Side Projects

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There are a lot of side projects and check work to be done.

There are uncertainties in the process that need to be reduced.

Examination of fall back positions if the preferred option fails.

And lots of new areas to explore.

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Fall Back Options

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The preferred option is to use inference fits and loose fits.

The problem is the lack of control over the tolerance of online laser cutting.

The next option is to glue the crank axle and crank pin to the rod.

If that fails then the fall back is the use thread rod and nuts:

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Two 3D (OpenSCAD) designs have been completed to cover the options.

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Part Orders

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Most parts (nuts, bolts, rods, washers, bearings etc) have been ordered (from China),

but this can take up to six weeks  to arrive.

Even then the parts may not be suitable.

For example, the longest M3 threaded rod I could get was 250 mm long.

The thread rod and nut version of the design needed a 312 mm long.

There are solutions but the parts need to be ordered.

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Reoptimisation

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I have used a steepest descent optimiser for this project.

They are not straight forward as the error function and constraints are rather tricky to setup.

One constraint (sub-goal) that was critical for good solutions was to enforce symmetry.

Indirect methods did not work. Balancing the competing sub-goals was more important than expected.

The error functions also needed to be quite specific.

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Until recently I thought that my optimisation was complete, with this solution:  

• Bar 1: Base Plate Points
  • Axle
  • PX0 =  0.0
  • PY0 =  0.0 
  • Hip Pivot:
    •     PX1 =-53.0
    •     PY1 = 53.0  

• Bar 2: Crank
  • L0 =  30.0

• Bar 3: Conrod (leg thigh)
  • L1 =  60.0

• Bar 4: Hip Bar
  •     L2 =  60.0  

• Bar 4: Extension (shin)
  • L3 =  60.0   Leg (shin)
  • A3 =  90.0   Knee Bend

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Foot Optimisation

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Struggled to work out how to do this. Not that I did not know the general shape.

The problem is the solution is specific to the walker design:

Finally worked out a method:

But now I have to reoptimise the foot with the walker at the same time.

After this reoptimisation, I will get the parts lasercut.

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Boolean Shape Options for DeltaCAD

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Delta CAD is now deceased. A shame!

It has a persistent menu system that reduces the cost  key strokes and mouse clicks.

Unfortunately the menu system was half finished. Still, it is very nice to use.

While the GUI works with Linux just fine, the macro language does not.

Now I run DeltaCAD in a VM. With two menu bars visible at all times, it is just one click to switch between Windows and Linux.

After using OpenSCAD, I really like the boolean operations: union(), difference(), intersection().

So I used Alan Murta's Generic Polygon Clipper (GPC, 2004) code and wrapped a DeltaCAD macro around it.

It's magic, select a couple of shapes, run the macro, select your option, and a few seconds later, the selected shapes are replaced by the boolean operation shape.

It saves so much time spent moving shape points over other shapes.

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Acrylic Glue

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Acrylic glue is very different to normal glue. It is very fluid (low viscosity) and wicks into the joints by capillary action.

I have bought a kit ($$$) so I am set for the Walker's acrylic  body assembly: 

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I am hoping with the right tools the process will be magic.

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AlanX