Bike Blender Using a Real Pitcher

The best way to understand the full potential of a bicycle-powered blender and identify the pitfalls of our particular model is to build a blender using  The first step in creating a blender using a “real” pitcher is to obtain a full blender and remove the motor, leaving you with a pitcher and base support.  The motor is the only piece that will not be used, because the blender will be human powered!  However, because the motor is removed, it will be necessary to build something that transfers the rotational energy from the wheel to the blade.  To complicate things slightly, the pitcher rests approximately 5 ½ inches above the top of the axle, so whatever is used to transfer the rotational energy must be 5 ½ inches tall. 

a commercially purchased blender.

It was very helpful to look at existing bicycle blender designs that use pre-made blenders to figure out how to go about building our blender.  There were a few options for how to get the energy from the top of the axle to the base of the pitcher, and the design that was ultimately built incorporates elements from different designs. 

A basic support made from wood blocks stacked on top of each other was the simplest and most logical way to fill the inside of the base and support/protect the more fragile elements.  Inside the top of the base there was room for a block of wood with dimensions approximately 2” X 3”.  The particular wood that was used had a height of ½ an inch; a stack of six blocks produced a three-inch platform that could be used in conjunction with the pre-constructed wooden donut to fully support the base of the pitcher.  Similar to the existing home-made pitcher, a plastic rod and ball bearing were used to transmit the rotation of the axle to the blade.  A hole slightly larger than the diameter of the rod was drilled through the wood platform, and then a larger opening was chiseled out at either end.  One side of the wood platform holds the ball bearing, so the hole needs to be just wide enough to have the ball bearing sit snugly, and should be as deep as half of the height of the bearing.  The bearing will be closest to the top of the rod and the pitcher, so, naturally, the other end of the wood plank will be close to the bottom of the plastic rod, the end of the rod with the piece of the nail inserted through it.  Thus, the hole chiseled into this end of the wood must have a diameter large enough to allow the rod and nail to rotate freely.  After the holes have been constructed the only steps left in assembling the wood block is gluing the bearing to the wood, (using wood glue or other appropriate adhesive) shaping the top of the rod so it will fit into the square opening in the base of the pitcher, and properly inserting the rod through the plank and bearing.

Wooden platform with a hole through the center for the plastic rod

Top of the wood block with the bearing and rod inserted

Full wood platform inserted into the bottom of the base.  A larger hole has been chiseled out so the plastic rod fits properly in the top of the axle. 

  

To finalize the blender, the wood platform must be secured to the base in the right location so the plastic rod reaches both the top of the axle and the base of the pitcher.  To secure the wood platform to the plastic base, small holes were drilled through the plastic and wood and a screw was screwed through both the plastic and wood to hold the two pieces together at the correct height.  The construction of the bicycle-powered blender using an actual pitcher is finished, all that needs to be done before blending is placing the pitcher on the base and placing the base on the rear rack above the axle in the correct orientation. 

Two screws hold the wooden block at the correct height

Fully assembled bicycle blender using a real pitcher

Blindly trying to properly fit the plastic rod into the top of the axle is almost a matter of luck, it takes a few tries before getting it right, and can be easily nudged out of place. Thus, it is necessary to construct a base support that helps guide the base onto the axle properly.  Getting the base on the rear rack takes a few tries, but is fairly secure once the rod is in place.  A basic structural support will allow the base to be guided onto the rear rack and ensure that it is held in place during blending.  The support will be constructed from two pieces of angle iron, one secured against one side of the base and the other fastened to the back of the base.  A screw will protrude from the iron and fit into a slot in the pitcher.  There will be a hole in the side of the pitcher and a slot in the back, as you place the pitcher the hole, it will simultaneously slide into the slot; thus, the pitcher will not be able to move from side to side or up and down.  

Prototype of angle iron base supports

prototype of securing mechanism

Getting the Blade into the Pitcher

Trial and error has been a huge part of making and refining the blender.  In tackling the blade and pitcher attachment, there has been a lot of trial and a lot of error.  The ideal solution is still waiting to be stumbled upon.  However, even with no end result, there is a lot to say about what has been discovered about how not to attach the blade to the pitcher.   

As mentioned in a previous post, a pitfall of the current blender is the amount of glue used to attach the blade apparatus to the pitcher, and finding an alternative method of attachment proves to be almost equally problematic. 

 

Initially, a small hole was cut in the base of the pitcher and the blade was inserted so the lip of the bottle cap rested on the base of the pitcher.  To secure the blade, the lip of the bottle cap was glued to the inside of the pitcher.  To reduce the contact between glue and blended matter the lip could be simply glued to the outside bottom of the pitcher.  The main problem with this solution is that the blade assembly would have to be finished after the lip had been glued to the pitcher because the diameter of the blade is greater than that of the hole in the pitcher (hole in the pitcher is approximately the diameter of the bottle lip).  It is possible to finish assembling the blade after the lip has been glued, but doing so adds an unnecessary level of complexity.  Although this may be the most straightforward solution, is it is not necessarily the most practical. 

To find the best way to attach the blade, it was necessary to think about completely redesigning the base of our blender.  Looking at the most successful commercial blender designs provided a framework a new design. A two-piece design composed of a pitcher with a threaded base, and a threaded cup that holds the blade and screws into the threaded base of the pitcher was pretty universal.  Unfortunately, the dollar store pitcher currently used for the bike blender does not have a threaded base, so to use the current commercial design there would have to be a major modification.  Regardless, a two-piece design seems plausible and would make blade maintenance much easier.  

  

Being able to insert and remove the blade apparatus from the bottom requires a larger hole in the base of the pitcher, and a larger hole means there is a larger area for liquid to seep through.  An initial idea was to cut the water bottle at a wider part and fit the diameter of the bottle into the bottom of the pitcher, secure it and make a watertight seal.  Conceptually, this seemed like a reasonable, good solution, however, the technicalities of how it would be constructed still had to be worked out.  Another point to consider was that using more bottle cap would mean pushing the blade higher and higher until the diameter of the bottle matches the diameter of the seal, whereas ideally, the blade rests ¼ of an inch or less from the bottom of the pitcher.  

Aware of the potential challenges of the design, it was time to start on a prototype.   Initially, most time was spent looking into ways to secure the extended bottle cap to the pitcher.  Using a paper bowl to simulate a rubber pitcher, a hole with a diameter of two inches was cut from the bottom and four nails were inserted so their heads protruded into the hole.  The idea behind the nails was that they would fit into grooves cut in the water bottle, effectively holding the bottle in place.  There were a few problems encountered during construction; first, a longer bottle makes inserting the ball bearing nearly impossible because the channel is too narrow for a hammer, the next drawback was that the neck of the bottle does not meet the screws at right angles which makes it difficult for the nails to fully support the cap, and the last problem was that connection was not watertight. 

 nails inserted in the paper bowl that is substituting for a plastic pitcher

full water bottle prototype

 

A few other initial prototypes:

 

Tin Foil seal

screw lock mechanism

rubber seal and screw lock mechanism

To revise the blade connection design, a more effective attachment and sealing mechanism was needed.  Going back to brainstorming, a convincing idea was to line the inner edge of the hole with rubber.  A rubber lining could potentially serve both as a sealant and a support.  The logic behind this new design was that the friction between the rubber and the bottle may be enough to hold the blade apparatus to the pitcher, and simply placing the rubber around the hole and jamming the cap into it may be enough to create an adequately watertight seal.  However, thinking jamming a bottle into rubber could be the solution was slightly too optimistic.  There were many leaks in the seal and the blade apparatus did not appear to be secure enough to be able to withstand the force acting on it during blending. 

bottle cap jammed into a rubber seal

Thus, currently no solution has been reached about how to connect the pitcher and blade.  This means it is back to brainstorming!

Ball Bearing and Blade Apparatus

One of the main problems with the current design of the blender is the amount of glue used to connect the blade and bottle cap to the pitcher.  Glue is currently being used in three different areas on the bottleneck; the rubber washer is glued to the top of the bottle cap, the bottle cap is glued to the bottleneck, and the base of the neck is glued to the bottom of the pitcher. Relying on glue is not ideal for a few reasons, glue is not necessarily reliable for the long-term, it is not the best idea to have such toxic glue come in contact with food that will be ingested, and glue around the ball bearing could potentially lead to accidentally gluing the bearing and preventing rotation. 

The rubber washer is glued to the top of the cap in the current design because it kept coming lose when placed inside the cap.  The problem with having the washer positioned on the inside of the cap was that there was not enough surface area for the glue to adhere to.  A different design and position of rubber seal could both eliminate the need for glue and yield a more effective seal.  The purpose of the rubber seal is to prevent the contents of the blender from leaking through the cap into the ball bearing, and out the bottom of the pitcher.  A good seal will also minimize friction between the rubber cover and the rod, allowing the rod to rotate freely in conjunction with the transmission wheel. 

Ideas for developing a new design for the rubber seal began with trying to completely cover the bearing, leaving only a small slit for the rubber rod to peek through.  Initially, just working with the bearing and cap it seemed as though securing the rubber to the bearing would require a tie of some sort.  Zip Ties presented themselves as a very good and durable solution, however, due to their locking mechanism, the top of the ball bearing is no longer round, and does not fit into the bottleneck. 

Zip Tie disrupts circular shape

Possible alternatives for Zip Ties are materials like rubber bands and string, however, because the rubber seal is quite rigid and difficult to work with, it is unnecessarily challenging to obtain a properly placed rubber seal.  The next option explored was to simply wedge the rubber between the outer edge of the ball bearing and the inside of the bottle cap.  Hammering the bearing into the cap is secure enough to ensure that the bearing remains in place. 

Rubber Seal

Rubber seal jammed into the bottleneck

Bottom angle of the rubber seal in the cap

With the ball bearing firmly placed in the bottleneck, the next step was looking at how the bottle cap could attach to the neck without glue.  Going back to look at the blender model that guided us during the semester, it was discovered that the bottle cap was not secured with anything, in could be unscrewed freely. Thinking about the potential benefits of not having the cap firmly glued to the neck, this design made more sense than worrying about developing a glue-less method because a semi-removable cover makes maintaining and cleaning the blender much easier.  The only potential draw back is that the seal may not be entirely water-tight; however, the liquid meets the cap at an angle where gravity is working to keep the liquid from dripping through the cap.  Thus, because the ball bearing and rubber seal were positioned in a way that made it possible to simply screw on the cap, eliminating glue from the cap was very simple. 

Full glue-less apparatus

The last place excess glue was used in the pitcher was the connection between the blade and ball bearing apparatus and the base of the pitcher.  Initially, we constructed the entire structure before inserting it into the pitcher from the top.  The widest part of the neck was on the inside of the pitcher, and because it is easiest to apply glue to the widest part, the majority of glue was on the inside of the pitcher with only a thin support layer on the outside.  It is not entirely practical to assume we can completely eliminate glue from this location on the pitcher, but we can minimize the amount that comes in contact with the blended matter.  Finding a better way to attach the blade apparatus to the pitcher can be looked at in conjunction with finding a better way to secure the pitcher to the axle connected to the rear wheel. 

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

 

Improving the Efficiency of the Blender - blade remodeling

The bicycle blender that was tested in the spring of 2013 was only designed to blend soft fruit, juice, and yogurt (or foods with similar consistencies).  Even with very soft foods, the blender still left chunks of food.  Ideally, the blender will be able to blend harder foods more thoroughly. 

There are three widely accepted features of good blenders; jar shape, number and position of blades and motor strength.  To improve the efficiency and functionality of the blender, the primary focus will be on improving the blade and being conscious of a good jar shape. 

Our current blade design is a single strip of sheet metal that is curled on the ends.  The flat part of the blade is positioned approximately 1 ½ inches from the base of the pitcher, and the bottom of the curls are approximately ½ an inch from the base.  Additionally, the outermost edge of the blade is approximately an inch from the side of the pitcher.  The blade does not have a very large reach, and thus requires a lot of pedaling which still does not produce a smooth blend.  In order to improve the quality and functionality of the blender, a new blade design must be developed.  

Current blade design

Number and position of blades-

The length and configuration of the blades plays a larger role in the performance of the blender than the number of points at which blades came in contacted with the blended matter.  To maximize efficiency, blades should be angled differently, and there should be a minimal distance between the sides of the jar and the end of the blade, ¼ of an inch is optimal.

The primary focus during the remodeling process was the shape of the blade.  The main problems with the shape of our current blade is that both ends of the current blade point in the same direction, and that there is a full inch between the edge of the blade and the side of the pitcher.  Both of these factors significantly detract from the efficiency of the blade by limiting the area the blade can reach.  The best blades have four prongs, two of which are angled up and the other two are angled down; however, it was also important to be conscious of how difficult a particular blade would be to manufacture. The benefits, increased cutting reach and efficiency, of a four-pronged design outweighed the additional difficulty to manufacture.

Remodeling options

Pugh chart

What was done to make the new blade:

-       3” by 3” cut out of thick sheet metal,

-       Cut the square into an X shape so that the legs of the X are ½ an inch wide

-       Drill a ¼ inch hole in the center of the X

-       Sharpen each edge of the X by sanding with a Dremel tool

-       Shape the blade by bending each prong approximately 45 degrees, alternating the direction of the bend

blade cut out

Folded Blade

The next step is to develop an easier method of holding the blade in place.  The current method of bent piano wire is very difficult to work with and can compromise the structural integrity of the blade.  Additionally, the piano wire may rust. 

Bicycle Blender Imperfections

There are many ways to improve the current bicycle blender.  Areas form improvement can be categorized into three main groups; the pitcher, the axle, and general structural support.

PITCHER

• Requires a lot of glue
• Blade can not chop ice / hard/ large items
• Blade shape often misses chunks
• Difficult to secure the nail to the blade
• Rubber sealant on the top of the cap does not hold well
• High potential for accidentally gluing the ball bearings and inhibiting rotation of the blade

AXLE

•            Fixed length
•           Transmission wheel
•           Should consider that axle may need to be removed

SUPPORT / STRUCTURE

•          Location of rear axle requires you to cut most rear racks
•          Wooden donut is very specific
•          Bungee cords are not entirely reliable / secure & look somewhat sketchy
•          Doesn’t work if the wood plank is loose
•          The blender attachment to base is not consistent