Building the SumoBot

Designing and Building the SumoBot is the first step to taking part in the MakerLessons' Sumo Bot Competition. Sumo Bots can be built from any variety of building materials from metal, wood, or crafting supplies. Depending on your budget and skill level you can tweak the design constraints of your competition. Because of the nature of the competition with the SumoBots smashing into each other, it is suggested that you build it out of a material that can handle continued abuse and an elongated competition. This page will show you how to build a SumoBot chassis, shell, and drivetrain using the standard rules and regulations using primarily sheet metal. Sheetmetal will allow for the double use of a sturdy chassis and protective shell as one. But before building the SumoBot we must start with the design. 

The Design

When choosing your design you should consider all your design constraints and the materials you want to use. Both of these will inform what you can design and how it must be shaped. You should follow the Engineering Design Process for this entire project. The EDP will help guide you and will be informed by the rest of this page. Remember that the Engineering Design Process is a cyclical and repeatable process. You can restart or modify your design at any point in the following steps. 

Your constraints are the rules and regulations that your SumoBot League agrees on- when using the official MakerLessons' SumoBot Rules and Regulations, your main concerns will be total size, weight, and safety. 

The Steps of Creating your Sheet Metal Profile

Step One: Start with Paper

Once you have a sketch or 3D model of your SumoBot you have to convert it into a surface development drawing. This is the process of laying down the sides of a 3D model into a 2D flat shape that we will use later to transfer to sheet metal and bend. You can use paper surface development to fold along your bend lines into a rough prototype of what your SumoBot will look like. Take some time to figure out where the motors, wheels, and other hardware or accessories will go. Paper is cheap and this step can be repeated as often as you need until you are happy with your product. 

Step Two: Paper Prototype 

Using the paper surface development to fold along your bend lines into a rough prototype of what your SumoBot will look like. You can use this model to test fit your motor and any drive train assembly prototypes that you have. Be sure to double-check the total size and other design constraints that are in the rules during this step. 

Step Three: Switch to Cardboard or Foam Core

Once you have settled on a design and are happy with your paper prototype, you should switch to another cheap consumable: cardboard (this can be substituted for FoamCore if you have access to it.) The purpose of this model is that the cardboard has some integrity to it and can be used to actually mount and test fit all your motors, wheels, and other hardware or accessories. This prototype can be used to actually move and test drive your SumoBot if you connect the controller. If something is wrong or the SumoBot doesn't work as intended, repeat Steps One and Two

Step Four: Bend the Cardboard or Foam Core along the Fold Lines

Using your Surface development that was transferred to a stiffer material, bend along the dashed bend lines. A helpful way to do this is to use the back end of an X-acto knife or pen, to crush the material along the bend line. This will allow the material to bend easier because you will have removed the compression component of K-Factor and Bending.

Step Five: Secure Prototype

Using a combination of hot glue and tape, secure the edges of your Cardboard or Foam Core where they intersect. This is also the time where we can re-add the lid to the SumoBot. When building a SumoBot, you should consider keeping the internal electrical and mechanical systems covered for long-term protection and durability. 

Step Six: Add You Electrical and Mechanical Systems

Now that your Sumo Bot Prototype is assembled, it should have some rigidity. This will allow you to mount your motors, gears, chain, sprockets, or any other electrical or mechanical systems you have chosen for your design. This is the last step before switching to a different material to make sure everything fits and works. Theoretically at this step, if you are done with your controller, you could test the full functionality of your SumoBot. 

Notice: Depending on your access to materials and supplies, Step 6 could be the final step to building your SumoBot but understandably, it will not be as robust as a metal or wooden robot.  If you do not have access to a sheet metal, punch, drill, metal break, and other tools you may skip the following steps. You can also choose to make a Chassis and frame out of wood 3D printing, or any other material. When building the SumoBot, just be sure to build it robust enough to be used over and over and get pushed around. 

Step Seven: Transfer your Final Design to Sheet Metal

Once you are happy with both Step One and Step Two it is time to transfer your Surface Development onto sheet metal- this is called a Sheet Metal Profile. When folding and binding corners with paper or cardboard, you can use tape, however, bonding the edges and corners of metal will usually be welded or riveted. The easier and cheaper method of using sheet metal fabrication is using rivets. For this project, you can use 1/8th inch pop rivets that can be installed using a drill and rivet gun. Because of this, you must add tabs to your sheet that can be used to fold in line with the adjacent side to rivet to. The tabs should be at least 3x the width of the rivet and have 45° cut out of each end to allow for the metal to fold and not intersect with each other. 

Step Eight:  Cut Out your Sheet Metal Profile

Once you transfer the sheet metal profile to the sheet metal, you will need to cut it out using aviation shears. (Be careful because the edges at this point could be sharp.) For any internal cuts, you will have to drill a hole large enough to fit in the aviation shear cutting tip.  Aviation Shears come in three main models: Left, Right, and Straight. These directions refer to the direction the waste sheet metal will deflect out of the way. 

Step Nine:  Line up the bend line on a Break

Line up your bend line just behind the break bar that is clamped over the piece. When using the break, this line will end up being halfway between the clamp and the break that is bending the material. Depending on your break, you will find out how tight of a bend you can make and where exactly you have to place your line for precision. This Harbor Freight model has a bar that has to be clamped down with other C-Clamps. Other models have integrated clamps. 

Bending Material: K-Factor

Let's zoom in on our material and look at its thickness and consider what is its neutral axis. The sheet's neutral axis is the line that passes through the points where the stresses and strains are exactly zero. To understand stress and strains, look at our Structural Forces page which explores typical engineering stresses. As a material begins to bend and the neutral axis shifts.

The cross-sectional area above the neutral axis experiences compression stresses. In contrast, the region below the neutral axis undergoes tension. The length of the neutral axis does not change when bent. Instead, it shifts along the thickness and direction of the material. The K-factor is the ratio of the measurement of the neutral axis from the surface of the material to the material's overall thickness. 

While understanding the K-Factor may not be entirely important to bending sheet metal and other materials at this level of precision, it is important to understand that when bending material the thickness of the material will limit the bend, and the material itself will oppose the bend and deform while bending. 

Step Ten: Bend using the Break

With your bed line lined up and your bar clamped in place, bend that metal using the handles on the break. Typically, you will have to slightly overbend to get the exact angle you want. This is because the material has to deform more than is required to keep the angle. For example, if you want 90°, you should overbend to about 100°. Again, this will be tuned in with your specific break. Be sure to be mindful of your bend order- typically you will want to bend the tabs first and in general work outside in.

Step Eleven: Rivet the Sheet Metal Together

Once you have made all the bends on your sheet metal profile, the final shape will have started to take place. Using a drill or sheet metal punch, create holes on your tabs and the side of sheet metal it will intersect with. You will use these holes to insert rivets. Rivets are a semi-permanent fastening tool. Our suggestion is to use 1/8" rivets which means your rivet hole needs to be just above 1/8"- something like 9/64" or 5/32" will work. 

Step Twelve: Add You Electrical and Mechanical Systems

Similar to Step Six, now that your final prototype is assembled you can mount your motors, gears, chain, sprockets, or any other electrical or mechanical systems you have chosen for your design. When you are done with your final assembly attach the controller and test the full functionality of your SumoBot. If everything works as designed and you are happy with the final outcome, you are finished. Good Luck in the competition. 

Drive Train Iterations

When designing your SumoBot, you must consider how you will mount your motors. Depending on the size of the motors and the mounting hardware, you will have to  The easiest way to mount your motors would be direct to the frame of your SumoBot. Depending on the total size of your robot and the orientation of the motors, you will probably have to mount the motors in unique ways to get them to fit inside the 8.5" x 11" sizing requirements of the SumoBot.

Inline Mounted

The easiest and most intuitive way to mount your motors would be inline with each other. This keep the wheels in line and simplifies the design process with a simple mounting pattern. That said, depending on the length of your motors and size of your wheels, the total length between wheel edge to edge will be the longest in this orientation. This will affect the orientation of the long dimension of your 8.5" x 11" SumoBot.

Offset Mounted

Another simple way to mount your motors would be to offset from each other. This method eliminates the downside of the long length between wheel edges by mounting the motors alongside each other. This way the length between wheels is just the length of one motor and not two in line with each other. The perceived downside is that your wheelbases are not on the same line of rotation. This leads people to think that if both wheels are moving forward at the same rate the robot would still skew to the left or right- this does not happen, or if it does, is negligible at these scales. 

Geared Offset 

Geared Offset provides the advantages of both the inline and offset miunting conditions. In this drive train you are able to keep you wheels inline with each other which keeping the total width of your assembly to be about the same width as an offset mounting. When one of the biggest constraints of the SumoBot challenge is size, this is a good design to get the most out of your drive train.