Today, Colin, a member of last year’s Small-Scale Controls Team and possibly our mentor/contact/guide, visited the Spartan Superway Design Center to provide us with advice, problems his team faced, features that they were hoping to implement but never got around to, and feedback on the design ideas we proposed.
Addressing our first idea of installing a differential drive system that would drive the wheels that move along the outer rail faster than the inner wheels when making a turn, preventing over-exertion of the servo motor steering the wheels when making a turn, Colin stated that we have two options:
(1) Use two servo motors and incorporate the drive differential. However, Colin warned that he and his team used up all of their extra servo motors (about six extra) during their exhibition at Make’s Faire. So, he suggested buying three servos for each day spent at the Faire (three servos x three days = nine servos). If we want to pursue this idea, he suggested looking into the differential drive system of RC cars. (2) Use one brushless motor. With proper gearing, the single brushless motor wouldn’t need a drive differential, as it is quite powerful. It is also very durable, and only one or two (one as backup) could be brought to Maker’s Faire. However, calibrations must be made to step down the speed, as Colin stated that these motors go much faster. We also have a third option suggested by the Small-Scale Bogie Team: (3) use conical wheels.
Secondly, Colin addressed the issue of powering up the small-scale system. He strongly suggested using the NMH (nickel-metal-hydride) battery first, as the LiPo (lithium-polymer) battery could possibly explode. The LiPo battery cuts-off voltage to prevent it from dropping below 3.7 V. A LiPo battery should never be discharged below 3.0 V, as it can permanently prevent its ability to absorb and retain a charge (https://rogershobbycenter.com/lipoguide/). A LiPo battery requires a unique charger, and Colin showed us where one can be found in the Superway shop; this charger can also charge some of the solar cells found in the shop.
Thirdly, we discussed the object detection feature of the small-scale podcar. Currently, the pod cars only have one ultrasonic sensor at the front; these proximity sensors can only detect in one direction. One idea that was voiced was the usage of a LIDAR (light imaging, detection, and ranging); however, after speaking with some people in industry, it can be complicated to implement LIDAR. LIDAR’s are very accurate as they can measure spatial surroundings a full 360° around the vehicle, but they are very expensive, and they cannot bend light, so they cannot see around corners. Radars, however, can bounce radio waves off of objects and measure that distance. Additionally, while rain has little effect on the radar (“radio detection and ranging”), it does have a crippling effect on LIDAR (“light detecting and ranging”). It all depends on the wavelength of the light. Another idea that Colin himself suggested was constructing a parabolic (curved) array of IR (infrared) sensors, as seen on the robots in the SJSU course, E10.
Fourthly, Colin briefly talked about the mobile application. The application runs on Linux operating system, so upon booting it up, it displays a Linux desktop. And, the XBee module was programmed via the XCTU IDE (integrated development environment). 01, 05 means pod 1, station 5. Altogether, the entire small-scale controls incorporated the following hardware: Arduino (programmed with Arduino), Raspberry Pi (programmed with Python), and the XBee RF (radio frequency) module.
Lastly, Colin advised us to re-solder the controller shield connected on top of the Arduino MEGA 2560 board, as they experienced a short-circuit during Maker’s Faire, resulting from wires touching, and creating sparks and burning out a motor.
Colin provided us with a lot of information and advice, which we have taken note of and will try to learn.