Alternative location for mounting a motor on a folder

[Desertprep]

Has anyone mounted an electric motor (cyclone, etc) in some place other than the bottom of the bike and still been able to use the gears with the motor? My bike has 16" tires and is already close enough to the ground as it is. I am hesitant to give up 4 more inches of clearance. Anyone mounted it over the rear wheel? near the seat post? I am hoping, of course, that it will still be foldable.

 

[amberwolf]

Sure. There are many ways to do it. The Stokemonkey mounts in the rear triangle, with the wheel mounted in an Xtracycle or similar. I've also seen one or even two motors in the front triangle, running down to the BB. It's also been done at least once from the rear rack, but the chainline is so long from there it may derail if the frame twists under load.

 

[jdcburg]

Here are 2 possibilities, both of which drive through the BB and derailleur. The red one is my dual freewheel design and the blue-green one is from the Cyclone-tw site - jd

 

[Miles]

Specifying which "folder" would help, pengyou :wink:

 

[mwkeefer]

peng,

Yes you can probably mount it slightly above the wheel, I would go as far forward toward the riders post and rig a bracket.

If you could post more about your 16" wheeled folder, we would be happy to offer some appropriate feedback for conversion purpose

-Mike

 

[Desertprep]

Sorry...I should have thought of that. I have a Dahon Boardwalk.

http://www.google.com/imgres?imgurl=http://www.thefitnessstore.com/uploads/07boardwalk.jpg&imgrefurl=http://jclist.com/modules/newbb/viewtopic.php%3Fpost_id%3D197947&usg=__FA8LKFi_YmGquRc1Q8Vocd4Bpt8=&h=500&w=500&sz=41&hl=en&start=0&tbnid=fuKoEDLjo6RGtM:&tbnh=151&tbnw=147&prev=/images%3Fq%3Ddahon%2Bboardwalk%26hl%3Den%26newwindow%3D1%26biw%3D1280%26bih%3D607%26gbv%3D2%26tbs%3Disch:1&itbs=1%20target=_blank&iact=hc&vpx=131&vpy=70&dur=1598&hovh=225&hovw=225&tx=134&ty=126&ei=ujdQTO74GYmWceSQ7L8J&page=1&ndsp=16&ved=1t:429,r:0,s:0

The space behind the seat tube looks like it is just begging for a motor. I have often thought also that putting a 24v or 36v, 250 or 350 watt motor in each of the wheels would make this a really interesting ride. I think it would be safer with debris on the road, or with heavy rains, both of which I experience in Shanghai. I have been scared to death of putting a hub motor on the front fork because I am not sure it would take the torque and I am not sure if they 2 motors would need something special to make them work in sync. I am sure it would be slightly less efficient with 2 motors than 1 larger motor, even if they had approximately the same top speed.

 

[mwkeefer]

Boardwalk!

Nearly identical frame (except for the steel part) as a downtube Nova (www.downtube.com) which I have also converted - currently a rear geared hub running about 75v and 20A for a top end of approx 32-33mph flats.

Dual motors is doable but that folder with a steel frame is already heavy enough... running both motors, if running them close or at their no load RPM (max speed for a given voltage) then they really wouldn't be very inefficient as you think - the load would be distributed between 2 motors and they would share assuming they were the same winding (kV) for the voltage used.

Now the funny part...

Given your frame, I would consider a below the space motor mount and use that space for a battery pack... Folders are designed (these anyway) to distribute much more of the weigh aft for a reason - hinge reliability at the folding joint.

A below bottom bracket (or that space) motor mount should still give plenty of clearance to chainline a large rear sprocket (search for Gary Goodrums 3spd Port Runner here on ES for a good example) and the total weight of such a system (depending on parts chosen) could weigh about 1/2 of a decent hub motor with a more central weight distribution for better handling - cause I know weight is critical to maintaining a nimble ride on a 20" it must be even more important on a 16" folder

Road conditions - debris, pot holes, rain... the answer is GOOD KEVLAR belted tires - look at stuff targeted for the 16" recumbent market to find tires narrow enough for your bike and yea with a tiny bit of work you can prob fit Maxxis Hookworks or Big Apples by Schwalbe - the latter are great on non sus bikes and have Kevlar protection, exactly what I run on my folders when space / clearnace permits... I'm testing some new tires "Primo" was the brand - recumbent targeted 1.5" wide and Kevlar belted and much better clearance within the frame rails.

Again hope this helps!
-Mike

 

[Desertprep]

Thanks! now that I think about it, maybe it is not boardwalk but it looks identical to that picture. It has a chromoly frame with 7 speed rear and weighs about 23 pounds. I will have to consider the weight distribution carefully. I also need to consider the folding aspect also because I will be folding the bike on an almost daily basis, to put it in its case and take it for a ride on the subway A motor on the bottom is more likely to get banged around or abused in the folding/unfolding process, whereas if it were tucked inside a cavity of the bike it is going to be protected.

Do you have any idea what size motor/voltage I would need to cruise at 30 mph on flat land? I weigh 175 now - will be loosing 10 more pounds in the next couple of months A lot of bike shops here in Shanghai sell a 36v 10ah life for about US$ 130 I think they weigh about 12 pounds. my dream is to get this up to 30 mph for 50 miles ....then after that dream is reached...i will think about installing the generator

 

[mwkeefer]

For the weight limit of the frame, I would look for 15C lipo locally... I'm sure it's there or available at reasonable costs from neighboring areas.

30 mph on a 16" right?

30 * 336 = 10080 / 16" = 630 RPM...

I would consider RC to be about your only choice here...

Normal geared hub motors in a 26" wheel at 36v (10S LiPo/12S liFePo4) will average about 18mph max to 15mph at battery cut out.

The idea of overvolting the heck out of a geared (for weight savings) hub and running it at 630 RPM (about 2x the design limit) will cause serious overheating...

Your better option would be even to look at a single stage RC drive system - or somthing similar, mount the motor behind the seatpost or beneath that same area - and direct drive it to a gear on the left side of your rear wheel, for lower power stick with #25 chain as it's lighter and still good for about 2-3kw.

Assuming you got an RC motor like a Tower Pro 5330 9T 235kv and approx 80% efficient - so again,
235 * .80 = 188 loaded kV (RPM per volt input)

Lets look at smaller packs, either behind your seat tube or mounted where the water bottle bosses are in the fore part of the main folding tube...

For arguments sake, lets say... 6S packs

Again we work with Nominal voltage figures so 6 * 3.7 = 22.2v nominal
22.2 * 188 = 4173.6 RPM - this is what your motor would produce at the drive shaft at nominal (average) 6S pack voltage...

If your going for 30.. we figured it at 630 RPM on 16" right?

4173 / 630 = 6.62 : 1 reduction required between rear wheel and motor to acheive 30mph sustainable on 6S packs.

Chargers for 6S packs are cheaper too... throw 4 packs together (15-20C) @ 5AH each for 20AH then set your current limiting around 1200w or:
1200 / 22.2 = 54A

Now you will need more AH for the range you are looking for, that setup would likely get you 25-30mi without pedaling maybe more even... Add a standard rack to front or rear and double up with another 20AH... if you can't get 50mi range out of 40AH of battery, somthing is wrong

If you are dead set on getting a hub motor, go for somthing geared but designed for Higher RPM of your 16" wheel - I can't think of any appropriate hub motors for that size off top of head but perhaps a PM to cell_man could help there - I know he has direct access in China and maybe could get you setup with some 16" mag style hub motors I've seen... not sure they would even fit.

Nice part about RC or BLDC motor design direct drive - parts weigh next to nothing and the power ability is there as needed + if done right, you can leave most everything on your bike (wheels) stock, may seem silly but first time you try to change a flat on a folder with a hub motor... you get the idea.

As far as folding goes...

All my folders are folded daily and usually many times a day... If I run to the city (Philadelphia), I take my bike to a local train stop... fold it down and get on... at the other end I unfold.. Most of the time if I am going in somewhere for a while like a coffee shop, I will fold it and bring it with me... plus when my children are home, I store the bikes folded (I have too many of them).

The only problem I have with folding is front fender scratching (on bikes I've put a front fender on)...

And your right - it may not be a boardwalk... sounds more like a D7 @ 23 lbs?

-Mike

 

[MitchJi]

Hi,

You could use either a hub motor or an RC motor going through the gears configured like this:

A geared hub would be a good match for cadence without requiring additional reduction. If you have space for a geared hub configured like that the only issues will be getting it mounted and mounting a FW (second sprocket on the motor shaft) to connect to the pedals.

 

[Desertprep]

Thanks! The hub motor mounted outside the hub is a great idea but I don't have any room for something the size of a hub that would put out 500 watts or so.

The RC motor is a good idea also, but I am not very familiar to the way they are rated. They are also expensive. If I were going to buy a motor that is more commonly used for ebikes - similar to the cyclone motors - what size motor - V and W - would you recommend? I have seen some longer and thinner motors that would fit in the space between my seat tube and rear wheel, and I have seen some 650 watt motors that weighed 5 pounds. I would like to stay with either 36 or 48 volts because of the cost of the batteries. If that doesn't work, I think the next jump would be 72 volts - 2x36? - and might be more economical than 60 volts...though I guess I could do 36V and 24V to get the 60 24V and 36V LiFe batteries are becoming somewhat of a commodity here in Shanghai, so the cost per watt is quite a bit lower than for a 48 or higher.

 

[geekybiker]

Its probably a speed D7. I have a speed d7 and put a cyclone on mine. I wanted to mount behind the seat as well initially, but that ended up looking like a lot of custom work to get the chain down where it needs to be. The 360w goes ~20mph for about 10miles on a 10ah battery. The biggest issue with the stock mounting on the d7 is that the chainline is really really crooked. This makes the chain love to jump and I'm sure its not good for efficiency. I'd suggest looking into a IGH for folding bike with the motor in the standard position. The other real alternative is to the the 3 chainring kit and try mounting the motor behind the seat that way. You'll end up with some fast moving chain right next to your leg though.

 

[MitchJi]

Hi,

Thanks! The hub motor mounted outside the hub is a great idea but I don't have any room for something the size of a hub that would put out 500 watts or so.

Would a geared hub (smaller than a dd) motor fit? This is a 500w rated (can handle over 1k at 48v) Puma in a 26" wheel:

Dimensions are here (download the pdf's):
http://endless-sphere.com/forums/viewtopic.php?f=31&t=17029&p=254422&#p254431

Here's a thread about small hub motors that accept 7sp fw's:
http://endless-sphere.com/forums/viewtopic.php?f=3&t=17368&

 

[mwkeefer]

Those will fit fine, 135 is the listed spec on OLD but the D7 has a tad (about 3-4mm) of flex (NOT BEND, flex).

I've wedged 9C hubs into them and the Nova from downtube (roughly same spec frame dimensions)

-Mike