New member with an ambitious first project!

[Sellick]

Hi all, just wanted to say hello really. I am studying MEng Mechanical Engineering at Brighton university. My dissertation project is to design, simulate, build, and test an electric off-road bike capable of 40mph. I prefer the mechanical side of things (I have no idea about batteries or motors), but this project really interests me. Luckily I will have access to laser cutters, lathes, CNC machines etc. and I will be building my own frame from scratch. I have done a lot of reading already, and have found this site to be unbelievably helpful.

The bike will be mid-drive. From what I have read, I want to use LiPo batteries. Ideally I wanted an Astro 3220, but I have recently been looking at more cost effective motors like the c80100 style units (possibly from Alien Power Systems?). I want it to be safe so I will be using a decent bms, voltage monitors and alarm systems, and using the electrical engineers/lecturers to help with my battery. Incorporating a planetary gearbox would be nice too.

I have a budget of around £2000, so it will be pretty tight! Obviously very few marks are available in proving my practical skills, so I need to get as much technical content as possible in the report (if anyone can think of any technical areas I could really go into detail on, that would be great! Preferably more mechanical than electrical). I am aiming to get all the practical work done ASAP so I can focus on the report, and therefore am aiming to complete the bike by the end of the year! I have a lot of reading to do, but hopefully I will be at the point where I can start buying up the parts and get drawing a frame design on SolidWorks, so I will start a progress thread soon.

Any help and/or suggestions would be great!

 

[Drunkskunk]

Welcome to the forum.

It sounds like you have an ambitious and fun project ahead of you. Depending on how you plan to use this bike, you may need to extend your budget, or re-evaluate your goals. A bike that can do 40mph for a short distance on a smooth paved road isn't so hard. A bike that can do 40mph sustained, or off road is a whole different beast. As you are an ME, you're probably familure with:

A 100 KG bike moving at 9m/s (~20mph) has 4.05KJ of kenetic energy. At 18m/s (~40mph) it has 16.20KJ of kenetic energy. In short, the energy increases by 4 times when you doubled the speed.
A bike is designed for around 20mph. At 40mph the brakes have to work 4 times as hard, the tires, rims, spokes, hubs, and axles have to transfer 4 times as much energy from bumps. the shocks have to disapate 4 times as much energy. The stresses on the frame and other componants will be higher, etc, etc, etc.
This is why Motorbikes are built so much more stout than bicycles.

But it is possable to build a bike that can handle 40mph sustained off road using heavy duty DH parts. Unfortunatly, those don't come cheap. Figure €500 just for a wheel set. another €1000 just for the front and rear shock, if you go cheap and used. You'll easily eat up another €500 on bolts, bearing, brakes, and all the other parts you need to make a bike work. (crank, pedals, bottom bracket, head set, chain ring, sprockets, chain, chain lube, derailers, cables, cable mounts, shifters, bar grips, seat post, seat, seat clamp, etc, etc, etc )

On the other hand, if you build a bike that's designed for 20mph sustained, just about any rusty €25 estate sale mountianbike can supply most of the componants you need.

 

[spinningmagnets]

"A smart man learns from his mistakes...a wise man learns from someone elses"

There have been a few 80-100 builds around here. Since the 80-100 has gotten more expensive and harder to find, fewer E-bikers are now using them. I'd say AJ's Blue Cruiser is probably the definitive 80-100 build.

For a controller, use the sensorless Castle-Creations HV-160, and a 44V-48v battery. Add four of the 50V low-ESR capacitors to the power inputs (in-between the battery and the controller). you can broaden a systems performance envelope by giving the motor some gears. AJ broke a 3-speed nexus trike IGH from his high-power spikes (he likes brisk acceleration), so on his current build he has added a very robust Thud 2-speed dog-shifting box.

One way to add gears to the motor is to let the motor use the bikes gear-set on the rear wheel (external sprockets with a derailleur can take more power than an IGH, plus if you break something they are cheap, available, and easy to swap-in). To do this, the most popular method is to install a freewheeling crankset with two chainrings.

The motor drives one chainring, and the other chainring drives the rear wheel. If you can find some way to snub the throttle, a set-up like this can survive 3,000W (plus or minus depending on a lot of different factors). The newest version of the Cycle-Analyst has a variety of throttle adjustments, plus you can adjust the Phase / Battery amp ratio to 2:1?

If I said that right, it makes take-offs easier, but you still get full power once you are at top-speed (no more wheelies, but at least the chains/sprocket-teeth are not breaking).

"Aussie Jesters Blue Cruiser"
http://www.electricbike.com/aussie-jester/

"Updated Cap choices for high power"
https://www.endless-sphere.com/forums/viewtopic.php?f=30&t=22194&start=25#p382837

"Strong freewheeling crankset"
http://endless-sphere.com/forums/viewtopic.php?f=28&t=47618

 

[arkmundi]

Hi all, just wanted to say hello really. I am studying MEng Mechanical Engineering at Brighton university. My dissertation project is to design, simulate, build, and test an electric off-road bike capable of 40mph. I prefer the mechanical side of things (I have no idea about batteries or motors), but this project really interests me. Luckily I will have access to laser cutters, lathes, CNC machines etc. and I will be building my own frame from scratch....

I'm totally jealous! But wow, you can do that these days? Course credit for having the most fun in your life doing stuff that's actually useful?

From what I have read, I want to use LiPo batteries... Any help and/or suggestions would be great!

Not so!!! LiFePO4. I've posted extensively on the reasons. I suggest:

• Since its educational, make it an education, meaning do the R&D work, starting with fundamentals. Learn as much as you can about batteries for LEVTs. This forum makes that possible, but now without, you-know, homewok.
• Everyone's on a budget, so making your dollars go far is part of the game. Doing so also means you'll pick up some useful skills for the rest of your career, regarding finance, budgeting, etc.
• Understandably you want to put in work designing & manufacturing a frame. But its the batteries that are the most cost-intensive, prone to failure and technically rich piece of the engineering, so at least put in some equal time on this.
• From a future career perspective, becoming competent with electrical engineering and with battery tech will take you a lot farther than any other component
• LiPo batteries are prone to more trouble than well made LiFePO4, like from A123. Its a design/use/cost thing - most of the LiPo batteries are made for the RC hobbyist market, not for real world transportation needs. A123 is a company making batteries for the latter, so they are a great deal more robust & safer. Again, do the research, and if you do, you'll like come to similar conclusions. Start here: viewtopic.php?f=14&t=42871&start=125#p787088

Best of luck with your project! Sounds awesome!

 

[Sellick]

Thank you so much for the detailed information! I wasn't expecting such a warm welcome, more "you're joking aren't you?". As for the goals of the project, I want the bike to be capable of 40mph, but not for long distances or rough terrain, just a very short run on grass/tarmac.

It is a very cool project. It is one that was proposed by a lecturer at the university, and I thought it sounded very fun and useful for the future. As for the bicycle components, I used to be heavily into downhill mountain biking. I already have some Fox 40 forks, along with a few other nice bits. It's the motor, batteries (majorly), and drivetrain that are concerning me at the moment!

I'm thinking about using a Shimano Alfine 8-speed internally geared rear hub. Seems like a cheap alternative to the Rohloff, and is a freewheel not fixed. I will be using 2 sprockets at the crank, one driven by the motor (with a freewheel at the motor end?), and one pedal driven. I've seen a lot of people use the Castle Creations controller so I definitely think I will go with that. Also, the cycle analyst seems pretty much essential. I will have a look into that 80-100 build too, thank you!

From what I have read so far the RC LiPo batteries seem so cheap and easy to package, but I will certainly look into LiFePO4 too.

Thanks again for the advice. Looks like I will be spending as much time as possible on here over the next few weeks..

 

[Drunkskunk]

Best place for your motor's freewheel is at the pedal crank. Otherwise, the motor will be trying to turn your feet as well. A freewheel crank lets the gears spin under power, but hook up when you want to pedal.

And Freewheel cranks are easy. ~$26 for the crank arms that use the same thread pattern as a rear freewheel, and the freewheel is cheap enough. But I'd recomend going with one of the better but costly Wight industries freewheels. They last, where the cheap ones often don't. Several sources out there, but I got mine from: http://www.sickbikeparts.com/catalog/index.php?cPath=21&osCsid=cf4277sko1q5tnknogs51rnks2 Sure, they sell parts for gas bikes, but it's the same idea. And they have lots of gear ratio options.

 

[arkmundi]

From what I have read so far the RC LiPo batteries seem so cheap and easy to package, but I will certainly look into LiFePO4 too. Thanks again for the advice. Looks like I will be spending as much time as possible on here over the next few weeks..

Well, as the adage goes, you get what you pay for. Don't say you weren't given a warning. :lol:

 

[Sellick]

Forgive me if I'm being stupid Drunkskunk (this just proves how little I know), but when pedalling, you would also be turning the motor, right? Is that ok to do? Those cranks are incredibly cheap, they have gone to the top of the shopping list! I'm guessing the cheap freewheel adaptors they sell aren't up to the job:

http://www.sickbikeparts.com/catalog/product_info.php?cPath=21&products_id=34&osCsid=cf4277sko1q5tnknogs51rnks2

I really need to work out the gearing before I can order a freewheel sprocket.

I'm really aware that I need to answer a lot of silly questions, I will try not to annoy everyone too much. I'm going to do a lot more research, write a shopping list, do some CAD drawings, then ask any remaining questions! I think the timescale is certainly very ambitious, so I'm keen to get started ASAP.

Also, Drunkskunk, your build is truly inspirational! Some amazing work, I love the way you have overcome some problems, and the finished product is incredible. I would love to have the power of yours, but I think that is certainly too ambitious for my first build!

 

[izeman]

Forgive me if I'm being stupid Drunkskunk (this just proves how little I know), but when pedalling, you would also be turning the motor, right?

for a DD in the rear wheel this is true. for a mid drive this can be the case, but in 90%+ you would install one/two freewheel/s that will make you pedal w/o turning the motor, and allow you to use the motor w/o turning the cranks.

 

[Sellick]

Ok, I can't visualise this, I don't know why! It's going to be a mid-drive setup. I understand the freewheeling cranks, they look great, and certainly saves me some machining time. I understand that with the freewheeling cranks, when the motor spins, the cranks stay in the same position, however, when you pedal, the crank freewheel will be engaged, and will spin the motor? So another freewheel is added on the motors output shaft, but with everything spinning in the same direction, how does this work? I'm sure I'm being stupid but that's the way I see it?

 

[Drunkskunk]

Ok, I can't visualise this, I don't know why! It's going to be a mid-drive setup. I understand the freewheeling cranks, they look great, and certainly saves me some machining time. I understand that with the freewheeling cranks, when the motor spins, the cranks stay in the same position, however, when you pedal, the crank freewheel will be engaged, and will spin the motor? So another freewheel is added on the motors output shaft, but with everything spinning in the same direction, how does this work? I'm sure I'm being stupid but that's the way I see it?

Yes. when you pedal the cranks, they turn both chains, and that also spins the motor. So if you plan to pedal, you'll probably want a freewheel at the motor as well.

But since you said this was a school project, and you're on a limited budget, you can skip the freewheel at the motor. it will be harder to pedal to the bike, but still functional, and save you a lot of expense and machining time. The Motor will function perfectly when powered, and the freewheel at the crank will keep the motor from trying to turn your feet as well. There would also be no problem with pedaling along with the motor this way.

 

[muffinman]

i see what hes saying. if wondered the same myself. i never could quite grasp the mid drive...
would the drag from the motor be akin to a dd hub?
im kinda jealous... if i thought i was any good at understanding engineering (of any kind), id be doing that, not poli sci. all i can hope for is to be wealthy enough to try and pay the drunkskunks of the world to build me a badass bike like theirs

good luck with the project! cant wait to see another custom build!