Rangefinder #1

This is a Coincidence Range Finder prototype I built for the Exploratorium late last year. Its essentially an optical trigonometry tool which allows you to measure the length to a distant object based on the distance between the pods and the angle of deflection needed to see the same thing from both pods. When the range finder is dialed in you will see 2 perfectly superimposed images of the same object, meaning you set the angle of the mirror in the control pod so it sees what is directly in front of the telescope pod. For a general overview of the theory behind Coincidence Range Rinders work take a look at this wikipedia article and the diagrams at the bottom of this page.

This is the inside of the telescope beam splitter pod. I mounted an inexpensive 10x monocular in some pvc pipe fittings. In front of the monocular I mounted a half height adjustable first surface mirror to receive light from the control pod window and the window directly in front of the monocular simultaneously.

This is the inside of the control pod, a larger first surface mirror collects light from the closed window and sends it out the removed one to the telescope pod. The mirror is adjustable via a knob driven screw which also drives a gear train to the range gauge.

Here is the back of the control pod. Note that the range gauge window is made to open as the ranges were written on by hand using a laser range finder for this first prototype.

Looking into the control pod mirror from the front you can see the light path back to the beam splitter and into the telescope. I used speed rail to connect the 2 pods for easy adjustment and disassembly.

While you could achieve coincidence (see 2 super imposed images) this range finder only proved vaguely accurate, mainly because the range gauge was driven by the control knob and not directly on the position of mirror. The gear train tended to slip disconnecting the mirror position thus the angle of coincidence from the read out on the gauge. In response to the problem of inconsistent accuracy I decided to look at some military range finder designs, which lead to the creation of Rangefinder #2.

Cardboard Scooter for the Exploratorium

The Exploratorium was having monthly material themed events earlier in the year, and when cardboard came around I decided I should try to push the limits of this material. So inspired by Phil Bridge's cardboard bicycle, I decided a kick scooter would be an interesting follow up on the idea corrugated transportation. After a lot of experimentation with laminating cardboard with different corrugation paterns to form beams, I took what I thought was half again as much cardboard to hold my weight (175lb) the scooter was born:

While its far from elegant, it was surprisingly durable surviving for about 3 months of on and off use by myself, other staff and museum visitors. Composed of entirely laminated laser cut cardboard with the exception of the wheels, axles and the steering hinge and hinge pins, the scooter only weighed about 6 pounds, and could carry people up to 200lbs.

The scooter is supported by two beams 3'' tall and eight layers thick that runs from the steering hinge to the rear axle with the corrugation running long ways. The deck is five layers thick, with the corrugation running at alternating 90 degree angles to prevent denting. The front wheel supports were again eight layers thick with ten layers in between to hold the hinge.

Here's a detail of the front end: ten aluminum hinge pins were used to distribute the weight of the rider to the cardboard and nylon bushings were added around the axles to spread out the weight of the rider to a larger amount of cardboard. The use of a steel steering hinge ultimately proved to be the scooter's downfall. After the first few weeks of heavy use the hinge plate started to slide around on the pins compressing the cardboard next to it and eventually making the front end very wobbly. The structural integrity of the board itself was actually very good, as it became clear that it was becoming overly wobbly I actually tried jumping on it lightly and did not break the cardboard beams. As the over all design seems to have worked I plan to make a sleeker second attempt abandoning the hinge for a caster based steering method.

Plastic Manipulation Tools for The Exploratorium

Vacuum forming activity at The Exploratorium

I built a simple vacuum forming rig for The Exploratorium consisting of a sealed wooden box with a peg board top and gasket, and a laser cut frame to hold the vacuum forming stock (PETG) while heating and forming it.

After the stock was heated over the hot plate for three or four minutes it was ready to form, a shop vac drew the air out of the box pushing the plastic down over the objects as a result of the pressure differential. I found that with my fairly low powered vacuum hot plate only provided enough heat to form the major shapes, but that a great deal of detail could be captured by going over the plastic with a heat gun.

Below are several examples of vacuum formed sheets visitors made while I had machine out on the museum floor.

A heat gun was used in this sheet to clearly capture the writing on the lower gear.

This is a crude water lens made by vacuum forming a glass lens with a small dowel to allow a filling port and hot gluing it to a flat sheet of stock to make a vessel. When filled with water it make a surprisingly low distortion magnifying glass.

Acrylic molding "press"

Preparation to cast the negative of the bowl: I made studded the top plat with screws hang down into the paster securing it to wood, and sprayed to the bowl with mold release.

Pouring the plaster positive through the top plate into the bowl.

The resulting casting.

Felt was stretched over the positive and adhered with a tacky non-permanent glue to prevent the acrylic from sticking to the plaster. After the felt was firmly in place I was able to easily trim off the excess felt using a razor blade, making the mold ready to use.

After about 15 minutes at 315f in a convection toaster oven the acrylic is ready to press. It has the consistency of probably most similar to slight dried out Provolone cheese, it sags and bends very easily but does not stretch.

Pressing the acrylic.

The first acrylic bowl came out a little small given I underestimated the amount of material necessary to cover the curve, but I have since dialed in the disk diameter and can produce bowls which are the same size as the original. I tried this activity a few time on the museum with some success though it is a time consuming process. In an effort to deal with the long plastic heating time for the bowls I laser cut a bunch of acrylic fork blanks and made a fork press from laser cure plywood again covered in felt to produce a nice s curve. The forks proved a much more realistic activity for the museum floor as it still displayed the behavior of thermo plastic only took about 8 minutes per fork . I'll try to post pictures of this some time in the future.

Simple blow molding flask

The mold flask was made by casting plaster around an acrylic tube with a plastic ball stuck it, in some old shipping tubes capped with plywood.

I used some cheap 1/4'' ply to make a linkage to bring the halves of the mold together and lock them shut. To turn a tube in to a ball I heated the acrylic tube for about 15 minutes in a toaster oven (which happened to have a convenient rotisserie function) at around 315f. When the tube achieved the proper provolone texture it was closed in the flask, one end was crimped off with players and a stopper with a schrader valve was inserted into the other side allowing it to be inflated by a bike pump. Inflating the bulbs is correctly surprisingly hard, the stopper always leaked a little so you had to keep pumping constantly. If you pumped to much the vessel could explode out of the seam in the flask. If you pumped to little you would never get the tube to expand to the sides of the mold as the acrylic is very elastic and would try to return to its tube form as soon as the pressure was released.

Here is mold opened just after the acrylic tube as been inflated and allowed to cool.

The resulting blow molded vessel is fairly strong but will actually tear not crack if you squeeze the bulb too much. Its not surprising the acrylic is not used to make thin blow molded objects given this odd behavior.

Light Painting Tools for The Exploratorium

RGB (CMY) Ball light painting tool

(Plastic vending machine pod, battery, leds, resistors, push button switches one for each primary color)

The general idea behind the ball was get away from sharp point source tools that are typically used and make a much wider more diffused source that would allow you to lay down a lot of color in a short time. Each of the three button activates one of the Primary colors (RGB) and multiple buttons can be pressed to create secondary colors. The photo above doesn't really do it justice, but if you look at the image from a distance you can see the blended RGB and the secodary CYM colors. White is only apparent when the ball is used in drawing and the colors get blurred together.

Simple line drawing.

A good example of the ball being used to cover large areas. Note the creation of yellow between the red and green zones.

White can be created by holding down all the buttons and moving the ball to blur the colors as seen in the X.

Light Stamp

(funnel, laser cut stencil holder, velum defuser, batteries, push buttom switch, resistor, led, stencil cards)

Designed to accept 5x5'' (laser cut or handmade) stencil cards, the device functions as a stamp in a light painting context allowing one to make multiples of a given image. Initial tests were with simple letter stencils, but I may try to make some laser cut rasterized images in the future.

Multi stencil Light Stamp example.

Light Stamp with a little blurring, perspective.

Light Stamp + cardboard Frank Oppenheimer.

Combination Light Stamp RGB Ball image.

The Light Stamp can also be used without a stencil as a source of defused light to illuminate small areas.

Light Pen

(plastic test tube, red led, push button switch, button batteries)

The pen works along the lines of a more typical led light painting tool, but is built into a minimalist and fairly indestructible plastic test tube shell.

Pinhole Camera Ring

Pinhole Camera Ring for Pipo Nguyen-Duy made with the generous help of Abrasha (a San Francisco Jeweler, see Abrash.com) who did the final assembly of the silver case and provided technical support throughout out the building process. The camera is fully functional and can produce a single .75'' paper negative.

Parts from left to right: Silver case and ring, steel bottom plate with rubber seal, magnet, machined ebony insert, pinhole plate, dime shutter, ebony insert cap and assembly screws.

Case and insert.

Insert detail.

Case detail.

Belt buckle pinhole camera

Belt buckle pinhole camera for Pipo Nguyen-Duy:

sanded mint tin, black walnut, copper plate and wire, aluminum plate, brass screws, aluminum rivets.   
Shutter assembly detail
Buckle detail

Experiments in personal electric transportation

This three wheeled skateboard built at Oberlin came to be known as the Electroped and was constructed using the propulsion system from a broken electric scooter I found and spare parts from other projects.  Acceleration and breaking are accomplished through the levers mounted on the control cable, and steering, as in a normal skateboard, is controlled by leaning. While the vehicles rate of acceleration is lack luster due to its low wattage motor, it can never the less reach a respectable top speed of 14mph.   

Steering was originally a problem with this vehicle. I attempted to use a large skate board truck to allow the front wheels to turn around the center of the axle, as a result a 90 degree turn could only be accomplished over about a half block.  In an effort to improve this uselessly large turning radius I built another truck which functioned much more like a car's: tie rods attached to a plate plate below the board move the wheels in parallel allowing for a much tighter turning radius.      

Drive train and battery detail