Thinking about building an e-bike, would love expert advice

Hi all,
I've been thinking about building myself an e-bike for a little while now. I've done a bit of research, tried to figure somethings out. Honestly I realize that it's probably best to get some advice from those with experience. Please let me know if you think my plans for a build are feasible or not. Caveats you think I may have to deal with, or any advice you have to possibly offer.
Firstly my proposed constraints are: atleast 30-35 mph max speed, 70-75 mile cruise range, $2,500 Max cost
From what I've read, it seems that to achieve this sort of range with that sort of speed, I would need a very large amount of Ah, as well as a relatively high voltage. Unless of course the e-bikes weight was very low. I could opt for a aluminium frame in order to reduce weight potentially. Of course, I have very little frame of reference on those constraints and how difficult they would be to achieve.
Some ideas that have been floating around for a bit, would be to implement regenerative braking. An Arduino controlled system to measure my pedal energy input as well as throttle response and electronically select the proper gear. It seems that in order to make the conversion of both mechanical and electrical into kinetic energy most efficient. I should probably program something to optimize gear automatically, rather than fidgeting with it while riding. I'm also concerned about theft and security if I end up sinking a bit of money into this project, if anyone has any experience with anti-ebike-theft, advice would be much appreciated. Please do not hesitate to let me know if you think this project would be a bit too ambitious or even almost impossible to achieve. I personally have a feeling in the back of my head like it can be done, but I haven't built an e-bike before. I do understand that there are quite a few variables involved here such as payload (rider + whatever is carried with), energy expenditure due to environment, whatever frame would be utilized comes with its own constraints and issues, just to name a few.
I really appreciate your reading of this post, and look forward to any advice you have to offer.
Thanks,
Dyson

You have it pretty well figured out. The extra 10 mph from a 25 mph cruise to a 35 mph cruise is costly.

A larger direct drive motor should be your starting point, but if you lower expectations to 30 mph top speed, then you can save a lot of weight using a standard motor from a "1000w" kit, and 48v battery.

But nothing really wrong with the idea of 35 mph top speed. You will want 18 cells battery, which I call 63v, and charges to 75.6v. That will get you 35 mph or more top speed, with a full battery.

Think in terms of what you really need for battery. No need to carry 75 miles range at 35 mph, ( like 40-50 ah) if your ride today is only 20 miles. Build a basic battery that gets you the daily needs, charging at work if you commute, and then find a way to carry more when you must.

Bear in mind on the long ride, you can carry half as much battery riding 20 mph, as you do riding 35. Not really that bad to ride slower on a weekend ride.

As for theft, it better park inside, or where you can at least watch it.

If you are planning a 75 mile daily commute, get one of these. It goes 85 mph for 100 miles on two gallons of gas.

The main problem is the range and your budget. They are incompatible unless you want to go very slow for those 75 miles. Like, 12 mph slow. And you will still need a large, heavy, and expensive battery. Going 35 mph max is no problem whatsoever though. A $250 1000w hub kit will do about that speed stock; add on a $150 Lyen controller and it will go 45 MPH. Lots of hubs will go faster, my Leaf 1500 on 6kw goes 55+ and the cromotor / scooter style hubs can reach 70 mph or more if you feed them enough power. Of course you will need safety gear, motorcycle skills, and a downhill mountain bike to safely do those speeds. But we're getting ahead of ourselves...

Explain why you think you want a 75 mile range. We will help you figure out a better way to accomplish whatever your goal is.

Play around with the motor simulator on Grin Tech site. It will give you some idea of the energy needed at different speeds and what size battery you might want to get. You can see the wh per mile and total range in the lower right box: http://www.ebikes.ca/tools/simulator.html

The reason I posted a long range is primarily because I'm worried about power draw.
I live in a very hilly area, where I could potentially have to climb 400ft or so, and I'd love to be able to get back home
I know that powering up a hill is really what will kill the battery. I think I could even be fine with 30mph and 50 mile cruise range. I'd just like to make sure I don't get stuck somewhere with a heavy e bike having to climb up a hill.

flat tire said:

The main problem is the range and your budget. They are incompatible unless you want to go very slow for those 75 miles. Like, 12 mph slow. And you will still need a large, heavy, and expensive battery. Going 35 mph max is no problem whatsoever though. A $250 1000w hub kit will do about that speed stock; add on a $150 Lyen controller and it will go 45 MPH. Lots of hubs will go faster, my Leaf 1500 on 6kw goes 55+ and the cromotor / scooter style hubs can reach 70 mph or more if you feed them enough power. Of course you will need safety gear, motorcycle skills, and a downhill mountain bike to safely do those speeds. But we're getting ahead of ourselves...

Explain why you think you want a 75 mile range. We will help you figure out a better way to accomplish whatever your goal is.

Click to expand...

Your speed of 35 mph will kill battery faster than a 400 foot hill climb. If you are going up and back over the same hills, the power draw is almost a wash since whatever you climb up you also get to coast down going the other way. The high and low point range on my commute ranges about 800 feet and my power usage is pretty much in line with what you'd expect if you merely estimated my power usage based on speed alone. It would be, of course, a different story with one way trips.

Agreed. a 400 vertical hill is going to cost you some power, but at 15 mph up the hill, it will not cost you more than 30 mph on the flat.

I know hill, live in the rockies, when I was commuting, work was 15 miles away, and 1000 feet below.

1 ah per mile worked perfect for me, including a decent reserve. I rode a 48v 15 ah battery for years. 20 mile range at 20 mph most days, and 40 possible at 15 mph.

I rode some very very long rides in the mountains on two batteries that size in watt hours. like 60 miles. 15 mph up hills, 25 down them.

Question is, what is your real range need? A 48v 20 ah battery is big, but not too big to carry. 1000 wh, 30 miles easy at moderate speeds, 20-25 mph. at 30 mph still a solid 20 miles range. including some hills.

Range will shorten greatly if its all uphill of course, one of my favorite rides would eat a 48v 15 ah pack in 10 miles. But another 10 miles back down it would take about a half an amp hour.

Here's the problem, you're trying to figure out what range you need yourself and hiding the reason you want that range from us. Just tell us exactly where, how far, and how you'll be riding, and how often you can charge the bike--the basics. We'll figure out how much range you would actually need. And climbing a 400 foot hill (400 feet distance, or 400 foot elevation?, big difference) is not a big deal either way.