Thursday, August 5, 2010

3D Scanning Gas Tank space - By Hand!

Now that the normal requirements of summer holidays have been taken care of, I have finally had time to get some things done on the Electricfly!

As to the Goal of verifying the car can fit specific Lithium Cells into a new location on the car and removing the Lead Acid Batteries, the first Job to work on this week, was the profile and volume measurment of the space under the back seat, or normally called, the Gas Tank area!

I am trying to see if the ThunderSky 100 Ah Cells can, in fact, be used, [Dimensions:179×62×218(mm)] or if the largest cells that might fit would be their 40 Ah cells [Dimensions:116×46×190(mm)]!

Not having the budget for a nice hand held 3D Scanner like the Zcorp's ZScanners - I opted for Slow-Mo 3D Measurment. I had the option of going low-tech and slo-mo, to save a chunk of money, and turns out - using about 8 hours of my time and time with the vehicle on a drive-on hoist to do the measurements by hand.

I used a 12" Digital Caliper, a piece of white painted peg board, 2' x 4' and trimmed to 45" length to fit between the rear wheels, and 4 tie-wraps (or Zip ties as Mike - the worker at Florida Garage, where I used the hoist, called them) to secure the panel under the rear of the car!

OK - Setup took about an hour, then the work began - Measuring the vertical 'depth' up from the face of the Peg board, at each hole, up to the first obstruction, or the external skin of the car in the gas tank well, and then writing the measurment onto the white face of the peg board at that hole, then measuring the next hole!

Wednesday, gave me setup and measuring for a couple hours. then Today - I was back at the Body Shop at about 7:20 Am - Shop hours - to continue. I finally finished measuring all 24 x 39 reference holes - 936 of them in total, at about Noon! Average time in total = 2.225 minutes per hole!

X-Y Measurment Precision:
Peg Board Holes diameter = 0.258",
Vernier Depth Stem (Tail), Approximately 1/8" x 1/16"
Position Accuracy of the depth measurment is therefor - based on the hole / Tail fit equation - very limited, ie: Hole Size is 200% to 400% of the Vernier Tail used for depth measurment, so X-Y Precision is quite variable, on the order of +/- 1/8".
Verical Precision
Vertial Angular Perfection = +/- 5 to 10 Degrees (Vertical Perpendicularity) hard to maintain precision tighter than 2 Degrees variation.
Target Precision therefore varies by as much as +/- 0.25" to 0.50"
Depth Precistion
Digital Vernier accuracy: 0.001" - 0.0005".

While the Digital Vernier is a very highly Acruate Instrument, the ability to get a net measurement precision close to it's capabilities for this excercise was compromised by all of the above reasons, plus one more:
the Inability to secure the Pegboard perfectly flat to the underside of the vehicle to start with. Due to the simple attachment technique, designed for minimalistic techniques, and speedy setup with limited precision tooling equipment, resulting in both a sloped peg board instalion in the fore and aft direction, and a slight slope in the left- right locations.

A Further issue compromising Accuracy, was the inability to see the point of impact or touch point of the tail of the vernier in many of the hole measurments,essentially it's hard to see clearly through the Peg board itself, limited light - mostly from the rolled up shop door to the rear of the vehicle, and hard to hold a well pointed light and simultaneously ensure good verticality of the Vernier, and good target selection and measurement.

Bottom Line - While the Vernier displayed 3 decimal accuracy, I wrote down to two decimals, will round off to 1 decimal and subtract 0.1" from the rounded off figure, for measurment of the EPS Foam for building a Volume & Fit Model to verify the Space and Volume as a package, and visualize the actual space available, suitable for using the space for fitting new Lithium Cells in the gas Tank Area.

The Process Continues!

No comments: