P08201: RP10 Drive Platform 2nd Generation
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Results

The RP-10 is able to be navigated wirelessly from a starting position to a second location where it can be stopped using either a gradual decrease in speed or an emergency stop which will stop the robot in a very short distance. The direction of the robot can then be modified by changing the steering angle of one or more motor modules. Each motor module can be controlled individually to allow the robot to turn in a wide variety of ways. Once the turn is complete the robot can continue to travel in either forward or reverse directions.

The turning radius of the robot was specified to be a zero meter turning radius. This would have been possible if two more powered motor modules had been constructed. The current turning radius of the robot with two functional powered motor modules is 0.39 meters which is the diagonal distance between motor modules mounted in the robot. When the robot turns at this radius one of the non-powered wheels remains stationary while the remaining three wheels rotate about it.

The payload capacity of the robot exceeds the minimum 10kg requirement. Static loading of the robot has exceeded 17.2kg, almost twice the required weight, with no damage to robot frame or motor modules. Loads of approximately 5kg have been placed on the robot while in motion but further testing must be done to find the maximum it can transport.

The unloaded weight of the robot is approximately 15.5kg with the minimum of two batteries on board which is less than the maximum allowable 20kg. When an additional two batteries are added for maximum operating lifetime the weight of the robot is still below the 20kg maximum at a weight of 19.5kg.

The final cost of the robot came to approximately $2,489 out of a total budget of $4,200. This cost represents the cost to build one robot and would be significantly reduced if multiple copies of the robot were to be built.

The regulator circuits used to achieve 9, 5 and 3 volt supplies operate without exceeding their 500mA, 200mA, and 80mA current ratings during all testing of the robot, respectively. Similarly the motors were able to run at a maximum load without exceeding the 5A current to which they were rated.

Endurance testing for battery life and electrical component stress was conducted both on the bench and with the assembled robot. First, the motor controllers were bench tested with motors which were unloaded, and run for over 2 hours non-stop at 100% duty cycle. The electronic motor controller did not have any heat buildup, or signs of fatigue. The motors were very hot to the touch, well over 130F. Two batteries total were used, and their voltages only dropped 0.3 V, from 12.4V to 12.1V. Once the robot was assembled, the unit was driven under many stop and go conditions, ramping all the way up to 100% duty cycle. After approximately one hour run time, the electronics were checked again. The H-Bridge circuits were approximately 5F above ambient. The battery voltage drop was also minimal at 0.5 V on bank one and 0.4V on bank two. The end result is that the electronics used are very robust and can be used for prolonged amounts of time without any special care required.

Documentation

Photos

Weight measurements of the platform with and without the payload. As well as with and without batteries:

Platform and Payload

Platform and Payload

Platform and Payload

Platform and Payload

Platform and 4 Batteries

Platform and 4 Batteries

Platform without Batteries

Platform without Batteries

Payload (Cinderblock)

Payload (Cinderblock)

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Final Assembly of Platform, 2 Motor Modules and Electronics:

Platform

Platform

Platform

Platform

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