Best way to add left-hand chainwheel at crank for motor?

Actually, I'm sure there's a best way and an easiest way. For my purposes, an optimum solution is probably somewhere in between, but it might be different for others.

I've decided I want to add e-assist to my bike, which will be my first e-bike project. Note that I did say e-assist - I still plan on pedaling, using the motor for higher cruising speed and climbing as needed. After much reading, I decided on a Cyclone 500W motor because I like the through-the-gears approach instead of raw wattage. But, instead of their standard setup, I'd like to run the motor through the crank so I have the full range of gearing available when pedaling. That will also give me wider gearing range for the motor because I'd set up the drive ratios so the optimum motor speed range matched the optimum pedaling cadence. I've ran some numbers to figure out what sort of ratios I need, speeds, etc, but I'll spare the gory details for now. Maybe I'll set up a build thread with all that later. The goal is to design a good, solid drivetrain now that I can implement for not-too-much cash and then upgrade incrementally later.

For now, I've been trying to figure out what the best way is to add a left-hand chainwheel to my existing crank setup. The bike is a Trek hybrid with a 3-speed 28/38/48 chainwheel in front and 7-speed 11-31 cassette in back. For the new left-hand drive, I figured that I probably want a ring in the 45T range to get the right ratios, give or take a tooth or two, which is in a nice range for standard rings. I'm not very familiar (yet) with the details of how all the parts fit together, different standards, etc, so sometime soon I'll need to tear into the bike to see exactly what I'm starting with. Based on what I've read so far, I'm guessing that my low-mid range bike probably has a square-drive crank and not one of the better spline types? I read through the very long freewheel resource thread and some others, which were helpful and informative. Speaking of freewheels, since I'm going for e-assist I don't care if I end up with free-wheeling pedals or not - I'll be pedaling anyway.

I figure I have a couple of options. Tandem bikes use a left-hand drive for the 2nd rider, so maybe I can mix-and-match one of those left-hand cranks with my existing right-hand one. I'm sure it's possible to somehow modify the existing left-hand crank to mount a chainwheel, but I'm not sure how easy or reliable that would be. Since the kit version of the Cyclone comes with a 44T freewheeling crankset, maybe there's a way I can modify that to work on the left side? The options probably increase the more hardware I'm willing to replace, so that's where the easiest-vs-best tradeoff comes in. I'm willing to modify what I've got (or buy) to some degree, but I really don't have the capability (i.e. tools and equipment) to do much besides very basic fabrication.

So, any advice or suggestions are appreciated. I might try to find a nice big bike shop near me to see if I can eyeball some hardware. Pictures are great, but its hard to figure out how stuff will fit together until you can get your hands on it!

http://cleverchimp.com/products/stokemonkey/

Nice, pretty much exactly how I want to set mine up. I don't think they sell the crankset separately, though, at least not unless I'm willing to pay $199 for a whole new setup. Maybe I can make friends with a local bike mechanic and talk them out of a spare right-hand crank from a junker or something... Anybody know of a place that sells right and left separately?

I also came across this:

http://www.bikexprt.com/bicycle/tancrank.htm

They suggest doing pretty much this, putting a right-hand crank on the left and just tightening it down like there's no tomorrow.

Sounds like you want to do exactly what I already did. Take a look at my "Stokemonkey knock-off": http://endless-sphere.com/forums/viewtopic.php?f=28&t=8665

I bought a pair of inexpensive tandem timing crank arms and used one of them with the existing right crank arm to make a stoker crank set. No freewheeling but I kept all my gear combos. I've since added a recumbent-like chain tube to keep the chain lube off my pants.

Hi,

I'd use a FW crank, if for not other reason than a safety issue. If the motor takes off you don't want your legs cut off by the crank set.

Its not necessary to drive through the left side or not have the crank FW to maintain all of your gearing:
http://www.bike-elektro-antrieb.ch/home.htm



His crank set prices are pretty high (about $400) but they use mostly all off the self parts so you can do something similar.

If you click on products/shop/crank you get this description (excerpt):

B-E-A Echo ISIS Free Wheel Crank Set 4-speed

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pat_smtih said:

I bought a pair of inexpensive tandem timing crank arms and used one of them with the existing right crank arm to make a stoker crank set. No freewheeling but I kept all my gear combos. I've since added a recumbent-like chain tube to keep the chain lube off my pants.

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Great idea. Did a little looking online, and found a place that sells LH tandem cranks separately:

http://www.ebikestop.com/sugino_xd_tand ... CR8875.php

That seems just the ticket. Match it up with a chainring and I'm in business.

MitchJi said:

I'd use a FW crank, if for not other reason than a safety issue. If the motor takes off you don't want your legs cut off by the crank set.

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That's a good point, but since I'm gearing the motor to drive the pedals at normal cadence speed, I'm not too concerned. If the pedals were doing 200 or 300 rpm and full throttle, that would be a different story! That is one of several reasons I can think of why a big red e-stop button would be a good idea, though. I'll put that one on my list of incremental upgrades.

rhitee05 said:

pat_smtih said:

I bought a pair of inexpensive tandem timing crank arms and used one of them with the existing right crank arm to make a stoker crank set. No freewheeling but I kept all my gear combos.

Click to expand...

Great idea. Did a little looking online, and found a place that sells LH tandem cranks separately:

http://www.ebikestop.com/sugino_xd_tand ... CR8875.php

That seems just the ticket. Match it up with a chainring and I'm in business.

Click to expand...

FWIW, You can get a pair of LH crank arms from "mrbikeman" on eBay for less than $10:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=150337196942

That's a good point, but since I'm gearing the motor to drive the pedals at normal cadence speed, I'm not too concerned. If the pedals were doing 200 or 300 rpm and full throttle, that would be a different story! That is one of several reasons I can think of why a big red e-stop button would be a good idea, though. I'll put that one on my list of incremental upgrades.[/quote]

You really should rethink the no FW idea. I have 2 bikes with 360w Cyclones and I had a freewheel problem on one of them and used it 1 time without the freewheel and was sorry I did. I was only trying to do a normal 60 to 80 cadence too. Trust me you do need a freewheel for your own safety.

I'm with you, dumbass. I think you will find a lot of other people here recommending you go with the freewheel, rhitee05.

Just imagine crusing at a comfortable speed, then coming up to a corner, and you lean in to take the corner. How often do you stop pedalling, if only briefly, to prevent your inside pedal from digging in to the bitumen?

Hi,

Or just imagine your foot slipping off a pedal and your leg getting whacked at 80 RPM with 1 HP (750W) of power.

dumbass said:

You really should rethink the no FW idea. I have 2 bikes with 360w Cyclones and I had a freewheel problem on one of them and used it 1 time without the freewheel and was sorry I did. I was only trying to do a normal 60 to 80 cadence too. Trust me you do need a freewheel for your own safety.

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Details, please. What exactly happened?

I would also be curious exactly what your experience was.

Pat_smtih, thanks for the eBay tip. Good find!

MitchJi said:

Hi,

Or just imagine your foot slipping off a pedal and your leg getting whacked at 80 RPM with 1 HP (750W) of power.

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No need to imagine. I've been riding with various Cyclone motors connected to the left-hand crank for about 3 years now and about 10k miles. Only once or twice has my foot slipped off the pedal while I was motoring, and when that happened, the pedal struck my calf uncomfortably but not injuriously. When this happened I instinctively released the throttle and the motor stopped within one crank revolution, so I only got struck once on each occasion. To keep the feet on the pedals it probably helps that I use clipless pedals such as Shimano's SPD pedals that, unlike "bear-trap" platform pedals, do not have any sharp components pointing outward.

http://tinyurl.com/cxl5ey

I'm using a 54t chainring to match my preferred cadence of about 70 rpm to the peak efficiency RPM of the motor, but I can see using as low as a 46t or 48t chainring if more motor power is desired. If you're using one of the 36 or 48 volt systems, then I would consider using a larger chainring or connect to the right crank with a freewheel as the Cyclone motor (with the planetary gearbox) can spin the cranks at an uncomfortably high cadence, even with a 54t chainring.

mrbill said:

I'm using a 54t chainring to match my preferred cadence of about 70 rpm to the peak efficiency RPM of the motor, but I can see using as low as a 46t or 48t chainring if more motor power is desired. If you're using one of the 36 or 48 volt systems, then I would consider using a larger chainring or connect to the right crank with a freewheel as the Cyclone motor (with the planetary gearbox) can spin the cranks at an uncomfortably high cadence, even with a 54t chainring.

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(kind of hijacking my own thread here)

Are you referring mainly to the higher-power 36/48V systems? I was looking at the gear ratios (for 500W motor) and thought that a 44T or 45T chainring would be appropriate. That would be 45/14 = 3.21 ratio to the motor shaft. Including the 9.55:1 planetary gear, 60 rpm at the pedals should be about 1840 rpm at the motor. Their data seem to show that would be about max power. And, a cadence of 100 rpm would be 3060 rpm at the motor, which looks to be about where the efficiency curve starts to taper off. Does the performance curve they advertise not match up with your experience, or do you just prefer the faster cadence?

rhitee05 said:

Are you referring mainly to the higher-power 36/48V systems? I was looking at the gear ratios (for 500W motor) and thought that a 44T or 45T chainring would be appropriate. That would be 45/14 = 3.21 ratio to the motor shaft. Including the 9.55:1 planetary gear, 60 rpm at the pedals should be about 1840 rpm at the motor. Their data seem to show that would be about max power. And, a cadence of 100 rpm would be 3060 rpm at the motor, which looks to be about where the efficiency curve starts to taper off. Does the performance curve they advertise not match up with your experience, or do you just prefer the faster cadence?

Click to expand...

At 24 volts the Cyclone motor (with planetary gearbox) freespins somewhere between 3000 and 3500 RPM. This varies motor to motor as I've discovered, and depends on variability of how the motor is timed. Some appear to have more timing advance, some less. I am almost certain that even with the motor tweaked for neutral timing (running the same freespin RPM both CW and CCW), these motors run more efficiently in CCW mode, especially in the high-RPM/low-power regime. I haven't yet figured out why.

So, from 3250 RPM the planetary gearbox reduces the spin by 9.33 to 348 RPM. From there it is geared down further to the crank by 14/54, the ratio of the 14t freewheel to my 54t chainring. That gives 90 RPM. The efficiency peak is about 80% of the freespin RPM, which is 72 RPM at the crank. Maximum motor power is around 55 RPM at the crank.

With 36 volts the motor freespin RPM will be 1.5 times that of the 24 volt system, and at 48 volts freespin RPM will be twice that of the 24 volt system, making the latter dangerous to connect to a non-freewheeling crank.

If I change the 54t chainring out for a 44t, the crank will spin at 111 RPM at motor freespin, 90 RPM at the motor's efficiency peak, and about 65 RPM at the power peak, roughly. This is O.K. if you like to spin. But, due to the higher crank RPM the hazard, small though it is, of being struck by a spinning pedal that has come detached from one's foot is, I believe, greater.

Unless you want to push the power envelope and are willing to accept the disadvantages (decreased reliability, difficulty matching motor/pedaling efficient cadence, etc.) I would stick with the 24-volt systems. I believe these motors are designed to run best at 24 volts nominal (between 23 and 29 volts actual) when properly geared down to match the load. I've been using both 360-watt and 500-watt motors this way for years now in a variety of conditions, and while they do have shortcomings (e.g. noise) and lose some efficiency through the gearbox compared to a single chain & sprocket reduction, they have held up well, never once shutting down on me due to overheating, in spite of the controller being inside the motor.

For best all-around use I recommend either the 360-watt or 500-watt motors, depending on the design objective. These two motors are physically different. The 360-watt motor is a smaller motor than the 500-watt. I would avoid the lower-powered motors as these are all built on the 360-watt motor but use a controller that limits the current progressively. The "650-watt" kit with external controller uses the same motor as in the 500-watt kit but moves the controller to it's own external chassis and increases the current limit.

If you want extra power but don't want to give up reliability and the ease of gearing it to pedaling cadence, then try Cyclone's "650-watt" kit that uses an external 24-volt controller that appears to be current limited at 50A (the controller box says pessimistically, "30A"). Maximum output power to the rear wheel with this kit is about 700 watts (max. input power is about 1150 watts), which is more than enough if you're designing for meaningful human contribution to power. The main downside of the external Headline controller is that the chassis is inconveniently large for mounting on a bike.

For photo albums and efficiency curves see:
http://tinyurl.com/55fnkc

You make an excellent point about the free-running speed of the motor. It would be a good idea to base the gearing on that speed, so the motor can never go faster than your feet. Thanks for the tip. Great pictures and data on your site, too! This is starting to come together nicely...