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Build A Micromouse Maze

This maze design is no longer supported because we designed a new maze in 2012.
Please see the page on the new design: 2012 Micromouse Maze Design


FIXME This image needs to be cropped and resized.

Purpose And Scope

The purpose of this tutorial is to walk through the specifications of the Micromouse maze, discuss the design of the maze, provide guidance in it construction, and furnish technical drawings for the maze.

Conventions Used In this Article

Coming Soon

Cost and Schedule

Based on our records, the maze cost approximately $1820.00 to initially build in 2008/2009. Another $200 was spent to add legs and leveling feet to the maze in 2010.


The maze took about a quarter to build, working about 30-40 man hours on the weekends. We learned a lot during the build and wasted a lot of time due to improvised and on the fly planning. Doing the maze build again, I estimate it would take about a month of on the weekend building to complete the maze. I would not build my own walls, I would buy them. Active Robots Store is out of the UK, so the shipping will be pretty high. The main motivation for buying versus making the walls, is the time needed to make the walls is quite high and number of setups required to make walls is the highest of the build. Furthermore, making the walls requires more tools.


For comparison, the following link is for a complete off-the-shelf maze, with walls

Links to two companies sell maze walls and corner posts

Tool Required

  1. Power Tools
    1. Table Saw
    2. Drill Press
    3. Hand Held Belt Sander
    4. Random Orbit Sander
    5. Hand Held Drill
    6. Compound Miter Saw
  2. Hand Tools
    1. Hammer
    2. Screw Drivers
    3. SAE/Inch Socket Set
    4. Clamps
  3. Measuring Tools
    1. 8' Builder's Level
    2. 2' Level
    3. Square
    4. Framing Square
    5. Saw Guide (>48” in length)
    6. Tape Measure
  4. Painting Supplies
    1. 2” Brush
    2. Roller Frame
    3. Roller Covers, use 3/8” nap.
    4. Roller Tray

FIXME

Bill of Materials

Coming Soon

The Specifications

CAMM Maze Specifications

  1. The maze is composed of multiples of an 18 cm x 18 cm unit square. The maze comprises 16 x 16 unit squares. The walls of the maze are 5 cm high and 1.2 cm thick (assume 5% tolerance for mazes). The outside wall encloses the entire maze.
  2. The sides of the maze walls are white, the tops of the walls are red, and the floor is black. The maze is made of wood, finished with non-gloss (flat) paint.
    1. WARNING: Do not assume the walls are consistently white, or that the tops of the walls are consistently red, or that the floor is consistently black. Fading may occur; parts from different mazes may be used. Do not assume the floor provides a given amount of friction. It is simply painted plywood and may be quite slick. Since maze floor is constructed using multiple sheets of plywood, there will be a seam between adjacent sheets on which any low-hanging parts of a mouse may snag.
  3. The start of the maze is located at one of the four corners. The starting square is bounded on three sides by walls. The starting square orientation shall be such that when the open wall is to the “north,” outside maze walls are on the “west” and “south.” “The start line” is located between the first and second squares. That is, as the mouse exits the corner square, the time starts. The destination square consists of the four cells at the center of the maze. At the center of this zone there is a post, 20 cm high by 2.5 cm square (This post may be removed if requested). The destination square has only one entrance.
  4. The small square zones (posts), each 1.2 cm x 1.2 cm, at the four corners of each unit square are called lattice points. The maze is so constituted that there is at least one wall at each lattice point.
  5. The dimensions of the maze shall be accurate to within 5% or 2 cm, whichever is less. Assembly joints on the maze floor shall not involve steps greater than 0.5 mm. Gaps between the walls of adjacent squares shall not be greater than 1 mm. The maze may have dents and other surface imperfections on the maze floor. These imperfections will not extend above the plane of the floor, but may extend below the plane of the floor up to 2.5 mm. Any dent or void will be less than 5mm wide.
  6. Multiple paths to the destination square are allowed and are to be expected. The destination square will be positioned so that a wall-hugging mouse will NOT be able to find it.

IEEE Region 6 Maze Specifications

  1. The maze is composed of multiples of an 18 cm x 18 cm unit square. The maze comprises 16 x 16 unit squares. The walls of the maze are 5 cm high and 1.2 cm thick (assume 5% tolerance for mazes). The outside wall encloses the entire maze.
  2. The sides of the maze walls are white, the tops of the walls are red, and the floor is black. The maze is made of wood, finished with non-gloss paint.
    1. WARNING: Do not assume the walls are consistently white, or that the tops of the walls are consistently red, or that the floor is consistently black. Fading may occur; parts from different mazes may be used. Do not assume the floor provides a given amount of friction. It is simply painted plywood and may be quite slick. The maze floor may be constructed using multiple sheets of plywood. Therefore there may be a seam between the two sheets on which any low-hanging parts of a mouse may snag.
  3. The start of the maze is located at one of the four corners. The start square is bounded on three sides by walls. The starting square orientation shall be such that when the open wall is to the “north,” outside maze walls are on the “west” and “south.” The start line is located between the first and second squares. That is, as the mouse exits the corner square, the time starts. The destination goal is the four cells at the center of the maze. At the center of this zone is a post, 20 cm high and each side 2.5 cm. (This post may be removed if requested.) The destination square has only one entrance.
  4. Small square zones (posts), each 1.2 cm x 1.2 cm, at the four corners of each unit square are called lattice points. The maze is so constituted that there is at least one wall at each lattice point.
  5. Multiple paths to the destination square are allowed and are to be expected. The destination square will be positioned so that a wall-hugging mouse will NOT be able to find it.


The CAMM and Region 6 specifications are basically the same, since CAMM is derived from Region 6's rules. The Maze that IEEE UCSD built in 2008/2009 is designed to comply with the Region 6 specifications. The differences between the CAMM and Region 6 specifications are in the handling of gaps, dents, discontinuities between the sheets of the maze sections.

The Design of the Maze

In progress

The maze is designed in a modular fashion to allow the user to move the maze in a reasonable sized vehicle, store the maze in a reasonable sized space, and most importantly, move the maze through a normal sized door. Although there are doors that are over ten feet wide or tall, the door to the lab where our maze lives is not, so the ability to move the maze from where it was built to where it lives was a paramount motivation in the design of the maze.

I also spent a considerable amount of time placing the seams of the maze modules. The module seams are the primary source of the Mice getting hung up, since the seams are where virtually all of the discontinuities occur. I placed the seams as close to the edge of the cells as possible, so that the seam was not running down the center of the cell. I constrained the possible sizes of each cell to be less than the size of a standard sheet of plywood. The following table shows the measurements for the sheet of plywood used in each type of module.

MeasurementSquare ModuleSmall Rectangular ModuleLarge Rectangular ModuleStandard Sheet Of Plywood (for reference)
Length 46.5” 46.5” 74.0” 96”
Width 46.5” 27.5” 27.5” 48”

Other variants that use smaller modules are shown in the table below:

FIXME These values have not been verified yet. A future CAD model will be posted showing these variants and the proper dimensions.

Variant A
MeasurementRectangular Module Square Module
Length 46.5” 27.5”
Width 27.5” 27.5”
Variant B
MeasurementSquare Module
Length27.5”
Width27.5”

I wanted to use standard dimensional lumber to create the frame under the maze. I selected 2×4's because they are practically ubiquitous and I knew their nominal dimensions off hand. In hind sight, using normal dimensional lumber was a bad idea. I would use engineered 2×4's or create custom frame pieces from plywood. It proved to be too difficult to find normal 2×4's that were straight, square, and true, especially with 10' long 2×4's. If and/or when I build another maze, I will not be using standard dimensional lumber.

Holding the modules together tightly is a critical step in limiting surface discontinuities of the maze surface. Looking at the CAD model, the maze can be broken up into 3 major sub-assemblies.

There are 2 types of the major 3 sub-assemblies. There are two Edge Assemblies, one on the left and one on the right hand side of the maze shown in the rendering above. The Spine Assembly is seen between the two Edge Assemblies. See the table below for the composition of the sub-assemblies.

Sub-assemblySquare Module (QTY)Small Rectangular Module (QTY)Large Rectangular Module (QTY)QTY Used In Whole Maze
Spine Assembly-111
Edge Assembly21-2

Each sub-assembly is bolted together with shorter bolts, like the ones shown below.

More on these shorter bolts later.

Then each Edge Assemblies is bolted to the Spine Assembly with 6 bolts. Before the maze had legs, the bolts to hold the sub-assemblies together had to be several feet long. They were made with a long threaded rod, a hex head bolt, a coupling nut and thread locker. The photo below shows a pair of these bolts.

This photo shows the long bolts installed on the maze.

The thread locker is used to prevent the coupling nut from being unscrewed from either the threaded rod or the hex bolt. Since we built the maze, several of the thread locker joints have failed and required reapplication of the thread locking compound to the threads.

FIXME A CAD Drawing or photo of this needs to be added.

For future builds that require this type of solution, I would recommend drilling the coupling nut, threaded rod and hex bolt to accept locking pins.

The locking pins have to be flush with, or slightly below the planes of the flats of the coupling nut. This prevents the long bolts from becoming stuck in the bolt holes on the maze frame.

As mentioned above, if the maze has legs under it, the long bolt assembly is not needed, because there is access for a normal size bolt to be used.

The shorter bolts shown in the picture above are carriage bolts. These bolts have a square shoulder under the head of the bolt and a rounded over head (See Wikipedia Article on Screws and Bolts for more information). Image showing two carriage bolts. Image credit: Wikipedia

The carriage bolts are nice because they don't require a second wrench or pair of pliers to prevent the bolt from rotating during tightening. The square shoulder provides a locking surface to do this. It's a great feature until someone over torques the bolt and reams the area of wood that the shoulder embeds itself into out. This is where a torque washer is useful. We used them on the maze with great success.

Sources for 3/8” torque washers

They prevent the carriage bolt's shoulder from reaming out the wood because the torque washer has teeth that bite into the wood, like a nail does, and a square hole that mates with the carriage bolt's shoulder.

Using a wing nut, instead of a hex nut removes the need for tools to tighten the bolt and nut.

Another feature of the design that is worth noting is using over-sized holes for the bolts. This makes assembly of the maze easier, but increases the importance of using washers with nuts and bolts. I choose to use fender washers whenever possible because of the increased surface area spreading the force of the bolt head or nut out. In other words, the fender washer exerts less pressure on the frame, reducing deflection and deformation due to local stresses on the frame materials.

The hole pattern for the maze corner posts is a simple gird, based on the specs for the maze. Again, the holes are slightly over-sized to prevent problems from tolerance stack ups.

The walls of the maze are created a wall section and a corner post with a metal pin aligning the corner post to the hole pattern on maze floor. A wall and corner post are shown below.

Wall Section and Corner Post w/ metal pin

In our build the corner posts were not painted; however, they should be painted to fully meet specs. The metal pin is a 1/8” diameter rod made of cold rolled steel. We spent a lot of time making the pins from 10' long sections of rod, because we thought it would be cheaper to make them versus buy them. In retrospect, buy the pins. They are sold as metal dowels. 1” to 1.5” long by 1/8” long should be fine.

Links for .125” ⌀ x 1.00” dowel pins.

Links showing .125” ⌀ round stock (1018 Alloy steel)

When calculating the required quantity of round stock, don't forget to account for the thickness of cut-off wheel. In our case it was .125” This means that every pin will require 1.125” of material. Also, make sure to round down when calculating. A 12' long piece of stock will yield approximately 128 pins. An 8' piece will yield about 85 pins.

The round stock is cheaper than the dowels; however the tooling and time required to machine the round stock to size will completely offset any savings over the pre-made dowels. We needed 2 pairs of locking pliers (Vice-Grips), a bench grinder equipped with a grinding wheel and a wire brush, a metal cutting/abrasive chop saw and almost 16 man hours to complete the machining and de-burring processes.

The wall sections and the corner posts should be made with MDF.

Don't confuse particle board and MDF. Particle board won't work for creating the corner posts. It will work for the wall sections, although the results will be mediocre to poor.

The dimensions of the walls and corner posts are driven by the maze specs.

PartLengthWidth/ThicknessHeight
Wall Section15.6 cm (less the tongue) 1.2 cm 5 cm
Corner Post 1.2 cm 1.2 cm 5 cm


The dowel pin is fit into a bore on the underside of the Corner Post. The bore should be .125”⌀ and 0.500” ± .05” deep and centered on each post (see photo below).

The reason for the centering of the bore is two fold.

  1. The grid pattern predicates the bore be centered.
  2. The Corner Post will be extremely weak if the bore is off center.

This Corner Post was damaged by burrs on the machined pin. This is another reason why I strongly recommend using off-the-shelf dowel pins.

Damaged Corner Post

As the picture shows, there is fairly severe cracking around the hole. The cracks extend from the hole to the outside edges of the corner post as well as extending up the groves that receive the tongues of the walls.

Building the Maze

This section covers how to construct the maze from the drawing package.

Material Selection

Being Written, current working copy (actively being written/edited) is below.

Based on our build, one of the key steps in making sure the maze meets or exceeds the specifications is selecting good materials. This means lumber that is straight and free of bows, checks, and similar defects. We did not use kiln dried lumber (KD), which in retrospect was a bad idea. KD lumber is ideal for this application because its moisture content is very low, which makes the lumber more predictable. If a KD 2×4 is good (straight, no bows, etc), then the odds are it will remain that way. Wet or green lumber has a very high moisture content (It can be wet to the touch) has a tendency to deform as the material dries out.

The term green in this case has nothing to do with the environmental friendliness of the material. Green is describing the fact that the lumber was recently felled from a forest, milled, and no additional steps have been taken to reduce the moisture content of the lumber other than natural drying that has occurred during milling, transport and so on. To avoid confusion; however, I will avoid using the term green in cases where it is not absolutely necessary.

Note, however, that FSC certified lumber is grown in an environmentally responsible manner. Most lumber companies are selling FSC certified wood and the additional cost is trivial, if any, over non-FSC certified wood.

Careful design and construction techniques can mitigate the impact of using wet lumber; however, in the interests of minimizing waste and headache, using is KD lumber is strongly encouraged.

Building The Maze

The maze is built in a modular fashion to allow the user to move the maze in a reasonable sized vehicle, store the maze in a reasonable sized space, and most importantly, move the maze through a normal sized door. Although there are doors that are over ten feet wide or tall, the door to the lab where our maze lives is not, so the ability to move the maze from where it was built to where it lives was a paramount motivation in the design of the maze.

Introducing modularity to the maze adds some headaches to the construction of the maze, namely that provisions for creating smooth surface that is nominally flat. The first version of the maze used a bunch of MDF sheets to smooth over the jumps in the maze deck. This solution yielded a very nice surface that, once painted, had nearly invisible seams. When we decided to put legs under the maze, we had to use magnets to find the screws used to secure the MDF. The second revision of the maze uses legs. The CAD rendering at the top of this article shows what the maze, with legs, looks like. The legs should be sized so that maze will fit though a standard door (our lab has an approximately 36” (91.44cm) wide door), 30” (76.20cm) is a good place to start. Our legs are are just under 30” long to fit some existing benches in our lab.

We attached the legs with a combination of 5/16” lag screws (also called lag bolts, but lag screws is generally considered the correct term). Braces are attached with course thread drywall screws. The bottom of the legs have a 5/16” leveling foot ordered from McMaster-Carr. The leveling feet allows the maze surface to be smoothed easily, without a huge amount of MDF and extra labor. This is critical if the maze cannot be left in a setup state forever.

The Drawing Package

This file set contains a complete set of solid models, but the drawing set is incomplete. Presently there are no PDF versions of the drawings in the file set either. These will be added shortly.
Maze Model and Drawing Package in SolidWorks Format

Related

 
tutorials/build_a_micromouse_maze.txt · Last modified: 2012/09/30 13:07 by jeffw
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