jateureka
10 kW
Some more Nexus / Sturmey Archery type fixed cog size options http://bikesmithdesign.com/cogs/index.html
Converting a hubmotor to a middrivemotor
- Thread starter crossbreak
- Start date
AHA! 24T and 26T steel sprockets with the 3-tab bore...THANKS!
edit: I ordered the 26T, the seller emailed me an invoice, and in the email he provided a paypal link. I paylalled him the money and the sprocket arrived 3 days later in a firm cardboard envelope into my mailbox. No complaints, very happy with the part.
http://bikesmithdesign.com/cogs/index.html
edit: I ordered the 26T, the seller emailed me an invoice, and in the email he provided a paypal link. I paylalled him the money and the sprocket arrived 3 days later in a firm cardboard envelope into my mailbox. No complaints, very happy with the part.
http://bikesmithdesign.com/cogs/index.html
SolarRay
100 mW
Original bpm really can give 80 Nm, without damage the gears/windings.?crossbreak said:
crossbreak
1 MW
Guess not. That's why I set the phase current to 60amps, not 90amps.
Just saw the BPM2 has threaded sideplate that need a special tool for removal
I hate these, they always fail. If the Motor is not spoked into a rim it is impossible to open it :x stay away from these!
Just saw the BPM2 has threaded sideplate that need a special tool for removal
I hate these, they always fail. If the Motor is not spoked into a rim it is impossible to open it :x stay away from these!
crossbreak
1 MW
It will take 2 weeks to machine the adapters...too bad it's holiday time 
crossbreak
1 MW
OK, got my BPM2, it's an 11T 
Too fast for Star->Delta conversion, too slow for a real high power setup :x The threaded side plate also cost me some of my nerves.
Tried to open it. One needs a special tool for that. I made one using a sheet. I drilled 3 holes into the sheet, one 35mm one for the BSA threads on the sideplate. And another 2 for the teeth that engage the grooves in the side plate. Just filed down two hex srews till they fit into the grooves and screwed them on my sheet. Used only two, but there are 4 grooves. A long lever on the sheet helps to input the right torque. A BSA threaded nut screws the self-made tool on the motor after the teeth engaged into the grooves (the nut has also 6-holes, that is a bit confusing, just had no other BSA nut at hand). This way, there is no way the tool can tilt and damage anything.
I was also able to open it without lacing it into a rim: I used the 6-hole interface for mounting the motor in my benchwise by drilling 7 holes into a 4mm alloy sheet: one 35mm hole in the center and 6 holes for the disc brake interface. After that I heated the motor (not the sideplate) and screwed of the sideplate anti-clockwise, I needed around 30Nm to do that, but this motor is unused. In a use motor this can be a lot more, since the chain drive further engages the threads of the sideplate when pedaling hard.
Too fast for Star->Delta conversion, too slow for a real high power setup :x The threaded side plate also cost me some of my nerves. Tried to open it. One needs a special tool for that. I made one using a sheet. I drilled 3 holes into the sheet, one 35mm one for the BSA threads on the sideplate. And another 2 for the teeth that engage the grooves in the side plate. Just filed down two hex srews till they fit into the grooves and screwed them on my sheet. Used only two, but there are 4 grooves. A long lever on the sheet helps to input the right torque. A BSA threaded nut screws the self-made tool on the motor after the teeth engaged into the grooves (the nut has also 6-holes, that is a bit confusing, just had no other BSA nut at hand). This way, there is no way the tool can tilt and damage anything.
I was also able to open it without lacing it into a rim: I used the 6-hole interface for mounting the motor in my benchwise by drilling 7 holes into a 4mm alloy sheet: one 35mm hole in the center and 6 holes for the disc brake interface. After that I heated the motor (not the sideplate) and screwed of the sideplate anti-clockwise, I needed around 30Nm to do that, but this motor is unused. In a use motor this can be a lot more, since the chain drive further engages the threads of the sideplate when pedaling hard.
Attachments
crossbreak
1 MW
thank you crossbreak for doing this, I bought a front bafang bpm motor to convert to a middrive because of this forum and this thread in particular. What are you going to do with the shaft? I might have jump the gun and file off the flange on the shaft that connects to the stator. Should have waited to see what you would of done.
crossbreak
1 MW
Before you do that, insert your heat bridge and drill the holes that connect the stator to the hub housing. I would want to add a flange to the side plate that center aligns the stator. I will see if I can make a part on the lathe for that of if I just got the simple route using a 2.5mm thick alloy sheet and glue it on the sideplate using epoxy putty. I'll take pics as soon mas I proceed to show that in detail.
My new Idea is to connect the windings themselves to the sideplate with thermal copund. This way the thermal path to the housing gets even shorter, making more heat dissipation possible. Also, more surface for heat dissipation leads to better heat dissipation. The sideplate is made of relatively thin alloy, so we should try to use a large diameter for the thermal path, keeping the thermal path to the hub cylinder short.
After mounting the mount plate of the stator side that connects to the frame, we could even add a heatsink to that. Space isn't limited so much in a right hand only drivetrain (using the new V5 adaters). Hope the V5 will fiit your front BPM, it is possible to make an adapter that needs 20mm axle length, so there shoult be 3mm left for the nut that fastens that adapter on the shaft/axle:
can you plz measure/confirm the axle length that exits the stator side hub?
My new Idea is to connect the windings themselves to the sideplate with thermal copund. This way the thermal path to the housing gets even shorter, making more heat dissipation possible. Also, more surface for heat dissipation leads to better heat dissipation. The sideplate is made of relatively thin alloy, so we should try to use a large diameter for the thermal path, keeping the thermal path to the hub cylinder short.
After mounting the mount plate of the stator side that connects to the frame, we could even add a heatsink to that. Space isn't limited so much in a right hand only drivetrain (using the new V5 adaters). Hope the V5 will fiit your front BPM, it is possible to make an adapter that needs 20mm axle length, so there shoult be 3mm left for the nut that fastens that adapter on the shaft/axle:
can you plz measure/confirm the axle length that exits the stator side hub?
I know the magnet backing is steel, but...are the wide spokes of the magnet bowl face made from cast aluminum?
http://endless-sphere.com/forums/download/file.php?id=115430
http://endless-sphere.com/forums/download/file.php?id=115430
crossbreak
1 MW
yes.
I updated the Wiki, reduction ratio for the BPM2 is 4.95:1, or 5.95:1: when converted. Is this the same for the BPM1?
http://endless-sphere.com/w/index.php/EBike_Motors_Hub_BPM
I updated the Wiki, reduction ratio for the BPM2 is 4.95:1, or 5.95:1: when converted. Is this the same for the BPM1?
http://endless-sphere.com/w/index.php/EBike_Motors_Hub_BPM
I counted the teeth twice very carefully, BPM-1 is
sun:____21T
planets: 42T
ring:___105T
One tooth difference on ring gear, almost identical. The pics of the sun and planets look identical.
sun:____21T
planets: 42T
ring:___105T
One tooth difference on ring gear, almost identical. The pics of the sun and planets look identical.
crossbreak
1 MW
didnt count the ring gear, just calced If sun and planets are the same, the ring gear must be: 2x planets+1x sun, so it's 105 for both :x So it is 5:1 exactly 
If sun and planets are the same, the ring gear must be: 2x planets+1x sun, so it's 105 for both :x So it is 5:1 exactly 
cal3thousand
10 MW
Some interesting stuff about mid-drives: http://www.topsecretev.com/blog.php?id=9153936975003633568
-dg
1 kW
It sure looks like it. Also, on my BPM that you have apart, I think the spokes/side of the magnet bowl is also cast aluminum. Can you please verify that?spinningmagnets said:
What is interesting is that the BPM II basket in this thread looks like the basket from an old BPM thread, and mine is different. Yet the BPM II has the screw-on sidecover, which I've thought was something on the newer motors, like the SWXK. Yet, I just got an SWXH and SWXU with bolted on sidecovers. I'm starting to think that Bafang have more than one production line that make different versions of the parts and they just assemble motors from what is on hand.
I expected to verify that the entire BPM-1 magnet bowl was steel, but...upon close examination and testing with a magnet, the magnet backing ring is steel (of course), while the 6-spoked face is indeed aluminum.
crossbreak
1 MW
My SWXH are all screw-on covers. The SWXB are all bolted. My bafangs all look like on their official homepage. Guess the BPM2 I bought was made in 2010, that's why it has the old style rotor hub.
nippynoo
10 mW
I've been following this very interesting topic and found the following diagram useful to help my understanding... which may help others. Its not a BPM, as you will observe that the axle is solid and the cable exits through the side, through the larger bearing, and it has a screw on cover. So could it be the Bafang SWXU or the QBPM or is it something else?
However after implementing the conversion suggested by crossbreak, on this particular motor, wouldn't the axle at the stator-end (LHS of axle - in picture below) incur rubbing friction on the stator assembly? Without any lubrication, wont using it as a jackshaft (with a lateral load at each end) cause friction and wear between the axle and stator? The other end of the axle (RHS of picture) rotates in a ball-bearing which is fine. But I notice that the two central ball-bearings also seem unable to take lateral loads as they transfer the force to the magnet housing which itself is rotating. So three of the four ball-bearings are not helping and there is only one fully functioning ball-bearing keeping the axle concentric. Am I missing something? Is another bearing being added? How are the loads going to be supported. Is the hollow-axle-type BPM/MAC mechanically different at the stator-end (i.e. is the bearing directly between cover and axle, or between cover and stator)? I'm confused looking at the diagram, and I haven't got any motors to examine, and I cant make it out from the photos. Maybe only the solid-axle motors have this problem??
However after implementing the conversion suggested by crossbreak, on this particular motor, wouldn't the axle at the stator-end (LHS of axle - in picture below) incur rubbing friction on the stator assembly? Without any lubrication, wont using it as a jackshaft (with a lateral load at each end) cause friction and wear between the axle and stator? The other end of the axle (RHS of picture) rotates in a ball-bearing which is fine. But I notice that the two central ball-bearings also seem unable to take lateral loads as they transfer the force to the magnet housing which itself is rotating. So three of the four ball-bearings are not helping and there is only one fully functioning ball-bearing keeping the axle concentric. Am I missing something? Is another bearing being added? How are the loads going to be supported. Is the hollow-axle-type BPM/MAC mechanically different at the stator-end (i.e. is the bearing directly between cover and axle, or between cover and stator)? I'm confused looking at the diagram, and I haven't got any motors to examine, and I cant make it out from the photos. Maybe only the solid-axle motors have this problem??
crossbreak
1 MW
i thought about this a lot. But without a motor at hand this can be hard to imagine. The none-hollow-shaft motors, that dont use the axle as wire exit are not suitable for a conversion as you can see. The bearing design is not optimal. The bearing is too large, there is no radial space left for the screws that mount the stator on the hub housing / side plate.
We grind down the center of the stator to make it run free without any friction on the shaft. This would not be possible with the motor you showed us. As you can see in the pics, the motor (rotor+stator) itself cannot run without an axle, since the stator is mounted on it. We mount the stator on the side plate instead of on the axle, using the "heat bridge" or thermal bridge that is screwed on the side cover. This way we can grind down th axle or the inner surface of the stator, so they dont rub against each other.
-dg
1 kW
nippynoo said:
That looks like my SWXK. And almost looks like the SWXU I just got except that the SWXU has the bolt on style sidecovers, not the screw-in kind like in your diagram.
Where did you find this diagram anyway?
cal3thousand
10 MW
I'm starting to work on the conversion of the motor (MAC 7T) in preparation for my frame in September. I've gotten the stator out and the circlips on both sides off as well as the key on the axle and the clutch pack.
In order to measure my laminations and thus set my expectations for this motor, I put coins on my puller legs and aligned everything to pull the magnet bowl off the stator core. But I only managed to mess up the axle. The "cutout" section for the wires to exist the end of the axle flared open under the force of the puller.
In order to measure my laminations and thus set my expectations for this motor, I put coins on my puller legs and aligned everything to pull the magnet bowl off the stator core. But I only managed to mess up the axle. The "cutout" section for the wires to exist the end of the axle flared open under the force of the puller.
- Is it a requirement to pull the collar off the other side first?
- I presume that I can just cut the flared portion off and hopefully not need that much of the axle (about 1 cm affected)
crossbreak
1 MW
be careful, you have to use this side of the axle as your output! removing the collar shouldn't be necessary, but ask spinningmagnets instead. I dislike the MACs, never striped one
You should screw a nut on your hollow axle end and read http://endless-sphere.com/forums/viewtopic.php?f=28&t=45245&start=450#p719603 again maybe :?
Always use just my hand with gloves to remove the rotor. did this with the BPM2 again, maybe I'm just too strong?
You should screw a nut on your hollow axle end and read http://endless-sphere.com/forums/viewtopic.php?f=28&t=45245&start=450#p719603 again maybe :?
Always use just my hand with gloves to remove the rotor. did this with the BPM2 again, maybe I'm just too strong?
nippynoo
10 mW
crossbreak said:
Thanks for your reply crossbreak. So are you confirming that this conversion won't work for a QBPM, SWXU, SWXK/5 or any solid-shaft motor where the cable exits through the side?? Even if there was room to bolt the stator to the side plate, there would still be friction and these motors would need an additional external ball-bearing?
-dg said:
I was just about to place an order for a SWXU when I came across the above cross-sectional diagram on http://www.8fun-motor.com
Does anyone know if there are equivalent diagrams for the MAC/BMC/BPM - I did look but couldn't find any?
crossbreak
1 MW
yes, you would want to add a smaller bearing into the sideplate, which would carry the axle.
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