My shredder construction log
Just thought I would make a thread of my shredder construction.
After a weekend of fiddling, I managed to get the machine to an assembled state (please ignore the welding quality, I have just started to teach myself how to weld).
I will be spending this week/weekend tuning it so that it rotates smoothly.
Ok, post 2 of my shredder.
I had been inspired by another post that mentioned hooking the shredder up to a bicycle, and I thought that this would be a good start as a proof of concept. So I purchased an exercise bike for $10 from the local tip shop, a steel frame that someone was selling at a garage sale, and after much modification, I have put together the following shredder.
I managed to get it to operational stage this afternoon, and though it does successfully shred, I find it very difficult to get a constant peddle action going. As soon as I drop plastic in, the resistance makes it too hard to pedal. I suspect/hope that it is just a case of getting the gear ratios correct, and I am wondering if there is any engineer who can help me with this because I can’t get my head around it.
As you can see in the photo, the cranks have one large gear. The Shredder has one small gear. The middle axle however has a rack of five gears on it.
Currently I have the following setup:
Crank to Large gear on axle & small gear on axle to shredder.
Is there a better settup that will give me more power? Any engineers/bike gurus who can give me some advice on this?
With that set up you have the about the best gear ratio possible, but really it needs to be much higher. If you could swap the sprocket on the shredder shaft and the chain ring on the bicycle crank it would give you much more mechanical advantage, but would involve a bit of engineering. Your best option with least work is probably to get a mountain bike crank with 3 chain rings, run from the smallest chain ring on the crank to the large sprocket on the cassette, Put as large a sprocket on the shredder as you can (maybe the large chain ring from the crank) and then run to that from the smallest sprocket on the cassette. If you can get 4-5 turns of the pedals to one turn of the shredder that should be enough, but the more the better!
Also if you remove the freewheel from the cassette (or mount it with the original spindle) you can pedal backwards to clear jams and set the pedals in the optimum position to apply torque.
Thanks for sharing your updates here! I missed the original topic but are following it now on. Your welds look great, don’t worry about that
Nice to see you tried the bicycle, we did a few tryouts with that as well and experienced similar problems. One thing that really helped us was to add a flying wheel. Something that stores the power. We made a heavy one out of concrete on the shredder axle. Made a big difference for us!
Good luck and keep us posted 🙂
The bike looks good!
Thanks for sharing.
Have you managed to improve your system? Have you tried a flying wheel as Dave advised you?
Keep us informed!
@saluc42, I am hoping to post an update video this weekend. In the photo that I posted, the bike was in an extremely rough state (I am not exaggerating when I say that parts of it were being held in place with tape). I have made a couple of changes thanks to the feedback I have received which has had a positive impact on the machine, positive enough that I will be spending the time removing the tape and making it sturdy. Once that is done I would like to create a video for peoples reference and comment.
I will note that I can’t promise that I will get it completed this weekend. I live in a part of Australia that has been experiencing some significant “rain events” over the last couple of weeks (with over 300mm falling over a 24 hour period a couple of weeks ago). We have a chance of another event this weekend and if there is a lot of rain my working area becomes a bit of a river.
It took a while, but I finally managed to get a video of the bike in action. Sorry for the quality, there is only so much you can do with a mobile phone.
Anyway, here is a link to the bike in action….
could you just use a weight plate from a gym as a fly wheel?
How about using more but thinner shredder blades?? If you’re only going to shred those milk bottles, it would make it easier to cut through them…
Is there another central thread for “Bike Powered Shredder Development” or is this the best place? I plan on using a bike to keep initial and future cost down. If anyone has any pointers that’d be great.
Where I can download the blueprints from?
literally just had the same idea after seeing a spin bike at the gym… (using a heavy flywheel) I think it’d really smooth out the shredding action – does it also add torque?
Hi @jacobroy-quebec, sorry for not replying earlier.
I will send you a photo of how the gear is attached to the shredder tonight when I get home from work.
Hi @katharinaelleke, no, I have not really improved on the design. The whole idea of this design was to provide a cheap shredder while I get the whole thing up and running. I am trying to build up the courage to do the injection mold next. Once I have that going and I am making items, I will see how they are accepted. If I am able to get some interested (and associated income) then I will be replacing the pedal-power with an electric motor.
we also built a pedal powered shredder very recently.
as is the video /construction from simonm, it is not very easy to get through the plastic with just pedal power. it cloggs sometimes. as the frame+shredder box and the bike are two separate items, conncetd with the chain only, everything moves, when something gets stuck. our gear ratio is about 1, so it might not be optimal also.
the fly wheel could be a possibilty.
Any suggestions/ideasa for us?
we are placed in Berlin.
sincerely yours, lisa
Has anyone tried a “treadle” configuration like was used on an old stone grinding wheel? Once you get the stone in motion, keeping it going requires pumping the pedal, but could allow a configuration where the shredder operator is also powering it. (Something similar to a “Stairmaster” would seem like it could also work, but the mechanism for driving it with two independent chains is a bit more complex.)
That will depend on the thickness of your blades, primarily, relative to the scree/sieve you have installed. If the blades are taking big “bites” that don’t pass through the screen on the first try, they’ll come around and get run through again. It seems as though a big difference between the screen and the blades runs the risk that you spend a lot of time churning half-chewed bits of plastic until they happen to hit the blades right and fall through.
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