Picture of Powercranks for less than $ 6.00
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.

Step 1: Materials

Picture of 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.")
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Excellent; such a wortkable copy for so little money.
Very cool.
dewexdewex4 years ago
I've never seen this idea before. Thanks for posting this, it's a fantastic hack you've done there.

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.

I came across your old post on the power cranks.this is a great hack,but power cranks can be a work out,if your not use to them.Their are a few ways to get around limited knee flexion,,the best I have seen is a modified the crank arm,through some measurements,you cut the crank into two pieces,the lower part with the pedal,pivots around the upper part.This is for experienced DIY,if the crank does not pivot, or fails you could be seriously hurt.Their are a few places you can buy them,or have them built.Google or Bing, Limited knee flexion bike cranks or similar word phasing
Dewex, independent cranks are truly a most powerful hip rehab device. If you have already tried this I would be interested in how it went. If you haven't tried this and still are having trouble please give me a call. We will see if we can help you out.

If you were planning on using just your left leg if the right was too tired, all you would have to do is just not move your right foot. As you can see in the video between :30 and :40, this system allows you to use just one foot to pedal.
I suppose they'd have to be toe-clipped or clip-ons. I reckon if I did build something, I'd probably only do rolling road with it indoors, as handling in traffic with all the stop/starts would be too tricksy.
This whole system doesn't work unless they have a retention system. In this video he's using special shoes that clip onto the pedal.
I understand now. Thanks. You'd have to be able to back pedal the cranks independently, so they'd have to be connected to your feet to enable you to lift them. I still think this would be OK for me on a rolling road. Thanks for your reply.
laubolgo3 years ago
Hey men!!! U R GREAT!!!! Super cool...
Brianaala4 years ago
Brilliant! I love this!
directx12224 years ago
great instructable - how did u make the rolling road thing for the bike (or where did u by it)?
Ob1kn0b (author)  directx12224 years ago
Thanks. I also made the rolling road (rollers) about 8 months ago since the one at the bike shop was too expensive for me. Soon I will post an instructable of how I made it.
ok thanks
juanvi4 years ago
hi, I didnt find any on www.benotto.com.mx, plus they dont sell in my area... I'm interested on those chinese freewheels, know any webpage or something?
I live in Spain
Ob1kn0b (author)  juanvi4 years ago
Sorry I don't know anything in your area but you can get in contact directly with the manufacturer in http://www.made-in-china.com just search for freewheel or any other bike part and it will display a list of companies, you could ask if they have an importer in your area or even you could become one, but I assume you need to place a large order.
desmonb24 years ago
what is the significance of this?
anres3214 years ago
haha this is awesome !! :D 5*
finnrambo4 years ago
that's pretty awesome! I thought it said PowerTap for 6.00 and I was jumping for joy before I noticed this will work well though :P, good 'ible
Ob1kn0b (author)  User14 years ago
Yes they will look very silly riding like a kangaroo, but maybe it could be a big thing in Australia...

people vs kangaroo bike race!?
skaar4 years ago
i've been working on a method to park my pedals, so when i put a motor on my bike i can have the pedals both at best spot for coasting. it's for a future project using a much larger motor, adding pedals to a light motorcycle.
Ob1kn0b (author)  skaar4 years ago
this could be a solution for your problem as both pedals go to the bottom but i don't know if that is the best spot, also how are you coupling the engine to the wheel????
skaar Ob1kn0b4 years ago
chain with the suspension pivot being a jackshaft, possibly a pedal crank below. was thinking that a pin to lock one side, and a locking freewheel on the other side would work.
BtheBike4 years ago
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.

thanks for the forcecast tip.
slavik14 years ago
Really nice
I think i'll try this as my next project.
Ob1kn0b (author)  slavik14 years ago
If you do post your instructable or send me a photo and I will put it here
juanvi4 years ago
hey! very nice hahah i think its really cool.

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 :)
Ob1kn0b (author)  juanvi4 years ago
I live in Mexico City, here a lot of people use their bikes as a transport or utility bicycle, so there is a demand for cheap parts, but as I said in another comment all parts are made in china and if they could sell here at those prices here i think they could do it in any part of the planet.

The webpage for the chinese store were I shop is:


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.
juanvi Ob1kn0b4 years ago
ok, thanks a lot, I live in Spain, I'll check out the web page and see if they sell here, cause as far as I know, its very difficult finding spare parts of bicycles and hardware in general here in Spain.

Thanks again!
dan03144 years ago
Ok, Am I missing something? What is the point to this. The video just looks like someone is pedaling a bike.
Ob1kn0b (author)  dan03144 years ago
Well the point is that the pedals are independent of each other so you need to coordinate your legs in order to ride the bike. It's more like a "Look ma! no hands" type of thing
chiefredelk4 years ago
Bless you... A man after my own heart, but.. Here in the states that little job would cost you MUCH more than 6 bucks... I expect just the epoxy alone would cost close to that and good luck getting someone to weld for less than 25 bucks for just half that much work... I just paid 16 dollars per inch to a welder.. I would guess in the states we are looking at a ball park figure of 45 to 75 bucks for that build and maybe more.... STILL it's a great idea and you did a jam up job... I am for sure, impressed,, Good day, Chief
Ob1kn0b (author)  chiefredelk4 years ago
I didn't take into consideration the cost of the epoxy because I always have some laying around but i used a little under half a stick so is about 2 or 2.5 bucks

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.
Fiction4 years ago
Great instructable... very clever solution.

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!
Ob1kn0b (author)  Fiction4 years ago
yes everything depends on the frewheels I will wait until they fail and then evaluate what to do next. i put that 2000k limit because if they last that long maybe there's no need to make another prototype.

Your ideas are very good I will take them into consideration if I make another crankset.
Fiction Ob1kn0b4 years ago
Yeah I was looking through a supplier catalog for better freewheels (I work at a bike shop) and I noticed that you could potentially use a freewheel with a larger tooth count (like a 22 or 24) as it would have a lot more steel reinforcing the outer race.

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.
rcousine4 years ago
Neat concept, and I admire the can-do engineering, but I'm not entirely sure (and I see you acknowledge this) that a freewheel has any design capacity for the offset forces you're putting on it.

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.
Ob1kn0b (author)  rcousine4 years ago
yes the only way to know what will happen to the freewheel is testing them, (at this moment they have endured 80 km) I will ride until they fail,( or if they not fail until I get bored) and then with that information decide where to go next.
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