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Author Topic: E-Chopper (ex. Expectations & Torque)  (Read 3739 times)
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I have what seems to be a pretty strong motor, permanent magnet.  The NPC-2212.  Maybe they make for wheel chairs or winches?
I wonder if it could be used to make a modest electric bicycle.
There are a lots of "what ifs": fit the existing pedal gear (or other) on this motor... welding a mounting bracket for the motor to the bike frame... -- I get that.

I wouldn't want to invest a lot of time and effort only to find that it's under-powered.
Can anyone venture a learned opinion?  
Do this motor have the goods (Y/N) ?

Some figures --
0.22 in/lb    6.2A   285rpm   0.001hp
28.1 in/lb   10.2A  252rpm   0.11hp
49.6 in/lb   23.6A  227rpm   0.18hp
69.1 in/lb   31.3A  199rpm   0.2hp
91.4 in/lb   41.4A  163rpm   0.24hp


« Last Edit: May 06, 2012, 07:04:01 pm by Runaway Pancake » Logged

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The idle current is pretty huge at 6A - indicates a lot of static friction.

0.24hp is a rather under-powered level though - 250W to 500W output would be better (1/3 to 2/3hp)

What's all this "in/lb" figures?  Is that meant to be torque?  Its nonsense units.

Ah, found webpage for it now - its very inefficient (gears don't help), may overheat in constant use, seems to be about 50% efficient or so - look for a chinese brushless hub motor, 90% efficiencies are more the order of the day.
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What's all this "in/lb" figures?  Is that meant to be torque?  Its nonsense units.



Not sure what you are used to working with, but In/Lb is an ordinary way to to write it, though the perfectionists might want to see In-Lb or even Lb-In 
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in/lb is distance divided by weight.  Torque is distance _times_ force.  in.lb  would do, but Nm is much much prefered.  I've seen this confusion over torque before, but always as N/m never m/N or equiv...
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The "Dynamometer Test Results" column was labelled "torque in in/lbs"
http://www.robotmarketplace.com/products/NPC-2212.html

I checked around since, some bicycle site had figures for a casual bicyclist ranging 150-200W. 
Like that's a benchmark?  How much hp (watts) to take off from a dead stop (no "pushing off")?

I'm < 170 lbs and the bike is, guessing, 40 lbs.
Going at a fair rate (what I'd be pleased to accomplish motorised) down the street here, I was pedaling about 80rpm.
I'm not trying to devise a daily-driver or anything, just a "little" experiment, a lark.

Thanks, MarkT, for your insight.
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I've built an electric bicycle. Here's the specs I measured:
Quote
Specifications:
300W DC Motor
2x 12V, 18AH Sealed Lead Acid Batteries
Max Speed: 25 km/h, based on passenger weight, road incline, and tail wind.
Maximum Unassisted Acceleration: 3.3 km/h/sec
Normal Speed: 18-20 km/h
Range: 8 - 11 km
Time to Charge: about 8 hours when empty

Time to build: about 8 months
Cost of materials: about $300
Cost to drive: less than $0.01/ km for the charge
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John_S,
Looks good.
Do you have a picture of the other "side"?

OK
I found a motor, "350W", probably much like yours, too, John_S.
http://tncscooters.com/index.php?route=product/product&path=52_55&product_id=55
It has a mounting foot/flange/whatever.
(found on ebay as tnc have a plenitude of out-of-stock)
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That motor should be ok. Just know that it is geared, so take that into consideration with your chain/sprocket selection.
I wouldn't go any less then 300W (the size I used). Right now it takes about 6 - 7 seconds to get up to full speed, which isn't even that fast. It has trouble going up hills. I want to put on a second gear, but I haven't found a suitable transmission. I made it before I found Arduino, so it's just a 555 timer PWM for the speed control. I do want to "Arduinoize" it, but I have a few other projects on the go  smiley

Here's a picture of the gears. It is direct drive to the wheel. It does not interfere with the pedals at all, so I can help by pedaling, or let it do all the work smiley-cool. There is no clutch on the motor drive, so it will be spinning when I'm going down a hill. As you can see, it's a 2 stage chain reduction. First stage is 22:8, and second stage is 6:1, for a total reduction of 16.5:1 . Rated motor speed is 2500RPM, so the wheel speed is 151.5RPM, which should give 17.1 km/h (60cm wheel diameter).

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Thanks for posting the additional pic.
My plan was/is to ditch the pedals altogether with the motor placed in that general area.

If I use the motor as is, shortening the chain to fit, will the motor wind out, like the way-easy gear on a mountain bike?
I'm not a mechanical wiz.

As it is, the front has "40" teeth and the rear has "20".
I was pedaling at 80rpm for an acceptable speed (Unk.), so the rear was going 160rpm.
The 9tooth gear, up front, for the rear to do 160, would have to be going > 320rpm.
Would that be asking for (inviting) trouble? 
Will I have to find another sprocket for the motor or modify and re-use the existing sprocket?

Unk.:
20 in diam, 62 in circ. [51cm * pi = 160cm]
62 in * 160 rpm = 10,053 in/min = 837ft/min = 50,265ft/h = 9.5 mph
[160cm *160rpm = 25600 cm/min = 256m/min = 15.36km/h]
Seems like it might have been in the "10mph" neighbourhood.
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The motor you linked to is 3000 RPM with a gear reduction of 9.778. The output shaft would be 307 RPM.
(3000 / 9.778 = 307)

Using the 9 tooth sprocket to your 40 tooth wheel sprocket will yield 69 RPM of the bike wheel.
(307 x 9/40 = 69)

On your bike that would be (69/160) or 43% of what you were pedaling. (4mph, or 6.6km/h)

Although you won't set any speed records, it will be amazing on hills. smiley-twist
If I were you, I would see if I can find a larger sprocket for the motor (~18-20 teeth) or a smaller one for the wheel (again ~18-20 teeth)
 
If you get this motor: http://tncscooters.com/index.php?route=product/product&path=52_55&product_id=54
and chain it directly to your 40tooth rear wheel sprocket, you'd be looking at a wheel speed of 728 RPM (43mph, 70km/h). The speed might be great, but I would expect the motor to be severely bogged down. It might work with a larger motor(>500 Watt) but a 350 Watt just wouldn't have the juice to make it go. Also, the sprocket on that motor is a different pitch than a standard bike chain, so you would need either a different sprocket on the motor, or a double step-down like I used.

When I built my bike (in 2009) I thought long and hard about the simplest way to build it. I found this blog quite helpful: http://www.electricycle.com/ 
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Thanks for the reply.  I appreciate your time.
The 3000 is before the reduction??  Phooey!
I'm "learning" already.

The bike's 40 tooth is on the front and the 20 on the back. 
So, if the 9 were linked to the 20 [2.2 front/motor revs yield 1 rear rev], then full-bore 300rpm from the motor would get me .45X on the rear (135), approx 8mph. 
I think I can, I think I can, but I better plan on sourcing a bigger sprocket. 

I don't want to have to drag my feet like till I really get going.
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Quote
would get me .45X on the rear (135), approx 8mph.
That sounds better. I misread the sprocket sizes in your last post. oops  smiley-fat
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Wow, that's super service.  Got the motor with today's mail.
Now I can think about how and where place it.  I guess this is where it'd be a bonus to have a friend who's a welder by trade.  Got to find some steel!
I ought to try it with the existing gear, with an eye to sourcing something bigger, for the sake of progress. 
It's flat here, no "hills" for miles and miles.
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Which motor did you end up getting?
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The 350W http://tncscooters.com/index.php?route=product/product&path=52_55&product_id=55
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