Blade attachment reexamined

To ensure that all of the energy from peddling is transferred to the rotation of the blade, the blade must be tightly secured to rubber rod that rotates in conjunction with the axle attached to the rear wheel.  The blade is currently connected by a piece of piano wire that lies perpendicular to the blade and bent around edge of the blade, effectively hugging it to keep the blade in place.  This design is very effective at preventing the blade from rotating independent of the plastic rod, however, it is very difficult to manufacture, rusts easily, and does not allow the blade to be removed for maintenance or cleaning.  

Current blade design, bent piano wire hugging the blade, bottom view

Current blade design, top view

 

Thick piano wire is very difficult to work with, and bending it in a way that successfully secures the blade is very time consuming.  A simple alternative would be to use a thinner wire that is easier to bend.  However, this thin wire is not as durable and cannot secure the blade as tightly.  Simply changing the thickness of the wire was not an appropriate solution, but because thinner wire is relatively easy to work with, we could change the shape of the wire to yield a sturdier connection between the wire and the blade.  By changing the shape, the wire would bend at right angles rather than folding back on its self.  After playing around with a few different ways to bend the wire, a weaving method appeared to be the most promising. 

Blade weave design, does not require as much wire bending

Although the weave required less fighting with the wire than the original hugging method, it was still difficult to fix the wire in place, and did not seem very durable.

Store-bought blenders secure their blade to the base of the pitcher by a screw that is inserted though the middle of the blade into the bottom of the rotating device.  To apply this tactic to the bicycle blender, a screw would be inserted through the middle of the blade and anchored in the top of the plastic rod.  A potential benefit of this design, is that it could be constructed so the blade could be removed for maintenance which would improve the longevity of the blender.  The potential problems with this method are ensuring that the blade does not rotate independent of the rod and that the screw is properly anchored.  Another drawback is that the screw method has more parts than the original piano wire method.

Commercial blade with center screw

With the general idea that a screw would secure the blade to the rod, there were two particular designs that appeared to be the most promising. 

Design 1 has a removable blade and involves four different extra parts (other than the blade and rod).  A screw is fitted through the blade, a washer and then into an aluminum standoff.  The screw should only penetrate about half the length of the standoff, so a second screw is used to connect the standoff to the rubber rod.  By cutting off the head of the screw, you are left with a threaded rod that will screw into the bottom end of the stand off and the top of the rubber rod. Because the blade is fastened into the aluminum standoff instead of the rubber rod, it is possible to unscrew the blade without harming the screw anchored in the rubber.  

Design 1 before assembly

Hole drilled in the top of the rubber rod

Design 1 assembled

Design 2 only includes three extra parts (two of which are the same part), but the blade cannot be removed.  The screw is placed through the blade, two hex nuts and directly inserted into the rubber rod.  Applying a small bit of Krazy glue to the end of the screw and the inside of the hole in the rubber helps ensure that the screw is properly anchored in the rod.  

Deign 2 before assembly

Design 2 after assembly