Technical Problems Resolved Through Prototyping

Exploring how to convert the squeezing force of the user on the press handle into rotational energy to spin the bingo tombola wheel through prototyping.

My initial hypothesis was that dynamo torches must have a mechanism that can convert the squeezing force on their handles into rotational force. (to spin magnets around copper wire coils to create electrical current to power their bulbs.)
So I investigated the possibility of borrowing this mechanism by reverse engineering a pre-bought dynamo torch.

The mechanism converted the force into kinetic energy with a curved rack gear attached to the press handle which engaged with a regular spur gear that in turn engaged with a custom one-way directional axle that only engaged with notches on the magnet wheel when it was spinning anti-clockwise. I took the torch internals and housing to use them directly in my prototype as the one directional turning was perfect, as I needed to keep the bingo tombola wheel spinning in one direction as opposed ti just spinning back and forth as the users hand clenched and un-clenched.

 

I then designed a housing to be affixed onto the torch mechanism that would contain two axles for cam wheels. Cam belts would run between them and between them and the magnet wheel in the torch mechanism. Below is the CAD modelling for the first iteration of this housing.

 

A two axle and two cam wheel design was chosen so as to avoid the cam belts interfering with a screw shaft that holds the two sections of the torch housing together and to avoid the bottom of the press handle which sits inside the torch housing.  The screw shaft in the torch housing that could have interfered is circled in red in the photos below .

To ensure I had designed the CAD pieces to the correct dimensions so they would fit with a high degree of precision (ie no gaps or being too large) to fit onto the ABS polymer torch housing, I first 3D printed test pieces so i could check this without wasting an unnecessary amount of material if they didn’t. Luckily the test pieces fit tightly and flush to the torch housing, as can be seen in the photographs.

 

On the next iteration these issues were remedied by redesigning the top axel to be much thicker so as not to be so fragile and the side locators were disposed of as the male and female locators at the bottom of each piece were sufficient. – The tolerance between the wheels and axles made larger to ensure both cam wheels could spin freely. This was done by extrude cutting a 1mm larger diameter centre hole on both cam wheels on Solidworks.

These parts were then 3D printed and assembled but the cam belt system was inoperative as there was too much friction between the cam belts and cam wheels for them to spin as can be seen in the video below.

 

 

The final iteration of the bingo spinner rotation mechanism was redesigned with a cog wheel system using the ‘Toolbox’ add in on Solidworks. Test pieces were initially printed to check that the gears meshed correctly.

 

Successful cog test pieces

 

Once it was established through testing that the cog system worked correctly, the body of the bingo spinner was printed and assembled. Below is a photo of the dry fitted cog assembly inside the bingo spinner body, followed by a video clip of the fully assembled working cog mechanism in the final prototype.

 

 

Making the stand adjustable

The initial idea for the stand was to make it adjustable using a wheel design. However due to human factorial reasons this was changed.

Stand Adjustability Mechanism

The chosen design was a long fulcrum accessibility handle and spur gear mechanism. The lever mechanism was designed on the CAD software programme ‘Solidworks’ using the ‘Toolbox Gear Spur’ add in. I stepped the gear ratio down 1.3 : 1 from the gear that’s attached directly to the lever, to the gear that raises the rectangular rack gear. This was done so the rate at which the body of the bingo spinner is heightened when the lever is raised is incremental, allowing the user to be more accurate when achieving the correct height for the bingo spinner so it can be attached to their bingo tombola wheel.

Below is a video of the mechanism working in CAD and the final prototype being tested

Dibber

The handle of the dibber tip was also design with human factors. A simple axle mechanism was chosen to enable the dibber prototype to be fully mechanically dynamic. Below is the CAD and videos of both the CAD simulation and assembled first iteration dibber prototype.

 

I added indents to the handle tips of the dibber to add affordance as it was not intrinsically obvious to the user in what way they were suppose to grip the handle. It is integral the user naturally interacts with the handle using a pinch grip as this is one of the areas of dexterity this part of the product is designed to improve. These were then 3D printed and tested for ergonomics.

 

These parts were again designed with human factors as the primary concern. If designing for manufacturing, then value engineering would change the form of them so they could be manufactured using an injection moulding process. Currently the idents, draft angles and holes in the dibber tip and handle would restrict this. It is also totally uneconomically viable to 3D print these parts as the price of materials to print just the dibber tip was £10.83 as can be seen in the screenshot below.

Below is a video of the final iteration bingo dibber being tested