery, or calm? Is it rural roads, freeways, city, or mixed? All of these factor in towards starts and stops and drag; starting from a dead-stop uses the most power with hill-climbing or bracing wind second. A good conservative ratio is to double the range and factor backwards; calculate battery requirements 70 mph for 40 miles.

Another approach might be to analyze the horsepower for the replacement bike: You suggested using a frame from a 125 cc motorbike. Crudely, and depending upon where you read, the ratio of cc to hp ranges from 15-25 cc : 1, therefore if we take the worst-case, 125 cc / 25 = 5 hp, or it can mean 125 / 15 = 8.3 hp! Pick a value, then match a motor/controller to meet the spec, and calculate backwards to determine the battery size. Without getting lost in a bunch of math, let’s play conservative and suggest 8 hp is a reasonable figure for a lightweight eMoto. 8 hp roughly equals 6 kW. Because we have limited the range to 40 miles at 70 mph, we don’t need 6 kW for the whole hour: (40/70) * 6 = 3.43 kWh.

I developed a spreadsheet that suggests the Wh/kg can range between 150-180; obviously we want the higher value. Let’s be optimistic and use 180 Wh/kg; 3430 / 180 = 19 kg, or about 42 pounds. Cost per kW varies between $360-700; let’s pick $500 after shipping and tax; 3.43 * 500 = $1715 estimated cost for your batteries. Wow this looks great on paper, but I don’t think these values are correct. Baptism by Fire (read: experience) is the only way to know for sure, however we have some place to start and I really think that there is a lot of room to add more batteries. I am not going to bother with voltage and current since that will depend completely upon the motor/controller.

Charging: Solve the battery capacity problem and the charging issue will fall into place. The good news is that the battery is sufficiently small enough that you could charge at home without any problems, and there are a plethora of configuration possibilities to choose from.

Drag: At 70 mph, this will hugely impact how much power you will consume. Simplistically, you want to be as slick as possible, like a bullet in the wind, crouched down and nestled into the body of the bike for the best slipstream effect. The reality is this is difficult to achieve for the casual commuter. There are threads dedicated to aerodynamics and it’s worth your time to delve deeply into the matter. Your ambitions though are reasonable and achievable because the required distance is so very short. Perhaps in this case, drag could be overcome by adding more battery capacity and call it good.

You have been given a concise brief on how to proceed; the world is your oyster. I am building my own contraption too and so I share. Let us know how it goes.

Cheers, KF

[jackie_black]

Wow, what an answer, Cheers!!

[jackie_black]

And you've completely changed my mind now. I was going to go for a trail type bike but due to the drag it will have, will now be looking for a broken cbr 125 or similar, with penny tyres and enhanced fairing.

This forum is amazing!! I knew a hub motor wouldn't work . The route is mostly flat, no real long hills or anything silly, very little stationary traffic or stop starting. My plan so far is.....

1. Buy a CBR or similar
2. FInd a motor and controller (help required)
3. Attach/fabricate a way to fit motor
4. Connect motor to rear wheel using chain or belt (whichever is most efficient)
5. build a massive lipo pack using 6s 8000 mah zippy bricks (was thinking 72v 40 ah so 15 zippys, what's the sum to work out power?)
6. Solve the problem of running lights etc off mega battery
7. Ride to work and claim my £5k e-bike is free and green

[Kingfish]

Comments:
1. CBR – as in Honda CBR? If so, nice pic, and what fun!
2. Motor: Agreed; I think the standalone motor (not DD/Hub) is better suited for your need.
5. Batteries: The 8 Ah batteries are more expensive. The best price/weight will be 5 Ah in either 4- or 5-cells. This allows for some great flexibility in configuring the pack size. 4-cell batteries adapt straight ahead to typical BMS out there, although 5-cells do not… and I don’t know why. I think that targeting voltage at or above 72V is good and leaves room for ebraking; better efficiency and less trouble below 100V.
6. Running Lights: Use a DC-DC converter. There are several out there that can take 74V down to 12V, and if you use LED indicators, that will greatly reduce the current draw. Can’t help though on the main headlamp; I haven’t seen a good legal LED replacement yet.

Excited for you! I am in a quandary over the frame: Do I make my own (presumed) or snag one from a wrecker, etc.? This last winter I was reviewing the Harley-Davidson frames; it was pointed out that the double-wishbone frame is a good candidate because the batteries could be slung in nicely. If however I had to design my own frame, the features began to circle around the 2012 Yamaha SuperSport FJR1300A for best median specs; falling in the middle of where I wanted to be for dual-use (commuter/cross-country), and auguring in on a more powerful long-distance bruiser.

Fun to spec! More fun to build
If wishes were horses that beggars could ride... KF

[jackie_black]

Both the frames you are looking at will have plenty of space for batteries! But they may be very heavy.

Very interesting points you make about the batteries, what kind of BMS works with them do you mean a cycle analyst or am i getting confused?

The machine you are planning sounds a lot more ambitious than the featherweight i am speccing up. Where do I get motors and controllers for this type of thing?

[Kingfish]

In review of my present ebike, it is as heavy as I care to go for bicycle. The next natural step would be in your direction; a light-duty motorcycle. I began speccing for 250 cc but didn’t like the frames I found. Instead, I’m leaping to the next level and going directly to the mid-sized motorcycle frame that can be loaded as I wish for commuter or road trip. These bikes begin to weigh in at 400 lbs. on upwards. If we take away the motor and transmission, (and gas in the tank too for that matter), what’s left is a bike that weights… what? < 150 lbs if counting tires, frame, etc. It is heavy when compared to a bicycle, yet mine weighs 70 lbs. before batteries (2WD + frame + augments). The extra frame weight for the motorcycle is in the form of structural protection and affords plenty of room to add 100, 200, even 300 lbs. of batteries.

Conversely, your needs are for short distance so you need a frame that is up to 250 cc; light, yet able to take a certain level of beating. A frame that size can accept 100 or even 200 lbs. of batteries. When I think about how to load these onto the frame, one has only to look at Tesla: Boxy battery pack assemblies that can plug in or out easily for maintenance. It begins a design process where the “Battery” is thought of as “units” in parallel, and this is where the geometry comes into play. 4- and 5-cell LiPo packs are more compact than the round A123 cells. However, the advantage of “round” is in the bus-bar design; I like that and wished it could be applied to the LiPo brick. Source of sleepless nights

Motors: I am designing my own DD system, so I really am out of place to say and cannot effectively guide you on motor and controller options, although other folks here can. Read the popular posts and see what members are using.

BMS: Battery Management System. The CA has nothing to do with BMS other than it can integrated to interrupt the throttle. I use a different (more risky) approach to battery balancing and management; perhaps you would be better served by those in the know. Frankly, I balance periodically, and try never, never, ever allow the battery pack to drop below 3V or rise over 4.3V per cell. Smart BMS systems can be as expensive as batteries; I have time so I do my own.

The best that I can say, which is what a lot do say around here, is to jump in somewhere and start to gain experience. Find someone that has a similar setup to your dream and ask questions. Lots of kindred people here

Cheers, KF

[jackie_black]

Well I built an e-bike with a really basic e-bay kit, it's great and I love the torque of e-motors (its addictive).

I've decided to get a few random builds on the go soon as they will all use the same cells (LiPo) and this is the major expense as far as I can see. WOuld I be able to use one of the motors that the chain drive e-bike builders are using? I can find loads of info about hub motors but not so much about non hubs. I think I see the point about bigger bikes too. More space for batteries in a safer not much heavier package could be worth investigating further.

[Kingfish]

Same batteries: Yes, exactly! I have one chemistry, one configuration, from one manufacturer for all my purchases and that pays back in dividends; one less – yet hugely important thing to worry about. If you’ve selected 8 Ah batteries and have them, far be it for me to say “use another”; stick with what you have, recycle, repurpose, leverage… go for it!

You want to lurk on the E-Scooter and Motorcycle General Discussion. Oh, here’s a great picture-post by full-throttle: Re: TTX-GP Australia, Winton Raceway, Benalla VIC September. Now that’s a motor to drool over! Not saying you need a race motor, no – I’d never tell you that but it sure would be fun!

Come to think of it, I don’t lurk enough on that forum; great stuff there.
~KF

[jackie_black]

I'm yet to buy batteries, just started to look into it at the moment. I thought the best bet would be 8000 ah as i live in the uk and the postage from HK is crazy so I could be worth the larger packs, although they are all 6s. I'm going to order a few soon and have a play.

[Kingfish]

Are you charged postage by weight or by unit?

As a lark, I ran the numbers on 8000mAh 6S1P from HobbyKing; There’s really only two choices there: FlightMax or Turnigy. They both pencil out as too expensive and heavy relative to other configurations. Keep this in mind: The larger packs will cost more and be less efficient than smaller packs because the cost of manufacturing is more due to higher reject rate. This is difficult to imagine without a spreadsheet. I don’t know how much time you have, but spreadsheets rule when chunking through a lot of similar data; it’s a great way to sort and compare values that on their own mean little, yet when combined into a query or chart or function, becomes an extremely powerful visualization tool.

This ES thread covers it well and links to my post: LiPo's for dummies
But enough of beating my own drum; it’s time I shut my gob and let you sort it out: The seed has been planted… shop and compare, take your time, and most importantly – be happy with your selection.

Best, KF

[jackie_black]

Holy shit, that's extensive.

I'm glad I came on here and asked a ton of questions because I now need to go and do a ton more reading!!

[Kingfish]

Holy shit, that's extensive.

I'm just here to help. A lot of really cool folk have helped me along the way. Pays to ask questions. I even ask stupid ones; makes you brave after a bit. The best that I can do is return the favor (pay-it forwards). All on the wheel, friend.

Cheers! KF

[oatnet]

And you've completely changed my mind now. I was going to go for a trail type bike but due to the drag it will have, will now be looking for a broken cbr 125 or similar, with penny tyres and enhanced fairing.

This forum is amazing!! I knew a hub motor wouldn't work .

Don't be misled by generic-speaking folks with theories but who haven't built motos or 70mph ebikes, instead use searches for other builds to do your research. My Vectrix - with a factory hub motor - does 70mph easily. I average about 160wh/m on my commute with stop-and-go traffic and 50-60mph sprints. Markcycle's hub motor also does just fine, and would be a great choice for a build: http://www.endless-sphere.com/forums/viewtopic.php?t=7718

Building a moto from scratch is a big engineering effort... Used low-milage Vectrix with old failing NiMh batteries are cheap these days, swap in a new battery and you have a 70mph factory-finished ride with Brembos, Sach's, and Pirellis. I replaced mine with a 165v/50ah pack, and I got almost 50 hard-driving miles from the pack on my range test: http://www.endless-sphere.com/forums/viewtopic.php?f=12&t=17071&start=60#p458412

Do you have a safe way to store/charge all that LiPo, and an easy way to eject the pack to save it if one of your sub-packs does the lipo fire dance? The a123 Prisimatics only weigh 15% more than LiPo, but they are good for 3000 cycles instead of 500, and now that the 20ah cells can be had for $25 they are cheaper too. Bare Lipo does take up 35-40% less volume, but the wiring harnesses and monitoring hardware eat into that space some, and volume is not as crucial on a moto as it is on an ebike. On Moto-sized builds drag is far far a bigger concern than weight. Unless I was driven by extreme volume/weight requirements, I would choose the a123 prisimatics with an inert cathode over LiPo every day of the week, for reduced cost, increased cycle life and safety.

http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=37955

[John in CR]

Build yourself a 70mph ebike instead. It will be 1000% more fun to ride. If legality is a concern buy the cheapest lightest licensed moto frame you can find, include the VIN# portion and incorporate it into your build along with proper lighting. I've got multiple ebikes capable of 60mph, and all could easily go 70mph simply by going to 24s instead of 20s and putting a bit of attention into aero. I don't because 50-55 is about as fast as I ride, and bumping the voltage increases controller cost and decreases efficiency during acceleration.

BTW, they all have hubmotors.

If you're skeptical about the fun factor, strap 50kg to your ebike and go for a ride. Take the weight back off and that's the kind of difference you can expect with the 80kg+ doing it as an ebike can save.

That's my $.02, and it's due to the fact that batteries aren't there yet, not and make any economic sense for a commuter.

John

[Kingfish]

Don't be misled by generic-speaking folks with theories but who haven't built motos or 70mph ebikes, instead use searches for other builds to do your research.

I'm confused: Who are you talking about?

~KF

[oatnet]

Don't be misled by generic-speaking folks with theories but who haven't built motos or 70mph ebikes, instead use searches for other builds to do your research.

I'm confused: Who are you talking about?

Lets find out. Prior to handing out advice on the topic, had you built a 70mph EV motorcycle or ebike?

-JD

[Kingfish]

No. I am currently designing a system that is capable of maintaining 75 mph for 3 to 4 hours as a performance target for my next long-distance road trip. The math and the physics I’ve made public since the inception wanting a better Direct Drive solution in 2010; the thread is called: Doing the Math.

But that’s not what you wrote and claimed:

Don't be misled by generic-speaking folks with theories…

By your own admission this is targeted at me; a character attack. Let’s explore for clarity:

With the very first reply on this topic, on the last line I plainly stated…

... I am building my own contraption too and so I share.

I qualified my status at the beginning. No deception here. The individual knew and replied with more information. I replied in kind, as in kindred, helpful, friendly, courteous … you know: Scout’s Law on the matters where I had experience, and also suggested in a positive manner to seek out others that had practical experience.

I directed the gent where to seek more information:

... You want to lurk on the E-Scooter and Motorcycle General Discussion.

Is that deceptive? Am I speaking too generically where to find information more about motorcycles?

... The best that I can say, which is what a lot do say around here, is to jump in somewhere and start to gain experience. Find someone that has a similar setup to your dream and ask questions. Lots of kindred people here

Was that not helpful and encouraging?

When the discussion shifted to batteries – well, that’s something I know about in detail having purchased 84 of them in the past 2-3 years. Am I being deceptive or generic in the information conveyed about batteries?

Let me just say straight up: I enjoy posting here, sharing what I know, and give credit where credit is due.

I'm just here to help. A lot of really cool folk have helped me along the way. Pays to ask questions. I even ask stupid ones; makes you brave after a bit. The best that I can do is return the favor (pay-it forwards). All on the wheel, friend.

Gosh, I just can’t fathom how I could be more accommodating, friendly, or guiding towards the individual, and I struggle to figure out how this fits to your demeaning classification. Frankly, I don’t feel comfortable with your statement because it’s inaccurate, deliberately seeks provocation, and does not add value. The term is called “mud-slinging”. I don’t recall seeking you out to do the same.

~KF

[Hillhater]

You wont hit 70 mph with much less than 10 kW. ( Kingfish,... most 125 performance bikes are 20+ hp).
and if you want to cope with any hills or headwinds, that will be much more.
I suggest you consider what John said about speed and re-evaluate your need for that speed since power and battery requirements reduce significantly at lower speeds.
50 mph max would half your power requirement.

[jonescg]

Voltron did about 110 miles per hour down the straight at Eastern Creek.

It weighs about 165 kg, cost me about $18,000 and took over 2 years to build. When it runs it's heaps of fun. But be warned, unless you are riding 20,000 km a year, it's not a very economical way to get around and even then the parity point with a petrol bike is at least 7 years.

[Jozzer]

I got a 70mph electric Aprillia RS125 down here on the south coast for sale if your interested is something already built..£4800 (pretty much cost of parts).