Electric Bikes - Who has the latest version of the Currie conversion kit?

If you do, I have a some questions.
My questions are about the kit for 26" wheel bikes.

The chain that is turned by the motor to drive the rear wheel, is it ordinary bicycle chain?

The gear on the motor, is it a freewheel AND is it like the ones used on BMX bikes?

The gear on the motor, how many teeth?

The gear on the wheel, how many teeth?

Hello GeoKrpan, below are the answers to your questions:
1. The chain is not an ordinary bicycle chain. It is called #25 chain.
2. It has a freewheel and it is not the ones used on BMX bikes.
3. The gear on the motor is 11 teeth.
4. The gear on the wheel is 54 teeth.

Also, there is a gear box in between the motor and the wheel. Therefore, you cannot calculate the ratio like the bicycle gear ratio.

Lastly, if your intenion is try to built or copy the Currie's left gear one, than you cannot because you need a unique gearbox. Technically you can, but you need to have 10 teeth for the motor and 120 or more teeth for the wheel in addition to the freewheel.

Thanks for the answers.
Is this the kit that you have?
http://www.nycewheels.com/currie-electric-drive-system.html

I was toying with the idea of driving a crank on the left side instead of driving the wheel.
If it used a regular chain and freewheel it would probably be a cinch.
I guess there might be a way to adapt the wheel gear to fit on a crank.

Geo
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I considered driving a 'stokers crank' on the left end of the bottom bracket so that the motor would use all of the bicycles gears. A lot is of it is doable. The motor sprocket could be replaced with a freewheel mounted on a BB cup. BMX freewheels have an ID like a BB. It would be a conventional "right hand"freewheel. But the smallest freewheel you can get is 13 teeth. That would mean that the stokers chainwheel would have to have about 65 teeth to get the motor to turn the crank at about a cadence of 60ish (like a person) so that the bikes gears could be used to both speed up or add power (about equally) from straight thru. I may not have all the numbers just right my thoughts on this were a year ago.
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Also the freewheel protects the motor from being forced forward (gear boxes don't like that) but nothing protects the rider from being batted by a powered pedal.
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for what it is worth, Don

Don, thanks for your sincere comment.

I went to a Currie dealer today and saw a Currie bike with the LATEST kit installed on it.
The drive chain from the motor to the wheel uses ORDINARY BICYCLE CHAIN.
It does NOT use #25 chain.

The freewheel has been moved to the wheel. There is a gear on the motor but it is not a freewheel.

That is unfortunate for my plans because now I will have to figure out how to mount a freewheel on the motor shaft.

If anybody has any ideas about how to do this, please post a comment.

Geo
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I guess I wasn't very clear. The freewheel has always been on the wheel.
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To put the freewheel on the motor, the idea I suggested of a 13 tooth BMX right hand freewheel threaded onto (with loctite) a Bottom Bracket cup slipped over the motor shaft (pinned if you have the skill/drill) and held on by the nut is a proven thing. I've done it.
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Let me know if you solve the gear ratio problem. The motor shaft rpm (at the gear box output) is posted lots of places. You can calculate the ratio you need based on how fast you want the crank or whatever to turn.
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For the idea I tried, the freewheel on the wheel had to be removed to give clearance for the chain headed to the crank. It has a lefthanded thread.
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Don

I own this style of ebike conversion. Although, I had always wanted a hub motor, I have to admit that this style is quite affordable and I really enjoyed it. I am committed to making good use of it, before I retire it for something nicer.

Don, thank you, thank you, thank you.

Will you, if possible, tell me exactly what BB to get?

I guess, I would start with the biggest chainring that would fit on the bike.

There is something called a freewheel cassette driver.
Example: http://www.customriders.com/prodshow.asp?prodid=5611&cat=17&parent=1001&sid=3

Gears are available for them as small as 9 teeth.
But, of course, I'd have to figure out how to install one of these on the motor shaft.

Do you know the diameter of the motor shaft. 10mm?

My "kit" is actually a better design because it uses a more powerful brushless motor instead of the brushed motor. The gearbox design is also more robust. I have optimized my motor set to go up to 22-23 MPH instead of 18MPH from the kit you mentioned below using the same battery. But basically it serves the same purpose. :)


Thanks for the answers.
Is this the kit that you have?
http://www.nycewheels.com/currie-electric-drive-system.html

I was toying with the idea of driving a crank on the left side instead of driving the wheel.
If it used a regular chain and freewheel it would probably be a cinch.
I guess there might be a way to adapt the wheel gear to fit on a crank.

George
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It's just the BB cup you need. That is the cup from any loose bearing BB. The OD is 1 and 3/8", the same as the threaded portion the hub that accepts the freewheel on any rear wheel.
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The center hole where normally the spindle would come out to accept a pedal accepts the motor shaft just fine.
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I'm not sure how you would make use of a cassette driver. This approach is for a freewheel not a cassette. The gear has to be, on the shaft, close to the motor output both to keep the chainline correct to the stokers chainwheel and to prevent side loading the motor shaft. You need a freewheel there. 13T is the smallest I found. If you can find a way to use a cassette rather than a freewheel, please share the news.
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As far as shaft diameter, RPM etc., go to http://www.evdeals.com/ they sell all the stuff and have a good page showing specs. They sell the transmission Lyen is talking about. It all comes to many times more expensive than Currie.


Don,

Will you, if possible, tell me exactly what BB to get?

I guess, I would start with the biggest chainring that would fit on the bike.

There is something called a freewheel cassette driver.
Example: http://www.customriders.com/prodshow.asp?prodid=5611&cat=17&parent=1001&sid=3

Gears are available for them as small as 9 teeth.
But, of course, I'd have to figure out how to install one of these on the motor shaft.

Do you know the diameter of the motor shaft. 10mm?

George
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If you buy a kit, I'd advise that you not make any irreversible mods. You may want to go back to the original design if you find you can't spin your legs as fast as the motor spins the pedals. From my experience, with the chainwheels I could find neither I nor Lance Armstrong could spin that fast.
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I might not have made it clear the freewheel (or freehub, if you could fit in) stops you from driving the motor against its will and ruining the gear box. Nothing prevents the motor from driving the pedals against your will or against your ankles.
.

Don

Ok, the cup from a loose bearing BB, haven't used one in years.
Profile Racing makes something called a mini cassette hub. The choice of cogs for this hub is 9 to 18 teeth.
What I'm thinking is to install the cassette body from this hub on the motor shaft, somehow.
I looked at EvDeals.com a little last night. I'll spend some more time looking at it.
More to come.
Thanks for your help, Don.

Ya' let go of the throttle and/or shift up to a higher gear. Put more load on the motor to slow it down.
That is the beauty of driving the crank as opposed to driving the wheel.
More to come. You've been great. Thanks.

Here is a link to a picture of a cassette driver with a 9 tooth gear.
http://www.danscomp.com/461082.php?cat=PARTS
It is available in left or right hand drive.
If you wanted to get the gear as close to the motor as possible you could get a left hand drive and mount it backwards.

Don, how big a chainring would you need with a 9 tooth cog to get 60 rpm at the crank?

Don, how big a chainring would you need with a 9 tooth cog to get 60 rpm at the crank?

http://www.sheldonbrown.com/gears/

It looks like normally an Odyssy Hazard Hub $80- $130 would accept a
Hazard Cassette Driver Price: $35.00
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The hub is a special product popular with BMX racers. It would normally be laced into a wheel. It has a special axel and bearings. It looks like the axel is one of those sorta splined one way clutch thingees, maybe.
But you want to put this on the motor. I guess you would have to make the motor shaft look like a Hazard axel.
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http://www.danscomp.com/428023.php
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Dan's Competition
1 Competition Way
Mt. Vernon, IN 47620
1-812-838-2000
Customer Service

International Customers
Toll Free USA: 1-888-888-3267, Options 3, 5
Fax: 1-812-838-2693
Mail: 1 Competition Way
Mt. Vernon, IN 47620
Email: customerservice@danscomp.com
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Dan’s might be able to clue you in by phone.
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About the chainwheel needed:
Unite Motor which makes the motor
∷SHENZHEN UNITE INDUSTRIES CO.,LTD
http://en.unitemotor.com/ProductView_41.html
They say rpm motor = 3000, gear reduction = 7.18:1 so output shaft rpm = 418 rpm
418/60 = 6.96 that’s the gear reduction needed.
Therefor to get 60 rpm at BB need 63 Teeth on the chainwheel, with 9 teeth . Pretty BIG.
For my 13 T freewheel it would be 90 Teeth at the chainwheel.

On the load the motor up and slow it down idea, could work, and yes I went to some trouble pursuing this because I too wanted the gears in the loop, but don't underestimate the torque a DC motor can put out if you try to slow it down. That's when its torque peaks. 'Aint no hill eZip won't climb' if you've got enough battery.

George
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A thought that I have communicated badly, or not at all, is that the main reason I wanted to use the 21 different gear combinations on my eZip was to increase efficiency. I don't really need more speed or more torque. I wanted to reduce the current draw from the battery by using the gears to reduce the torque and battery current needed in some conditions. Your ' gear up' = punish the motor into slowness kinda defeats that.
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I'm trying to tread carefully and not discourage your creativeness, but battery life per charge is one of the factors in the equation.

be well, think well
Don

Thanks once again, Don.
No one has actually built the bike that I propose to build. So, no one really knows how it would work out in the real world.
So, for the time being, I'm going to plan on going with the BB cup, 13 tooth freewheel, and biggest chainring that will fit on the bike.
If it's a bust I'll have to think of something else but I might as well try what's easiest for starters.
On comment about chain line. The length of the chain from behind the wheel to the crank will mitigate the issue significantly.
More to come.
PS I'm thinking of installing the Currie kit on a Kona Smoke 29.

You're thinking of the Currie Pro Drive Conversion Kit, which may not be available anymore. I believe it has been replaced by the Electric Drive Motorkit, which is what I recently installed on my mountain bike.

http://www.ezipusa.com/img/p/159-326-large.jpg

If you want the old design of the Pro Drive Conversion Kit, you should check the stokemoney kit for the xtracycle. http://ebikes.ca/store/images/stoke_xtra.jpg

I know about the Stokemonkey. It's what inspired me to have a "through the gears" electric bicycle.
But, I don't want a long bicycle and it's $1700. I'm not saying it's not worth it.
The current Currie kit was recently on sale from Currie for $299.

Will you do me a favor? Count the teeth on the gear motor and on the freewheel on the left side of the rear wheel.

I know about the Stokemonkey. It's what inspired me to have a "through the gears" electric bicycle.
But, I don't want a long bicycle and it's $1700. I'm not saying it's not worth it.
The current Currie kit was recently on sale from Currie for $299.

Will you do me a favor? Count the teeth on the gear motor and on the freewheel on the left side of the rear wheel.

The OEM freewheel has 20T. I think you might want to read this thread on ecoforumz regarding one member's efforts at increasing the speed of his eZip by decreasing the size of the freewheel (he couldn't find a comparable motor sprocket so was limited to changing the size of the freewheel for his project). It's very interesting, he's easily getting 20MPH using the standard OEM SLA battery pack. Here's a link to the thread. http://www.ecoforumz.com/electric-bicycle-scooter/80982-20mph-ezip-24-volt-oem-pack.html

FYI, here's a picture in his thread of the OEM freewheel (larger) next to the new, smaller freewheel he's using to get increased speeds.

http://www.ecoforumz.com/attachments/electric-bicycle-scooter/583d1247333418-20mph-ezip-24-volt-oem-pack-20vs16.jpg

I'm thinking, by powering the cranks instead of the rear wheel, and thereby utilizing the bicycles drivetrain that 30 mph will be easily attainable.

If you haven't already, you might check out the design of the DreamE bikes. Their power assist motor connects to the bike's crank. (There are two motor options 360W and 500W.) Here are some photos from a retailer's web page.

http://www.sanluisrides.com/data/default/images/catalog/large/power-3.jpg

http://www.sanluisrides.com/data/default/images/catalog/large/power-2.jpg

http://www.sanluisrides.com/data/default/images/catalog/large/power-1.jpg

Looks like the Cyclone kit. Do you see how they used an ordinary bicycle freewheel on the motor?

It does have to be a lefty though, since it pulls chain counter clockwise. AND there is another freewheel built into the chainwheel. Those chainwheel freewheels (Cyclone) have a bad reputation.
BTW did you notce the size of the Cyclone motor output shaft? I guess you could make a similar collar (smaller ID) to fit a rightway freewheel to a Currie/Unite motor.

I wonder what that "black sockie" on the bottom tube, between the crank and the motor, is hiding.

Hi Don.
Check out these roller clutches.
http://www.tinyclutch.com/roller-clutches.htm

They have a knurled section for mounting gears which they can supply.
There is a standard model for a 3/8 shaft with a set screw and keyway.

Do you know the diameter of the Currie motor shaft?

Geo

That clutch looks interesting. They say they can supply Metric bores. 10 mm (to match motor) slightly bigger than 3/8 is pretty standard. It would be really good if you could get it to match to the flat on the shaft. You might have to cut off the threaded part of the output shaft to use this.

This is the sprocket. This defines the shaft.

9 Tooth 10mm D-Bore Sprocket For 1/2" x 1/8" Bicycle Chain
1-5/8" OD, 8mm x 10mm D-bore ID. Fits 10mm OD single-flatted motor shafts with nut and washer on end to secure sprocket in place. For 1/2" x 1/8" bicycle chain.
Item # SPR-B109
$14.95

This defines the motor/shaft:
24V 450W
electric bicycle motor

24 Volt 450 Watt Electric Bicycle Gear Motor
24VDC 450W electric bicycle motor with built-in gear reduction transmission. Output shaft speed: 550RPM. Includes 9 tooth sprocket for 1/2" x 1/8" bicycle chain. Powerful four brush permanent magnet electric motor design. 100% ball bearing construction. 24" long power leads. Shaft rotation reversible by reversing power leads. Three bolts on front side of motor for mounting. Motor dimensions: 4-1/4" outside diameter x 3-1/2" long excluding transmission and output shaft, 4-1/2" long including transmission and output shaft.
item # MOT-24450G $99.95

You can buy these and other sprockets and freewheels at:
http://www.electricscooterparts.com

I meant to include these images of the motor:

113656

and sprocket:

113655

Hi Don,

Thanks for checking out that roller clutch and for the info on the sprocket and motor.

I think the easiest thing to do is find an establishment that deals in this kind of stuff and bring it to them and show them what I need. You never know, there may be an "standard" part made for exactly this type of application.

Cheers,
George

Geo

You should look at http://www.bike-elektro-antrieb.ch/. Neat idea. Gives what you're after, I think.

Geo

You should look at http://www.bike-elektro-antrieb.ch/. Neat idea. Gives what you're after, I think.

Hi Don,

Thanks for that, looks like good potential resource.

How does throttle position affect RPM and power?
In other words, if at full throttle the cranks spin too fast then couldn't backing off the throttle reduce
the crank speed to a manageable cadence?
If, for instance, 3/4 throttle spins the crank at just the right speed then is the motor producing 3/4s of
it's power? 3/4s of 450 watts is 337.5 watts.
337.5 watts of assistance would be like being twice as strong while only increasing weight marginally.

Do you see what I'm trying to say?

Furthermore, wouldn't the most efficient speed of the motor be at some point less than full throttle?

Geo

I’m not sure how familiar you are with this stuff. I’ll give it in broad strokes and you can ask for parts I left out.

The throttle sends a control voltage to the motor controller (often that voltage is 0 – 5V, with 5V meaning full speed ahead and 0 meaning NO GO). The motor controller converts that signal into various % ON times during a period of time, for example 50 milliseconds. A millisecond is 1/1000 of a second. So over and over the controller generates 50 millisecond periods. Each ON TIME can be 0% or 0 milliseconds on, or 100% = 50 milliseconds on, or 33% = 16+ msec.. 100%, full throttle 50 msec. on, for every 50 msec. looks like what we normally think of as DC. Half throttle means 50% power => meaning for each 50 msec. period the power is on for 25 msec. then off for 25 msec. So the current looks like this:


This is called Pulse Width Modulation or PWM. The width of the ON part of the period is modulated/changed to give varying average current/voltage. A 24 V supply at 50% PWM shows pretty much the same effect as a 12V supply for many applicatiions.

There is a difference though when the power is applied to a DC motor. Based on the number of windings and the materials involved each motor has a speed (rpm) that it wants to run at. The motor wants to run fast enough that the back EMF (back Electro Motive Force) generates a voltage equal and opposite to the applied voltage. The back EMF is generated by the wires in the winding passing through the flux field of the magnets (permanent in our case). In theory the motor would reach this speed and then no current would pass through the wires or from the battery. In real life even an “unloaded" motor has friction so some current will be required

In the case of a motor trying to propel a bicycle and rider the current will never get close to zero and the motor will never get to its favored rpm. BUT.. and that’s a big but, the motor will try for all its worth to get to its favored rpm. It will produce HUGH torque to get itself moving. Of course, big torque means BIG current. BIG current means little battery life, short distance between charges.

So now, we have PWM trying to trick the motor into thinking that there is only 12V applied (50% duty cycle), but the motor knows that for 25 msec. it has 24 volts applied. So it tries for all its worth to get to the favored rpm for a back EMF of 24V. It sucks HUGH current. Then the 24V goes away and the motor just dumps the current from its 24V EMF into a protection loop in the controller for 25 msec..

I think you can see the picture: the motor sucks big current to get rpm up then dumps that energy into a loss loop in the controller. So PWM doesn’t do much good for energy conservation. It is good for allowing the rider to move the bike at safe (low) speeds, but not good for the battery or motor. Earlier on this forum there was a story of a guy who nearly fried his motor riding slowly on bike trail in order to stay with his non eassisted wife.

I guess they use PWM for a good reason. I guess there isn't a convenient way to TRULY vary voltage.
My last experience with motor driven electric thingies was slot cars when I was a kid.
The further you pulled the trigger the faster the cars would go. But the power came from a wall socket and not a battery. I never recall any burnt motors from not running the cars at full power.
So, what is your technique for running your electric bike? Full throttle all the time to get up to speed as quick as possible? How long does it take for the motor to get up to speed?
Do you ever run the motor at less than full throttle and have you determined the minimum safe throttle setting?
Is there an electrical solution to the dilemma? A different type of controller? Lower voltage? A different motor with a lower speed? Etc.
Thanks again, Don, for your help. You have exceeded all expectations.

Here's a link to the motor page of ElectricScooterParts.com.http://www.electricscooterparts.com/motors.html

The 10th item down is an bicycle motor that looks exactly like the illustration in an earlier post of yours.
It is a 24 volt motor but it is only 250 watts and the output shaft speed is 382 RPM versus 550 RPM for the motor that comes with the Currie kit, according to the specs that you posted.
The output shaft of the 250 watt motor spins 37% slower than the 450 watt motor.
What implications does this have on the dilemma?
Of course, there is bound to be some drawbacks.

Geo

That's a very good thought using the lower torque, slower 250W version of the motor. Using the bicycle's gearing less torque shouldn't be an issue. Now it looks like you would have an extra 450W motor if you buy the Currie Kit. I'd bet that would be easy to sell.
This rpm would make the 65 T chain wheel into about 40T. That's doable. I'm relying on memory to say 65T would give a cadence of about 60 with the 450W. That probably should be checked.

As for how I use the existing system: Yes, full throttle always. I think most people who ride eZips would say the same. If the throttle were to fail, I'd replace it with a non-latching switch. I do start out no throttle, pedal only to save battery. From a few mph (pedaling) to 15 mph pedaling with power is just seconds.
The only time I ever use partial throttle is while walking a heavily loaded bike through crowds. I don't think you need to worry about a safe lower limit on throttle position. You just don't want to go a long ways on partial throttle. It's good to be aware that you are not helping the battery or the motor by using partial throttle.

Don

It's a good feeling to hear you say that my idea has potential. Yes, I agree that for pedal assist that 250 watts is probably adequate. The wattage output of some of the riders of this years Tour de France could be monitored via the Internet. Most of the time, even while climbing, the wattage was below 300w. I think it's not unreasonable to say that 250 watts would double my power, or, halve the effort required, not a bad prospect.

ElectricScooterParts.com sells the Currie kit ($299). I have a thought to call them and ask them if they could substitute the 250 watt motor. The retail on the 250 watt motor is $10 less than the 450 watt motor, $80 vs. $90, they sell both. They could also tell me if the 250 watt motor is indeed identical to the 450 watt motor with respect to the fitting to the Currie kit.
The next question I have is whether the controller that comes with the kit will work with the 250 watt motor. It's possible that I'd have to buy another controller, no big deal, another thing that ElectricScooterParts.com could help with.

So, you're thinking that a 40 tooth chainring would work with a 13 tooth freewheel.
The bike that I'm going to be installing the kit on can probably handle up to a 53 tooth chainring.
So, I'd have a lot of leeway for experimentation, fine tuning.
I was considering a Kona Smoke 29 but now I'm thinking Motobecane Outcast 29.
The reason is because the Motobecane has horizontal single speed dropouts and this might be valuable in getting the chain tension right from the motor to the left crank.
On the right side I would use a chain tug with a tab for installing a derailleur and run a full length cable housing from the shifter to the derailleur.
I would run a single chain ring with no front derailleur. With a mountain bike cassette and 44 tooth chainring the gearing range is 37.5 to 115 gear inches. I have a similar setup on another bike and it is both low enough for me to climb anything and high enough to go very fast.
The Motobecane is $349 delivered. I should be able to do this project for well less than $1000.

Well, thanks again, Don, you are super.
George

Before switching out the motor, I would try the 450W motor that comes in the kit . I chose the Currie kit for it's excellent price and its reputation for great torque. I'm west of Glacier National Park and need torque to get up mountain roads and trails that I ride. You can't beat the Currie kit with the 450W motor. It's performing better than I'd hoped for.

This is the area I ride. We have very few flat roads here. You're generally going up one hill or down another.

http://pic50.picturetrail.com/VOL442/7447283/14154973/370628303.jpg

Before switching out the motor, I would try the 450W motor that comes in the kit . I chose the Currie kit for it's excellent price and its reputation for great torque. I'm west of Glacier National Park and need torque to get up mountain roads and trails that I ride. You can't beat the Currie kit with the 450W motor. It's performing better than I'd hoped for.

This is the area I ride. We have very few flat roads here. You're generally going up one hill or down another.

That's a really good thought.
But, what Don and I are afraid of is that the 450 watt motor would produce to high a cadence.
I have a couple of things in my favor for using the 250 watt motor.
Although I live in a hilly area it's not the mountains AND I am a strong cyclist.
But, it's entirely possible that our concern is for naught and the 450 watt motor is the way to go.
We will see.

Geo

A quick thought about one of your comments:

"The reason is because the Motobecane has horizontal single speed dropouts and this might be valuable in getting the chain tension right from the motor to the left crank."

The horizontal drop outs aren't necessary. The Currie mount accommodates moving the motor to adjust chain tension.

I look forward to hearing how this all works out, I think the slower output motor is key.

A remaining issue is the concern with getting an ankle batted by the pedal. You might try the idea of only using power when clipped in.

I'm pretty sure Currie uses the same controller with the 250 Watt version. The new Ecoride is 250 Watts. The original, way back Currie kit was 250 also.

Currie is using a new controller on the conversion kit so it may not be the same as on the 250W.

Geo

A quick thought about one of your comments:

"The reason is because the Motobecane has horizontal single speed dropouts and this might be valuable in getting the chain tension right from the motor to the left crank."

The horizontal drop outs aren't necessary. The Currie mount accommodates moving the motor to adjust chain tension.

I look forward to hearing how this all works out, I think the slower output motor is key.

A remaining issue is the concern with getting an ankle batted by the pedal. You might try the idea of only using power when clipped in.

I'm pretty sure Currie uses the same controller with the 250 Watt version. The new Ecoride is 250 Watts. The original, way back Currie kit was 250 also.

Hi Don,

I know the Currie mount allows tensioning the chain but how much? There's going to be loooong chain
between the motor and the left crank.

I'll do like you do and pedal away from a stop. That way I'll be sure to be clipped in.
I was reading that the new Currie kit can be operated in two modes. In one mode the throttle doesn't work unless you're pedaling. In the other mode the throttle works whether you're pedaling or not.

Tell me about the Ecoride controller. Send a link.

Do you think this is possible? Run the kit in the "no pedal no throttle" mode and have a switch(es) in the brake lever(s) that would interrupt power reaching the motor. The throttle is jammed wide open. When you hit the brakes the power is cut. If you also stop pedaling the power won't resume unless it detects some pedaling cadence.

So here's how I envision it working. You're riding along with the motor on. You're approaching a red light so you tap the brake levers and stop pedaling. You stop at the red light. You don't have to keep your hands on the brake levers because as long as you're not pedaling the motor won't come on. The light turns green and you start pedaling and the motor comes on. If the motor comes on too strong before you're clipped in you continue to pedal BUT you lightly drag a brake which cuts the motor until you're fully clipped in and then you let go of the brake lever which lets the motor resume.

I'm thinking an on/off switch on the handlebar and the throttle jammed open but not on handlebar rather tucked away somewhere else.

Let me know your thoughts.

Geo

I'm sorry I made a very significant error in memory or arithmatic regarding the size of the Stokers crank. If we do the math straight it looks like this:

Motor rpm = 382
Desired crank rpm = 60

Ratio = 382/60 = 6.37

If the freewheel has 13 teeth, the stokers crank needs 6.37 x 13 = 82.8 teeth

As I've been driving around (biking leads to happier thoughts) I've been playing with numbers in my mind, fearing I misled you. I did. I'm sorry.

80 teeth is a pretty big crank.

The other thought I had, back when, was to add a jack shaft, with two sprockets, an extra shaft between the freewheel and the stokers crank that would allow dividing the required 6.37 into two pieces. 13T freewheel to pretty big chain wheel on jackshaft. Then a small chainwheel on the jackshaft to a pretty big stokers crank. 6.37 would be pretty easy to get this way. The higher rpm of the 450 watt could be made to work too. nwmtnbiker would be happier. It is true more torque, more better.

The problem with this is "How do you support the jackshaft?" Here the laid back lay out bike might offer something. It probably would require some welding/fabricating.

Yeah, I think I've seen recumbents with some sort of arrangement where there is an extra chainwheel or cassette.

Here are two other things I thought of.
Changing the reduction gearing in the motor to get the wanted shaft speed.
Use #25 chain. ElectricScooterParts has a 15 tooth freewheeling motor cog and a 90 tooth chainring. According to you calculations a 15 tooth cog would need a 96 tooth chainring, so it's close.

Or, just abandon the Currie kit idea altogether.

Cyclone-USA makes a 360 watt kit for $445 not including battery, 500 watt kit $495.
The motor mounts under the bottom bracket (sorta) and drives the chain on the right side, no stokers crank needed. You are limited to one chainring but I wasn't intending on using more than one with the Currie kit.
The trouble with this kit is that, unless unmodified, it needs 3 1/2 inches of chainstay between the bottom bracket and tire.

Misled me? Nah, better to know now that it won't work.

Geo

I like your persistence.
One thought regarding "Use #25 chain. ElectricScooterParts has a 15 tooth freewheeling motor cog and a 90 tooth chainring. According to your calculations a 15 tooth cog would need a 96 tooth chainring, so it's close." That big sprocket is meant to go on a hub,
From Electric Scooter
"7-1/4" OD, 1-3/8" ID. Compatible with Currie and Powercats Tiger electric scooter models with 12-1/2" wheels. Fits 1-3/8" OD threaded scooter and bicycle wheel hubs"

So you would need a lashup to link this sprocket to the Crank/ BottomBracket.

About Cyclone, again, they have a freewheel so that only the chainwheel is turned by the motor. The BB axle and pedals don't. Many reports say that freewheel is not robust.

Hi Don,

Cyclone-USA's motor runs at 2800 with 9.55:1 reduction.
I think that calculates to an output shaft speed of 293 rpm (2800/9.55).
They use a 44 tooth chainring and a 14 tooth freewheel.
44/14 = 3.38 reduction
293/3.38 = 86.7 rpm crank speed

If we can accept the same crank speed for the Currie kit the chainring size requirement is
much more favorable.
Motor rpm = 382
Ratio 382/86.7 = 4.41
Chainring size = 4.41 X 13 = 57.3

If I used a 53 tooth chainring.
53/13 = 4.08
382/4.08 = 93.6 crank speed, 8% faster than the Cyclone crank speed.

I would imagine that Cyclone chose a conservative crank speed and that it was chosen after a
lot of trial and error.

I think it reveals that 60 rpm is very very conservative.

Do you like my logic? Are my calculations accurate? I don't do much math these days so if I've
blundered please point it out.

Also, I am a very experienced cyclist. Three weeks ago I did a 96 mile ride with 9200 feet of vertical
gain ON A SINGLE SPEED. I rode with a guy on a carbon fiber bike with 20 speeds and uber light wheels. I got ahead of him on most of the climbing and on the descents. I have really good leg speed.

If my calculations are correct it means the Currie kit is still in the running.

Geo

I'd say your calculations look fine. One thing to remember though Cyclone has a freewheel on the chainwheel so that the chainwheel, chain, ..., rear wheel can turn without the pedals or axle turning. 86.7 wouldn't be so bad if you were just watching it, not doing it.

This is a quote from Wikipedia:
"Cyclists typically have a preferred cadence at which they feel most comfortable, and on bicycles with many gears it is possible to stick to a favourite cadence at a wide range of speeds. Recreational and utility cyclists typically cycle around 60–80 rpm; racing cyclists around 80–120 rpm and sprinters up to 170 rpm for short bursts[1]. The professional racing cyclist and Tour de France champion Lance Armstrong is known for his technique of keeping up high cadences of around 110 rpm for hours on end to improve efficiency."

So at 93.6 you would be approaching Lance levels and get rapped in the ankle if you didn't keep up.

With the Currie kit idea the Bottom Bracket axle has to spin that's how power gets from the left side to the right side. Cyclone applies motor power/spin TO the right side. I'm not saying that it's not worth a try. But I decided it wasn't for me.

Hi Don,

Yes, I forgot about the freewheeling crank.

But, won't the crank only reach maximum speed when there is no load on it?

I have calculated the potential speed of a Currie Trailz bike.
I believe the motor has a 9 tooth cog and the freewheel has 20 teeth.
Output shaft speed is 550 so the wheel is turning at 247.5 rpm (9/20 x 550).
That's 4.125 revolutions per second (247.5/60).
The circumference of a 26 x 2.0 tire is 2099 mm.
The wheel is traveling 8658 mm per second (4.125 x 2099).
According to OnlineConversion.com 8658 mm per second is 19.37 mph.
Currie says that a Ezip Trailz can attain speeds of up to 15 mph.
15 mph is 29% under it's potential speed.

I think it's safe to say that the difference between potential and actual speed is due to load.
If my crank spun 29% slower, I would be looking at about 67 rpm (94 rpm - 29%).

Do my calculations appear sound?

I'm wondering if the 450w motor WOULD be better?

Geo

I think your calculations are consistent, but may be misleading. It would be better to say 15 mph is 77% of 19.37 mph. 15/19.37 = 0.77 or 77% . So the loss is 23% of the speed. 77% of 94 rpm is 72.79 rpm. Still pretty fast.

Also I regularly hit 18 mph on my eZip in its standard configuration using just the motor. That's 93% of the speed used in your calculation. So rpm would be 87.4 (93% of 94 rpm). All of this says pretty fast cadence.

You might want to look at http://endless-sphere.com/forums/viewtopic.php?f=28&t=11771&p=179780&hilit=+freewheel#p179780 there is a discussion of the need for a freewheel there


"Re: Help with outline of set-up. Newbee question

New postby Grinhill » Thu Jul 30, 2009 10:49 pm

Manuel

You should avoid driving the pedals with the motor. Try and include a freewheel system somehow.

It would make your bike very unsafe. The two most obvious problems would be having a pedal hit your leg, and the other is having a pedal dig into the road as you lean to go around a corner.


1995 Giant Hybrid - Zeta2 with 12V 7AH SLA - removed after one year.
2006 Converted Giant to Geared Brushless Rear Hub with 24V 17AH SLA - bike stolen 2007.
2008 Hardtail MTB Disc Brake - lightweight RC/LiPo system.
Grinhill's Medium-power RC-Motor Hardtail build
The Grinhill Mk2 RC-motor drive"

This forum has lots of info on using a motor to drive through the bike's gears.

Geo

I have an alternate idea that you might want to look at. This kit provides the jack shaft, mounts for it, the front freewheel, dual chainwheels (one for chain from jackshaft, one for pedals), hardware to mount everything.
I picture a chain from the Currie motor to the jackshaft and then the standard use of this kit. This kit is made to connect a small gas engine to that jackshaft. It has a mount for that engine that wouldn't be needed for use with the Currie.

http://www.sickbikeparts.com/Manuals/Shifter%20kit.pdf

The kit costs $179.50 but looks like all pretty sturdy stuff and would give you the use of the bike's gears that you want and the safety of a freewheel.

take a peek, Don