The Amazing Dr. Nim Scale Model

The Amazing Dr. Nim is a toy invented by John Thomas Godfrey and manufactured by Education Science Research (E.S.R., Inc.) in the mid-1960s. It consists of a marble-powered plastic computer capable of playing the game of Nim. The machine selects its moves through the action of the marbles falling through the levers of the machine.

The "game board" is a based on the mechanical Digi-Comp II digital computer (also a Godfrey creation). It has memory switches that hold bits of data. The unit is programmed by lobed levers that affect and are affected by marbles that are released from the top of the game. Three of the levers set the start position. The fourth lever is the 'equalizer' option; if set, the player can win if they play perfectly. The last lever is used to indicate who's turn it is, the human or Dr. Nim's.

There are many good online references for the game. The following video is especially informative and entertaining:

The Unbeatable Game from the 60s: Dr NIM

And this article speaks to the relevance of a game like Dr. Nim in today's digital world:

Evil Mad Scientist Laboratories - Dr. Nim

Along with the STL files for this project, you will find a PDF of the manual that came with the original Dr. Nim. I brought this file to a local copy center and had them print me a few stapled booklets on glossy paper and was super happy with the results.

The Dr. Nim offered here is a 2/3rd scale model of the original (.673 to be precise). This keeps the size of the game down to about 210 mm x 205 mm which will hopefully make Dr. Nim accessible to more 3D printers out there (including mine ;-). I have tried to keep the game as true to the original as possible within the constraints of the differing technologies (FDM vs injection molding) and the information available to me. One other concession was to 3D print the folding stand rather than attempting to employ the wire stand of the original.

I did not in fact own an original Dr. Nim when I created this model. The model you see here was developed from pictures obtained online, and from pictures and information graciously provided by Dr. Nim owners. Thank you so much Jaap Scherphuis and Charles E. Leiserson!

Recently I did acquire a vintage Dr. Nim. Upon inspection the only thing I changed was the angle that the game is played at (about 30 degrees) as determined by the Hinge Stoppers.

Design Notes

As with my other E.S.R. project (Think-a-Dot Replica) the real design work for Dr. Nim happened back in the mid 60's. I just did the modelling. The Amazing Dr. Nim game was mostly modeled in Fusion 360 with some of the simpler pieces done with Tinkercad. What I liked about this project was that once the Base was done, all of the other pieces are quite small and print quickly. This allowed me to iterate and fine tune them with short turn around times.

The Amazing Dr. Nim was done as a tribute to John Thomas Godfrey and E.S.R. for their brilliant work many decades ago. My hope is to re-introduce these toys to a whole new generation of inquiring minds.

Step 1: Print the Parts

Print Resolution: 2 mm

Infill: 20% and 100%

Filament: AMZ3D PLA in Red and White

Notes: All parts were printed with PLA at .2mm. The Base unit was printed with 20% infill and 5 top and bottom layers. Everything else was printed at 100% infill. To create an Amazing Dr. Nim you will need to print the following parts:

• 1 Base (the main Dr. Nim board)
• 3 Flip Flop
• 1 New Game
• 1 Player Select
• 1 Hinged Stand
• 2 Hinge Stopper
• 5 Shaft Support
• 5 Shaft Cap
• 1 Trigger
• 2 Trigger Fulcrum
• 2 Trigger Support Long
• 2 Trigger Support Short
• 1 Trigger Lock

Step 2: Preparing the Parts for Assembly

Here are some tools that you will need to complete this build: fine grit sandpaper, a hobby knife, some good glue, tweezers, and a medium size paper clip.

Using a fine grit sandpaper (I used 220 grit) lightly sand the shafts of the Flip Flops, New Game, and Player Select switches close to the switch piece itself to about half way up the shaft. We are trying to get these parts to swivel easily and smoothly when installed into the Base holes.

I have my first layer set pretty aggressively and as a result I end up with a bit of a "lip" around the edges of the first layer. I used a hobby knife to carefully remove any of this excess material from bottom of the 5 through holes in the Base, and from the 5 Shaft Support pieces, so that the holes are an even 4 mm all the way through. Also the trigger slots might need some attention to ensure a consistent 2 mm width throughout.

Step 3: Install the Shaft Supports

Attach the 5 Shaft Support pieces to the bottom of the Base. For each, push the shaft from one of the switches through from the front to use as a guide to align the Shaft Support with the hole in the Base. They should be lined up as precisely as possible. Use a small amount of glue near the outside bottom edge of the Shaft Support to attach it to the Base, being careful not to get any glue of the shaft itself. When the Shaft Support is in place remove the guiding shaft while the glue dries.

Step 4: Install the Trigger Supports

Attach the Trigger Support pieces to the back of the Base. The most important of these are the two Trigger Fulcrums. These need to be lined up with the horizontal opening in the middle of the Trigger area. It is essential that the groove in the bottom of the Trigger Fulcrum piece aligns with the horizontal opening in the Base.

Attach the other Trigger Fulcrum and Trigger Support pieces as in the picture above. Make sure that all of the Trigger support pieces approach the edge of the vertical openings but do not go over. When the Trigger is installed it must be able to move freely within the vertical slots.

Step 5: Install the Front Switches

Install the 5 switch pieces: the 3 Flips Flops, 1 New Game, and 1 Player Select by sliding their shafts through the appropriate Base holes. Use the picture above as a guide. It's important that the pieces be positioned as depicted when installing. The pieces should slide easily into the holes without binding. If they do bind a bit sand the shaft a little at a time until they insert readily and can be rotated without any sticking.

Attach the switches to the Base by pushing the 5 Shaft Caps onto the shafts from the rear of the Base. The Caps should slide all the way down into the Shaft Support rings and should hold the switch in place without having to use any glue. Once installed you should still be able to freely rotate the switch. If the piece sticks a little when rotated, remove and lightly sand the outside of the Shaft Cap and try again. If a Shaft Cap does not hold the shaft in place use a small amount of glue to attach it, being careful not to get any in the Shaft Support. Check the free rotation of the switch while the glue dries.

Step 6: Install the Trigger

Cut a 6 mm piece of wire from the paper clip. Position the Trigger into the vertical slots as in the picture above. While pushing the central part of the Trigger gently up from below slide the short piece of wire into the Trigger's pivot hole (this is where the tweezers might help). Once the wire is in, release the tension on the Trigger. The wire should drop into the grove in the Trigger Fulcrums.

When you are satisfied the trigger has been positioned correctly and the wire pivot is seated, snap the Trigger Lock in place.

Step 7: Install the Stand

Glue the two Hinge Stoppers onto the Hinge as pictured above.

When the Hinge Stopper glue has dried, position the hinge onto the back of the Base as shown above. The Hinge aligns horizontally with bottom of the Base, and can be pushed up against the Trigger Fulcrum support on the left for the vertical alignment. Apply glue to the top of the Hinge (under where the Stoppers are) and attach the Hinge to the bottom of the Base.

Step 8: Finishing Touches

That's about it. I used white satin hobby paint to highlight the Dr. Nim logo on the game board. Some of the pictures I have seen have the Dr. Nim in white and some are just red plastic. I do not know if the white just wore off over 50+ years of use or if there were two different batches. I like the white look best.

Step 9: Try to Beat the Amazing Dr. Nim

This scaled down version of Dr. Nim has been optimized to work with 10 mm (3/8 inch) steel balls in lieu of marbles. The picture above shows the setup for a 15 ball game where the "player" left with the last ball bearing loses. There are multiple other starting positions listed in the manual.

In this case the human goes first. By lightly tapping the Trigger button the human releases one, two, or three balls one at a time letting them completely cascade through the game before initiating the next press. When the player is done, flick the Player Select switch from Player to Dr. Nim and tap the trigger button only once.

Dr. Nim will automatically select one, two, or three balls and when done flick the Player Select switch back to Player. Human and Dr. Nim alternate turns in this manner until there is only one ball left and a loser has been determined.