Mini-Sumo Robot: How to Build from 0!

Introduction

First of all I'll introduce you what is a Mini Sumo Robot.
Similar to Japanese Sumo Battles, when two fat guys must push the other away the ring (called there "tatami"), the Mini Sumo battles consist of matches where two autonomous robots must drop the other. Why autonomous? Because they are not radio-controlled outside, they must have their own sensors to decide themselves how to win the battle.

As every single sport, each of the robots has physical maximum specifications, that are

• Max Weight of 500 g (aproximately 17.6 oz)
• Max Size of 10cm x 10cm (aproximately 3.9 in)

 The robot can extend its maximum size deploying structures that must be always attached always when the round has already started.

By the other hand, the pitch used in the competition has also standard sizes and colors that also can vary little on each tournament. Usually looks like this:

There are other rules such as activation mode or robot starting placement, but these are the elemental ones that are in every mini sumo competition.

Our approach

The rules and understanding of what to make are absolutely easy as the interesting and more tricky part is the knowledge need to build a successful and competitive robot. 

There are things every robot must own always to work, that are:

• Motors and wheels (to move)
• Battery (to supply energy to motors and sensors)
• Ramp (optional, but you need it to defend your frontal side)
• Enemy detection sensors (to detect other robots in the distance)
• White ground sensors (to detect the end of the pitch)

And the most important things robot's skills we'd like to remark are

• The wheels traction
• The edge of the ramp (that must own the best ground contact)
• The robot speed
• The sensors distance range (how far away they can detect the others)
• The robot's strategy

Other things such as battery duration or motors torque are important, but are not determinant on the moment of the match.

We'll try to make all of them the best as possible while making it affordable.

Robot's components that are needed to but in the internet:

• LiPo rechargable Battery 7,4v 1320 mah: The mili-Ampere-hour (mah) are excessively high, and could be lower (and we would have a smaller battery), but we managed to make it fit in the robot. The MiliAmperHour unity defines how long a battery will last. Higher value means more time the robot can work without charging (formally speaking, 1320 mah means that if the battery is used at 1320 mili-ampere power consumption, it will last for 1 hour). NOTE: If you want cheaper battery you can use a standard 9v battery, but in the long run as it can not be recharged you will spend more money. 
• Pololu Micro-Metal Gearmotors HP,  We used a 30:1 reduction stage that given us a really high speed although that makes our robot to have a lower reaction to inertia. Also as our wheels' diameter is as low as 28 mm so if your robot has a higher value you should consider the 50:1 and 75:1 stages. Consider that a bigger wheel means more speed but lower torque while lower gear stage means higher speed but lower torque. You should compensate a small wheel with a low gear stage, and a big wheel with a high gear stage.
• Solarbotics High Traction Wheels, that 28 mm diammeter high traction wheels are compatible with pololu motors (you'll need a Allen Wrench to stick them. 

Robot's components that are needed to buy (but that are easy to find in any electronic shop:

• Robot ramp: There are several materials you can test, pololu and finger-tech sells a version, but we currently used a standard putty plate {image} that was found in a ironmongery store. It works well. This topic is really open and you should try what you think that works better.
• Electronic Universal PCB 5cm x 10cm. There's no need to make a normal; PCB, and in our case we preferred to use that kind of circuit as it costs less space than a though hole PCB (we currently don't own the SMT technology so we think that this is the easiest way to lower the small space of a minisumo robot
• PIC18F4550 Microcontroller, 
• IRM8601 Infrared receiver 
• Infrared emitters, 
• ULN2803
• L298 H-Bridge
• 7805 tension regulator
• resistors 10k ohm, 47 ohm, 330 ohm
• Diodes 1N5819
• 100 nf ceramic capacitors
• 47 uf electrolytic capacitors
• Wires of two kinds, single-core wire for the universal PCB bridges and multi-core wire for the external connections (we crimped the wire terminals)

Total Robot Price

Part	Amount	Unit Price	Total Price
Pololu Motors HP	4	15.95$	63.8$
LiPo Battery	1	14.36$	14.36$
High traction Wheels	4	3.56$	14.24$
PIC18F4550	1	$5.75	$5.75
L298 H bridge	2	$4.29	$8.58
Rest			<20$
Total			126.73$