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 waynebergman » Tue Nov 20, 2012 11:47 am

mac opened up.jpg
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Crossbreak, this is a pic I took of the motor after its demise. I don't think this is quite what you are looking for but I am in the middle of a move and everything I own is in cardboard boxes stacked in a huge hay pile. Wont have access to my new shop or possessions for a couple of weeks so maybe Whiplash can chime in with a photo or two to shed some light on the mac conversion.......wayne
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Re: Converting a hubmotor to a middrivemotor

Postby Whiplash » Tue Nov 20, 2012 4:38 pm

Hey Cross, I am using 12S LiPo sorry for not posting that... Thanks for the help, I will look everything over when I get home tonight...
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 7:03 pm

thanks waynebergman, this will tell us a the reduction ratio, no one ever posted (i'll update the wiki as soon as i counted :) ). I'm waiting keen for pic's of the stator from this side!
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Re: Converting a hubmotor to a middrivemotor

Postby crossbreak » Tue Nov 20, 2012 7:10 pm

Whiplash wrote:I am using 12S LiPo


then it's geared a little fast... you should have gone for 16T motor sprocket, making it better drivable. Should not feel lame with a smaller one at higher speeds (27mph / 44kph max speed for your drive), does it?
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Re: Converting a hubmotor to a middrivemotor

Postby crossbreak » Tue Nov 20, 2012 7:47 pm

a heatpipe cooling would be also something we might reconsider... thinking of my old geared rc hubmotor
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Re: Converting a hubmotor to a middrivemotor

Postby Whiplash » Tue Nov 20, 2012 8:51 pm

crossbreak wrote:
Whiplash wrote:I am using 12S LiPo


then it's geared a little fast... you should have gone for 16T motor sprocket, making it better drivable. Should not feel lame with a smaller one at higher speeds (27mph / 44kph max speed for your drive), does it?





Well this sprocket was for my existing drive and it does quite well, on the flat it'll do about 35mph and in low it tops out about 10-12mph. I was just trying to figure it out for now..
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 8:55 pm

Then try a 16T and you will see a great difference in torque and driveability and drivetrain lifetime - of course your top speed will drop to 27mph@which you can still pedal

Just fooling around: If we do a crank to jackshaft reduction of 48/12 and a final reduction of 42/15 which would still look okay with a MAC (and which would be ok for the chain), we would do 66mph@80rpm (that's 108kph))cadence :twisted:

with controller and a first mount, figuring out the next ones...
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Re: Converting a hubmotor to a middrivemotor

Postby Lenk42602 » Tue Nov 20, 2012 9:12 pm

crossbreak wrote:hub is a bafang swxb 250W 28" 24V. Is has a 17:73T reduction.



cross,

I have one of these exact motors on hand and pulled it apart tonight. I have removed the hub covers from the stator/gear/axle assembly. The snap ring is removed. How does one pull the axle out and separate the planetary gear/clutch assembly from it?


it looks as though I am going to have to cut the hall and phase wire connections, and then pull this wiring through the axle before pushing the axle out of the stator carrier. Are there any tricks to this or do you just go for it?

cheers,

Len
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Re: Converting a hubmotor to a middrivemotor

Postby Whiplash » Tue Nov 20, 2012 9:14 pm

Lol! Yeah I think the Mac would DIEEE!!
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 9:45 pm

Lenk42602 wrote:...or do you just go for it?

go for it, but be careful. You may take off the rotor first.

Whiplash wrote:I think the Mac would DIEEE!!
of what?
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Re: Converting a hubmotor to a middrivemotor

Postby Whiplash » Tue Nov 20, 2012 11:12 pm

Overloading! I seriously doubt it would handle the 4000ish watts it takes to go that fast but I could be wrong;-)
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 » Wed Nov 21, 2012 7:49 am

I'd say 6000Watts would be necessary for 100kph. Too much for the MAC, just fooling around :) . Your 12T MAC is wound a bit too slow if you want to convert it, you waste potential if you only use 12s lipo. You should go for 16s and keep the amps at max 40 to make the gears last.

We should keep the efficiency curve back in mind, since this will highly effect the efficiency of the bike. I always try to gear so that peak efficiency and power are reached near 80rpm crank cadence. The e-bikes.ca simulator gives good info to calc with if one uses it right, I simulate the driving forces by increasing the CdA value (air resistance constant of the vehicle) and played around with the battery voltage till I got a good match with the chosen reduction (the 39kph)and the power you wanna get (the 1946W).

My proposal for your 12T MAC:
With 16s battery and 44/13 crank to MACshaft reduction you get 270rpm@MACshaft@80rpm cadence.
That's equivalent of an unmodified MAC (with only 1:5 internal reduction) of 324rpm, which would be 39kph if mounted in a 26" rim.

The peak efficiency can sadly only be reached with a very high crank to MACshaft reduction and a very high battery voltage if you want 2000W.
Or you disclaim power :lol:
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Re: Converting a hubmotor to a middrivemotor

Postby Whiplash » Wed Nov 21, 2012 9:19 am

OK great, THX for the info! I need to look things over again since I don't want to go backwards in performance. I can currently do 35mph and don't want to give that up for a little efficiency...
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 » Wed Nov 21, 2012 10:24 am

can currently do 35mph and don't want to give that up for a little efficiency...

This make no sense to me.
35mph you pedal at 116.5rpm...i'd like to see that :shock: ATM your drive has much less than 2000W, so what I calced for you must be huge increase.

To make things clear:
The crank to MACshaft drive ratio sets the efficiency at normal crank cadence
The theoretic max speed is set by the MACs output gear
The burst power is set by bat_voltage*_max_amps*efficiency
The continuous power is set by efficiency in most used Q-point, eg. @80rpm cadence, cause it defines the rejected heat

if max heat rejection of a MAC is let's say 400W unmodified. So @ 80% efficiency a MAC can do max 1600Watt continuous if driven in it's best efficiency point

you see, these things are completely independent. The 39kph i mentioned are a "virtual" number to calculate with (to make it possible using the data from ebikes.ca in a middrive setup). read my calc carefully, i'm certain you'll get it in the end.
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Re: Converting a hubmotor to a middrivemotor

Postby crossbreak » Wed Nov 21, 2012 10:59 am

This would be the best one could do with a stock MAC


59.1kph=492rpm stock MAC shaft
410rpm converted MAC shaft
5.12 crank to MAC overdrive, for example 61/12 using #35 chain

If we can increase heat dissipation to maybe 800W, than this hole thing must be recalculated.
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Re: Converting a hubmotor to a middrivemotor

Postby Whiplash » Wed Nov 21, 2012 3:37 pm

I usually pull around 1300 watts when going top speed. The motor will take it for a good while but not forever, it does get warm but never hot to the touch even after a long run at WOT. I am confident the stock unmodified Mac will take 1000 watts almost indefinitely in normal ambient temps. Just for the sake of knowing...
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 Whiplash » Wed Nov 21, 2012 3:37 pm

Oh yes and my cadence right now is much higher than 80 ;-)
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!!

"People who say it can't be done are often interrupted by those that have already figured out how to do it!"

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Re: Converting a hubmotor to a middrivemotor

Postby spinningmagnets » Thu Nov 22, 2012 8:39 am

If it were possible, would you prefer to have all the other performance perameters the same, and have the cadence around 80? or is a little higher cadence when at top speed acceptable?

I ask because the MAC-geared being used as a non-hub is my most desired next project, and I'm pondering several engineering options such as a "sliding bottom bracket shell"
edit: $71 at Problem Solvers http://problemsolversbike.com/products/sliding_bottom_bracket_shell

Image
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Re: Converting a hubmotor to a middrivemotor

Postby Cyclebutt » Thu Nov 22, 2012 9:29 am

spinningmagnets wrote:If it were possible, would you prefer to have all the other performance perameters the same, and have the cadence around 80? or is a little higher cadence when at top speed acceptable?

I ask because the MAC-geared being used as a non-hub is my most desired next poroject, and I'm pondering several engineering options such as a "sliding bottom bracket shell"
Image


OhhHHhhOOO, SNAP! That little bracket is BRILLIANT!
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Re: Converting a hubmotor to a middrivemotor

Postby litespeed » Thu Nov 22, 2012 9:57 am

Where would one find a sliding bottom bracket shell I wonder?

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Re: Converting a hubmotor to a middrivemotor

Postby Lenk42602 » Thu Nov 22, 2012 10:49 am

http://problemsolversbike.com/products/ ... ket_shell/

used for allowing children to ride as stokers on tandems by raising the crankset. I have one.

Spinning magnets, I also planned at one time to have a MAC mid drive. here is the layout I came up with, which circumvents the need for freewheeling cranks:
viewtopic.php?f=28&t=33416

In my design, that BB carrier would be placed behnd the seatpost.

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Re: Converting a hubmotor to a middrivemotor

Postby crossbreak » Thu Nov 22, 2012 10:50 am

spinningmagnets wrote:If it were possible, would you prefer to have all the other performance perameters the same, and have the cadence around 80? or is a little higher cadence when at top speed acceptable?


I would not use anything higher than 80. Makes no sense to me. If you want to pedal faster, then shift a gear back. If you dont want to pedal then built a motorcycle. Makes the hole thing much easier. If you pedal more often @85rpm then use this number for your calcs. I'm more the slow and strong pedaler, that's why I always calc with 80.

This sliding bottom bracket shell looks interesting. What will you use it for? From my experience,a bracket build like the GNG one is much stiffer. You could combine both to get a decent jackshaft mount. But that's OT here, there is no BB jackshaft with this topic conversion topic or did I miss something?
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Re: Converting a hubmotor to a middrivemotor

Postby crossbreak » Thu Nov 22, 2012 11:00 am

Hey Len, I like this one:
Subject: mid drive project for pikes peak

LI-ghtcycle wrote:...
Actually, since you're going rigid (or heck, keep the suspension), and we know that longer wheel bases help out at higher speed, I would actually do something more like this:

Image

This is using an extended swing arm that could be built out of steel or just extend the one you have, and I'm only talking 6 - 8 inches, keep the same geometry, and now you don't have to worry about remounting the rear triangle on a custom mount!....


What did you do with your MAC in the end?

my prototype ATM:
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Re: Converting a hubmotor to a middrivemotor

Postby Lenk42602 » Thu Nov 22, 2012 11:15 am

sold it.....

putting the motor behind the seatpost takes up too much space and requires compromises in handling,etc. Thats why I bought one of the kids stoker bb adapters. I was planning on using it to isolate back driving the cranks and motor, with freewheels/adpaters, and then going back to figuring a way to ount the hub in front of the seat tube.

Besides, I think now that modifying the axle to spin/drive reduces the space required and resolves additional mounting issues when attempting to adapt a rotating hub as a mid drive.

Perhaps this BB adpater -turned - drive isolator, coupled with your BPM hub modification + a left hand crankset, would minimize space cosnumption in that critical area on the bike.

Len
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Re: Converting a hubmotor to a middrivemotor

Postby Lenk42602 » Thu Nov 22, 2012 11:18 am

this guy is heading in the same general direction...

viewtopic.php?f=6&t=45259&p=659595&hilit=kona+stinky#p659595

watching neptronix's testing of those BLT motors. My next motor buy may be one of the BLT 500's specifically for this application...

Len
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