Converting a hubmotor to a middrivemotor

I try to run 36v LiFePo4. I am a commuter rider, so not wanting to run faster than 25, but I like to get off the line fast and be able to climb walls.

Right now I am pulling about 1300w tops from my pack, but I know I have some inefficiencies in my set-up that is sucking a bunch of that up.

Also, it looks as though you are using a freewheel on both sides of the motor. Is this necessary? It seems like one on the crank side is enough since the rear wheel will have a freewheel on it. Could you not use a fixed gear on the output side of the motor?

I have been thinking of ways to use #219 cart chain in a mid-drive setup and it seems like using a fixed gear on the output side of the motor and one of the crossfire 10-hole freewheels on the back (I'm using Nuvinci hub) would be a good solution for using #219.

http://www.ebay.com/itm/321024484944?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649
 
StudEbiker said:
I try to run 36v LiFePo4. I am a commuter rider, so not wanting to run faster than 25, but I like to get off the line fast and be able to climb walls.
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That's fine. You just can go for the 8T MAC, I assume you use 12s lifepo

Right now I am pulling about 1300w tops from my pack, but I know I have some inefficiencies in my set-up that is sucking a bunch of that up.
Click to expand...
I can sing a song about that

Also, it looks as though you are using a freewheel on both sides of the motor. Is this necessary? It seems like one on the crank side is enough since the rear wheel will have a freewheel on it. Could you not use a fixed gear on the output side of the motor?
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Not necessary. Only used the freewheel on the output for testing, since I have no output gear yet. Tutorial how to make one will follow next week. HOPE that there will be no issues using the 3-screw input freewheel design, I have not tested yet. Tests will follow next week also.

I have been thinking of ways to use #219 cart chain in a mid-drive setup and it seems like using a fixed gear on the output side of the motor and one of the crossfire 10-hole freewheels on the back (I'm using Nuvinci hub) would be a good solution for using #219.
Click to expand...
Of course this would work, but is not necessary or reasonable, since 1/x3/32 inch is more common and cheaper and will last longer than your NuVinci. If you do such a setup go for the old heavy NuVinci and exhange the oil after a few thousand kilometers. THEN you might try, but not with a NEW BOUGHT Nuvvincy, it has to wore in first (and still might fail with 3hp+). Problem is, we will get a quite good efficiency so most of the power we push in will really make it to the rear wheel ;) Instead do a #219 chain overdrive on the pedal side. Getting 5:1 ratio for example using 60/12 and buy a fast BPM. I have not figured out how you can get a freewheel into a #219 12T sprocket. At least you can do this using a freewheel crank :? but that's something I would want to avoid.
 
I have been using the Nuvinci N171 (big heavy) auto shifting dev kit for the past 1,000 miles on the Bike E. As I understand it, bike chain is only good for around 1,000w and the Nuvinci (I thought) was supposed to be good for at least 3k watts with some people running as much a 5k successfully through them. I would think the 2.25k (or more) watts that this setup would be put to the hub would stretch bike chain very quickly.

With the Bike E, I can easily use a 60t (or more) standard chainring without any clearance issues so the reduction on the crank side should not be too difficult though the cost of those size rings are a little pricey.

Just to clarify, is this the BPM motor you think would be ideal for this set up?

bpm.jpg

Edit: The one in the picture is a rear motor. It is better to use a front motor for what you are doing right?
 
can I buy instant hardware to mount mini-hub as middrive to classic MTB ?
 
The easy route to better cooling if your shell is fixed in place is to turn it into a centrifugal blower. An output duct at the perimeter pointed down and rearward will keep crap out. Add a few blades to the rotor bell to ensure the air spins well. Put the intake to bring fresh air onto the exposed side of the stator with some ducting to keep gunk out. Simple and effective.

I've done similar to your approach, but I wanted to retain the static axle for easy mounting on my swingarm, so I attached a hollow axle at the sun gear with a bearing at the sprocket to center my hollow output shaft on the original axle. I did turn the sun gear's teeth down to flatten the ends so the ID of the output shaft fit well on sun gear leaving good spots for a few grub screws to secure it.

It works fine, I just shelved it in favor of higher power and efficiency motors. Too bad those manufacturers don't wise up and use better and thinner lamination steel instead of the cheap stuff. With the heat issue resolved and higher rpm capacity the motors would be great little solutions for 4-5kw peak or higher.

John
 
Hey John, guess you mean the one you posted on the first page?
file.php


If you would have seen my tongxin from the inside after 6500km you would agree that ANY tiny hole in the housing makes it fail after time. No blades can keep all of the crab out. When using a direct drive this would look different, since it has no gears, sad that they are that heavy :(

StudEbiker said:
With the Bike E, I can easily use a 60t (or more) standard chainring without any clearance issues so the reduction on the crank side should not be too difficult though the cost of those size rings are a little pricey.

Just to clarify, is this the BPM motor you think would be ideal for this set up?



Edit: The one in the picture is a rear motor. It is better to use a front motor for what you are doing right?
Click to expand...

Looks like you already have a sophisticated drive. If you mind changing chains go for the #219 chain or just for bigger sprockets on both front and rear. If you go for the "through the hub" drive like I do your output gear can be small, so if you use 36T output sprocket and a 32T at your NuVinci, chain pull will be very small even at 3KW - it will last a while.

Yes, that's the Bafang BPM i talk of (there is no other, is there?). If you want to use a front or rear hub for the conversion depends on how you want to fix the sprockets on the shaft. The front motors have flattened axles on both ends, which makes mounting sprockets easier IMO, also they are cheaper (get the 250W bafangs for 30€ each, rear ones cost at least 50€). The BPMs are all the same, can't tell why bafang sells the front ones as 350W motors and the rear ones as 500W. BMSbattery also sells the CuteQ128 as 500W motor LOL, so this does not have to mean anything. You should think about what wind you need. If you have problems with calculating it, just PM me and tell me your bat voltage, cadence, rim size and the topspeed you wanna get.
 
iperov said:
can I buy instant hardware to mount mini-hub as middrive to classic MTB ?
Click to expand...

instant hardware? maybe buy the GNG Gen2 drive? It's almost the same but does not have the option to build a "through the hub shaft" drive, using the left side for crank overdrive and the right side to drive the wheel directly from the hubmotor shaft (no freewheel crank necessary), like i do on my build. Maybe I should post a vid that shows the function of the whole system, just to make things more clear.
 
crossbreak said:
bob, did you need a puller do get off the plantery carrier?
Click to expand...

No, You can remove it with your hands after you remove the restraining cir clips.
bØb
 
Sorry about the repeat posting. I should have looked thru the whole thread first.

FWIW, it turns out that sealed is probably worse for corrosion. Justin proved there's no way to keep the moisture out, so you might as well let it dry out. Sealed motors will even suck water in through the wiring like a straw. Get your motor up to running temps and then hit it with some rain, and it slurps the stuff in. I've seen sealed hubbies locked up from the buildup of rust in the magnetic gap. We haven't seen any of that with ventilated motors. Even the guys who didn't put their exhaust at the perimeter, so grit and sand has no way out haven't had issues. Zappy had the only failure I know of and that was a couple of computer fans that got killed running through a muddy stream.

With the rpm of those little motors you can easily pull enough pressure to use a filter of some sort. It will impact flow, but getting fresh air in far better than roasting it in a sealed housing.

It's a good idea to put some rust prevention coating

John
 
ImageUploadedByTapatalk1354503723.864081.jpg
Started making the heat bridge for my BMC. Since there is no cover plate in the center of the stator like the Mac I found this old threaded hub - disc adapter that fits closely to the flange of the BMC stator. Now I will drill some holes and add screws. This heat bridge may prove to be too thick. I will mill it down with a grinder if needed once the holes are drilled.
 
ImageUploadedByTapatalk1354503926.078262.jpg
Heat bridge in place. I had to file the id of the adapter to make it drop down over the shoulder on the stator
 
ImageUploadedByTapatalk1354512652.924467.jpg
Threaded on another adapter to help drill through the cover.
ImageUploadedByTapatalk1354512688.324571.jpg
Holes seem accurate enough for my purposes.
 
Looks great! As we know now these holes do not have to be drilled that accurate like the ones in my bafang due a different bearing config (more conversion friendly) in the MAC/BMC. But working that accurate does not harm the final product :)

BUT you should try taking out the shaft before going further. I guess that relieving the axle axially (bad english sorry) will not be as easy as with the MAC. Keep that advance in mind, it may slip on the axle in the end.

Hey John, I saw the video about deposits in hubmotors a year ago. A small hole to let water/steam out at the bottom of the housing should be all it has to take. Works also with CroMo frames. Car alternators also work for years in the dust and they are even brushed. All i'm talking of is keeping the dust out of the gears. A more sophisticated drive would separate motor and gears further. Like some RC-drives we see on the sphere from time to time. Not only miles and me dream of things like that :D
 
I would imagine it would be fairly simple to divide the geared portion from the motor portion in the MAC with a simple dust plate is something out of rigid plastic or fiberglass no? Then you could vent via side cover just like a DD hub..
 
Just a little teaser about what I did after supper
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A friend brought me a heatsink today. Modified it some, but still need to mill out clearance around six bolts that hold the heat bridge and stator carrier.
Anybody got in their junk box an old 1-3/8" - 24 lock nut for an old cup and cone loose bearing bottom bracket. I want one to screw on the freewheel mount of the MAC motor case. Gonna call it quits for the night.
 

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Bob,

Nice. Now you have me wanting to put oil in a hubbie. Mount it with the stator oriented with the hall board up, somewhat less likely to create problems. If small drips of oil leak out it's just automatic lube of the chain instead of getting on tire or brake disk. Not only does the oil conduct heat to the shell rapidly where your extra surface area dissipates it better, but it should help repel water. It all seems perfect for a beach and rainy day bike. :mrgreen:
 
There will be very little oil in the housing. Maybe an inch or less when the motor is not running. Just enough to dip the edge of the rotor in while the motor is running. The main heat path out of the motor will be from the stator to the aluminum carrier that the stator is pressed on, to a header/ heat bridge, that holds the stator in position, to the motor cover, to the heatsink, to the air :p There is hopefully some lube and corrosion advantages also.

I am going to mill slots in the back of the heatsint to run the phase and hall effect wires through to holes in the cover. Seal the wires and the covers with silicone. The case will vent through the hollow shaft where the wires originally ran. The hole in the shaft comes out in a quiet place, for oil splash, in the motor.

bØb
 
Good point about the wire hole! I never thought of it but its dead center and should almost never see any oil especially since its spinning! Centrifugal force is on your side!
 
crossbreak said:
where exactly would you place this plate?
Click to expand...


I was thinking between the gear portion and the motor, you could maybe seal it with silicone around the perimiter?
 
This heatsink fits awesome! Good luck when milling it. Keen to see if you use a hand tool (dremel) or a machine. I always try to get better in hand milling.

the hollow shaft is fine for venting. nice idea! This steam will still get in and condensate during cool down. it would be easy to push in a steam barrier that keeps steam out, but stil letting it out (just like GoreTex).

I can only sign what bob says about inserting oil. This will do best.

Using ScotchWeld for mounts and sprockets is a cool thing i did not know yet :idea: i'll try. Thx to Doctorbass for this great video!

@ whiplash: Sounds like a nice idea. But there is so little space. I can imagine using a thin sheet between motor and planetary carrier. But that might slip on the rotor bell doing friction. But doing a conversion to the hub might have the option to get some space here, by giving it more space. You will have to take a look into details, but this sounds like it will be worth it. You can give distance by adding washers between planet carrier and motor, but this will make the whole hub wider :? this might somehow work since you only need 1mm.
 
Yes I won't know till I have it apart...
 
Finished the heatsink after supper:
 
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