Safe's Electric Bike Project #001

[safe]

This is my (newly painted) electric bike that I made from scratch. It's about as far as SLA will go. (well I could imagine a few improvements) The next project will be NiMh and I'll be searching for speeds near 60 mph. The present range is about 25 miles or an hour of hard riding. Oh, and the 46 mph is not on true flat land (that was the top speed attained here in the relatively flat midwest) the real world limit is more like 38 - 40 mph on the flat.


Note: This used to be called "46 MPH Electric Bike".

 

[Mathurin]

Nicer then last I saw it!

I see you went for gears, too.

 

[safe]

Next time I'm going for direct drive from motor to an 8-speed internally geared hub. In order to get the gearing right I'll be using a Go-Kart #35 chain. They have a large selection of sprockets and I can go as high as 114 teeth on the rear. So a 4000 rpm motor comes down to earth when you have a gearing like 12-114. Without Go-Kart sprockets I'd be forced into another "transaxle" which is complicated and wasteful. The internal mutlispeed hub will let me get rid of the derailler, no more "bouncy" noises as I hit bumps...

 

[knightmb]

Oh wow, that looks like a rocket cycle, awesome!

 

[D-Man]

Cool bike. How much voltage are you running? What kind of motor, controller, etc..., are you using?

 

[safe]

Cool bike. How much voltage are you running? What kind of motor, controller, etc..., are you using?

It's your basic "plain vanilla" 36V 750 Watt Unite motor with a typical unmodified 40 Amp limit controller. People seem obsessed with fiddling with the controller so as to bump up the current limit, but you're better off having gears and just "downshift" when needed. Better to downshift and hum along in the ideal powerband than throw current at the problem and turn your motor into a "space heater". :wink:

I notice that you are running a hub motor. That pretty much limits you in the gearing department, but if you wanted more power you could always add another hub motor on the rear. Given the weird ways that electric motors use power you would actually do better with two hub motors than with one both in power output and in overall efficiency. (it would be a wiser strategy than raising the current limit which is probably correct for what you already have)

Gears are the future though... or LARGE motors like an Etek...

 

[D-Man]

Yeah, I'd rather stick with the 20 amp controller I have and run higher voltage with a smaller wheel like a 24." I've seen how hills can hurt my range with only 20 amps. I can't imagine increasing to 35+ amps when all that is needed is a "gear change" or smaller wheel.

 

[Lessss]

Anyone got any good websites on gearing ratios that an idiot like me can understand?

 

[safe]

Anyone got any good websites on gearing ratios that an idiot like me can understand?

The one I use:

http://www.arachnoid.com/bike/index.html

 

[safe]

Yeah, I'd rather stick with the 20 amp controller I have and run higher voltage with a smaller wheel like a 24." I've seen how hills can hurt my range with only 20 amps. I can't imagine increasing to 35+ amps when all that is needed is a "gear change" or smaller wheel.

Okay, here's the thing...

If you reduce the size of the wheel you make your climbing better, but you lose your top end speed. Do the opposite and you get the reverse problem of no climbing ability.

If you increase your current limit to 35 Amps what this does is FORCE the motor into a LOWER efficiency conditon because it must carry more load for a given speed. That's bad.

The "brilliant" solution for more power is to double your motors size by adding a second hub motor on the rear. You can then use 30 Amps and DIVIDE that power as 15 Amps and 15 Amps to the two motors. The efficiency goes UP along with power going UP. It's a "win win". :wink:

As a general rule you want twice as much motor as you need and then run it at half power all the time. Industrial electrical motors are sometimes designed at 5 times this limit. These little tiny motors are NOT the way to go when it comes to efficiency.

P.S: I know it's counter intuitive, but that's how electric motors work...

A while back I was thinking of making a "Twin 750 Watt" bike and this is what the performance would look like. The top curves are for efficiency and the bottom for power and everything is relative to rpms. It's a comparison of what a single verses a twin can do using the exact same energy.

 

[Reid Welch]

That's a beautiful testament of form following function.
The lean and mean look reminds me of Ford's famous 999





What size are those batteries?

 

[safe]

What size are those batteries?

They are 38 Ah each, so the total weight comes to 86 lbs.

I used to be heavily into motorcycle road racing (and motorcycle building) over 20 years ago. (I'm an old guy now, retired from the computer industry) In the distant past (before the Japanese got into production road racing motorcycles) you had to design and build your own motorcycle. So I was one of the only guys riding around with a full fairing motorcycle road racer (RD400 with extra parts purchased from friends that raced F2 at Sears Point Raceway) and it was a lot of fun. When it came to actual racing as a "career" I didn't get into that, realizing that you really can't make money doing it. (only a few pros make a career of it) But I did manage to do some pit work at Laguna Seca Raceway, which was exciting. (Monterey California)

So the idea of building something from the ground up doesn't intimidate me at all. I've done lot's of "big projects" and it seems to me that there is a need for a "mid sized" electric bike that is between the full motorcycle weight and the limited bicycle size. There's a "sweet spot" that most people don't realize exists.

Long ago I also had an MB5 which I totally tricked out with rearsets, clipons and the works and I used to ride a 200 mile loop every sunday and it only cost me about $2 per ride. That bike weighed about 175 lbs and did everything I wanted as far as speed and performance. (top speed was about 55 mph after changing the gearing) Since it was a 50cc machine it didn't even require a motorcycle license.

My electric bike weighs about 140 lbs and is a little down on the power, but otherwise is getting close. In my next version I'm hoping to get closer to the "ideal" that I'm after...

 

[knoxie]

Hello Safe

Cool ride!! like that a lot, can see a nice upgrade in the NIMH that's a great Idea for sure, neatly turned out machine the lack of peddles would lead me to getting pulled on it around these parts but I am sure your cops are more forgiving than ours.

60mph will take quite a lot more in the power department to achieve and It will drain your batteries a lot faster, Lipo would be nice on that rig you could run 4 x 37V 15AH Lipo packs!! hmm maybe 72V 30AH!! the batteries in total would only weigh 40lbs!! not sure your wallet would weigh much either though!!

Thanks for posting the pictures that's the coolest eclectic only bike I have seen for a long while.

Cheers

Knoxie

 

[safe]

I live in Missouri and the law here says:

1. Less than 50 cc OR less than 2 hp. (1500 Watts)

2. No clutches allowed. (a weird rule, but "whatever")

3. Top speed is supposed to be 30 mph on flat land.

...as a matter of fact a cop tailed me yesterday and when I came to a stop the motorcycle cop stopped next to me and we talked a bit. He liked it and he "tried" to get me to confess to a higher top speed than the limit, but I stuck to my story of it being "less than 2 hp". He smiled and rode off. We laughed about gas prices going down. (can you believe only $2.06 a gallon?)

Streamlined (small frontal area) bikes use less energy at speed than situp styled bikes. The tight "tuck" road race position is very "slippery" to the wind. The estimated power to speed numbers for a road racer style bike like mine are:

50 mph - 1200 Watts

55 mph - 1600 Watts

60 mph - 2000 Watts

Using a 1200 Watt motor (rated) and if you allow the current to go up to the maximum power level (peak of the power parabola) you get 1771 Watts which creates a "calculated" top speed as being 57.2 mph.

The human powered speed record is 80+ mph, so streamlining is EVERYTHING once you get past about 30 mph, so until I actually make the fiberglass fairings for the bike I won't know what the true top speed will be...

As for batteries:

How about 120 "D" NiMh @ $4.75 each. Total price becomes $600 for a 48 Volt 30 Ah pack. (I'm going to use pvc tubes to contain them, no soldering, just paste)

 

[knoxie]

Hi Safe

Those figures for the bike sounds mighty impressive given the weight of it but you are right they tie up perfectly with the online calculator here http://www.kreuzotter.de/english/espeed.htm

Its amazing isn't it the efficiency of recumbent bikes, you hardly need any power to keep them moving you are right its all about wind resistance, I know this from running my 3 wheel KMX bike and my MTB with similar set-ups.

Gas prices at 2 dollars a gallon!! I wish :-( here in the UK we pay your equiv of 10 dollars a gallon! im not kidding, imagine the ev's on the roads in the US if you guys were paying 10 bucks a gallon! it will come in time though and probably sooner than a lot of people think.

The D cell NIMH option is a good one, you could go with f cells for less total cell joins? either way you need to dump the Lead Acid use them as the storage for your wind generator!! or solar cell to make your machine a true friend of the earth!!

Great Rig thanks for posting the pictures.

Knoxie

 

[safe]

The D cell NIMH option is a good one, you could go with f cells for less total cell joins?

What I did is calculate the cost of the batteries verses the amount of energy that they produce. From a purely cost savings perspective the "D" cells are ALMOST the least expensive. Amazingly the LEAST expensive are the "AA" batteries. The problem is that you would need literally hundreds of batteries to do the job, so that's too many. Even at 120 "D" cells that's a lot, but if I package them in 12 tubes of 10 each (no tabs, silver paste instead) I can make a nice little 3 wide by 4 deep rectangular cube than will fit where a gas tank would fit for a motorcycle. At about 7" wide it's the right width for the frame and it's not so tall as to be a problem that way. The length of each tube is about 24" and the wheelbase of the bike is 50" so it will just fit in the middle.

 

[knoxie]

Yes

Good idea a friend did this he hid AA cells totally inside a bike frame!! amazing job he did getting them all in.

It may be a good Idea though as you will have paralell banks of NIMH to put in a power Diode between packs as I assume that you will be splitting them.

Lithium is coming down in price all the time, those Lipos I am about to test were cheaper than NIMH believe it or not! if they perform then the scales may start to tip in a year or so, esp. if the big car makers get on board with it, but that's another story!!

All the best

Knoxie

 

[safe]

Lithium is coming down in price all the time, those Lipos I am about to test were cheaper than NIMH believe it or not!

It kind of depends on how you do your calculations. When you go from Lead Acid to NiMh for the same energy output you end up with at least twice the price for NiMh, but 1/4 the weight. When you go from Lead Acid (as a baseline) to Lithium it's closer to four times the price, but 1/8 the weight. So when you calculate the power/weight/cost ratio they all stack up with similiar proportions.

For my application the 46 lbs that the batteries will weigh is low enough for me to design the bike around it. At present my Lead Acid batteries weigh 86 lbs and give only half what the next project configuration will yield. If the rider weighs 185 lbs (like myself) plus the bike and motor at 50 lbs a difference of 20 lbs (NiMh to Lithium) is less than 10%, so it doesn't effect the actual performance numbers very much.

When Lithium equals the price of NiMh based on power output and not the "weight proportional" calculation then I'd go with them. At present $600 seems like a lot to spend on a 48V 30Ah NiMh battery. (but cheap compared to buying one already packaged)

 

[RatoN]

Dang, now THAT is a prototype.

Safe, you probly know about this but, carful with bicycle tires. They are not meant to revolve at exceeding speeds. I cannot back up my claims, but just look at records speed attempts, they all have the same tire probs. They disintegrate resulting in spectacular crashes. Same for downhill and stunts.

Super cool rig. Cant wait to see the new one

 

[xyster]

They are not meant to revolve at exceeding speeds.

I was wondering about this the other day as I biked down the road at 37mph avoiding potholes, rocks, etc...

Do the downhill racers have problems with tires/wheels flying apart?

What speed might be "excessive" in general?

Any bike tires sold with top-speed ratings like for cars?

Due to wheel reliability concerns, I'm hoping more 20-26" mag-type bicycle wheel options soon become available, including with/for hubmotors.

 

[RatoN]

Can't find any data about bicycle tires maximum speed, rpm's or even maximum load, on the intire WEB!

EDIT: Looks like bike tires coming apart is a thing of the past...

One problem in descending steeply is that the brakes may get too hot. After exiting the Blue Ridge Parkway this last year, I went down an incredibly steep hill, and I was afraid my brakes were going to melt. I was forced to stop several times to let my brakes cool off, as continuing could lead to tire or brake failure, as not only do the brakes and rims get hot, but the tires as well. The old glued-on tires used to come off sometimes because the glue would melt. Modern tires won't come off, but the brake pads can lose the ability to stop the bike.

I'm still waiting for an answer to my email to Maxxis about their tires.

I guess you can go nuts, Safe

 

[safe]

I'm currently running these tires:

"24 X 3 Kenda Kraze"

...but I plan to begin testing these:

"24 X 3 Kenda Krusader"

...and also the same tire in a smaller size:

"Tire 24 X 2.35 Kenda Krusader" (for the front tire)

My guess is that it's the size that really counts. A thin tire will place a lot of stress in one small area, but a big one... well it's kind of obvious... a bigger tire absorbs better. The 26" rim doesn't have tires that are much bigger than 2.125 so you don't have much "bounce" to protect the rim at speed. So the 24" is really the only way to go. The "height" of the tire is a full three inches, so it's like having a shock absorber. I'd really like to get wider rims... they do sell wide rims, but they cost a lot, but one day I'll upgrade. This will make the sides stronger... just like wide rims on motorcycles... Rolling resistance is a very small percentage of power usage above 30 mph, so you can virtually ignore it. With disk brakes front and rear there is no worry about heat buildup from the old style brakes rubbing the rims and getting them overheated.

"Rim Only 24 X 3 Black" - $59.99

http://www.choppersus.com

 

[RatoN]

my o my, there is some really nice bikes there. That large rim and tire and fender is absolutely beautiful.

You are right, there are less rims and tires sizes choices with the 26''. Lots and lots yet, all the same. I wish they would make the same in 26''. Not only for style purposes, but like you've explained, for safety too. I just don’t trust those bike tires.

Did you ever consider going with motorcycle wheel and tire at the back, or have a mag machined instead, like xyster, suggested? I'm surly thinking about it

Being able to do with the standards and what is available on the market is always a good thing, as it is less costly and less complicated, but I wonder how well all those parts fit our needs, considering the applications?

 

[safe]

Did you ever consider going with motorcycle wheel and tire at the back, or have a mag machined instead, like xyster, suggested? I'm surly thinking about it

Not really. My current tires are "okay" and my current rim is "okay". But I just figure that if a truly new vehicle is invented (the "electric road racer") then over time the parts will follow. It's sort of the "build it and they will come" philosophy. At each step of the way you are always going to have to deal with the limitations of the parts that are available.

Where I'm LUCKY is that the "Chopper Bike" is now very much in fashion so there are a lot of tire options to choose from. Those rear tires for choppers are about the same size as small motorcycle tires, but they don't weigh very much. It's a very good situation.

One thing... if you replace your 26" wheels with a 24" rim and a 3" tire the OUTSIDE DIAMETER is the same. So you can swap your old ones out really easily. (if the frame has clearance for a 3" tire that is)

 

[RatoN]

OMG, YES

I barely clear 3'' inside the swing arm. What about them spokes though?