MidMacMod (Mid-drive Mac motor Mod)

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MidMacMod (Mid-drive Mac motor Mod)

Postby j3tch1u » Fri Oct 17, 2014 3:16 am

2014-10-13 00.13.03 sml.jpg
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modded 12T mac hub motor mounted at the BB, fan cooled, shaft drive with pass-thru crank axle. initial tests indicate +3kw peak, 2kw continuous. driven by custom FOC controller (200A phase). drives a sturmey archer cs-rk3 (3sp internal, 8sp cassette).

more pictures and write-up to follow..
Last edited by j3tch1u on Sat Oct 18, 2014 2:02 pm, edited 1 time in total. View post history.
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Re: MidMacMotMod (Mid-drive Mac Motor Mod)

Postby j3tch1u » Fri Oct 17, 2014 3:17 am

the goal of this project was to convert a 12T Mac front hub motor into a bottom bracket mid-drive unit. the Mac is a nice choice because it utilizes a one-way clutch. when converted to shaft-drive, the clutch isolates pedal input from the motor cogging. originally i used an 8T but found that the motor ran too fast relative to pedal cadence since we are increasing the speed ratio through the bike gears.

i reused/modded as much of the hub as possible, resulting in only 3 custom parts--the stator fixing plate (aka heat-bridge), output drive flange and mounting shell. the unit bolts onto a cylindrical shell that is welded to the bike. this places the unit cleanly behind the chainring. the aluminum shell and bike frame also sinks a lot of heat from the motor as evidenced by the tentative touch test.

the test-mule that you see in the pictures was put together with spare parts that i had on hand. it will get a nice coat of paint and some shiny new parts after testing is done.

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Last edited by j3tch1u on Sat Oct 18, 2014 10:14 am, edited 3 times in total. View post history.
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Re: MidMacMotMod (Mid-drive Mac Motor Mod)

Postby j3tch1u » Fri Oct 17, 2014 3:17 am

hub shell. machined off the spoke flanges. later on, drilled and tapped mounting holes radially around the flanges where the aluminum is thickest (not shown in picture).

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stator fixing plate (aka heat bridge). fixes the stator to the left side cover. makes use of the original holes on stator for the wire cover plate. bearing supports the BB spindle. replaces the original bearing on side cover (this one is beefier). made from solid aluminum and maximized in size to sink a lot of heat.

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internal clutch. thru-holes drilled to mate with pins on output flange.

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output flange and chainring. instead of bolting directly to clutch (too rigid), couples to the clutch via hardened steel pins. allows a degree of tolerance (tightening crank bolt affects the depth of engagement) and protects clutch from axial distortions when pedalling. also makes installation/servicing easier.

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right side cover. bearing and disc brake area machined out for larger skirt bearing. output flange rides on this bearing effectively supporting the BB spindle (since it is fixed to the crank freewheel and output flange).

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output flange peeking out from the right cover (does not have the pins in this picture). disregard the needle bearing as well (found it wasn't needed).

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crank freewheel (external clutch). i don't like the clickety-click of a freewheel when the motor is running so i used a 2nd clutch instead. it has threads cut for freewheeling crank arm. now comes the tricky part. the clutch rotation must be reversed. i did it the hard way by milling new (tiny) grooves in the pawl carrier for the pawl springs so i could reverse the pawls. turns out, a simpler way would be to machine a new V groove on the outer flange (for the clutch bearings) and just install it backwards. now you know how to reverse a Mac clutch and make a bullet-proof, silent freewheeling crank! oops almost forgot, also had to knock out the gear pins and drill a few more bolt holes for the output flange.

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lost a few springs, so just used some wire insulation instead. ghetto you say? doesn't matter, i make maybe 200W to the pedal at most :oops:

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also machined out the back for freewheel removal tool. big OOPS on the pocket at 9 o'clock.

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man, this unsaved post is soo long i'm afraid i'm gonna lose it. to be continued (on another post) :lol:
Last edited by j3tch1u on Thu Oct 23, 2014 9:59 am, edited 2 times in total. View post history.
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Re: MidMacMotMod (Mid-drive Mac Motor Mod)

Postby spinningmagnets » Fri Oct 17, 2014 8:08 am

Very Impressive! I can't wait to see how it turns out...

http://www.sturmey-archer.com/products/hubs/cid/8/id/59.html
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Re: MidMacMotMod (Mid-drive Mac Motor Mod)

Postby waynebergman » Fri Oct 17, 2014 10:41 am

Wow cool. Looks like you have unpinned the stator from the axle and made your BB spindle part of your axle. I hope you can share some of the motor mods with some photos for us. Very pro with the phase and hall wire exits out the side. Awesome!
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Re: MidMacMotMod (Mid-drive Mac Motor Mod)

Postby kfong » Fri Oct 17, 2014 6:52 pm

Nice job Ben, good seeing more work coming out of your shop.
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Re: MidMacMotMod (Mid-drive Mac Motor Mod)

Postby Avitt » Sat Oct 18, 2014 12:26 am

Do you have any experience running that much power through a SA 3-speed IGH? I'd be very concerned about sheering off the axle key.
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Re: MidMacMotMod (Mid-drive Mac Motor Mod)

Postby j3tch1u » Sat Oct 18, 2014 9:21 am

duly noted. i've blown up a few IGH on Dogati running higher power levels. this SA-3 is going to be strictly reserved for the steepest of hills (most motored shifting will be on the cassette).

3d printed chain guides to prevent derailment from high speed shifts:
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Avitt wrote:Do you have any experience running that much power through a SA 3-speed IGH? I'd be very concerned about sheering off the axle key.
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Re: MidMacMotMod (Mid-drive Mac Motor Mod)

Postby j3tch1u » Sat Oct 18, 2014 9:28 am

not exactly. i have removed the original axle completely and have a drive flange connected to the inner clutch ring. the BB spindle is completely isolated from the motor. it will become more clear in the write-up.

waynebergman wrote:Wow cool. Looks like you have unpinned the stator from the axle and made your BB spindle part of your axle. I hope you can share some of the motor mods with some photos for us. Very pro with the phase and hall wire exits out the side. Awesome!
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Re: MidMacMotMod (Mid-drive Mac Motor Mod)

Postby panurge » Sat Oct 18, 2014 9:49 am

Wow! That's super cool....this will be a serious competitor for any system.....
Looking forward to know everything about it!!!
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Re: MidMacMotMod (Mid-drive Mac Motor Mod)

Postby j3tch1u » Sat Oct 18, 2014 10:25 am

that is the challenge! to be more powerful, cheaper, stealthier and better looking than any other system. i also detest complex, proprietary mounting interfaces designed for hegemony and profit :P this interface uses a simple circle that anyone can fit using a cardboard template and angle-grinder (it is also impossible to patent the Circle).

panurge wrote:Wow! That's super cool....this will be a serious competitor for any system.....
Looking forward to know everything about it!!!
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Re: MidMacMotMod (Mid-drive Mac Motor Mod)

Postby panurge » Sat Oct 18, 2014 11:00 am

So consider I'm yet thinking about a frame for It :D
Uh, ah! what sort of frame is that? I see a QR in an unconventional position, It is foldable I guess, for just a moment I figured out a softail's lock/unlock system.... :mrgreen:
You are an artist, man.....

P.S. Do you know Achiever Bikes? It is nothing concerned to that but the coaxial design and the circle mount....A bit smaller, perhaps...but 1/10 the power.....
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Re: MidMacMotMod (Mid-drive Mac Motor Mod)

Postby j3tch1u » Sat Oct 18, 2014 12:24 pm

frame is not mine. it is a taobao special (aka copyright bait). taobao is like aliexpress but with honest (ie. lower) prices for chinese speakers. learn chinese, save more money HAHA! :mrgreen:

never heard of them before. but i'm not likely to achieve to get up the hill to my home with those modest watts :D i think the perfect size for a BB mid-drive is exactly the diameter of the chainring (not smaller nor larger). in my case it is a 42T.

panurge wrote:So consider I'm yet thinking about a frame for It :D
Uh, ah! what sort of frame is that? I see a QR in an unconventional position, It is foldable I guess, for just a moment I figured out a softail's lock/unlock system.... :mrgreen:
You are an artist, man.....

P.S. Do you know Achiever Bikes? It is nothing concerned to that but the coaxial design and the circle mount....A bit smaller, perhaps...but 1/10 the power.....
Last edited by j3tch1u on Sat Oct 18, 2014 1:15 pm, edited 2 times in total. View post history.
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Re: MidMacMotMod (Mid-drive Mac Motor Mod)

Postby j3tch1u » Mon Oct 20, 2014 8:32 am

spinningmagnets wrote:Very Impressive! I can't wait to see how it turns out...

http://www.sturmey-archer.com/products/hubs/cid/8/id/59.html


yep, that's the one. thanks ron for the prior research you did on this motor--it gave me the idea.
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Re: MidMacMod (Mid-drive Mac motor Mod)

Postby spinningmagnets » Mon Oct 20, 2014 10:19 am

thanks ron for the prior research you did on this motor


I only converted one for the fun of it, and to document the process with pictures so others can more easily convert one themselves. izeman is now using the motor I converted, and I am very happy to see others experimenting with this. I give all the credit to crossbreak for showing that this is possible, and identifying the BPM and the MAC as the most viable candidates.
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Re: MidMacMod (Mid-drive Mac motor Mod)

Postby j3tch1u » Mon Oct 20, 2014 3:30 pm

spinningmagnets wrote:
thanks ron for the prior research you did on this motor


I only converted one for the fun of it, and to document the process with pictures so others can more easily convert one themselves. izeman is now using the motor I converted, and I am very happy to see others experimenting with this. I give all the credit to crossbreak for showing that this is possible, and identifying the BPM and the MAC as the most viable candidates.


oh sorry, it was crossbreak's thread viewtopic.php?f=28&t=45245
that actually got me thinking about this :oops: must have read it on electricbike.com as well.
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Re: MidMacMod (Mid-drive Mac motor Mod)

Postby liveforphysics » Mon Oct 20, 2014 5:35 pm

Beautiful work as usual my friend!

How does the riding experience compare?
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Re: MidMacMod (Mid-drive Mac motor Mod)

Postby oatnet » Mon Oct 20, 2014 5:41 pm

Beautiful, elegant, I love it. Thank you for sharing it!

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Re: MidMacMod (Mid-drive Mac motor Mod)

Postby j3tch1u » Mon Oct 20, 2014 9:06 pm

liveforphysics wrote:Beautiful work as usual my friend!

How does the riding experience compare?


i am glad you asked my friend :D

handling. compared with all my other bikes, this one handles the most like a regular bike. steering is noticeably quicker without the gyro effect from the two spinning motor masses. although, at higher speeds the 2wd feels safer. this bike is approx 5kg lighter. the c.o.g. just about makes it invisible. i can almost bunny hop this thing. endos and wheelies almost like my old 82' chromoly red-line bmx :) RL Osborne is the man!

acceleration. not as fast as dogati or duty cycle 2wd but still feels like a slingshot in the first couple of gears. with the addition of the dual chain guides, shifting is very reliable and bang on each time. i let off the throttle just long enough for the forward momentum of the drive-train to spin the chain into gear (my twist shifter and throttle are on the same hand). the internal 3-spd shifts fine this way as well (though i don't wanna push this hub).

top speed. not sure yet cuz i'm still configuring this new FOC controller /w field weakening. using the old 12-FET infineon on an 8T stator, top speed was around 7kph slower than the 2wd. haven't top speed tested the 12T stator yet.

hill climbing. makes it up the super steep slope near my house but works harder and climbs slower than my 2wd bike with the same battery. i've really gotten spoiled riding the 2wd.

pedalling. easiest to pedal cuz it's lighter. however, the motor:pedal cadence is still a little high even with the 12T. if i wanna assist with my legs, it won't be in the most efficient gear for the motor. with the hub motors it doesn't matter.

stealth. duty cycle hardly got any "i know that's an ebike look". but then peeps here are pretty clueless. after this bike is done, i don't think it will draw any attention at all. with the open side cover, driving this thing in 6-step is loud enough to disturb my "connecting with nature" experience. in FOC it is nearly dead silent--quieter than my 2wd in 6-step. my crank freewheel is silent as well. gotta hand it to Mac for the very noiseless clutch.

looks. dogati, hands down.

fun. as with driving stick, it's fun to hammer out the gears..sometimes.

if i had to choose between dual hub motor and mid-drive, now i'd have to say 2wd. the duty cycle with 200A pack and dual FOC controllers would still be my preferred urban utility, mountain exploration and cross-country vehicle--gives me peace of mind and just works. the dogati would be for the weekend, night-time sprints through downtown. duty cycle mid-drive..when i'm out riding with non motorized cyclists and want to remain incognito.

and that is the "trews" my friend :mrgreen:
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Re: MidMacMod (Mid-drive Mac motor Mod)

Postby j3tch1u » Thu Oct 23, 2014 3:20 am

continuation from the last post.

freewheel screwed onto crank:

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chainring and output flange installed on freewheeling crank (very modular):

2014-10-12 22.14.29.jpg
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Re: MidMacMod (Mid-drive Mac motor Mod)

Postby j3tch1u » Thu Oct 23, 2014 3:30 am

standard BB spindle machined down to 15mm OD in order to pass thru rotor and clutch. slip fit with bearing on stator bridge. although it is not shown in this picture, there are also two notches for the retaining rings (located on either side of the stator bridge bearing).

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Re: MidMacMod (Mid-drive Mac motor Mod)

Postby j3tch1u » Thu Oct 23, 2014 4:07 am

25mm fans added to left side cover. considered using those crazy wild turbo fans (http://www.wildturbofan.com/) but i was worried they might be too loud. instead i used sunon MC25100V2 (http://www.digikey.com/product-detail/e ... ND/2757806). decent 3.0cfm, much cheaper and very quiet 16db due to their vapo-bearing maglev technology: http://www.sunonusa.com/pdf/VapoBearing ... nology.pdf

in order to fit between the stator and cover, i used my mini lathe to machine the front faces of the fan so that they are circular and sit recessed into the cover 5mm (sorry, forgot to take pics). the two fans sitting above the halls and phase wires are recessed 1 extra mm. i turned the fans using a very low speed and used a live center to keep them from being pulled out of the chuck (which is very lightly tightened).

wired all six in parallel and run them off a separate dc-dc 5v regulator.

also made a mini version of the phase cover on Mission RS motorcycle using my ultimaker2 3d printer. material is red abs. acetone vapor treated version at the bottom of the picture. I've attached the solidworks and stl files in case anyone wants to print their own.

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[The extension rar has been deactivated and can no longer be displayed.]

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Re: MidMacMod (Mid-drive Mac motor Mod)

Postby izeman » Thu Oct 23, 2014 7:51 am

damn. and i thought i had the coolest mac mid drive converted bike ;)
that's a very nice piece of art. very well done. i'd like to ride it and compare it to my bike. how is motor noise (not the fans)? i'm REALLY happy with my motor (can't get it over 90°C even riding it at 2kW+ for over an hour) but the high pitch noise is all but stealthy. could you please post a video with the motor running alone, and one with the whole drivetrain + chain connected.
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Re: MidMacMod (Mid-drive Mac motor Mod)

Postby j3tch1u » Thu Oct 23, 2014 8:47 am

hi izeman, i will definitely have to check out your build. i shot a video with the bike on the stand but it doesn't sound at all like this when there is a load. i'll try to get a recording on the bike. in FOC there is no high pitched whine or growl from torque ripple. all i hear are the fans and chain (sound of chain is not that bad once there is tension). 6-step is much louder especially if your side covers are open. i can see why you are bothered by it.



izeman wrote:damn. and i thought i had the coolest mac mid drive converted bike ;)
that's a very nice piece of art. very well done. i'd like to ride it and compare it to my bike. how is motor noise (not the fans)? i'm REALLY happy with my motor (can't get it over 90°C even riding it at 2kW+ for over an hour) but the high pitch noise is all but stealthy. could you please post a video with the motor running alone, and one with the whole drivetrain + chain connected.
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Re: MidMacMod (Mid-drive Mac motor Mod)

Postby spinningmagnets » Thu Oct 23, 2014 8:58 am

The crank freewheel made from the MAC's internal freewheeling sprag clutch is brilliant. izemans MAC mid drive was using 3000W-ish and sometimes the clutch would get stuck (fixed in both directions). He lowered the power to 2,000W and it is reported to be running fine ever since. https://www.electricbike.com/hannes-cro ... mid-drive/

Regardless of the power used, I am interested in a silent freewheeling BB crankset. In the izeman/crossbreak configuration, the motor bypasses the crank freewheel, so using a high-powered but "clicky" and expensive ENO in the crankset would no longer be necessary, but...as the rest of a drive gets very quiet, it is a nice luxury to have an almost silent system. The MAC clutch being re-purposed for a freewheeling crank would be overkill for a crossbreak-style, but...they are only $25 (plus tax/shipping) http://em3ev.com/store/index.php?route= ... uct_id=110
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