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RipSaw

The RipSaw project was submitted by Jack Kelly

This robot has been designed run in the DARPA 2005 Grand Challenge.

I am the lead systems and software designer so I can not give too many details about the mechanical aspects of RipSaw.

At present the RipSaw contains three BASIC Stamp modules. One controls the pneumatics for the braking and steering system. Another one controls a servo for the throttle and the last is used to detect track movement.

ripsaw2.gifThe NavBoard
This unit contains two stamps. The one on the left is the master and the one on the right is the servo slave.

Master Stamp
The master stamp communicates with the NAV computer through a RS232 serial port. It is responsible for firing the twelve MOSFET channels and serial communication of the slave stamp for throttle servo control. The master stamp is capable of performing quite complicated hydraulic maneuvers from a singe 8bit command. This allows the NAV software to be continuously updated and modified without the need to redesign the NAV board when new maneuvers are required.

Slave Stamp
The slave stamp receives commands from the master stamp through a serial connection. Pins 14 and 15 from the master and pins 0 and 1 on the slave make this connection. The slave is a dedicated servo device. The servo must have its position updated every 20ms. When the stamp is not receiving commands it continuously updates the servo through i/o pin 15.

MOSFET Board
This board contains twelve channels. Each channel has a 5v trigger from the master stamp that opens a 12 volt MOSFET gate. Each gate is connected to a solenoid that actuates various hydraulic aspects of the RipSaw machine. Currently this board controls 4 brake power levels, both left and right and the transmission, forward, reverse and neutral.

ripsaw4.gifNerve Board
This unit contains one stamp. There are two Hall effect sensors connected to pins 15 and 14. The stamp communicates with the NAV computer through a RS232 serial port. There are eight metal plates attached to both the left and right track rims. The stamp counts the number of pulses on each sensor and sends that data to the Nav computer roughly every 200ms. With this information we can determine the distance traveled by the tracks, the speed of the bot, what direction we are turning and whether or not we are in a tread spin situation.

ripsaw6.gifNAV Software
The nav software currently consists of five separate applications.

Compass Application
The compass application communicates with the solid state compass via a RS232 com port. After performing a CRC check on the compass data it sends the results to the nav software via a TCP network connection.

ripsaw5.gifGPS Application
The GPS application communicates with two Garmin GPS units via two RS232 comports. Each time a GPS reports, the software selects the GPS with the most satellite connections. After performing a CRC check on the GPS data it sends the results to the nav software via a TCP network connection.

Nerve Application
Ripsaw’s nerve application communicates with the BASIC Stamp module on the track sensor. Send the results to the nav software via a TCP network connection.

LIDAR Application.
Communicates with a SICK LMS laser radar. Sends the results to the nav software via a TCP network connection.

ripsaw3.gifNav Application
This is the heart of the system. It communicates with sensor client applications via a TCP network connection. Also has a serial connection to the Nav board. Whenever a new sensor is required or desired it simply needs to make a TCP connection to this software. All incoming data is analyzed to see if a RipSaw maneuver is required. If so, the nav software communicates this desire to the master stamp on the Nav board.

I can not thank Parallax enough for their support. They are truly an outstanding and professional company.

 

 

 
   
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