by Tom Eng
This year’s game, Ring It Up!, has a Corner Goal Bonus where an alliance can earn extra points by placing special weighted rings on a Corner Goal structure. The weighted rings look identical to the standard rings, but they weigh approximately three times as much as the standard rings.
HiTechnic has a new LEGO MINDSTORMS force sensor (HiTechnic product number NFS1074) that is ideal for measuring the weights rings. The sensor has a receptacle that accepts a MINDSTORMS cross axle piece. As force is transmitted through the cross axle piece, the sensor outputs a value that can be read by the MINDSTORMS NXT.
The new force sensor looks like a HiTechnic/LEGO light sensor to the LEGO NXT. When using LabView or RobotC, you configure the sensor as an ambient light sensor (i.e., a light sensor with the active LED turned off). The raw output of the sensor (and not the normalized output) can be used to determine the force in grams applied to the cross axle using the following table,
There is a Technical Document (FTC Technical Document #FTC-TD-0002-Rev-004) available on the FTC website that describes in detail how to use the new HiTechnic force sensor using LabView or RobotC. The document includes code samples for displaying output from the sensor.
It’s also possible to build a mechanical mechanism that can be used to measure the weight of a ring. There is another Technical Document (FTC Document #FTC-TD-0003-Rev-001) that describes how you can build a LEGO MINDSTORMS scale to check for the presence of a weighted ring.
The two technical documents mentioned above describe two approaches for measuring the weight of the rings. However, there is an endless variety of techniques that you can use to get the job done. I hope that you will find a technique that works best for you and your robot so that you can score some bonus points using the corner goals this season. Best of luck and have a great season!!!