Brainstorming...

Whiplash

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May 10, 2010
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Just brainstorming here, but if I was to install the motor in the middle of the frame, shave off the spoke flange to minimize the size, and then mount a gear on the disk brake flange of my MAC so I could drive the pedals with a length of chain and have a freewheel on the crank, could I not achieve the same basic thing that the R/C guys are getting? It would allow me to run the power through all the gears so I could have that stump pulling power I really want for going up the big hills and then still have MORE top end than I would have had with the hub mounted in the wheel! Plus, the added gearing would make the MAC internal gears last MUCH longer due to the fact that they would not have to work so hard on take off most of the time! I am surprised nobody has done this? Is there any reason I should not try it? I am at the stage where I can do just about anything with the bike, and this would allow me to get the best of both worlds would it not? It seems to me the real reason the Hubs don't do what we really want them to do is mostly due to the fact that they are locked to a single speed, but this would change that completely! What do you think, should I try it? The MAC is only about 9lbs, and by the time you add in the gearbox for the R/C, it HAS to be more than that! This could be just the ticket I have been looking for! Any opinions or especially any experience trying this would be GREATLY appreciated!
 
Whiplash said:
... I was to install the motor in the middle of the frame, shave off the spoke flange to minimize the size, and then mount a gear on the disk brake flange of my MAC so I could drive the pedals with a length of chain and have a freewheel on the crank, could I not achieve the same basic thing that the R/C guys are getting? ... I am surprised nobody has done this? ...
Search ES (and google) "stokemonkey", it may be close to what you are considering.
 
Yes, that is very similar, I would think it needs a freewheel on the left side though, and I would be giving the motor a lot more than 500 watts into a geared motor as well so it will have HUGE torque I would expect. I just am not sure if I want to take my nice motor and wheel I just got from Lyen and chop it up yet. I was hoping to find someone who has done this in a more performance oriented way than the site you suggested. Anyone else? I really think in a custom chassis, this could work very well, the only real problem on a regular bike is space...
 
IIRC, someone has a setup like you describe. If you edit your original post's title to something like "anybody done a hub to mid-drive configuration?", you might draw some fire.

EDIT: you might repost with the new title in the non-hub section.
 
TylerDurden said:
IIRC, someone has a setup like you describe. If you edit your original post's title to something like "anybody done a hub to mid-drive configuration?", you might draw some fire.

EDIT: you might repost with the new title in the non-hub section.

Yep, your right I remember reading a few posting about using a hub motor and mounting it in the "V".

Whiplash...
If your worried about cutting up your hub motor before you know if your can do what you want to do or if you will even like it why don't you buy a cheap test motor? You can but 450w 24v Currie look alikes for 60 bucks. Their brushed motors so they can be run in any direction. You could do all the work without effecting your current setup. Actually I guess you could run with of them. If you like the results you could then change to your hub over the winter when you don't need the bike. I am assuming you have a non-brushed hum so you would also need a controller and maybe a throttle. Just a thought..........
 
Yea you could do this but at 9lbs - I think you could get better results with a lower kV Astro and single stage reduction... Or even a direct RC drive to somthing like an SA3 for more gearing options, with less or the same weight impact but more power available at a higher level of efficiency :)

-Mike
 
Certainly possible, it is called mid drive or stokemonkey as already posted. The only problem I see is the efficiency and mounting problems of typical hub motors. The upside is the low costs and easy gearing.
 
That is what is interesting me here, the low cost and easy construction. I am really trying to build a bike that will climb with the best of them, maybe not as fast, but do it and do it well, but for a smallish price point. We all have seen the R/C setups like Recompense makes, but they are costly, and to offer a drive like that in a bike that's custom built, I would have to sell it for 5000 bucks to make any money on it. I was thinking of this setup works, I could possibly keep the price around 2500 and still have a machine that will climb just about anything and still go down the road on the commute at 35-40MPH if I get the gearing right! Keep it right in the sweet spot for torque/efficiency and then just get the gears to do the work... Just thinking out loud....
 
My only concern about a Stokemonkey type is that rotating mass spinning between my legs. I wish they made a version of a hub motor that just spun the shaft. The wires would have to exit somewhere else. :shock:
otherDoc
 
BMC and MAC both make relatively inexpensive inrunner motors that are chain drive and capable of of single or double stage reduction. The performance and power to weight isn't superb, but that is always the tradeoff for lower $$.
 
docnjoj said:
My only concern about a Stokemonkey type is that rotating mass spinning between my legs. I wish they made a version of a hub motor that just spun the shaft. The wires would have to exit somewhere else. :shock:
otherDoc

They do it's called a non-hub motor. :lol:
 
Whiplash, what you are talking about is similar to what I did on my tadpole trike. I don't have the kind of top end speed you are talking about, but that is mostly about gearing. On level ground my 8 gears top out from about 7 MPH in low to 21 MPH in high, at 2 MPH intervals. Up to about a 20% grade you can keep the motor in its sweet spot without pedaling. I always pedal and the longest hill i've been up is about 2 miles of 5 to 10% grade. No heating up.

Anyway, I am very happy with the results and you are right, it was fairly inexpensive and easy to do.

http://www.endless-sphere.com/forums/viewtopic.php?f=28&t=18606
 
Hey, THANKS and I will check out your build!
 
Sounds plausible. I'm not clear on which motor you're thinking of using, but direct drive is your friend here - if you're running a chain, you can accomplish the gearing using the chain, there's no point having a extra set of gears in the system - this increases torque & efficiency at low speed in a hub motor set-up, but it does you no favours at all (in terms of power, weight, efficiency or bulk, or the ratios between these) if you're running through the gears. In fact, not only are gears in the hub motor a waste of space here, running the chain between the motor and the BB shaft at a lower speed and higher tension will increase chain losses significantly too.

From what I've read, a 1:4 or 1:5 reduction ratio from motor 'shaft' to BB shaft should be ideal for a DD hub, and easily accomplished using spare bike bits (52 tooth chainring, 11 tooth sprocket) and a bit of basic fabrication - not sure about getting an 11 tooth sprocket onto a 44mm BCD disc brake mounting though, you may have to have use a short 'shaft' to connect the brake-disc-hole mounting plate to the sprocket - just long enough to let the chain clear the bolts. I'd be concerned about guarding it, I like my calves un-friction-burnt, but that shouldn't be too hard.

As you no doubt know, you should work out your preferred pedalling cadence and match it to the best operating speed of the motor to find the best ratio - if you're looking for power to weight over efficiency, or you like to 'spin', or the motor has a relatively low no-load speed, or you hook it up so you don't have to pedal for high-speed use, you might be able to use a smaller reduction and save some fabrication effort by bolting the sprocket directly to the mounting holes. Measure the no-load speed by running it flat out with the hub 'bare' - no rim/spokes/tyre - and recording the rpm (not exactly the theoretical 'no-load' speed, but close enough for all practical purposes) then at 50% of this you'll get max power and 75% will be max efficiency (as a rule of thumb / 'ideal model' result). You should be able to get a very good idea of what step-down ratio you need, this way.

And please post the no-load speed of your motor if you measure it! Not enough hard data on properly measured no-load speeds floating around, if you ask me (measuring with rims & spokes attached is a bit dodgy - measuring with only the hub is a much nicer way of doing it)...
 
Thanks for that, I was not sure how to calculate those figures. I will have to finish the main frame of the bike to see if this will fit but I think it will. I will have to get a new back wheel now, but it will allow me to have them match easily and I can get spokes and everything to match now too! If I can get it in there, I will do it this way, I think it will be really good to be able to use the gears on the bike. The MAC hub I have has a no load supposedly of 365RPM @ 38.2V but I don't know how to figure it for the 74V hot I am planning on running through it. This gearing will likely allow me to run less amps through the motor and still have the same acceleration, but time will tell. I will keep you posted here or on my build log about how it works out..
 
Hmm...so I happen to have a bunch of different brushless servo motors meant for cnc use...I wonder if one of those could work in your type of system, or if the hub motor would actually make a better mid-drive power source. The only slight issue is most of them are longer than they are wide...
 
I didn't do it with a hub motor, just a powerchair motor with gearbox, but CrazyBike2 is similar to what you describe.
http://www.endless-sphere.com/forums/viewtopic.php?f=2&t=12500&start=0
I am also working out how to do it with a hubmotor (probably a 9C) in the bolt-together semi-recumbent cargo bike thread, but I haven't gotten very far yet. Will end up working like CrazyBike2 except the motor type is different.
http://endless-sphere.com/forums/viewtopic.php?p=291768#p291768
 
Whiplash said:
The MAC hub I have has a no load supposedly of 365RPM @ 38.2V but I don't know how to figure it for the 74V hot I am planning on running through it.

No-load speed is limited by back-emf, which is equivalent to the voltage you're running it at - as you've almost doubled the voltage, you've almost doubled the no-load speed. So, the no-load speed will be 707rpm, and you're going to hit max power at around 353rpm and max efficiency at around 530rpm. If you had a 11:52 reduction to the pedals - assuming you use standard bike bits, a 52T chainring (the largest commonly available on bikes, though I've seen up to 56T as a standard part) at the BB and 11T sprocket on the motor (the smallest commonly available on bikes), that would give you cadences of around 75 rpm and 112rpm respectively.

Now, that's just about perfect if you're planning on getting the most out of your legs ala Lance Armstrong - i.e. if you're used to riding in the style of a racing cyclist, this would be ideal. On the other hand, if you like to pedal at a more sedate pace (as most casual cyclists do), you have two options, either (a) go for a larger step-down ratio, which might make fabrication trickier - you'd need a sprocket of about 7 or 8 teeth, and mounting the sprocket might get more interesting - to get it around the hub's shaft might be a concern, or (b) run it around the 48V mark, which with a 52:11 step-down would give you a cadence of 49rpm at max power and 73rpm at max efficiency. If you're a seasoned cyclist but not into 'spinning', I'd say go for 11:52 and a voltage somewhere in the 55V-65V range - for my personal preference in riding style, I'd be going for max efficiency at a cadence of about 90rpm, so about 60V, which also puts max power at cadence of 60rpm, perfect for those long uphill slogs where I can't be bothered pedalling fast :wink:.
 
http://endless-sphere.com/forums/viewtopic.php?f=16&t=3348&p=48700&hilit=+dom#p48700

I think you will find these pics interesting, the motor is mounted under the downtube leaving the frame open for batteries.

Barrie
 
madact said:
Whiplash said:
The MAC hub I have has a no load supposedly of 365RPM @ 38.2V but I don't know how to figure it for the 74V hot I am planning on running through it.

No-load speed is limited by back-emf, which is equivalent to the voltage you're running it at - as you've almost doubled the voltage, you've almost doubled the no-load speed. So, the no-load speed will be 707rpm, and you're going to hit max power at around 353rpm and max efficiency at around 530rpm. If you had a 11:52 reduction to the pedals - assuming you use standard bike bits, a 52T chainring (the largest commonly available on bikes, though I've seen up to 56T as a standard part) at the BB and 11T sprocket on the motor (the smallest commonly available on bikes), that would give you cadences of around 75 rpm and 112rpm respectively.

Now, that's just about perfect if you're planning on getting the most out of your legs ala Lance Armstrong - i.e. if you're used to riding in the style of a racing cyclist, this would be ideal. On the other hand, if you like to pedal at a more sedate pace (as most casual cyclists do), you have two options, either (a) go for a larger step-down ratio, which might make fabrication trickier - you'd need a sprocket of about 7 or 8 teeth, and mounting the sprocket might get more interesting - to get it around the hub's shaft might be a concern, or (b) run it around the 48V mark, which with a 52:11 step-down would give you a cadence of 49rpm at max power and 73rpm at max efficiency. If you're a seasoned cyclist but not into 'spinning', I'd say go for 11:52 and a voltage somewhere in the 55V-65V range - for my personal preference in riding style, I'd be going for max efficiency at a cadence of about 90rpm, so about 60V, which also puts max power at cadence of 60rpm, perfect for those long uphill slogs where I can't be bothered pedalling fast :wink:.


OK Thanks for the math! Just so you understand I will be adding a freewheel to the front sprocket that the motor drives so that I can basically pedal if I like, or not. I really can't see pedaling at 30+MPH unless you are really spinning it! But I think this system might just work! We will see if I have room for the batteries and such when I am finished, but the chassis is going to be roomy..

0725001644a.jpg


I really like this idea as I will hopefully be able to produce a bike for relatively little money and still deliver great performance! Especially with something like a Rolhoff Hub in the back!
 
Whiplash said:
Just so you understand I will be adding a freewheel to the front sprocket that the motor drives so that I can basically pedal if I like, or not.
That will restrict you to having both sprockets/chainrings on the right-hand side, of course.
 
Whiplash said:
I really like this idea as I will hopefully be able to produce a bike for relatively little money and still deliver great performance! Especially with something like a Rolhoff Hub in the back!


rohloff hub > relatively little money.

http://www.universalcycles.com/shopping/product_details.php?id=10657&category=2713
 
YIKES! I didn't know it cost that much! I guess I will be doing a traditional gear cluster on the back! LOL!
 
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