Reminder: Restrictions on robot size and mass in Race to the Wall

Over the last few days, I have been surprised to receive quite a few queries about the restrictions on the size and mass of robots in the Race to the Wall. As clearly stated in the rules:

  • The mass of the robot must not exceed 500 grams. This includes absolutely everything contained in or attached to the robot during the race. This includes the batteries.
  • The footprint of the robot (its total area when viewed from directly above) must fit within a square 10 cm by 10 cm at all times throughout the race. This includes all parts of the robot, including wheels, sensors, wires, etc. i.e. absolutely everything.

In previous years, we did systematically measure and weigh every single robot, since most were clearly compliant. Instead, we carried out a detailed inspection of any robot about which a query arose. I expect we will apply a similar approach in this year’s competition.


[Download editable SVG image]

Please leave some margin for error!

We recommend that teams leave a margin for error. That is to say, don’t try to make your robot exactly 10 cm x 10 cm and 500 grams. Instead, make it (for example) 9 cm x 9 cm and 450 grams. That way, if you’ve forgotten something that will make the robot slightly bigger or slightly heavier than you thought you’ll still be ok. Leaving a bit of room to spare will also give greater flexibility when you’re trying to iron out the last few problems. In many cases, the improvised solution to a problem that comes to light on the day of the competition adds a few millimetres or several extra grams to the robot.

“My robot is 10.1 cm long and/or 503 grams… that’s close enough, right?!”

Sorry, no. There is no “close enough” – only compliant and non-compliant.

If your robot is non-compliant, you need to start chopping and don’t stop until it’s within the specified size and weight. I have seen people literally shed tears while butchering their lovingly crafted, but overweight robots in order to make them a little lighter. Life is life. Bad things happen to good people.

If you need to shave off just a few grams, here are some ideas:

  • Drill some holes in any metal plates or bars to reduce their weight.
  • Remove redundant wires and shorten remaining ones that are longer than necessary.
  • Remove redundant clip-on sections of breadboard – e.g. unused power rails.

Reducing the footprint of the robot is often more difficult, but here are a couple of things I’ve seen work in the past:

  • Remove the outer casing (if any) of the robot. This also reduces the weight.
  • Use a sharp knife to pare back plastic or rubber parts, such as the tyres to make them thinner / smaller.
  • If your robot has two motors, each with a wheel attached, have you considered positioning the motor axes on different lines? For example, one wheel might be near the front of the robot’s left side, while the other is near the back of the right side. This sometimes allows the motors to be positioned one in front of the other, rather than side by side, reducing the width of the robot.

“We’ve done everything we can, but there’s no way we can make our robot compliant )-;”

We reserve the right to allow a non-compliant robot to attempt the task and, if successful, to record an official time. However, no non-compliant robot can be positioned higher on the leaderboard than a compliant robot which has successfully completed the task. Non-compliant robots will be allowed to compete only at the discretion of the tutors – it is not an entitlement – and will be considered on a case by case basis.

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