Crankin' It - Mid-Mounted Crank Drive

Discussion in 'Electric Bicycles' started by DrkAngel, Jan 20, 2014.

  1. DrkAngel

    DrkAngel Member

    For years now, I have been considering a mid-mounted freewheel crank drive.
    Running a geared reduction motor through the 7 speed freewheel sprocket, or freehub cassette.
    Most any bike could be converted, adding less than 10lbs of motor hardware. (Battery additional.)

    Stage 1.
    Typically, this involves using a geared reduction motor connected through the front chainring.

    A big improvement over most any type eBike drive!
    With a 11-34T 7spd freewheel you can have the equivalent of a 7 speed motorcycle, with +300% the torque at low speed.
    Great low speed torque and high speed assist ... right to 30mph(?) ... from the same motor!

    Stage 2.
    An important option is a 2 chainring freewheel crank.
    This allows motor power without pedals being turned ... much safer!

    There is the variable of matching motor to pedal speed.
    The size of the 2 chainrings can be varied, and / or voltage adjusted, to match your rhythm.

    Stage 3.
    The next stage option is a freewheel sprocket, instead of a fixed sprocket on the motor, this allows easy pedaling when motor not engaged.

    My project motor is the Unite MY1018z gear reduction motor.
    I've poked-prodded-tested and tried this model for ~20,000 miles.
    As a demonstration,
    I graphed the speed and torque available from running the motor through the 7 speed sprockets.

    MY1018z motor @24V w/9T sprocket
    At 24V Low gear (34T) will give you great power-acceleration till 7mph, great for the worst hills.
    Then, there are a variety of optimal hill climbing, or acceleration, choices till about 16mph.
    Of note is that a 34-13T would limit maximum speed to the "legal" 20mph.


    I just finished purchasing the individual components and will continue to post build reports.

  2. DrkAngel

    DrkAngel Member

    Motor Frewheel

    Previous graph is for the MY1018z 24V motor with the OEM 9T sprocket.

    Stage 3.
    In order to operate pedals without using the motor the use of a freewheel sprocket on the motor is required.
    The smallest compatible freewheel sprocket I've found is a 13T.
    Of course, this will vary the motor applied speed noticeably.

    MY1018z motor @24V w/13T sprocket

    Sadly, this loses much of the low speed torque advantages of a multi-speed mid-drive, might be OK on a 20"er?
    On the other hand...
    In lowest gear as I am accelerating from a red light, I hit 10mph at my max pedal speed.
    So I would be shifting right at maximum torque of motor and pedal assist, maybe ... not so bad.

    Personally, I could be happy with a 9T sprocket with motor always engaged and pedal assist.
    Optimally shifting at a more casual 60-70 pedal rpm.
    A larger chainring from the motor can offset some of this loss.
    With an intermediate jackshaft, most any gear ratio can be accomplished.

    Stay tuned for more developments ...
  3. Fabian

    Fabian Well-Known Member

    I am eagerly awaiting the "new developments".
  4. DrkAngel

    DrkAngel Member

    Crank Drive Build #1 - Stage 2

    Huffy dual-suspension mountain bike
    Dual chainring freewheel crank (40T/40T will change after testing)
    33.3V 25.92Ah 9s12p homemade recycled Lipo battery
    Unite MY1018z 24V (450w) gear reduction motor w/9T sprocket (624w@33.3V)

    MY1018z motor @ 33.3V though DNP 34-11T 7spd Freewheel

    I think this to be nearly ideal for my 1st trial
    90rpm pedal speed looks to match optimal shift points at full throttle
    Partial throttle can move optimal shift points towards a more casual 60rpm.

    Low gear torque is excellent, and top motor only speed looks to be ~26-27mph
    Lowering seating profile or moderate pedal assist should make 30mph possible.
  5. DrkAngel

    DrkAngel Member

    Stage 4.
    Important, IMO, is the survivability of the drive train!
    Shifting under throttle will produce a (un)healthy "clunk" ...
    an impact on all drive train components: motor > chain > chainring > chain > 7spd freewheel > hub

    This "damage" can be moderated by not shifting while under throttle, release throttle before shifting then gradually re-engage.
    This works but kinda degrades performance ... substantially!

    So, I propose the addition of a heavily sprung idler roller.
    Place behind the chainring, pushing chain down, roller should be ~ 50% sprung under full throttle.
    Instead of a shift inducing a straight line immediate impact the "impact" will be spread over the unsprung distance the idler provides.
    "Impact" might be reduced 90%(?), providing a great increase in durability-reliability!

    [​IMG] - $4.74

    Surprising to most, there is minimal abuse or wear on the Bottom Bracket!
    With motor positioned in front of the BB, motor to BB abuse is evenly offset by BB to wheel abuse.

    The exception being the crank freewheel bearing which must endure a constant twisting, worse under heavy throttle.
    This "twisting" abuse could be largely eliminated.
    The use of an intermediate jack shaft positioned directly behind the BB, (if there is room), inside the wheel chain path, would even up the stress on the freewheel crank bearing.

    But, of course, doing this would apply greater stress on the BB bearing ...
  6. Fabian

    Fabian Well-Known Member

    This is sounding like a very interesting thread.
  7. DrkAngel

    DrkAngel Member

    Crank Drive - Parts-n-Such

    Some Components:

    SunRace 13-34T MegaRange - $16.99 shipped

    DNP Epoch 7spd 30-32 to 11T Freewheel - $34
    Upgrades EZip w/44T Front Sprocket to near 30mph pedal assist (90 crank rpm)
    More sizes - 11- 28,30,32,34T - $32

    Quality ACS Freewheel for freewheel crank! $16.50
    BCD not specified ... might bolt directly to certain chainrings?
    Also available _ more components, from

    Freewheel Cranks - Choices ... >$32

    450w 24v, gear reduction motor, standard 1/2" x 1/8" chain (MY1018Z) - $95 + shipping

    The "silent" motor (well ... not real loud)
    XYD-16 motor w/mounting bracket - $108.89 - Will try to find working link
  8. Fabian

    Fabian Well-Known Member

    I haven't had a positive outcome with the low cost freewheel design as shown in your post photo. They chop out rather quickly with excessive bearing freeplay.
  9. DrkAngel

    DrkAngel Member

    Freewheel cranks

    Got 1, then got a spare.
    These are some unknown items with original source unknown, so don't ask me.

    Got a double chainring, then a discount on a single.
    All 3 chainrings are 40T, ... OK for initial trials.
    They have an offset so that there is a nice spacing, but with a single, flipped over, chain is positioned directly over the center of the freewheel. This should eliminate the "twisting" stress common with the doubles and greatly extend usable life.

    I believe I will try the single ...
    Positioning the motor sprocket in front of and below the chainring, I will stretch, or lengthen the chain around a single path, ensuring a ~120 degree motor sprocket contact.


    Freewheels are the Pheasant brand ... the equivalent of what we would call a turkey ... but I have an ACS Crossfire for when it fails.
  10. DrkAngel

    DrkAngel Member

  11. DrkAngel

    DrkAngel Member

    450w (24V) Gear Reduction Motors (Brush) - thin profile
    25.9V = 485w
    29.6V = 555w
    33.3V = 625w ... partial throttle at low speed recommended to be more efficient and to reduce damaging heat
    37V = 695w ... reduced amperage controller (or throttle restraint) recommended to reduce low speed heat damage
    44.4V = 835w ... reduced amperage controller (or throttle restraint) recommended to reduce heat damage
    48.1V = 900w ... reduced amperage controller (or throttle restraint) recommended to reduce heat damage and prevent shearing the sprocket key

    - Confirm with seller! White label States XYD-16 and "C" on cover - 7th item down

    Triangle on Cover
  12. DrkAngel

    DrkAngel Member

    Single Chainring Advantages - Disadvantages

    Eliminates the twisting (off-center) stress-wear on the crank freewheel = greatly increased reliability-usable life
    Reduced cost! "Standard" crank freewheel with single centered chainring will survive longer or as long as super duty freewheel with multiple chainrings

    Negates the possibility of shifting between multiple front chainrings
    Eliminates the variance of chainring sizes to match motor to pedal speed.
    Doesn't look as complex = doesn't impress the simple minded as easily

    Perhaps not obvious ... It is still possible to modify motor and pedal speeds

    Motor speed can be varied either by:

    Changing the size of the motor sprocket

    The Currie motors, MY1018 & XYD-16, have 8T,9T,11T,13T available (mod-able 15T also found)
    Adapter is available for 13T-14T-15T small freewheels
    Additional adapter is available for the "standard" 16T - 22T freewheels

    Changing the voltage of the motor
    At 24V, gear reduced (sprocket) speed is ~400 rpm
    22.2V = 370 rpm
    24V = 400 rpm
    25.9V = 432 rpm
    30V = 500 rpm
    33.3V = 555 rpm
    37V = 617 rpm
    40.7V = 678 rpm
    44.4V = 740 rpm
    48.1V = 800 rpm

    Then ... rear sprocket can be adjusted
    14-34T to 11-28T to 21-26T 7-speed freewheels (or cassettes) available

    Front Chainring
    Now you adjust your pedal ratio by changing the single chainring ... 32T - 62T+.
    This has no effect on the motor speed ratio! ...

    Motor speed is now determined by motor sprocket to rear wheel sprockets ... not by chain ring.
    Chainring is effectively an idler sprocket for the motor contribution, varying the size has no relation to motor speed.

    I do not see any reason to use dual chainrings of equal size ... ?
    I have 2 - dual 40T and 1 - single 40T.
    Advantage of chain contacting 20T rather than 10T?
    I can't justify that as any reasonable advantage ...

    So, I will likely post up, at least, 2 40T chainrings with "standard" 5 hole - for ACS CrossFire etc. - Appear new - steel.
    Or swap for compatible 44T 48T ... other?
    Last edited: Feb 3, 2014
  13. DrkAngel

    DrkAngel Member

    Chainring selection

    24T does not offer the recommended "offset"

    24T, 30T, 36T, 44T, 48T -

    I'm surprised at the lack of a 40T chainring, 36 to 44T is a pretty drastic jump, limiting fine tuning motor to pedal speed.

    It should be reasonably simple to build an adapter from the common 5 hole freewheel to the 130 or 144 BCD chainrings.
    The adapter would supply the desired offset to any flat chainring.
    This would enable a large selection of readily available chainrings ... up to 62T+?
    Larger chainrings might create increased "twisting" wear on dual chainring setups but single setups should suffer no additional stress.
  14. Fabian

    Fabian Well-Known Member


    Using the SickBikeParts optional low range jackshaft gearing 9T - 48T, you really need a 40T chainring to bring the gear ratio back where it needs to be. The 36T isn't really suitable in that situation, hence i have to purchase another jackshaft freewheel bearing system from another manufacturer which happens to have a 38T chainwheel, just so i can get the 38T sprocket.
  15. DrkAngel

    DrkAngel Member

    Bargain I couldn't pass up!
    A Schwinn Front Freewheel (FF) crankset


    Circa ... late 70's, this item was touted as "a solution ... in such of a problem!"


    Interesting to me, the freewheel seems to possibly run, at least partially, against the BB bearing race.
    Dependent on actual construction, this could bypass some of the problems with modern freewheel chainring crank systems.


    Just had to get it, cost less than $25 including shipping.
    I will post up evaluation after arrival.

    Better picture shows freewheel bearings to be easy to keep lubricated and adjustable.
    Durability looks to be a big improvement over "modern" methods!

  16. Fabian

    Fabian Well-Known Member

    That Schwinn Front Freewheel (FF) crankset is a nice looking unit, and appears to be a full compliment bearing housing.

    The SickBikeParts higher end Heavy Duty freewheel bearing system (made by White Industries) is the best component i've used, when compared to the standard duty freewheel bearing versions which in my opinion (and going from personal testing of two different manufacturers) is not a particularly durable bearing system in operation, despite the fact that by design, it should be a better system than the White Industries freewheel. Ironically, the White Industries freewheel (even though it uses a single bearing) can take a heck of a lot more punishment and maintain significantly better sprocket stability than the cheaper dual bearing design.

    From what i understand White Industries is going to release a "dual bearing system" for their heavy duty freewheel, which should make it an even more effective sprocket drive system. Unfortunately we might have to up to 2 years before the dual bearing design is released.
  17. DrkAngel

    DrkAngel Member

    Hot Damn!
    Schwinn freewheel crank arrived.
    A 37 year old item in excellent condition! (1977)
    No noticeable wear on the chromed teeth and no traces of rust near the bearings.
    Freewheel is nice and tight and smooth ... best of all it is adjustable.
    It can be tightened up after it wears a bit.

    I do believe that a single chainring is preferable.
    But this looks to have good potential as a double ... if I ever go that way.

    Now just gotta find the "proper" bike to transform.
    My Schwinn Searcher 700C, (rescue bike), looks to be the prime candidate.
    14-34T 7speed looks appropriate for the 52T chainring @ 33.3V.
    Steel frame gives good motor mount options.

    Will probably build a cheap Mountain bike conversion with cheapo single chainring as my first testbed ... tho.
  18. DrkAngel

    DrkAngel Member

    Just found a 46T Schwinn-Shimano FF 46T Single freewheel crank.
    Perfect for my pedal assist at my preferred 33.3V.

    Newest addition seems advantageous over the dual chainring. Chainring is perfectly centered between the freewheel bearings, eliminating the "twisting" that destroys the dual chainring variant.

    There is a speckling of rust on the chrome, but teeth and bearings appear to be in excellent condition.
    (1978 vintage)


  19. libranskeptic

    libranskeptic Member

    The voltage vs rpm thing is of great interest to me.

    I have a 24v my1018 (which seems a very durable unit) powered bike with a dog of a lead acid battery, and a 12ah 36v ebike with nice panasonic bottle battery that needs upgrading to a 15ah lifepo4 pouch cell battery. It would be neat to use the panasonic 36v as a hand me down on the 24v bike.

    Are you saying i can simply swap the 24v for a 36v and the 24v my1018 & controller will un-protestingly run at higher rpm & presumably with more zip? It seems counter intuitive that the motor and controller are happy with 50% more voltage.

    My plan was to reduce the 36v panasonic battery output to 24v somehow. I have been assured this is simple.

    Your advice would be appreciated.

    fyi, my 24v bike is a longer silverfish type ladies bike with no gears, just a second dedicated chain to a second freewheel sprocket on rear axle.

    It sounds crappy, but there are things to like. a/ the chain can be much stronger and durable than for derailleurs and b/ the pedals are not stuck with the same, probably unsuitable, ratio as the motor. I still don't have much luck finding a gear that suits both on my 36v 24 speed mid drive.
  20. DrkAngel

    DrkAngel Member

    Many 2008 and earlier and some few 2009 eZips are 24-36V+ capable.
    Test by jumpers from battery to pack terminals - insure pos and neg terminals to avoid damage!
    $15 20-50V controller available -eBike Toolbox (requires connector adaptation)