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Discussion Starter · #1 ·
I'm new to this area of electronics, but I feel I have a decent idea of what I'm doing. I'm basically just throwing this out there for any help from some seasoned veterans in this area. I should probably start by stating my skill level. I am 17 years old, a high school senior, attend Electronics Technology at Mercer County Career Center (Mercer PA, USA) for my 2nd year, have received high praise from those already in the field, and have already been accepted to Pittsburgh Technical Institute for Electronics Engineering.

I don't care too much about the legalities for this project. I'm doing it more so when I ride around my small town I can be lazy and I don't want to be pedaling at all. I plan on using the existing lower 7 gears, attaching the motor to the crank through a chain. I would disconnect the pedals (3-peice crank) and attach the pedals further up the frame for foot rests. And for the sake of range, I wanted to attach a car alternator to the front tire (a modified back tire with a single gear freewheel) to charge while riding. I'll probably need some sort of regulator here, but I'll work that out more once it's at least road ready.

I originally wanted to use a AC motor I pulled out of a washing machine. 1/2 hp, 120vac, about 10A max draw, and 1750 RPMs. I realized that with the batteries I wanted to use (2 12vdc sealed lead acid at about 12Ah), a inverter for this would be useless. With the motor pulling over a 1000W, this would drain the battery in a few minutes from the sheer amps it would pull.

Then after talking to some friends, I got the idea to use a wheelchair motor. I found one, but couldn't find any specs from it. I would guess that it would pull quite a bit of weight, but not sure of the speed and battery specs of it. Any help here would be very nice.

Then I started to think of a treadmill motor. They reach speeds of 10MPH with their current gearing and are designed to pull along plenty of weight already, so I thought that this would work well for me if it could be geared for some more RPMs. I found one on ebay for about 30 bucks and it has already been re-listed once, so I say it's a good bet I can get it for that price. Specs are 1.75 hp, 4800 rpm, 15 A, 90vdc. For the additional voltage, I think I would just run it through a simple DC-DC converter to step it up. A problem here that I can see is that while increasing the voltage, I may decrease the total amp I produce. But I'm not 100% sure on this.

For throttle control, I will use a 555 ic based PWM (Pulse Width Modulation) device to cut the voltage using a high voltage and amp NPN transistor. I figured this would work better than my original idea which was just a push button and then speed control through shifting. Not only will I save battery life at slower speeds (since it wont run full speed all the time), but I reduce the chance of popping the chain.

As you can tell, I have done my homework on this. I'm not just some kid asking obvious questions that I'm too lazy to answer myself. I would just like some advice from people who have had far more experience than I had before I invest money and time into something that might not work. I've been playing with this idea for a few weeks now, and have come across this site googling some info. I would really appreciate some help on this. And it might help my case if I say I hope to use this for my high school senior project (needed to graduate from my school).

And if any of my ideas (or those given in responses) are any good I would say feel free to use them. Knowledge is power, so power is limitless.
 

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Don't bother with the alternator driven from the front wheel, it will consume more energy then it will ever give out. Losing the drag and the weight will increase your range far more then the alternator will put back, especially on such a light vehicle.

Some manufactured electric bicycles do regen on the drive motor but it is more of a drag brake, with benefits, more useful for commuting in a hilly area.
 

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Discussion Starter · #4 ·
Farmkid4, thanks for the website suggestions. They seem like they will offer a lot of help.

Woodsmith, thanks for the input. After reading some of your EV trike thread, I'd like to know your overall opinion of my plan. I'm not looking for the 70mph range, but I'd like to at least go 15ish. More would be great though.
 

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The treadmill motor and DC-DC converter will work but you have to remember that its output power can't be greater than the input power. More likely, the best DC-DC converter you will be able to get will have about 80 to 90% efficiency. So from 100 watts input power you'll get 90 watts out, max.
The motor is rated at 90V, 15 amps - that's 1350 watts. Assuming 90% efficiency, you'll need about 1500 watts input power; from 24V that's about 60 amps, give or take. The batteries will sag (drop in voltage) when you're pulling that much current from them, but you won't be doing that for long periods of time.

You will find that 1.75 HP would move your bike like a rocket - most E-bike motors are in the 400 to 700 watt range, and even they are electronically speed limited. To get the best efficiency you'd need to gear your motor to the bottom bracket so the motor hits 4800 RPM at your desired top speed in your highest crankring / rear cog combination.

When you're doing PWM on your motor, you will need a flyback protection diode to prevent the inductive voltage spike, that happens when you turn off the transistor, from frying your transistor. Also, some 555's don't have very much output protection and they can latch up if you drive anything with inductive characteristics straight from the 555.
Good luck - this should be a cool project.
 

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I think your best, read that as simplest, motor option would be to use a DC powered bicycle motor designed to run at 24V or 36V. It would save converting DC to AC and then back again to drive a higher voltage AC motor.

Bike motors come in a variety of types, most are hub motors to build into a wheel but crank drive is also available from Bocsh and Panasonic to name two off the top of my head.

They are usually rated for the legal power allowed on the road but I have seen, every now and again on Ebay, very high power hub motors for off road use.

Your average off the shelf Ebike bought from a cycle shop can usually do up to 25 miles on a charge depending on use and terrain so I think your 15 miles should be possible with the right battery pack and controller.
 

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Discussion Starter · #7 · (Edited)
So from what Tigernut is saying, the more voltage I have the less current being run through the batteries (If I'm understanding watts law) 1500W/72VDC=20.83A which is much better than the 60A. If I get some high current batteries then I should have a decent battery life. Can't believe I forgot that, my instructor would beat me over the head with a oscilloscope if he found that out. lol

And I have already considered hub motors Woodsmith, the problem there is that it looks to commercial for my school's intelligence level. If I walked into the conference room and said "This is my Senior Project", they will take one look at it and fail me because it looks stock and claim that I didn't build it. I live in a small, ******* filled area where no one takes students seriously.
 

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Ahhh, in that case build your own crank drive system but use a lower voltage DC motor to make your life easier.

The wheel chair motors could be a good start. They come with a gearbox and often an angle drive. You could develop a system that allows additional motors to be added in the bike frame to improve off road performance. I can imagine a pair of them in the bike frame looking like a V twin ICE.

Did you know a very long slim motor was developed that fitted inside the seat post tube on a bike and drove the cranks with a bevel gear inside the bottom bracket? I read about it a while back as a very 'stealthy' method to get an Ebike without a motor in the hub or bolted to the frame.
Here's the link: http://www.vivax-assist.com/en/unternehmen/index.php?we_objectID=204

Yes, higher voltage equals lower current.
Lower current equals less heat and greater efficiency.

It all means you will be drawing less current from your batteries to achieve the same performance and so extend both your range and your battery life.
 

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Hi Weasle

I have a single awful hill to climb so I have been modifying my old mountain bike,

- Cheap and nasty
I have a wiper motor with its built in worm gearbox driving another rear wheel with its freewheel fitted in place of the front wheel

The wiper drive output is about 80 rpm - just right to drive the front wheel through a chain to the freewheel

The intention is to cycle along and switch it on when going faster than it is going - then when I slow down going up the hill it will help me along

real cheap and cheerful
 

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Hi Weasle

I have a single awful hill to climb so I have been modifying my old mountain bike,

- Cheap and nasty
I have a wiper motor with its built in worm gearbox driving another rear wheel with its freewheel fitted in place of the front wheel

The wiper drive output is about 80 rpm - just right to drive the front wheel through a chain to the freewheel

The intention is to cycle along and switch it on when going faster than it is going - then when I slow down going up the hill it will help me along

real cheap and cheerful
That's a really neat idea.:)

Have you got a photo of the set up?
 

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Discussion Starter · #11 ·
That does sound like a good idea Duncan. Find some of those pics if you don't mind.
 

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Hi Guys

You have caught me out, I started modifying my bike
then I had to use the wiper motor to make a broken thicknesser work
to make a table for the boss

I have a picture of the table, the thicknesser and the bike with a rear wheel in the front forks

The wiper motor on the thicknesser drives a 10ft long 8 inch x 2 inch plank through the blade at about the right speed

So I think it will help me up my steep hill

Do you like the table? Jane loves it, its macrocarpa - a cypress type wood

I have picked up another motor and I will make a bracket for it sometime,
currently got to get on with my car - The batteries are here! - or at least at customs awaiting something
 

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Ahhh, in that case build your own crank drive system but use a lower voltage DC motor to make your life easier.

The wheel chair motors could be a good start. They come with a gearbox and often an angle drive. You could develop a system that allows additional motors to be added in the bike frame to improve off road performance. I can imagine a pair of them in the bike frame looking like a V twin ICE.

Did you know a very long slim motor was developed that fitted inside the seat post tube on a bike and drove the cranks with a bevel gear inside the bottom bracket? I read about it a while back as a very 'stealthy' method to get an Ebike without a motor in the hub or bolted to the frame.
Here's the link: http://www.vivax-assist.com/en/unternehmen/index.php?we_objectID=204

Yes, higher voltage equals lower current.
Lower current equals less heat and greater efficiency.

It all means you will be drawing less current from your batteries to achieve the same performance and so extend both your range and your battery life.
that's the neat sick idea- always been thinking about something like this...
silk-great
...and nobody (cops) doesn't even know : ))))))
 

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I used a starter motor, instead of wiper one, for my bike, powered by a single 12V small car battery fitted behind the seat.
This bike was like flying on uphills, but the range was only about 2 kilometers.:)
 
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