Converting a hubmotor to a middrivemotor

Discussions related to motors other than hub motors.
This includes R/C motors, botttom bracket, roller and geared drives.

Re: Converting a hubmotor to a middrivemotor

Postby crossbreak » Fri Nov 09, 2012 8:16 pm

thx for the link. Sadly there is no sun gear in the pics :? I'd say it should be less than 5:1.
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Re: Converting a hubmotor to a middrivemotor

Postby crossbreak » Mon Nov 12, 2012 10:25 am

Only had three hours to get further since my garden needed some digging on sunday. Got the additional bearing done. Sadly I forgot to take pics, sorry for that. There is not very much work left to get the motor done, so maybe I can already start making the bottom braked mount next sunday - wont forget the pics then.

I'll also try again pulling out the axle from the stator carrier. If that's possible somehow the hole mod would be half the work (and I'd be hopping mad since I already sawed the shaft :mrgreen: ) I'm a bit confused since the factory inserted a key to stop the stator carrier from turning, so it should not be a press fit.

I'm not sure whether I should use a 14T or 15T sprocket. I guess I'll order both, since they are relatively cheap at 5€ per piece. I'll like to further test the drive with 48V and a 11T sprocket, using my 10s lipo with a 12V motorcycle lead battery in series.
Last edited by crossbreak on Mon Nov 12, 2012 10:30 am, edited 1 time in total. View post history.
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Re: Converting a hubmotor to a middrivemotor

Postby crossbreak » Mon Nov 12, 2012 3:39 pm

just found out that the bafang BPM is has only 18slots (it is the same dia as the MAC/BPM if I can trust bmsbattery info), making it maybe preferable for speeding it up over the mac/bpm/puma because of the lower field changing frequency and due this, smaller eddy current losses (if they have the same lamination thickness). I'll try to collect info about speeding up hubmotors in this thread. plz help me doing this. I have no idea of the stator lamination thicknesses of both motors. I just bought a 250W bafang to see how it's opened up, if it may be converted to axle output and to see what the lamination thickness is. Plz help me if you find any info which can helpand post it, thx!
Last edited by crossbreak on Mon Nov 12, 2012 3:40 pm, edited 1 time in total. View post history.
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Re: Converting a hubmotor to a middrivemotor

Postby crossbreak » Thu Nov 15, 2012 6:38 pm

Got the shaft removed from a bafang sxwb. This way the mod seems to be much easier.
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bafang_2.jpg
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Re: Converting a hubmotor to a middrivemotor

Postby crossbreak » Thu Nov 15, 2012 8:22 pm

hub is a bafang swxb 250W 28" 24V. Is has a 17:73T reduction.
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Re: Converting a hubmotor to a middrivemotor

Postby crossbreak » Fri Nov 16, 2012 5:05 am

This is the SWXB stator. It's 25mm thick and made from 0.5mm sheets. The motor has 20p, so the max rpm with acceptable eddy current losses should be around 1200rpm (200Hz field changing frequency). I'll do 1400rpm on it. At lazy 67rpm crank cadence at half throttle i'm right in the place of best efficiency, if i calc right.
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Converting hubmotor to a middrivemotor - got the motor spin

Postby crossbreak » Fri Nov 16, 2012 7:03 pm

Today I got the motor spinning. I'll install another sheet to make the motor mount stiffer. This mod really can be done with home tools only i am certain. On sunday, I will make a mount. Still have to do some rework since the motor is not connected thermally to the hub, only mechanically due the screws.

Love my cell phone cam, even if it sucks sometimes, hope you enjoy it :D
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Re: Converting a hubmotor to a middrivemotor

Postby crossbreak » Fri Nov 16, 2012 7:05 pm

the pic above shows also an early version of the adapter ring ( right down in the pic) , which is actually the part which connects the stator mount with the hub housing (3 holes are missing yet. Sadly took no pic which shows the final product.
This part is the most important one.
If this is not aligned perfectly, the hole mod will not work at all. Fortunately you can perfectly align it using the existing fit to mount it :) my stator turns perfectly (spins freely about 3-4 sec if i turn it b hand), so i hope it will work fine. Hope it will not move under stress (it will after time). In a real live build (not a test) I would now glue the stator, the adapter and the hub housing backplate together to make it fit perfectly.
Last edited by crossbreak on Tue Nov 20, 2012 8:25 pm, edited 2 times in total. View post history.
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Re: Converting a hubmotor to a middrivemotor

Postby crossbreak » Sun Nov 18, 2012 2:21 pm

Finally got it running and installed the thermal conducting bridge (yet without thermal compound) , but the mount and the freewheel adapter are not finished yet. Will follow next sunday. Will just use a cyclone 30mmx1 adapter (20mm inner dia with a single key) and make a 20mmto 12mm adapter.

Made a vid that shows it spinning, it's still uploading. Could spin more freely if I used a polyamide bearing between stator and shaft instead of just lubricant. IMO it got harder to spin the shaft by hand than before the mod. Still, the no-load current draw is below 0.5amps so i can not measure it with the wattsup. I'll make some measurements when it's finally installed.
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trio_1.jpg
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trio_2.jpg
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Re: Converting a hubmotor to a middrivemotor

Postby crossbreak » Sun Nov 18, 2012 2:41 pm

weight of motor (including sprockets, chain and mounting sheet) is almost 4kg

Edit:
Motor to crank reduction is 44/13*(73/17+1)=17.92
so motor speed is 1434 rpm @ 80rpm cadence

compared to GNG:
Motor to crank reduction is 44/12*80/14=20.95
so motor speed is 1676 rpm @ 80rpm cadence
total weight is 4.3kg+primary chain


cost breakdown (all shipped):
bafang SWXB motor: €37
cyclone freewheel adapter: €18
13T freewheel: €8
chain: €8
sheets, bars and screws: <€25
Ku123 controller 36V/30amps: €30
total: €126
Last edited by crossbreak on Sun Nov 18, 2012 3:14 pm, edited 1 time in total. View post history.
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Re: Converting a hubmotor to a middrivemotor

Postby crossbreak » Mon Nov 19, 2012 9:08 am

Got rid of the axle friction i mentioned yesterday. It was caused by the stator carrier touching the snap-ring which axially aligns the bearing at the motor side. I have dremeled down the stator carrier about 2mm and have inserted a 0.2mm shim. Now the frictions gone, I can turn the axle easily by hand.

So the stator carrier must be released from the axle both radially (by removing the key) and axially (by dremeling it down) to make it spin freely.

Also managed to fit the cylone sprocket by inserting a brass bushing, it still needs setscrews, i'll use four M4 screws.
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bafang_shortened_carrier.jpg
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Re: Converting a hubmotor to a middrivemotor

Postby Whiplash » Mon Nov 19, 2012 10:11 pm

OK so a quick rundown on the new version would be helpful. I am considering doing this to my Mac to simplify, lighten and redo the gearing setup to delete the high stressed freewheel crank. So if you could do a step by step that would be great! I'm having s hard time understanding how the planetary gearbox portion still functions correctly. It seems like if you just remove the keys, then yes the axle will spin, but how does it reduce the RPM?
Power is a fascinating thing, the more you have, the more you want, but the real power is having the restraint not to use it all at once...............Um...Yeah..

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Re: Converting a hubmotor to a middrivemotor

Postby waynebergman » Mon Nov 19, 2012 10:19 pm

Great that you are going to tackle this one with your mac Whiplash. I also have mac that has a broken key and slightly burnt phase wires. Actually I cut into the phase wires with a gear puller as well so this old motor now out of commission may also be a good candidate for this. I will be following with interest how this one pans out for you both. Awesome!.......and thanks for sharing.
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Re: Converting a hubmotor to a middrivemotor

Postby Whiplash » Mon Nov 19, 2012 10:47 pm

I am mostly doing this to see if its a viable option for the MAC since it will greatly simplify the mounting of the motor MID style and should significantly reduce weight due to lighter brackets. I am hoping this mod coupled with oil cooling will allow the power I am looking for to get around 40mph sustained speed capability since having the motor fixed rather than turning should make it easier to heat sink it to the bike frame... I am slowly working toward a custom aluminum frame that will do all of the above!
Power is a fascinating thing, the more you have, the more you want, but the real power is having the restraint not to use it all at once...............Um...Yeah..

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Re: Converting a hubmotor to a middrivemotor

Postby crossbreak » Tue Nov 20, 2012 8:22 am

Whiplash wrote:I'm having s hard time understanding how the planetary gearbox portion still functions correctly. It seems like if you just remove the keys, then yes the axle will spin, but how does it reduce the RPM?


This article describes the function of a planetary transmission: http://science.howstuffworks.com/transport/engines-equipment/gear7.htm

In geared hub motors, the reduction is: (tooth count of ring gear)/(tooth count of sun gear), since the planet carrier is fixed. If you now fix the ring gear, the reduction ratio is increased by one since the direction of movement is reversed

There was once a complete table with all cases on Wikipedia, some fool deleted :( . I should have saved this table once. The german version still has a table, hope you can read ("Sonnenrad fest" means sun gear fixed, "Steg" means planet carrier, "Hohlrad" means ring gear): http://de.wikipedia.org/wiki/Umlaufr%C3%A4dergetriebe#Kinematik

I'm glad to see i'm not the only one who will try this. Guess a converted MAC plays a league above my bafang or the GNG Gen2

For oil cooling your heat bridge plate would best be a short circuit spiral heat exchanger (the inner connections 1 and 2 would be short circuit), do you know someone who can mill such a heat exchanger?
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Re: Converting a hubmotor to a middrivemotor

Postby crossbreak » Tue Nov 20, 2012 8:29 am

Instead of milling a lightweight alloy heat exchanger, you could also use square copper pipes and bend them to a spiral
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Re: Converting a hubmotor to a middrivemotor

Postby crossbreak » Tue Nov 20, 2012 8:49 am

Whiplash and waynebergman, could one of you be so kind to disassemble the motor, take out the rotor and take some pic's so we can figure out the best solution? Be careful when you take off the rotor, the strong magnets can hurt you easy, wear motorcycle gloves if you do so.

Here is a pic that already helped me to imagine how it might work:
Image
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Re: Converting a hubmotor to a middrivemotor

Postby Miles » Tue Nov 20, 2012 8:58 am

crossbreak wrote:There was once a complete table with all cases on Wikipedia, some fool deleted :( . I should have saved this table once. The german version still has a table, hope you can read ("Sonnenrad fest" means sun gear fixed, "Steg" means planet carrier, "Hohlrad" means ring gear): http://de.wikipedia.org/wiki/Umlaufr%C3%A4dergetriebe#Kinematik
I traced back to the revision from the date I posted the link:
http://en.wikipedia.org/w/index.php?tit ... =450074822

Thank goodness the history is retained :)
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Re: Converting a hubmotor to a middrivemotor

Postby Whiplash » Tue Nov 20, 2012 9:15 am

Hmm very interesting indeed! I never knew fixing different parts of a planetary gearbox produced different ratios! hat being the case, this should work even better than I had originally thought! If I understand correctly if I start with a 5:1 ratio, fixing the outer hub will deliver 6:1? That's great because I am hoping for lower gearing doing this!
Power is a fascinating thing, the more you have, the more you want, but the real power is having the restraint not to use it all at once...............Um...Yeah..

The harder you work.....The luckier you get!!

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Re: Converting a hubmotor to a middrivemotor

Postby Miles » Tue Nov 20, 2012 9:22 am

Whiplash wrote:If I understand correctly if I start with a 5:1 ratio, fixing the outer hub will deliver 6:1? That's great because I am hoping for lower gearing doing this!
Yes. That's correct.
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Re: Converting a hubmotor to a middrivemotor

Postby Whiplash » Tue Nov 20, 2012 9:31 am

Boy unless I'm doing something wrong with a 20t on the motor shaft and a 11/34 on the back I'm looking at 4 MPH in low gear and like 17 in high with my 12 turn Mac. I don't know the motors exact gear ratio, so I simply took the loaded RPM, multiplied it by 5 for a guess to get motor RPM then divided by 6 (one ratio lower) and then used Sheldon browns speed calculator. Does this sound close? If so I might HAVE to use my 6 turn Mac to have decent speeds! Maybe that's a good thing?!
Power is a fascinating thing, the more you have, the more you want, but the real power is having the restraint not to use it all at once...............Um...Yeah..

The harder you work.....The luckier you get!!

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Re: Converting a hubmotor to a middrivemotor

Postby crossbreak » Tue Nov 20, 2012 10:21 am

Awesome, miles! May we copy it to our own wiki?

I never knew fixing different parts of a planetary gearbox produced different ratios!


That's exactly how an internal geared shifter hub works ;). U get 6:1, thats right.

I'm looking at 4 MPH in low gear and like 17 in high with my 12 turn Mac


The 12-turn MAC has 200rpm@36V and 1000rpm motor speed. Let's say unloaded speed is 1.3tims the loaded, so we look at 1300rpm unloaded. That's a KV rating of 36.

Made a table you so can play around with the numbers (check the attachment). It's the version i assume you use ATM (with 5:1 MAC reduction and 20/44T crank reduction). I see you use a 20T sprocket on your MAC. SO I assume you only use 36V (that's perfect match after my calc). Why don't you just switch to 72Volt by connecting your batteries in series?

Edit: corrected an error with the climbability value
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Last edited by crossbreak on Tue Nov 20, 2012 9:53 pm, edited 5 times in total. View post history.
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Re: Converting a hubmotor to a middrivemotor

Postby Miles » Tue Nov 20, 2012 10:25 am

crossbreak wrote:Awesome, miles! May we copy it to our own wiki?
Having actually looked at your link, I'm not sure I have the table you're referring too... :) Sure. We can mine the revision history for the best material.
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Re: Converting a hubmotor to a middrivemotor

Postby Miles » Tue Nov 20, 2012 10:28 am

Image


That looks neat...
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