Robot Arm

Robot Arm is slated as a Division C national event for the 2011-2012 season, replacing Mission Possible, after being run as a Division C trial at the 2011 National Tournament. The event involves the construction of a robotic arm to grab, lift, and deposit specific items in prescribed locations. The Trial rules can be found Here

Base
In order to have a functioning Robot Arm, you'll need a base. This can be made out of any material, as long as it fits within the designated 30cmx30cm box. Something to keep in mind is that the base needs to be heavy enough to prevent the device from tipping over when the arm is moving objects around.

The base can also contain a motor used to spin the arm. One possible design of a base can be seen below:



The Arm
Due to the event being named Robot Arm, one should probably include an arm in their device. If a team wishes to get maximum points then they're arm needs to reach about 58cm(from the center if the designated arm square to the top of the bonus boxes). They really only need to reach 10-15cm outside of the base box if the operator plans on only utilizing the East and West Goals. In order to utilize the North Goal, you'll need to build with a sturdy enough material to keep the arm from breaking or flexing, while also keeping it lightweight enough for your motors to still be able to handle the load.

Your arm will most likely include a number of joints as not only will it need to lift the objects off the arena and up into boxes, but also it needs to bend up to fit inside the 30x30cm base box. Each joint will probably be controlled by a motor. It's up to you how many joints you use, though 2 on the arm and one on the "hand" should be more than enough if done properly. Keep in mind that the number of motors on your device is a tie breaker.

Motors
If you're new to robotics choosing motors can be one of the most daunting parts of the construction process as you have quite a few choices. One of the best choices for this event are servos. Servos are extremely useful in robotics. The motors are small, have built in control circuitry, and are extremely powerful for thier size. Most teams will obtain these through the VEX robotics company. While VEX has somewhat of a negative reputation with some people, there isn't really much wrong with it. Even the national trial winner in 2011 used a VEX robot.

If you're a more advanced builder you might want to look into stepper motors. A stepper motor is a brushless, electric motor that can divide a full rotation into a large number of steps. The motor's position can be controlled precisely without any feedback mechanism, as long as the motor is carefully sized to the application.

The "Hand"
The "hand" is one of the most important parts of the arm. It must also be the most versatile, as it needs to be able to grip pencils, pvc pipe, and nails in order to be a high scoring device. The rules allow for electromagnets which should prove useful for the ferromagnetic nails, so with that part down, you'll have to design a "hand" that can pick up rounded objects.

Kits
The rules state that teams can utilize kits as long as they modify them in some way. The way that you modify them is completely up to you. Here are a couple common choices for kits.


 * Lynxmotion
 * OWI (specifically, the OWI Edge robot arm)
 * VEX
 * Lego Mindstorms

Controls
There is a wide variety of methods to controlling your arm, ranging from simple plug-and-play systems to fully automated computer control. You can also choose between wired and wireless, though in most cases wireless with be much more exspensive.

Toggle Switches
This is by far the simplest and cheapest way to make a control system. Just use switches hard wired to simple DC motors and a battery. Flip the switch to turn a motor on or off.

Remote Control
Using an RC system is usually rather simple, but can be exspensive ranging from under hundred to several hundred dollars. I suggest visiting a local hobby shop and looking for a good deal on a used system. An RC system comes with a transmitter and a receiver. You can plug a battery and servos into the receiver and use the controls on the transmitter to control the position of the servos. You can also use an Electronic Speed Control(ESC) to throttle a DC motor. The only downside to using an RC system with servos is that most limit the servo's range to 90°; some systems can be programmed to fully extend the range, usually to 180°, however these systems can cost more.

Microprocessor
The use of a microprocessor really opens of the possibilities and at around $100 isn't enormously expensive. However, to fully utilize, one requires knowledge in both programming and electronics. With a microprocessor, you can use a variety of input devices, including laptops, joysticks, buttons, and completely custom built controls. If you really want to be fancy, you can program the arm to do the event by itself, with or without sensors to correct errors. You will need a control board, such as the Lynxmotion Bot Board II or the Arduino, and the actual microprocessor, such as the BASIC Atom family.

Master-Slave System
One particular type of contolling system which is dependent on a microprocessor is the master-slave system. With this, you build a "dummy" arm, an arm identical to the actual arm, except where there are motors in the actual arm, you put pontentiometers. You then wire the potentiometers through the microprocessor so thatas you turn them, your corresponding motors in the actual arm turn the same amout. This way, you can mimic the movements that you want your arm to make by moving the the dummy, and the arm will move the same way. It is a relatively easily and incredibly efficient control system to set up.

Running/Practicing
This competition is about 30% design and 70% practice. You could have a design that could win at nationals, but without practice, that means nothing. The best way to practice is to put yourself in the situation you would be in at a competition. To do this, you'll need an arena to practice in. Printable layouts can be found here. After practicing for a while, you should develop an efficient plan for the order you will move the objects, as well as how you will move them. A finalized version of this is part of the documentation you will hand in to the event director on the day of the competition.