Step 4: Choosing Components
Every bot is made up of a combination of both manufactured and purchased components. Choosing the right components is crucial for a successful robot. In this step I will step through some of the major components for small to medium robots and how you choose which is right for your bot.
Motors: The driving force behind any size robot you build. They make your robot move and in many cases power your weapons. The motors used in combat robots are DC or Direct current motors, designed for anywhere between 3 and 72 volts. Just like every other component you need to make decisions to choose the right one. The four traits to consider in on each motor is torque/speed, voltage, size, and weight. Motor torque is typically rated in oz-in or in-lbs at the "stall" area. Since dc motors produce their maximum torque with minimal RPM stall torque is only a reference point. I only use the torque as a baseline for comparison for different motors and try to get the most torque I can within my other constraints. Size and weight go hand and hand since the larger form factor your robot is the more it will weigh. When defining the size of your bot try to make it as small as possible without sacrificing functionality. Voltage is one of those things that is my last priority, most motors are 12 volts but for those that aren't you just need to make sure that your electronics all match the voltage of your motors.
Common motors used for 12-30lb robots:
Drill motors - cheap drills from discount tool store harbor freight are stripped from their housings and mounted for the drives. Many people also use the battery packs from these drills as well. While the cheap drills are common many people spend the extra dollars for high quality ones such as ones made by DeWALT.
Banebots - banebots is a company founded a few years ago for the sole purpose of providing parts for combat. They have a large range of motors and transmissions which are "ready to run" out of the box. For the convenience of not having to modify drills to get the motors I chose these for my robot, the old 36mm series (which I used) broke easily, but I have had good results with the new 42mm ones. http://www.banebots.com
Other motors: A wide assortment of motors exists you can check out many of them at the robot marketplace. http://www.robotmarketplace.com
Wheels - The wheels on the robot go round and round.... The saying don't reinvent the wheel comes to mind for this section as there are as many different styles of wheels as there are builders in this sport. The main question you need to ask yourself is if you want a live axle or dead axle system.
In live axle system the wheel is hard mounted to the axle similar to a wheel in a car. The challenge with this system is that now you will need to have bearings on the shaft and find a way to couple the wheel to the axle.
In a dead axle setup the wheel freely spins on a shaft and is usually driven by a sprocket or belt attached directly to the wheel. While this system may seem easier it still has it's own challenges like the need for a power transmission method (chain or belt) and in the small spaces for this size robot direct drive systems work better.
The most common wheel used for most all combat robots is made by the colson company and is a soft urethane wheel which performs well on the many different arena surfaces. The major problem with these wheels is that they don't have a way to drive them for live axle applications. For my robot I made custom hubs on a lathe but you can buy pre-made colsons' with hubs from places like
http://cncbotparts.com or hubs that you can use to fit from http://andymark.biz.
Banebots recently came out with some of their own wheels similar to colsons' but I have not seen or tested them.
Building Materials - Small robots use a variety of materials from composites like carbon fiber sheets and aluminum. Just like any other component on your machine each material will have advantages and disadvantages. These are a few of the ones used commonly.
Aluminum: is a light weight common metal which can be easily formed and machined. It is used for the chassis of most machines for those reasons. Aluminum comes in many different alloys but the most popular ones are 6061-T6 which is heat treated and suited for machining and welding. This alloy can be soft and not great for impact resistance so use it for components which arn't going to see direct contact. 7075 is the other major alloy and is much tougher of a material which makes it harder to form and weld but has better resistance to hits.
UHMW - is a durable plastic commonly used for internal components as mounts. It has a bit of give to it, but it holds up well under competition. It is also very easy to form with even hand tools.
Polycarbonate - or lexan as it is commonly known is a clear durable plastic which is for the most part impact resistant and light weight. pound for pound it compares to aluminum but it bends and bounces back instead of deforming like metal will. Under extreme impacts it can crack and break away so use it for top panels but not armor.
Titanium - a great material for armor but it is very cost prohibitive, although many builders still use this for high end machines.
For my robot I used both 6061 and 7075 aluminum. Mainly 6061 for my supports and chassis and 7057 for my outer frame supports. I used a live axle setup with banebot 12:1 transmissions powering 3" x 7/8 coloson wheels with a custom made hub.
Step 5: Computer Aided Design (CAD)
CAD is the system used by all professionals for the creation of the products you see and use everyday. It allows you to make 3D computer renderings, seeing how things fit together on the computer before you build. This step can revel potential problems on your bot which will reduce your time and cost overall.
It is a common thought that CAD systems are difficult to use and build if you are not an engineer or have been trained to use them through some class. Recent CAD software has been shifted from even five years ago so that they are easier to build models with a user interface that anyone can pick up and learn within a few hours.
Within industry the three most popular pieces of software are Autodesk Inventor, Solidworks, and Pro-e. Each one of these has advantages and disadvantages to their own right but all are comparable for this type of design. I will not be going into how to use CAD in this instructable but there are many resources online for using this type of software.
Buying CAD software can be very expensive but fortunately there are many opportunities for free licenses of software if you are a student, or if your company has licenses of the software.
Students can get autodesk inventor for free from http://students.autodesk.com All you need is an email with a .edu ending
You can also get a copy of student version of solidworks very cheep/ free from time to time online.
They also have a great tutorial for robotics design located here http://www.solidworks.com/pages/products/edu/Robotics.html?PID=107
For robot design with little to no CAD experience I recommend Inventor or Solidworks both provide a simple interface, and more importantly there are lots of models available for free download. Stock parts like bearings, screws, motors, etc can be found. Using these models will save time when modeling.
The most important thing about CAD design is that you have your dimensions right. Now that may seem like a straight forward piece of advise but I see loads of people trying to make realistic renderings and spend too much time making their parts look nice instead of focusing on the real goal of CAD to make models which are accurate.
I am going to leave this step because if you take the time to learn CAD the process steps for design in the software become more apparent. If you choose to skip this step due to the inablity to run the software or the lack of interest I recommend a "cardboard template" method. Take cardboard and cut out scale models of each one of your parts for layout, before you cut your real material. A good example of this method in the webshow by revison3 called Systm located here http://revision3.com/systm/robots/
Ultimately the purpose of this design step is to minimize the mistakes with your expensive.materials.
Additional notes:
*modern CAD software can assign weight properties so you will know how much your bot should weigh before you build
*Ensure that you have sized things correctly so they fit together, for example a 1/2" shaft will not fit through a 1/2" hole. For exact machining you are dealing with thousands of an inch (.001")
It is a common thought that CAD systems are difficult to use and build if you are not an engineer or have been trained to use them through some class. Recent CAD software has been shifted from even five years ago so that they are easier to build models with a user interface that anyone can pick up and learn within a few hours.
Within industry the three most popular pieces of software are Autodesk Inventor, Solidworks, and Pro-e. Each one of these has advantages and disadvantages to their own right but all are comparable for this type of design. I will not be going into how to use CAD in this instructable but there are many resources online for using this type of software.
Buying CAD software can be very expensive but fortunately there are many opportunities for free licenses of software if you are a student, or if your company has licenses of the software.
Students can get autodesk inventor for free from http://students.autodesk.com All you need is an email with a .edu ending
You can also get a copy of student version of solidworks very cheep/ free from time to time online.
They also have a great tutorial for robotics design located here http://www.solidworks.com/pages/products/edu/Robotics.html?PID=107
For robot design with little to no CAD experience I recommend Inventor or Solidworks both provide a simple interface, and more importantly there are lots of models available for free download. Stock parts like bearings, screws, motors, etc can be found. Using these models will save time when modeling.
The most important thing about CAD design is that you have your dimensions right. Now that may seem like a straight forward piece of advise but I see loads of people trying to make realistic renderings and spend too much time making their parts look nice instead of focusing on the real goal of CAD to make models which are accurate.
I am going to leave this step because if you take the time to learn CAD the process steps for design in the software become more apparent. If you choose to skip this step due to the inablity to run the software or the lack of interest I recommend a "cardboard template" method. Take cardboard and cut out scale models of each one of your parts for layout, before you cut your real material. A good example of this method in the webshow by revison3 called Systm located here http://revision3.com/systm/robots/
Ultimately the purpose of this design step is to minimize the mistakes with your expensive.materials.
Additional notes:
*modern CAD software can assign weight properties so you will know how much your bot should weigh before you build
*Ensure that you have sized things correctly so they fit together, for example a 1/2" shaft will not fit through a 1/2" hole. For exact machining you are dealing with thousands of an inch (.001")
Step 6: Construction of manufactured parts
Depending on how much design and your resources you can start building parts. There are many ways to do things, hand tools (jigsaw, hammer, etc), Manual mill lathe, full cnc; Which ever method you choose Make sure you are Safe.
If you are building a budget robot you will most likely be using hand tools or light power tools. This is the method used by more bots than anything else. The only advise that I can offer for doing this is to take your time and use the templates or CAD drawings you created to help in the process. One of my preferred methods for this when I am unable to use the machine shop is to make drawings from CAD in a full scale and paste them to the material then use those guides to cut your parts.
The next step up from manual tools is a standard machine shop. If you have access to a Mil or a lathe you will be able to create highly accurate parts. These tools can be very dangerous if you don't know what you are doing so make sure supervision or proper instruction happens before you start. If you are looking for access to a machine shops most towns and citys have them and you should be able to open a phone book and find someone to help. Sometimes they are willing to donate their time other times you will need to pay for their time. At this day in age there are some great resources online for manufacturing which can help you out. http://www.emachineshop.com/ and www.cncbotparts.com both are great sources.
Advanced manufacturing can come into play for many complex robots. For my past few robots I have been fortunate to have access to CNC (computer numeric controlled) and waterjet for my bot parts. This makes building the components very easy but it makes the CAD design even more crucial for accuracy, as any machine shop will build EXACTLY what you give them. If you are going down this road make sure you take the extra steps to ensure that your design is right. I would even go as far to find someone else who knows CAD to review your designs to make sure you have not overlooked something.
If you are building a budget robot you will most likely be using hand tools or light power tools. This is the method used by more bots than anything else. The only advise that I can offer for doing this is to take your time and use the templates or CAD drawings you created to help in the process. One of my preferred methods for this when I am unable to use the machine shop is to make drawings from CAD in a full scale and paste them to the material then use those guides to cut your parts.
The next step up from manual tools is a standard machine shop. If you have access to a Mil or a lathe you will be able to create highly accurate parts. These tools can be very dangerous if you don't know what you are doing so make sure supervision or proper instruction happens before you start. If you are looking for access to a machine shops most towns and citys have them and you should be able to open a phone book and find someone to help. Sometimes they are willing to donate their time other times you will need to pay for their time. At this day in age there are some great resources online for manufacturing which can help you out. http://www.emachineshop.com/ and www.cncbotparts.com both are great sources.
Advanced manufacturing can come into play for many complex robots. For my past few robots I have been fortunate to have access to CNC (computer numeric controlled) and waterjet for my bot parts. This makes building the components very easy but it makes the CAD design even more crucial for accuracy, as any machine shop will build EXACTLY what you give them. If you are going down this road make sure you take the extra steps to ensure that your design is right. I would even go as far to find someone else who knows CAD to review your designs to make sure you have not overlooked something.
Step 7: Assembly of components
As you are in the process of building your components test fit your parts together. Don't be surprised if you have to modify some of them as they won't always fit. Depending on how they were manufactured your parts will fit together differently.
Ones made in a machine shop or with a CNC will most likely go together as designed, the more manual the manufacturing the more modification you will need to do. Just make sure to use the montra of "measure twice cut once" as it is very hard to make material grow once you cut it away.
The main advice in this process is don't get discouraged if you take your time things will go together just fine.
Notes:
if you are using threaded fasteners make sure to use high quality ones. The fasteners at the big box stores (home depot and lows are of low quality. I recommend ordering from McMaster Carr www.mcmaster.com or another industrial distributor.
Ones made in a machine shop or with a CNC will most likely go together as designed, the more manual the manufacturing the more modification you will need to do. Just make sure to use the montra of "measure twice cut once" as it is very hard to make material grow once you cut it away.
The main advice in this process is don't get discouraged if you take your time things will go together just fine.
Notes:
if you are using threaded fasteners make sure to use high quality ones. The fasteners at the big box stores (home depot and lows are of low quality. I recommend ordering from McMaster Carr www.mcmaster.com or another industrial distributor.
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