mr.electric
10 kW
message Green Machine he has the frame I bought.teklektik said:
Converting a hubmotor to a middrivemotor
- Thread starter crossbreak
- Start date
crossbreak
1 MW
mr.electric said:
This is a serious issue i did not yet think of. We have to lock the pedal threads in some way. Maybe loctite may help. I will keep an eye on this.
[/quote]
rapid fire type levers dont like grip throttles, I had to cut the lever and extend it. I used eopxy/alloy for this. Be aware that these levers are steel with plastic around if you cut it. But really this has nothing to do with hub conversion please stay on topic. Make a build thread instead and post a link here
mr.electric said:
With a double freewheel the forces on the bracket will be more balanced (at least while pedaling). In the jackshaft configuration, there will be a huge twisting force on the bracket. If the bracket is strong enough, it won't be a problem.
If you take both cranks off the bottom bracket and swap them around but keep the bottom bracket axle going the same way, the bolts should be going the favorable direction. Not sure if it would fit like this.
That frame is really bad ass looking with those fat tires.
You need that with the bad roads around SF these days.
What's the power rating of that fry pan?spinningmagnets said:
mr.electric
10 kW
Just spun it a grabed a short video.
http://www.youtube.com/watch?v=LuDCl05uQRA
I like the sound this motor makes, not so whinny as an rc motor but not choppy and coarse like a hub motor. It sounds like precision engineering. Test drive will tell the full story.
http://www.youtube.com/watch?v=LuDCl05uQRA
I like the sound this motor makes, not so whinny as an rc motor but not choppy and coarse like a hub motor. It sounds like precision engineering. Test drive will tell the full story.
Fyi to those who are looking to make some mid drives..
The grin sale thread has a bunch of ezee motors that need side covers. Given that you are trying to shave these motors down and such, it would concievably be very easy to make your own side covers, or just substitute some MAC/BMC side cover plates if they fit ( MAC covers probably do! ).
The bang per buck factor here would be very high.
The grin sale thread has a bunch of ezee motors that need side covers. Given that you are trying to shave these motors down and such, it would concievably be very easy to make your own side covers, or just substitute some MAC/BMC side cover plates if they fit ( MAC covers probably do! ).
The bang per buck factor here would be very high.
StudEbiker
100 kW
Okay, I think I successfully got my rotor back on the hub/shaft. So I'm back in business!!
mr.electric
10 kW
Getting closer to test drive time. Is there a chance this motor will turn too slow ?We went from 4:1 up to 5:1 right. So reduce the speed the motor did in the wheel by 25% to find the speed the bike will go in the 1:1 gear ratio right?
crossbreak
1 MW
No, you start from 5:1 and get to 6:1 after conversion. Again, what battery voltage and turn count will you use?
I see you do single speed. That's a decline of this conversions purpose You do all this struggle for no benefit in hill climbing at all 
I see you do single speed. That's a decline of this conversions purpose
You do all this struggle for no benefit in hill climbing at all 
The jackshaft configuration of a converted motor will only need a single freewheel on the left side (which is originally the right side of the motor), so without a gear cassette, a rear axle will now have its fat part on the left (with the stock threaded gear-mount removed).
What is the diameter and exposed length of the MAC and Bafang shaft (the part which is normally under the stock gears)?
What is the diameter and exposed length of the MAC and Bafang shaft (the part which is normally under the stock gears)?
mr.electric
10 kW
I am just running a single for the first test drive. I need to order a few parts to be able to set up gears. The motor sprocket has teeth for a bmx chain, the rear sprocket must match otherwise the chain is a mix match and will not mesh. I will need to use a sprocket removed from a cassette or a front chain ring on the motor to allow use of a 7sp chain and then I can switch the back to a 7sp freewheel and add the derailer. First I want to test drive to get an idea of what size sprocket I will want to run on the motor shaft.crossbreak said:No, you start from 5:1 and get to 6:1 after conversion. Again, what battery voltage and turn count will you use?
I see you do single speed. That's a decline of this conversions purpose
The motor is a "BMC 1000" speed wind at 48v. I believe this is equivalent to a Mac 8t. I will probably run 35 amps although I have a 50 amp controller sitting here.
bØb
1 W
spinningmagnets said:
Don't know about a Bafang, but that part of the shaft in a MAC that shaft is 17mm.
bØb
mr.electric
10 kW
thanks Bob for measuring I was about to check for spinning magnets.spinningmagnets said:
I think you only need one freewheel wether you do jack shaft or both on one side.
17mm = 0.669 inches, Staton-inc.com has a 17mm ID freewheel adapter (among other shaft sizes) for $15 + tax/shipping (4mm wide keyway), left handed threads available if needed.
http://www.staton-inc.com/store/products/17_mm_ID_x_1_3_8_24_OD_right_hand_threads_x_1_10_wide_6mm_key_way_Schwinn_Meridian_Adaptor_for_freewheel_sprocket-1308-46.html
If someone wanted to make a left-side drive to the rear wheel, while limiting themselves to easily/cheaply sourced off-the-shelf parts...130-BCD chainrings (38T-60T Vuelta for $36) with an ACS Crossfire FW ($16) available in 14T-18T, possible 14T/60T = 4.3:1 reduction.
For a NON-freewheeling fixed gear to use crossbreaks original configuration with the motor as a jackshaft (relying on the original hubs internal freewheel), you can easily find threaded fixed gears from 13T-22T with a locking ring to add to the Staton adapter.
Googled Miles, and found this
$7 sprocket 11T with 17mm bore from TNC scooters (double-D bore, so you must file two flats onto the shaft or drill out bore)
http://tncscooters.com/index.php?route=product/product&product_id=367
http://www.staton-inc.com/store/products/17_mm_ID_x_1_3_8_24_OD_right_hand_threads_x_1_10_wide_6mm_key_way_Schwinn_Meridian_Adaptor_for_freewheel_sprocket-1308-46.html
If someone wanted to make a left-side drive to the rear wheel, while limiting themselves to easily/cheaply sourced off-the-shelf parts...130-BCD chainrings (38T-60T Vuelta for $36) with an ACS Crossfire FW ($16) available in 14T-18T, possible 14T/60T = 4.3:1 reduction.
For a NON-freewheeling fixed gear to use crossbreaks original configuration with the motor as a jackshaft (relying on the original hubs internal freewheel), you can easily find threaded fixed gears from 13T-22T with a locking ring to add to the Staton adapter.
Googled Miles, and found this
$7 sprocket 11T with 17mm bore from TNC scooters (double-D bore, so you must file two flats onto the shaft or drill out bore)
http://tncscooters.com/index.php?route=product/product&product_id=367
bØb
1 W
mr.electric,
About your gearing: I think if you start with a motor sprocket that is about the same size as the largest sprocket on your rear cassette or freewheel. That will give you 17% more torque and everything else from there is faster with less torque. It will at least give you a base line to work with. Everybody can tell you what you are going to get, BUT, that's not usually what you really get
It's usually it's just a SWAG :lol: http://www.acronymfinder.com/SWAG.html
I agree about not needing a freewheel on the drive (what use to be the brake side), the internal clutch will take care of that. If you already have a freewheel mounted of the right size, run it and record the data! If you know what rpm your motor runs (loaded or free) you can modify Shelton Brown's gear calculator to give you MPH for motor RPM. You can plug in your motor RPM and sprocket sizes and get MPH. On the new left side of the motor you can run a freewheel on the pedal crank or the motor. If you run it the freewheel on the motor, the chain doesn't move, but the freewheel ratchets more. But only about twice as fast as it would if the freewheel was on the pedal crank.
bØb
About your gearing: I think if you start with a motor sprocket that is about the same size as the largest sprocket on your rear cassette or freewheel. That will give you 17% more torque and everything else from there is faster with less torque. It will at least give you a base line to work with. Everybody can tell you what you are going to get, BUT, that's not usually what you really get
It's usually it's just a SWAG :lol: http://www.acronymfinder.com/SWAG.htmlI agree about not needing a freewheel on the drive (what use to be the brake side), the internal clutch will take care of that. If you already have a freewheel mounted of the right size, run it and record the data! If you know what rpm your motor runs (loaded or free) you can modify Shelton Brown's gear calculator to give you MPH for motor RPM. You can plug in your motor RPM and sprocket sizes and get MPH. On the new left side of the motor you can run a freewheel on the pedal crank or the motor. If you run it the freewheel on the motor, the chain doesn't move, but the freewheel ratchets more. But only about twice as fast as it would if the freewheel was on the pedal crank.
bØb
mr.electric
10 kW
I'm having trouble with the motor pulling so hard that it swings forward bending the area of the frame the bracket bolts to. I will probably add another anchor point to the bracket and add an axle puller type chain tensioner to the rear wheel and see how it goes. I think a larger motor sprocket will help too. I would like to make an adapter that allows me to run a small crank chain ring on the motor shaft. I'm not sure if I should start with an old crank or start from scratch on this type of adapter hub. I think it should be nice and wide covering a good two inches of axle to avoid axial run out.
mr.electric
10 kW
Man this bmc is one torquey sob. 
This bike will clearly out accelerate a hub motor running a comparable 2000 watts.
I think I will plug in a CA and do a long ride at 1250 watts current limit first to break things in a bit more gently. I need another adapter to hook up the pedals but that should be pretty easy.
FYI the bms battery ku 123 and ku 93 controllers don't work well with the bmc speed motor. I had to bite the bullet and replace hall sensors. Two hours of brain surgery later the motor runs nice and smooth with a bmc 50 amp controller.
This bike will clearly out accelerate a hub motor running a comparable 2000 watts.
I think I will plug in a CA and do a long ride at 1250 watts current limit first to break things in a bit more gently. I need another adapter to hook up the pedals but that should be pretty easy.
FYI the bms battery ku 123 and ku 93 controllers don't work well with the bmc speed motor. I had to bite the bullet and replace hall sensors. Two hours of brain surgery later the motor runs nice and smooth with a bmc 50 amp controller.
What did you end up doing on the bracket?
Imagine the torque you'll get in low gear with a full cassette.
There is definitely something funky about the BMC timing that doesn't play well with many controllers. It seems like it should be possible to make it work, but seems difficult in practice. The BMC controllers are designed with this in mind and handle it electronically (apparently). One thing is for sure that the electronic commutation speed is way higher than for a direct drive hub motor.
Imagine the torque you'll get in low gear with a full cassette.
There is definitely something funky about the BMC timing that doesn't play well with many controllers. It seems like it should be possible to make it work, but seems difficult in practice. The BMC controllers are designed with this in mind and handle it electronically (apparently). One thing is for sure that the electronic commutation speed is way higher than for a direct drive hub motor.
mr.electric
10 kW
I have not completely solved the motor pull issue but improved it. Another anchor point on the seat tube should complete the job. The bracket is made by a local machinist and is very impressive work. He will add the extra anchor point and it should be sturdy enough to allow for wheelies and tire spinning in low gears.
Regarding bmc weird timing. Does this apply to Mac puma and others geared motors or just bmc?
I am looking forward to trying the ku 123 controllers on other motors. After replacing hall sensors I realize how much I like sensorless options.
Regarding bmc weird timing. Does this apply to Mac puma and others geared motors or just bmc?
I am looking forward to trying the ku 123 controllers on other motors. After replacing hall sensors I realize how much I like sensorless options.
bØb
1 W
small sprockets + big torque = big chain pull
The small drive sprocket, along with the large distance above the chain stay is the problem. If the drive sprocket was larger the pull on the chain will be less for the same torque because of the longer moment arm of the larger sprocket. Also a compression brace between the drop out and the top of the motor bracket should solve your immediate problem. I have also become concerned about the radial bearing load on the motor bearing in this configuration. They are small bearings that were that only had to contend with the weight of the bike originally and not the pull of a chain. I have been considering using two pillow blocks with a longer shaft through the motor at chain stay level. That way the pillow block bearings would absorb th chain pull and the motor torque could be absorbed by a torque arm.
bØb
The small drive sprocket, along with the large distance above the chain stay is the problem. If the drive sprocket was larger the pull on the chain will be less for the same torque because of the longer moment arm of the larger sprocket. Also a compression brace between the drop out and the top of the motor bracket should solve your immediate problem. I have also become concerned about the radial bearing load on the motor bearing in this configuration. They are small bearings that were that only had to contend with the weight of the bike originally and not the pull of a chain. I have been considering using two pillow blocks with a longer shaft through the motor at chain stay level. That way the pillow block bearings would absorb th chain pull and the motor torque could be absorbed by a torque arm.
bØb
crossbreak
1 MW
mr.electric said:
The best soltution is a bar connecting both chain sprocket axles.
Mary christmas!
mr.electric
10 kW
Yes a larger motor sprocket is on the list of things to fix. I like the idea of a brace from motor bracket to chain stay / drop out. That would be the end all of chain pull.
mr.electric said:
All the MAC, BMC and Puma motors that I've seen have the same issue. They may have changed something on the newest ones.
Sensorless operation would be one way to avoid this.
bØb
1 W
mr.electric said:
This is a plate sprocket adapter for 5/8" shaft from http://sickbikeparts.com/
You can put two sprockets on it and manually move the chain over for LO & HI ranges.
They also have 24, 30, 36, 44 & 48 tooth 3/32" sprockets for it. It also fits their BB cartridges for a left side chain wheel. I ordered one but after seeing the amount of work required to rework it for my purposes I just ordered me a piece of 3-1/4" 6061T351 rod extrusion to make one from scratch. That way I can make the whole thing in one chucking and not have to turn it over.
I have tentatively calculated that I am going to have to run a 36 tooth motor sprocket because of the small 20" rear wheel I am going to run. I am probably going to make another shaft for MAC so it will be longer on the brake (new right) side. You can get 17mm close tolerance annealed drill rod from http://mcmaster.com/
bØb
mr.electric
10 kW
B0b,
Nice work a custom shaft would be the ultimate.
Nice work a custom shaft would be the ultimate.
Whiplash
1 MW
- Joined
- May 10, 2010
- Messages
- 2,906
Yes, I too thought a good solution would be to make a new shaft that will fit whatever sprocket adapter you desire, it would be easy to simply weld the adapter in place as long as the metals were similar... I would just machine a press fit and then TIG or MIG it in lace with a couple small welds..
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