Team 24 - Electronics & Software

Accelerometer

For this project, we ended up using four different accelerometers to get the desired feedback we wanted. The first two accelerometers we attempted to use were on the MPU-92/65 PCB. The first was the 9250 series and the second was the 6500 series. We were not able to get acceleration readings through online libraries and research for these accelerometers. We were able to get gyroscope readings from the 9250 but this only led to getting angular velocity and not linear acceleration or velocity. We then tried using the MMA7455 accelerometer. This accelerometer worked perfectly and we were able to get some basic feedback code written for it. We designed a housing for this accelerometer and began to mount it when we started having problems with it. When we changed the wires it would lose connection to the Arduino and become unusable. We tried many many different wires, changing the type and length to no success. After the presentation, we were able to obtain a fourth and final accelerometer that we were able to mount on the mechanism and control its velocity. This model was the MMA8452.

Re-load stop

Since the accelerometer was placed on top of the dart holder, it records the acceleration of the xyz axis as it is returning and launching. 

In its re-load position the accelerometer Z values read between 0.3 and 0.6, the Z values read between 0.6 and 1.0, and the x-readings were out of plane motion.  So when the sensor reads the position, the motor will stop for 6 seconds, then a signal for full speed is sent. Then it goes back to its feedback loop. 

Feedback loop

The feedback loop consisted in keeping the motor at full speed. When the mechanism engages in release, the motor has to lift the weight of the mechanism as it rotates the link. In an open loop, the motor would stop when trying to move up since. Also when run in open loop, the motor would seem to do a quick return because of the effects of weight on the input link. With the close-loop, the effects of gravity were combated to keep a consistent speed.