Introduction: Powercranks for Less Than $ 6.00

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.")

Step 2: Cut the Cranks

Picture of Cut the Cranks

Before you cut the crank you want to measure your crankset so you could rebuild it with the same dimensions specifically crank length and pedal offset.

Just cut the crank arm and file the part that attach into the bottom bracket so it can hold the freewheel. I was very lucky that the inside diameter of the freewheel was almost the same diameter of the round part of the crank arm.

Cut enough material to make sure that the axis of rotation of the two pieces is concentric and parallel mine is misaligned by 0.4 mm, which I considered it was good enough. The front part of the freewheel (the one with the brand on it) need to point to the right side of the bicycle in the two arms.

Cut the crank arms to the correct length and file some of the teeth of the freewheel so you can connect the crank arm to the exterior race of the freewheel.

This is a good opportunity If you want to change the lengh of your cranks if you are too tall or too short. I suggest you read this http://www.nettally.com/palmk/crankset.html

Step 3: Assembly

Picture of Assembly

Assemble the cranks using the epoxy putty or if you have an arc welding machine just weld the three pieces together.

I used the epoxy because that way when I go to the welder he will not misalign my cranks, What he did was to put a piece of metal between the crank arm and the exterior of the freewheel an weld the center of the crank arm to the interior of the freewheel. He charged me $4.00 for that.

Just be careful not to weld the freewheel mechanism together.

Step 4: Enjoy

Picture of Enjoy
Put some paint in your cranks and back into your bicycle and enjoy the ride which will be much more difficult than ever.

From the little testing I have done so far I draw the following conclusions

1.- You feel which one of your legs is the weakest because you lose your coordination. In my case the right leg is the weak one
2.- You feel muscle pain from other muscles that probably you never exercised before. In short you feel like you when stop riding for the winter and start again.
3.- Is a little bit difficult to maintain coordination but I think I'm getting better at it.
4.- You could drive both of your legs in parallel like a kangaroo, is funny as hell and very hard.
5.- I haven't got outside to test this in traffic. I will get out as soon as I feel more confident.

Now I would expose the disadvantages of this design:

1.- Is ugly as a neimodian. Well yes, but if you are or have access to a good welder you could skip the epoxy and just weld the components and it will look better, also you could file all the teeth of the freewheel, but as I said this was the first prototype maybe I made another one.
2.- I don't know how much radial force and torque the freewheels are designed to withstand. but seem they are holding up well.
3.- The freewheels have a backlash of 16 degrees. I suppose that is desirable to have this backlash as minimum as possible but I don't know if this is small enough.

I will test this design for at least 2000 km or until I get bored to see what else comes up and probably will make another design a little bit more refined, but  all things considered I think the results are good for just an afternoon of work and less than six dollars of total expenditure.

Here is a sample of how they work.

Comments

FriendOfHumanity (author)2013-07-06

Excellent; such a wortkable copy for so little money.
Very cool.

dewexdewex (author)2011-03-06

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.

godscountry (author)dewexdewex2012-09-09

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.

Frank
PowerCranks

harmburger (author)dewexdewex2011-03-06

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.

dewexdewex (author)harmburger2011-03-07

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.

harmburger (author)dewexdewex2011-03-07

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.

dewexdewex (author)harmburger2011-03-07

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.

dewexdewex (author)harmburger2011-03-07

Thanks!

laubolgo (author)2012-04-05

Hey men!!! U R GREAT!!!! Super cool...

Brianaala (author)2011-06-04

Brilliant! I love this!

directx1222 (author)2011-03-20

great instructable - how did u make the rolling road thing for the bike (or where did u by it)?

Ob1kn0b (author)directx12222011-03-26

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.

directx1222 (author)Ob1kn0b2011-03-27

ok thanks

juanvi (author)2011-03-10

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
thanks

Ob1kn0b (author)juanvi2011-03-26

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.

desmonb2 (author)2011-03-20

what is the significance of this?

anres321 (author)2011-03-20

haha this is awesome !! :D 5*

finnrambo (author)2011-03-18

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

skaar (author)2011-03-08

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)skaar2011-03-08

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 (author)Ob1kn0b2011-03-11

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.

BtheBike (author)2011-03-10

Ha.
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.

slavik1 (author)2011-03-07

Really nice
I think i'll try this as my next project.

Ob1kn0b (author)slavik12011-03-08

If you do post your instructable or send me a photo and I will put it here

juanvi (author)2011-03-07

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)juanvi2011-03-08

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:

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.

juanvi (author)Ob1kn0b2011-03-08

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!

dan0314 (author)2011-03-07

Ok, Am I missing something? What is the point to this. The video just looks like someone is pedaling a bike.

Ob1kn0b (author)dan03142011-03-08

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

chiefredelk (author)2011-03-07

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)chiefredelk2011-03-08

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.

Fiction (author)2011-03-06

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)Fiction2011-03-08

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 (author)Ob1kn0b2011-03-08

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.

rcousine (author)2011-03-06

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)rcousine2011-03-08

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.

The_Cloaked_One (author)2011-03-06

I believe you mean.... " HI BILLY MAYS HERE! WHEN I GO ON THE INTERNET, I AM FORCED TO USE CAPSLOCKS!"

Ob1kn0b (author)The_Cloaked_One2011-03-06

Oh no, how could I forgot that, I will correct that horrible mistake

The_Cloaked_One (author)Ob1kn0b2011-03-07

THank you. I am a grammar nazi after all......it was bugging me......

thefrankofpowercranks (author)2011-03-06

I am the inventor of PowerCranks. Independent cranks are a great training tool for anyone who uses their legs for strength, running, or cycling. For the DYI person, what has been posted here is a great way of saving some substantial money because patents only protect inventors (me) from the others commercializing the idea. You can build your own (although the time investment for doing this is substantial). For those who are intrigued by this here are some of the issues I see with this "fix" as posted.

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.

Well, if there's a bright center to the universe, I'm on the planet that it's farthest from.

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?

I was simply giving some "heads up" to those who might want to do this for themselves that went beyond your instructions.

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.

AbbiesAcres (author)Ob1kn0b2011-03-07

Outstanding Instructible! I've always wondered why bicycle parts are so expensive when they are turning less than 120 RPM (it's not an F1 racing engine after all). And I couldn't agree more with your "pricing for exclusivity" theory.

Remember, keep it rubber side down!

carycary (author)2011-03-06

That is a great idea. May have to try it. Just one question, what in the world was that horrible music in the background? Someone was just destroying Madolin Rain. Made my ears bleed..

Ob1kn0b (author)carycary2011-03-06

I was listening to The Forcecast it's a parody song called Mandalore Reign, it's a podcast about Star Wars you can check them out in http://www.forcecast.net/

flamerider (author)2011-03-06

Very inventive, I had to read this to find out how you did it. I had a thought instead of stock steel to weld the crank/freewheel junction wrap a section of chain around the freewheel teeth down to each side of the crank and then weld. Recycle some chain and really leave people scratching their heads about what you've got there.. Keep on cranking!

Ob1kn0b (author)flamerider2011-03-06

Thats a very good idea, maybe I try it to make them look less like frankenstein

ralfhotchkiss (author)2011-03-06

Thanks, Obie...very, very nice, and gives me ideas for better wheelchair design!b And thanks to the feedback you attracted...gems of relevant info.

Ob1kn0b (author)ralfhotchkiss2011-03-06

Glad to be of help.

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