The other day I found some videos on the internet about powercranks and they seem quite interesting until you get to know the price, more than a thousand dollars in the US plus the smuggler fee and bribes to import those things to my third world country, we will be talking about $3,000, I could buy a car for that, and considering that my bike cost less than $100 this things are just wild dreams.
But that doesn't stop me so I decided I would construct my own, so after seeing some more videos I figured out how they work, but before I could design and manufacture an equivalent product I need to make a fast prototype for testing. This instructable is the way i made that prototype which really exceeded my expectations and you could use it to make your own and save a lot of cash.
But what exactly are this things, well to my understanding they have a freewheel mechanism between the axle of the crankset and the cranks which make each crank independent from each other so you need to actively maintain the 180 degree separation of the cranks.
This supposedly makes you go faster (hence the price tag), but I really don't care about that, they just seem fun to me.
But that doesn't stop me so I decided I would construct my own, so after seeing some more videos I figured out how they work, but before I could design and manufacture an equivalent product I need to make a fast prototype for testing. This instructable is the way i made that prototype which really exceeded my expectations and you could use it to make your own and save a lot of cash.
But what exactly are this things, well to my understanding they have a freewheel mechanism between the axle of the crankset and the cranks which make each crank independent from each other so you need to actively maintain the 180 degree separation of the cranks.
This supposedly makes you go faster (hence the price tag), but I really don't care about that, they just seem fun to me.
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Signing UpStep 1: Materials
You will need the following things
1.- Cheap chinese steel crankset. I used the one that came with my bike but a new one cost about $11.00. You could buy one new or salvage one from another bike if you don't want to destroy your actual crankset.
2.- 2 cheap chinese frewheels. One speed freewheel BMX type, I got these for $0.90 each at the chinese store
3.- Mighty Putty (HI BILLY MAYS HERE!!!)
4.- A handsaw, a file, a grinding stone and welding equipment.
5.- Patience. (Yoda: "The boy has no patience." Obi-Wan: "He will learn patience.")
1.- Cheap chinese steel crankset. I used the one that came with my bike but a new one cost about $11.00. You could buy one new or salvage one from another bike if you don't want to destroy your actual crankset.
2.- 2 cheap chinese frewheels. One speed freewheel BMX type, I got these for $0.90 each at the chinese store
3.- Mighty Putty (HI BILLY MAYS HERE!!!)
4.- A handsaw, a file, a grinding stone and welding equipment.
5.- Patience. (Yoda: "The boy has no patience." Obi-Wan: "He will learn patience.")
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I've just had a total hip replacement after 27 years of having a very weak and oft painful right hip. I think, in terms of range of movement, it was about 40% before the surgery, now it's 60% flexible after 3 months, but I can only motor it to 40% range with still little power. I've used a bike for mobility for the past 15 years, as my good left leg can compensate for all the weakness in my right. I can see instantly that something like this may be beneficial for my rehab, but I'm not sure that I'd be able to ride it at all. I wonder if I could ride something like this, that some form of lock on the cranks wouldn't be a bad idea, so I could lock it out if I was too tired to operate it properly. I guess it would take a couple of sliding lock pins.
Frank
PowerCranks
I live in Spain
thanks
Good job on putting it together though.
thanks.
I love it when the cycling industry tried to gouge$ the heck out of people,
only to force folks like yourself to put it in their face with this piece of WIN.
Dude , i sooo recommend calling a patent attorney asap. I can't wait to buy
a few of yours at walmart or sport authority for 1/15th the price of powercrank.
=D
thanks for the forcecast tip.
I think i'll try this as my next project.
btw,Ive, been looking and didnt found, where can I find these cinese stores that sell this kind of hardware? online store maybe¿ in witch country do you live?
thanks :)
The webpage for the chinese store were I shop is:
www.benotto.com.mx
the prices are in MXP (mexican pesos) and is in spanish but just remember
1 USD is about 15 MXP
freewheel = rueda libre
crankset = multiplicacion
I think they also have stores in south america.
Thanks again!
maybe if you approach to a technical school or other place where they teach welding you could get a better price.
also at those prices maybe it will be a better option just buy the machine itself, I've seen on amazon welding machines between a 150 and 350 bucks, if you like to do things on your own the machine will pay for itself in a short amount of time; is a very useful tool and it's not hard to operate.
Thanks for you comments and support.
It is unfortunate that most freewheels are so poorly made... I feel like that is certainly the weakest link that is going to go, before you make it to your desired 2000K or whatever.
If anyone wants to do this and has access to a lathe, it would be very easy to turn the spider-side bit of crank down and then thread it to accept the freewheel. That way, it would be a stronger connection and would even be replaceable when the freewheel bearings eventually fail.
One possible workaround for the crappy freewheel would be to cut off ALL of the teeth of the freewheel (so it was a smooth cylinder on the outside) and then sleeve a thicker piece of steel tube around it before welding on the crank arm... reinforcing the outer race of the freewheel. You could even cut a slot in the tube sleeving over the freewheel and put a pinch bolt on it, and weld that sleeve to the crank arm ONLY, effectively creating a BMX-style crank with a larger diameter hole. (You might want to leave one nubbin of freewheel tooth unground if you do this, as it could act as a spline to strengthen the connection between crank and freewheel) Anything you can do to prevent welding to the freewheel will extend it's life, as the heat during welding definitely destroys the delicate heat-treat on the freewheel.
Anyway all of these suggestions increase the complexity of the design considerably... but I think you've nailed the basic implementation, so any future efforts need to be stronger and cleaner!
Your ideas are very good I will take them into consideration if I make another crankset.
Also it appears that name-brand freewheels (DICTA) have a thicker outer ring and might hold up better in this application. They do cost a bit more though, $12-20 depending on where you're getting them.
Let us know how many miles you get out of your current setup.
Because you've decoupled the crank arm from the spindle, you're using it as a 170mm lever trying to roll the bearing off the side of the crank. The freewheel bearing may be able to cope with this out-of-design load, but it's not clear to me that's true. The pawls and bearings in there might be up for quite a wild ride.
I am not sure where this fellow is located but I would be surprised that in the United States I could find these freewheels for 0.90 each or a welder to do this welding job for $4.00.
That having been said, the major problem I see with this "cost saving fix" is one of reliability as related to fatigue failure. My guess is, if this fellow puts any kind of miles at any kind of power on these cranks, that those welds won't last him a year. I guess they might because everything is made of steel, but I would guess these also weigh about 5 lbs.
Next, he will have issues getting the cranks to line up at 180º when being used without extreme attention to detail.
And, then, he will have trouble making sure the cranks are the same length, assuming he wants them to be so (looking at the video, his left crank looks to be substantially longer than his right crank).
These are "small" details that probably are of little concern to those most interested in saving the maximum amount of money to achieve most of the potential benefit but they are probably big issues to the serious cyclist/athlete.
And, lastly, for that $1,000 or so that we charge, the athlete also gets a 2 year warranty and the ability to experiment with and the ability to easily adjust crank length to further optimize the transition and benefit of the device. And, a probable 10 year or more product life ( we are only 10 years old and most original cranks are still out there with few failures)
Whether you build your own or purchase ours I encourage you, if you are a semi-serious athlete, to explore the possibilities of independent cranks, but most of all, to have fun.
I live in Mexico City. but those freewheels and almost any bicycle part are made in china or in the pacific rim so I guess you could find them in any part of the planet at those prices (but if you can't the cheapest in Amazon is about $5). As for the welding well yes the prices will vary according to region and to the skill of the welder but how much they could charge you even in the US maybe $50 at much, it's just welding not brain surgery!!! besides many people own or have access to an arc welding machine so the cost for them is 0.00
I don't see an afternoon as a substantial amount of time for this project. If someone makes more than a $1000 in that amount of time maybe he will see it that way
How much is "any kind". They have resisted so far about 50 km of riding (one week) so, yes, metal fatigue is the only way they could fail, but as you know because of the probabilistic nature of material fatigue you can only estimate when the material fail, and you need a lot more data than is presented here to declare that it will last less than a year, it could last 1 month or a hundred years, who knows, personally I'm not going to make an stress analysis of the cranks just to obtain an educated guess, and if they fail, well, I just weld them again.
In the beginning the left crank weighted 530 g and the right one weighted 950 g the final weight for the left one was: left 700g and right 1200g. I don't see a problem with 420 g more.
You will have the same issues (whatever those are) with the original product to line them at 180 degrees, I think that ability is in the user not in the product.
The left crank actually is the shorter one, by about 1.5 mm. We always worn out one shoe more than the other and you don't feel that difference when riding. Also check out your legs and you will find they aren't of the same length, and that difference is more than 1.5 mm.
The "serious" cyclist/athlete will buy anything that promises any improvement at any cost and for him the more expensive the product the better the product is. That's why we have carbon fibre seatposts or titanium saddles. This product can bear such a big price because of this irrational thinking because if everyone can afford it, how good can it really be?
Fatigue failure is a real issue for bicycle parts. It has nothing to do with doing an analysis. If one wants to avoid this possibility one should pay a lot of attention to this aspect to get a good weld. Small imperfections in the welds will eventually lead to fatigue failure. It is not a matter of if but when.
And there is an issue of getting the left and right cranks to line up properly. The freewheel is a pawl mechanism and has fixed points at which the cranks engage. If these points do not line up when the cranks are manufactured nothing can be done by the user later to make them line up. A couple of degrees off is pretty well tolerated but much more and the rider is not going to like it. The PowerCranks use a roller clutch so the engaging points are essentially infinite, and this is not a problem because if the cranks are not at 180º the rider can change it on the fly. It sounds hard but it is really easy.
And, yes, people tolerate small changes in crank lengths without much problem and most people do have leg length differences. But, again, it is a potential issue if one doesn't pay enough attention to the build detail. And, if the long crank is on the "short leg" side, any problem could be magnified.
Anyhow, to those of you who make this for yourself, enjoy.
Remember, keep it rubber side down!
they do look interesting.
http://www.instructables.com/id/REPLACE-A-BICYCLE-BOTTOM-BRACKET/
http://en.wikipedia.org/wiki/Sprag_clutch
my original idea was to make them in CNC (since I know about that) but I made this prototype to evaluate the principal variables of the design to my surprise the first prototype works just fine so it occurred to me that you can make the without the aid of CNC.
But using the sprag clutch you suggest I calculate the cost of making them in CNC will be around a 100 dollars, (if you know how to operate/program the machine.)
With a freewheel in the rear, would putting more/less force on the desired/developed leg, have a similar mechanical advantage as power cranks?
With less $,€,£? ¥. Less epoxy. Welding.
My 2 sense.
Otherwise, it IS a cost effective solution to the capitalist world. An instruct=> able, indeed! Kudos.
If you don't change the length of the crank the mechanical advantage will be the same as before.
You could buy a freewheel for a trials bike. The have between 72 - 108 engagement points so the backlash would be smaller. However, this would defeat the purpose of a cheap build as those freewheels cost $70 - $90 US dollars.
Great build! I love it when someone out builds "the man" for pennies on the dollar.
WOW ! THAT was funny looking - I was watching the video after reading your entire 'ible - I actually laughed out loud when I saw what you meant ! :-) GREAT job ! I am not a biking enthusiast, being restricted to a wheelchair, and had NO idea where this Instructable was going (no offense intended !) until I reached the end and saw everything in action - excellent work, you made a fan out of me !
How do you lift the lower pedal to stop it hitting the road when going round a sharp bend??
really tempting to get a cheap crank to train with though...
any quicker. Maybe if I were a trick rider I'd find a use for it, but it
it seems like a lotta work just to add extra weight to my bike. When
my weak leg gets tired, i simply shift most of the effort to the other
leg. However tinkerers the world over have my full support; they're
the ones that make things happen. There'd be no progress without
them. So keep at it; we need more creative minds to tackle tough
challenges.
Maybe not actually that pricey.
Now I want to make a pair for me!!
Is not difficult to get used to?
Post a photo when you build your own.!!
http://en.wikipedia.org/wiki/Bicycle_pedal#Clipless_pedals