5 things to think about when building a combative robot

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5 things to think about when building a combative robot

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By: Rob Karpinski
Project Engineer, Embedded Systems

21st June 2017

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Advances in computer science and engineering have brought in great change for robotics over recent years. From four-armed marimba robots being capable of composing original music to self-balancing quadrupedal robots capable of negotiating rough outdoor terrain, robotics has come a long way since the Roomba, one of the first robot vacuum cleaners.

However, if there is one thing better than putting together robots, it’s taking them apart again with other robots. With that in mind, and with the arrival of Series 9 of Robot Wars earlier in the year, here are five things to think about if you’re looking to build a combative robot for the hit TV show.

1. Get a good team together

Building a heavyweight, 110kg robot is hard and, talking from experience, there is a steep learning curve. It’s better to share this with a team of 3 – 4 people than taking it all on yourself. You may find it helpful to divide the responsibilities into certain roles like, design, construction, and buying. Alternatively, you can split the roles by system: drive, weapon, and chassis for example.

2. Choosing a chassis & materials

Most robots use a special type of steel, called Hardox, for armour. This wear-resistance steel is often used in digger buckets and is as strong as Titanium. However, unlike Titanium, it will bend rather than crack.

The limiting factor for robot size is the weight. A bigger robot will have to have thinner, lighter armour than you would have for a smaller robot. Keep in mind that an ideal robot is as small as the weapon and engine will let it be.

There is a growing trend to using Computer Aided Design (CAD) packages to design your robot. With many professional quality packages being offered for free by companies, this allows you to send design files directly to the metal working companies. They will then cut and shape parts of your robot for you, for a cost. This method is often quite expensive, however, will allow you to build a robot if you don’t have access to a fully-equipped workshop. Local makerspace/hackerspace communities may also have access to suitable workshops with metal working tools.

A good substitute for metal is a plastic called high-density polyethylene (HDPE). Using this resilient plastic can cut costs down and can be shaped with easily accessible woodworking tools. However, the thicknesses required to build a suitably robust robot leaves little to no weight advantage over using Hardox.

3. Have an exciting weapon

Robot Wars is an entertainment show, therefore the live audience and the viewers at home, will want to see destruction. Being a combative robot, it is common advice to plan the weapon first and then design the rest of your robot around it. Before getting started on the weapon, familiarise yourself with the Robot War rules first as they are quite specific. This is mainly due to safety but also to keep it exciting for the audience. Also make sure that your robot is robust enough to handle a hit from your own weapon.

Common weapon types are spinners, flippers and thwackbots. Spinners will do the most damage, both to your opponent and your own robot. Flippers are not as devastating but can be very impressive and effective if used tactically. It’s always entertaining to watch a robot sail a couple of meters into the air! Thwackbots are the simplest to make, but quite hard to make exciting.

4. Choosing motors and steering systems

In Robot Wars, if your robot doesn’t move for 10 seconds it will be counted out and you lose the match! However, if your weapon stops working, you can still dodge and push your opponent into the house robots or the dreaded pit.

Most robots use a 2 wheel tank-style steering system, however, 4 or more wheels allow for increased grip on the arena floor. Very few robots use tracks as they’re very tricky to get to work reliably.

The Bosch 750 brushed motor is a fan-favourite among the Robot Wars community as these have a good power-to-weight ratio. However, they’ve been discontinued now, so finding replacements and spares may be difficult but, because of its popularity, not impossible.

800W scooter motors available from China can make for good alternatives. The quality is not as great but they are more affordable and easily available. Regardless, having a brushed motor is recommended for most teams as they don’t require pricey speed controllers and are easy to set up. Brushless motors have a much better power to weight ratio but the controllers can be complicated so very few teams use these. Tune your robot for acceleration over speed as the secret to winning is quickly positioning your robot into a good spot to avoid the opponent’s weapon whilst attacking with your own.

5. Be an interesting robot

As a final note, have fun with it. Robots with amusing and interesting themes are more likely to be accepted than boring wedges or tin cans. LED’s are cheap and don’t require much power to light up your robot. Robots with great paint schemes, team costumes, and novel backstories can become hugely popular. Get the audience to buy into your robot with a catchy name that is easy to chant. This can be hard to get right but is worth the time spent. You can always run suggestions and ideas past friends to see what they think.

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Advances in computer science and engineering have brought in great change for robotics over recent years. From four-armed marimba robots being capable of composing original music to self-balancing quadrupedal robots capable of negotiating rough outdoor terrain, robotics has come a long way since the Roomba, one of the first robot vacuum cleaners.


However, if there is one thing better than putting together robots, it’s taking them apart again with other robots. With that in mind, and with the arrival of Series 9 of Robot Wars earlier in the year, here are five things to think about if you’re looking to build a combative robot for the hit TV show.

1. Get a good team together

Building a heavyweight, 110kg robot is hard and, talking from experience, there is a steep learning curve. It’s better to share this with a team of 3 – 4 people than taking it all on yourself. You may find it helpful to divide the responsibilities into certain roles like, design, construction, and buying. Alternatively, you can split the roles by system: drive, weapon, and chassis for example.

2. Choosing a chassis & materials

Most robots use a special type of steel, called Hardox, for armour. This wear-resistance steel is often used in digger buckets and is as strong as Titanium. However, unlike Titanium, it will bend rather than crack.

The limiting factor for robot size is the weight. A bigger robot will have to have thinner, lighter armour than you would have for a smaller robot. Keep in mind that an ideal robot is as small as the weapon and engine will let it be.

There is a growing trend to using Computer Aided Design (CAD) packages to design your robot. With many professional quality packages being offered for free by companies, this allows you to send design files directly to the metal working companies. They will then cut and shape parts of your robot for you, for a cost. This method is often quite expensive, however, will allow you to build a robot if you don’t have access to a fully-equipped workshop. Local makerspace/hackerspace communities may also have access to suitable workshops with metal working tools.

A good substitute for metal is a plastic called high-density polyethylene (HDPE). Using this resilient plastic can cut costs down and can be shaped with easily accessible woodworking tools. However, the thicknesses required to build a suitably robust robot leaves little to no weight advantage over using Hardox.

3. Have an exciting weapon

Robot Wars is an entertainment show, therefore the live audience and the viewers at home, will want to see destruction. Being a combative robot, it is common advice to plan the weapon first and then design the rest of your robot around it. Before getting started on the weapon, familiarise yourself with the Robot War rules first as they are quite specific. This is mainly due to safety but also to keep it exciting for the audience. Also make sure that your robot is robust enough to handle a hit from your own weapon.

Common weapon types are spinners, flippers and thwackbots. Spinners will do the most damage, both to your opponent and your own robot. Flippers are not as devastating but can be very impressive and effective if used tactically. It’s always entertaining to watch a robot sail a couple of meters into the air! Thwackbots are the simplest to make, but quite hard to make exciting.

4. Choosing motors and steering systems

In Robot Wars, if your robot doesn’t move for 10 seconds it will be counted out and you lose the match! However, if your weapon stops working, you can still dodge and push your opponent into the house robots or the dreaded pit.

Most robots use a 2 wheel tank-style steering system, however, 4 or more wheels allow for increased grip on the arena floor. Very few robots use tracks as they’re very tricky to get to work reliably.

The Bosch 750 brushed motor is a fan-favourite among the Robot Wars community as these have a good power-to-weight ratio. However, they’ve been discontinued now, so finding replacements and spares may be difficult but, because of its popularity, not impossible.

800W scooter motors available from China can make for good alternatives. The quality is not as great but they are more affordable and easily available. Regardless, having a brushed motor is recommended for most teams as they don’t require pricey speed controllers and are easy to set up. Brushless motors have a much better power to weight ratio but the controllers can be complicated so very few teams use these. Tune your robot for acceleration over speed as the secret to winning is quickly positioning your robot into a good spot to avoid the opponent’s weapon whilst attacking with your own.

5. Be an interesting robot

As a final note, have fun with it. Robots with amusing and interesting themes are more likely to be accepted than boring wedges or tin cans. LED’s are cheap and don’t require much power to light up your robot. Robots with great paint schemes, team costumes, and novel backstories can become hugely popular. Get the audience to buy into your robot with a catchy name that is easy to chant. This can be hard to get right but is worth the time spent. You can always run suggestions and ideas past friends to see what they think.

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Further Reading