The ABC-s of Constructing a Combat Robot

It should be mentioned that the technological solutions for building a combat robot are endless. We'll try to describe some of the simpler and cheaper options we've tried, but there are certainly many alternatives to all of the above.

What does a combat combat consist of? In a very general way, we'll list the components without which a combat robot would not be able to function as a rule:

Motors and wheels that insure the movement of the robot. You also need a remote control to make them work.
Weapon and it's motor or other mechanism to activate the weapon. You will also need a controller for that.
Armour for defence against opponents' weapons that can also constitute the body of the robot.
A set of remote control transmitter and receiver.
Battery or several of them.

Motors

When choosing motors, probably the biggest decision point is whether to choose brushed or brushless motors.
Today, I would venture to say that the majority of competitors have found a way to use brushless motors in their combat robots. At the 2022 competition, the most common version of brushless motors were the wheel and motor combination from widely used hoverboards, i.e. a brushless motor built into the wheel. Or, to put it another way, in the case of the wheel of a hoverboard, the rotor of the brushless motor is also its tyre.

When buying brushless motors it is worth keeping in mind their power and kV value (unit shows RPM for one volt). The higher kV value motor you use the more necessary it might be to add a belttransmission or double transmission to achieve the desired torque (otherwise the robot might not be able to take off from the spot despite a high final speed).

Motor Controller (Brushless)

In this case the first determining factor is the tension tolerance of the controller. For example when the plan is to use Li-Po batteries then it is necessary to check that the controller will withstand the intended voltage (12,6V with 3S batteries and up to 25,2V with 6S batteries). With traction motors it is also necessary to be sure that they are able to change the direction of rotation (If there isn't a plan for the change of direction without the controller).

Here I will pass on some knowledge that has come out in context with brushless motors:

Flipsky FSESC. A programmable motor controller that has been shown in various tests to be perfectly suitable for most brushless motors. At the moment, I can't point out any serious drawbacks, except maybe the price of this controller. It should be mentioned that on a couple of occasions problems have occurred with the CAN signal driving two controllers simultaneously, which resulted in both controllers being rendered unusable (fortunately they were restored). After these incidents, I have stopped using the CAN signal to connect the controllers - instead I have split the signal from the receiver into two using a Y-cable.
DC 6-60V 400W BLDC Controller. There is no way to change the configuration of this motor controller, but various tests have convinced us that it can be used quite successfully to control the balancer motor. However, this motor controller needs an inverter to convert the PPM or other signal from the receiver of the RC remote control into a PWM signal suitable for this controller. We are ready to provide information and, if necessary, a specific converter to the participants of the RoboBattle. It is also worth noting that this controller is not suitable for motors that do not have HALL feedback sensors, but balance motors always have them. There is no direct experience with these controllers in robotic combat, but at the moment all the indications are that it should be a significantly cheaper alternative to the aforementioned Flipsky controller.

Motor Controller (Brushed)

At this point, I can only point to one controller that can be used to run brushed motors in a reasonable way and that is the Cytron MDDS30. I am sure there are others (e.g. RoboClaw 2x60A), but no experience with them.

Weapon and Controller

Depending on the type of weapon chosen, most of the electric motors and controllers mentioned above are suitable for operating the weapon. If you should choose one of the higher-current models, e.g. the Flipsky 75200 or Flipsky 75300, it will be worthwhile to unscrew the housing and glue or otherwise secure any loose connections before going into battle. In general, this applies to all electronic connections in the system.

If, for example, the starter motor is to be used as a weapon motor, it will be necessary to incorporate a solenoid or similar circuit with a higher current rating into the system - one possibility is to use a winch solenoid with a rating of up to 500A. At these currents, of course, it is advisable to create a double circuit so that the robot maintains motion even when the weapon is switched on.

Simplified schematic diagram of the robot's electronic

Armour and Body

Building an armour and/or body for your robot is rather a creative activity. You just need to keep in mind not to go over the weight limits. One of the most brilliant materials to use in building armour is Hardox, which availability shouldn't be a problem.

Remote Control Set

Suitable for the vast majority of models that use transmitter and receiver sets (2.4GHz is recommended to reduce interference). One example is this.

In the case of using a single remote control to control the robot, it should have a minimum of 3 channels to ensure control of both the robot's traction motors and the weapon.

Battery

With batteries the recommendation is quite easy. Considering energy density the easiest way to go is Li-Po batteries. You just need to keep in mind that the number of battery cells needs to be suitable for your motors and their controllers. So from three celled battery, 3S Li-Po you can get 12,6V and 6S Li-Po you can get up to 25,2V.

Makita 18V batteries have also been used successfully as batteries and under certain conditions, the original balance drive can also be used to drive the robot. In the case of the latter, however, it is worth bearing in mind that both of the above have a built-in BMS (battery charge and discharge controller), which will temporarily or, in the worst case, permanently cut off battery power in the event of unsuitable conditions (short circuit, overheating, etc.).
This guide was written by Mihkel Sild, a RoboBattle participant who has been participating in RoboBattle with the robot Mõlvar since 2018. For questions or suggestions for corrections, etc., please contact: mihkel.sild@ahhaa.ee.