# How to build big robots(Material/Method)?

I am interested to know, if I want to build middle/big size robots(50*50*150 cm^3), which material and which method is better to use?

I mean, when I want to build a robot with this size(20*20*20) I do designing with solidworks and printing by 3d-printer very happy and simple! But what if I like to bigger my robot?

I think this photo may help to clarify what do I mean:

If someone wants to build robots in this scale, what should he learn?(except going to university and getting a master in mechanical engineering:) ). I mean is it possible to learn or not?

Edit: I wanted to write this for Mike but it was to big for a comment and I thought maybe it's better to add it here:

It was a great answer, thank you! But maybe it was better to mention I really don't want to build a robot lonely by myself. My goal was about learning how can I make a big prototype of my robot? I have made a robot in 20*15*20 cm^3 size by 3d printer. it's an educational robot. I designed it by Solidworks and made it by my Prusa i3 printer. Also I programmed it myself. And I thought if I can build this robot in 50*50*150 cm^3 size I can sell it to schools! or even build other types of robots like servants. So I was looking toward a way to build a prototype of that and show it to some investors and make a team to build it functional as you said it in your answer.

## 2 Answers

I am interested to know, if I want to build middle/big size robots(50*50*150 cm^3), which material and which method is better to use?

I am assuming you don't want to go the way of designing a robot using a CAD software followed by tons of machining to bring all the custom parts to life. If you are looking to build a robot using off-the-shelf materials, I would say aluminum extrusion is the way to go. It is the machine builder's lego. Using aluminum extrusion and aluminum plates, you can rapidly build a large, rigid base onto which you can mount all your electronics, motors, sensors, computers, etc.... I prefer Bosch aluminum extrusion (which officially is called 'aluminum structural framing'). Have a look here: https://www.boschrexroth.com/en/us/products/product-groups/assembly-technology/aluminum-structural-framing/index. For plates, round shaft, angle, etc... you can go to metal supermarkets (if you are in US or Canada. If not you should have something local). An example of an ongoing robotic project that was built with extrusion and plates can be seen here: https://answers.ros.org/question/271819/please-suggest-all-packages-to-achieve-slam-for-robot/

I think this photo may help to clarify what do I mean: Aluminum extrusion will allow you to build the two robots that have a rolling base. As for the middle biped robot, you will need to get more fancy... WAY more fancy. Building biped robots is very challenging, and you will most likely will need to machine your own components around off-the-shelf parts that you are utilizing. Rolling bases with robots on top are much easier to build than biped robots. I guess I am trying to say that the images you included are robots that are not all in the same league. So far I have focused on a moving base. If you are trying to build arms with end effectors, you will need to start machining custom parts (whether your own design or open source).

If someone wants to build robots in this scale, what should he learn?(except going to university and getting a master in mechanical engineering:) ). I mean is it possible to learn or not?

Usually advanced robots (like the 3 you have in the image) are built by teams. Teams allow members to specialize in different disciplines (mechanical, electrical, electronics, programming, etc...) which produces the best solutions in each discipline. However, a single person can also build an advanced robot, it just takes longer, and it will be very challenging to come up with the perfect solution in every discipline every time. My question is why do you want to build a robot? if you are trying to learn, then join a robotics club, or start building miniature robots. If you are looking to build functional robots (entirely on your own), to achieve actual tasks, then I suggest you learn the following:

1. CAD software - drawing your robot out will save you time as you discover issues before you start building. I recommend solid works, so you can later do 3D printing.
2. Machining - you will need to build some pieces that link off-the-shelf parts in your mechanical design.
3. Electrical - You can always pick up a textbook and run through basic AC/DC theory and do some experimentation. You will need to have some basic understanding to use off the shelf parts and how to integrate them together. you will need to understand how to step down/up voltage, limit amperage, etc...
4. Mechanics - Before you start building you will need to double check your design (catch items such as robot will not flip as it's too top heavy, or motor is underpowered to move limb, etc...)
5. Programming - May I suggest C and C++? You will need to program the robot to control all your hardware to perform the task you want. I am relying on the ROS framework.

Robotics is an amalgamation of mechanical, electrical and programming. All robots rely on these disciplines to various extents.

My advice is first figure out why you need a robot. this will guide what you will build. Then start building each system out independently of each other; once you are done amalgamate all your parts into a single unit.

• Thank you Mike! I edited my post. Maybe it clarify my goal better.
– WDR
Nov 23 '17 at 14:19

From what I understand, your question is purely about how to manufacture a robot that looks like it when you have the know-how for programming it and stuff.

Manufacturing such robots as in your picture uses mostly polymers(fancy name for plastics). They are created using injection moulding machines and other similar processes. For the aluminium/metal parts, metal additive manufacturing or aluminium extrusion is used. All g

Now, when you are scaling your robot up, you have will have different mass for every link and joint. Therefore you will have to scale up your power supply and actuators torques, and then work around with other requirements from there.

Now for determining the torques required at the joints, you will need to know the mass and the moment of inertia of every joint and link, which depends upon the material and design, of course.

For understanding everything, you will need to study forward and inverse kinematics and then learn about robot dynamics. Ideally, its best if you study everything from the basics and make sure you understand everything about it so that you will built a very reliable robot that does exactly the way you expect it to. I am afraid I will have to leave the part about whether it is achievable on your own or not upto your discretion. Most people who studied this subject at university with me found it quite difficult.

However, I know people who just winged it with simple robot designs of similar dimensions and they worked. However, If you plan on building a bi-ped robot of that scale, Gob bless you! It will involve tremendous amounts of trial and error which maybe very expensive.

Since you are planning on building a team to help you out, I suggest you get someone from mechatronic/mechanical, electronic and computer engineering background.

I hope I have answered all your queries correctly. Cheers!

• Thank you for reply! do you know an opensource robotic project in that size, or any tutorials to learn how they build them step-by-step?
– WDR
Nov 24 '17 at 16:29
• best would be to go through online courses such as coursera or edx. They do have courses in robotics, but may not be covering this particular field of robotics. Search these sites for courses with any of these keywords: Forward Kinematics, Inverse Kinematics, bi-ped robotics, manipulators, robot arms. Alternatively there are these youtube tutorials by milford robotics, which I found pretty useful when I was studying the subject: youtube.com/playlist?list=PLB46C8B9857C32201 I will add other resources as a comment here, if I remember more. Nov 26 '17 at 15:00