Soccerates - Pneumatics

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Soccerates uses an innovative pneumatic system which controls both the robot's kicker and the raisable "roof" which acts as a large sail which can black flying balls, and with some modifications can be converted into a ramp. The two systems run off the same air and share a compressor and storage tanks, but are otherwise seperate. The roof system is simple, but the kicker system, which supports varialbe kicking pressures and recycles a large amount of the air it uses (to reduce air waste and the amount of air which must be re-pressurized) is complex. This page describes each system in detail.

Download Diagrams and Valve Fact Sheets of Soccerates' Pneumatic System as a PDF

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Contents

1. The Shared Pneumatic System
2. The Kicker Pneumatic System
3. The Roof Pneumatic System

The Shared Pneumatic System

The Shared Pneumatic System in Soccerates is used by both the Kicker system and the "Roof" system. It consists of an air compressor, air storage tanks (which hold compressed air at 115psi), a regulator valve which allows air to flow to the Kicker and "Roof" systems at only 60psi, an emergency automatic vent, which will vent the system if the air in it exceeds 125psi, a switch to tell the cRIO (the robot's onboard computer and controller) to turn the compressor on and off to keep the stored compressed air between 90 and at 115psi, and a manual release valve which vents the air stored in the Shared Pneumatic System to atmosphere. The purpose of the Shared Pneumatic System is to store compressed air at 115psi for use by the other pneumatic systems on Soccerates and to supply this air to the other systems at 60psi. This difference in "working" air pressure and "stored" air pressure is a requirement of FIRST rules. Soccerates is usually pre-charged before competing, meaning the air in the Shared Pneumatic System is pressurized to 115psi before the robot even goes onto the field, allowing every pneumatic system to be ready to go as soon as the robot is powered on.

The Kicker Pneumatic System

The kicker portion of Soccerates' pneumatic system provides power to Soccerates' kicker device. This is the most advanced part of Soccerates' pneumatic system and is able to provide variable power (which allows different kick distances) while recycling some of the air used back into the pneumatic system, lessoning the load on the compressor which results in a more responsive pneumatic system and increased battery life. The system has a total of 8 phases and 7 running phases. The system cycles through the 7 running phases while in operation. Most of the phases take very little time to run, however, so the system is able too kick, reload, and kick again quickly.

Power Off Phase

When the robot is off, the kicker pneumatic system is in the Power Off Phase. This is not a normal operating phase. The power off phase allows all air to be stored at high pressure in preparation for a match. The system can also be vented to atmosphere via a manual pressure release valve (the robot has three pressure release valves, one for each part of the pneumatic system) if needed. The Power Off Phase is the only phase of the kicker pneumatic system which is not used while the robot is running.

Start/Lock Phase

In the Start/Lock phase, compressed air flows from the compressed air storage tanks into the front of the kicker piston, forcing the piston's arm back. When the piston is forced completely back, a mechanical latch (not shown in diagrams) locks it in place so that air pressure is no longer required to hold the kicker back. Once the kicker has been mechanically latched in place, a momentary switch is closed and the pneumatic system moves to the Pre-Charge Phase.

Pre-Charge Phase

In the Pre-Charge Phase, compressed air flows from the high pressure front (Retard Side) of the pneumatic piston to the low pressure back (Fire Side) until the pressure in the front and back are equalized. This allows some of the air used in the Start/Lock Phase (used to pull the kicker back) to be later re-used to kicker the ball. When the pressures measured in the Retard Pressure Sensor and the Fire Pressure Sensor are nearly equal, the kicker pneumatic system moves to the Load Phase.

Load Phase

In the Load Phase, compressed air flows from the compressed air storage tanks to the Fire Side of the pneumatic kicker piston. The Fire Pressure sensor monitors the pressure in the back of the piston and moves to the Ready Phase when the desired pressure in the back of the kicker piston is reached. The desired pressure is set via a thumb wheel on the Driver's Station. The amount of pressure in the back of the piston determines the kicker's force when fired, and therefore the distance the kicker will kick a ball. More pressure will cause the system to kick with more force (and further), while less pressure will cause the system to kick with less force (and not as far). The kicker pneumatic system moves into the Ready Phase once the desired pressure in the back portion of the kicker piston has been reached.

Ready Phase

In the Ready Phase, the air in the front part of the pneumatic system is vented to atmosphere, while the air in the Fire Side of the piston (which will provide the energy for the kick) is kept constant by sealing it from the rest of the pneumatic system. The kicker does not fire, however, because it is still held back by the mechanical latch which was locked into place during the Start/Lock Phase. When the robot driver (or software in autonomous mode) gives the "KICK" signal, the kicker pneumatic system moves to the Fire Phase.

Fire Phase

In the Fire Phase, the mechanical latch holding the kicker in place is released via a servomotor, and the air in the back portion of the kicker piston forces the kicker forward, kicking anything in the front of the robot. No air in the pneumatic system is vented or lost during the kick, since the air in the front of the piston was vented in the Ready Phase (and remains vented during the kick). The pressure in the Fire side of the piston will decrease during the kick, however, because as the piston moves forward the volume of the back portion of the piston increases. Because, the total amount of air stored in the back of the piston does not change, the pressure must decrease proportionaly. After the kick is complete (which is instantaneous), the kicker pneumatic system moves to the Pre-Balance Phase.

Pre-Balance Phase

The purpose of the Pre-Balance Phase and the succeeding Dump Phase is to prepare the Kicker System to be reset. Because of the valves used, there is no single valve setting that allows air from the Fire Side of the Cylinder to vent directly to the atmosphere, This air must be vented so as to allow the kicker to be returned to to Start Lock Position, therefore it must be done via a two step process. In the Pre-Balance phase, the air remainiung in the kicker side of the piston is allowed to flow to the front portion of the piston, equalizing the pressures in the two sides of the piston. When the two pressure sensors are nearly equal, the kicker pneumatic system is moved into the Dump Phase.

Dump Phase

In the dump phase, the air in the front portion of the kicker cylinder is vented to atmosphere. Since this air originally came from the Fire Side of the piston, this has the effect of reducing the amount of pressure in the Fire Side of the piston. When the Retard Pressure Sensor is sufficiently low the system will move to the Balance Phase.

Balance Phase

In the Balance Phase, the air from the Fire Side of the kicker piston is once again allowed to flow to the Retard/Front Side of the piston, just as in the Pre-Balance Phase. This equalizes the pressure on both sides of the piston and reduces the amount of force being exerted on the piston. The Fire side force needs to be reduced until it is weak enough to allow compressed air entering the Retard Side of the cylinder to push the piston back in the Ready/Start Phase. If the pressure is not low enough for this to happen, the kicker pneumatic system will move back to the Dump Phase (and repeat this Balance-Dump-Balance-Dump cycle) until the pressure in the Fire Side of the cylinder is low enough to allow the piston to be pushed back to its Start/Lock position. Depending on the Kick Pressure used, this generally takes more than one dumping. The Fire Pressure sensor determines when the pressure is low enough to allow the system to return to the Start/Lock Phase. The Balance-Dump-Balance-Dump cycle allows some of the air used to kick to be used to return the kicker to the Lock Position, since the back of the piston is not completely vented. Each Balance-Dump cycle happens quickly, there is little to no speed penalty to doing this verses simply venting the air in the Fire Side of the kicker directly to atmosphere. In fact, it may be quicker to Balance and Dump, since it reduces the strain on the air compressor, which is slow. This cycle continues with every kick.

The Roof Pneumatic System

The Roof Pneumatic System is much simpler than the Kicker Pneumatic System. Unlike the Kicker system, it is not a cycle (any phase of the Roof system can be switched to from any other phase) and it recycles all of its air (unlike the Kicker system, which vents some air to atmosphere).

Hold Position

The Hold Position holds the roof in place. In this position, the air is locked in both the front and back sides of the roof piston, thereby holding the piston in any position. This position corresponds to the center/OFF position of a ON*-OFF-ON* Momentary Contact Switch on the Drivers Station.

Raise Position

In the Raise Position, air is allowed to flow from the compressed air storage tanks into the back of the roof piston, forcing the piston forward and the roof up. Any air in the front of the piston is vented. This position is selected by an ON in an ON*-OFF-ON* momentary contact switch on the drivers station. When the roof has has raised to the desired level, the switch is released and the Roof System returns to the Hold Position.

Lower Position

In the Lower Position, air is allowed to flow from the compressed air storage tanks into the front of the roof piston, forcing the piston backward and the roof down. Any air in the back of the piston is vented. This position is also controlled by the momentary contact switch on the drivers station. When the roof has has lowered to the desired level, the switch is released and the Roof System returns to the Hold Position. The speed that the roof raises and lowers is controlled by independent flow control valves on both the raise and lower ports of the Roof Cylinder.

Download Diagrams and Valve Fact Sheets of Soccerates' Pneumatic System as a PDF