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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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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.