Omni-Directional Robot

Prototype Omni-Directional Robot
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Omni-Directional Beetle-Weight prototype drive.

 

Introduction.

One thing that I have noticed from watching robots fight is that there are three things that make a winning robot:

1. Good design.

2. Reliability.

3. Well driven.

The 3rd point is what I am looking at here. The robots that perform the best are the ones that can out maneuver their opponent. They can keep out of the way of their opponents weapon while attacking weak spots and all while avoiding hazards in the arena. I wanted a robot that is easy to drive to help accomplish this.

A vast majority of fighting robots have 2 degrees of movement, they can drive forwards and backwards and/or turn. I can’t think of any robots in the last 10 years that did not have a 0 turning circle and while this allows the robot to maneuver out of any spot it does have problems. For a robot to move on a new heading it will first need to stop or slow, turn and then drive in the new direction. There is also the problem that if the robot has a weapon on the front it has to be driving toward the opponent to use the weapon and can’t use the weapon while re-positioning.

The solution is to have a robot that can drive sideways as well as forward and reverse. This means that the robot will not need to turn before driving on a new heading and can also keep its weapon pointed at its opponent while re-positioning.

 

Types of Omni-Directional drives

Robots that can drive in any direction is not a new idea. This isn’t even the first omni-directional robot Hellfire labs has made. Daniel had Feather-Weight robot called Sidewinder that worked well and looked cool. It is the inspiration for my robot.

 

My thoughts on different omni-directional drives are outlined bellow. these are not the only options but are the best suited for the hard, flat floor of a robot fighting arena.

The first omni-directional robots I saw years ago were experimental robots with powered casters.

Neobotix Omnidirectional robot MPO-700 http://www.neobotix-robots.com/omnidirectional-robot-mpo-700.html

The robots wheels are mounted on powered casters and can be pointed in any direction. While this allows for smooth control in any direction it does require many more moving parts than a regular 4 wheel robot. Complexity and Combat Robots do not go well together. I can’t remember any combat robots that use this method.

The more popular method is to omni-directional wheels that have free wheeling casters built built into the tread of the wheel. For example here are the wheels I am using:

These wheels provide plenty of grip perpendicular to the axis of rotation but the casters allow the wheels to slip sideways without any resistance. Three or more  wheels are mounted in a circular pattern around the robot. Each one of the wheels provides a force in a different direction and the combination of forces will either move the robot in a certain direction and/or rotate the robot. Sidewinder and my robot are examples of three wheel robots with the wheels mounted 120 degrees around the robot. 4 wheel robots with the wheels mounted 90 degrees apart also popular. An example of a 4 wheel omni-wheel robot is Root Canal built Donald Hudson of Mutant Robots for Battlebots Season 4.0.

The problem with this drive is that the drive motors and gearboxes need to be mounted at an angle to each other while conventional robots have all their drives parallel to each other. A method of omni-directional drive that allows all the drives to be parallel is to use macanum wheels.

https://www.3ders.org/articles/20141228-olaf-diegel-oddbot-3d-printable-omnidirectional-robot.html

Macanum wheels are simmilar to the previous mini-directional wheels in that they have free wheeling casters mounted in the rim but the casters are offset by 45 degrees to the wheels axle. By using 4 of these wheels driven independently the robot can move forward and reverse and turn like a regular 4 wheeled robot but when the motors at the front and rear are turned in opposing directions the casters cause to robot to move sideways. An example of a combat robot using mecanum wheels is Alcoholic Stepfather from Team Kahuna.

 

I have decided to use the 3 wheel omni-directional wheel design because of the way it looks.

 

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