Portable Goal Invention Job

I got the opportunity to help engineer a portable goal against the competition. The competition goal had an innovative un-packaging mechanism, but had a few drawbacks. It was very long, and required a few tedious set-up motions to be stable.

I wanted to try and make it more compact,

but alas I came across the same problem, the competing engineers came across which was how to stabilize the folding member of the front and rear long members.

The client asked to make this cross member smaller to have more of a rectangular profile. I gladly took on the challenge but I kept hitting a lot of problems when trying to make it with trial and error with the tools in my shop. The problem wasn't the physical tools I was using, it was not using the best tool in the shop to ultimately tackle this tricky problem.

Simplifying the problem into geometric variables, gave me the flexibility to play around with the variables to make everything work.

This is the set up before the button press. I standardized the Arm Length, Pulley Diameter, and optimized the system for an efficient button push stroke.

This is the system for how when the user presses down on the button to unlock both arms.

Optimizing this condition I came up with the following values:

•  LA  = 5.5 in
• θA     = 6.2478923 °
• L0  = 0.404186 in
• ɸP  = 0.613633 in
• θP     =  72.23502 °
• L2  =  0.3868155072 in

My second biggest headache was trying to come up with a locking lever arm geometry that worked well. I designed the pin slot so quickly and was thinking about mass manufacturing when I placed the pin slot directly in the middle. My idea was that symmetry is always a good thing so that the parts can be easily switched from one side to the other. Unfortunately in this case, it would have been best to move the pin slot up to allow room for structural support around the pivot point of the lever arm. To get a proper prototype to work I had to cut a square hole underneath for clearance to allow enough "meat around the pivot point to endure heavy testing. I also had to cut an angular alot off the length at and angle and having the locking cross cut slot very thin for it to work.

Even though the metal underneath the middle cross cut is thin, I think  it would be okay since there aren't any excessive downforces being placed on the member. When the shoulder screw is being exerted pressure from the large aluminum square frame, it pushes diagonally across from the middle cross slot to the pivoting member across the length of the lever. Any downforces are held by the pin slot on the square frame.

For mass manufacturing, The square frame members should be U shaped out of stamped metal for this helps lower cost, and also eliminates this need of creating a tapered locking lever design. 

The pin slot sliding mechanism was again not working as smoothly which was increased in complexity from using two lever arms working in unison. The shoulder screw was not moving freely for some reason. 

So the first thing I did was try and make the sliding surface on the lever more smooth and taking off material for further clearance.

This helped a bit, but it was still sticking and wouldn't result in a smooth operation. 

To provide further clearance, I decided to file down one side of the pin slot walls to open up further clearance.

I was finally seeing much better results with this:

Another issue which arose from making the cross bars move more inwards was the length of the cross bar had to change with the change in the pin slot length as well. Keeping the length constant from the prior 45 degree configuration left a bit of excess pin slot length

I tried to set up the problem to solve with trigonometry, but it was getting a bit complex. It would of resulted in a large system of equations and solving ultimately in a matrix.

Therefore, I tried to go another route. In essence I could vary "r1" which was the distance from the hinge of the arm to the hinge of the cross brace. and see the resulting Lengths of L1 the resting length of the cross brace in the open 90 degree position to L2 the resting length of the brace in the close 0 degree position. By guessing the R1 value, I can generate length value of L1 and L2 which should be the same to prevent the brace from being stretched or compressed.

By generating values of L1 and L2 from R1 values, I was able to create two functions where the intersection of them would result in the best length of the cross brace to work best.

The final calculated length of the distance between hing pins which accommodates the 7 inch long pin slot length was 3.516 inches.


Next on the list was creating the sliding locking bars

After cutting in half the threading begins to attach the anchors