By: Sherman Xa (Mission, Systems, and Testing Engineer)
As all parts were ready to be assembled, we started to do our final testing on our PCB, before assembling our chassis with it. Using our 7 rechargeable AAA NiMH batteries, we will hook them in series to gain roughly an 8.4 V, 850 mAh power supply. This is due to a shipping complication from our original power supply store. We also connected our two motors to the PCB connections, and pinned in our servo connection. However, after looking at the PCB layout, we realized that the pinning of the servo was wrongly created on the PCB. A servo has a pin connection of signal, power, and ground. However, on the schematic, the pinouts were signal, ground, and power. As a result, we had to switch the wiring on the servo, to allow to us have the correct pinning.
After discovering this layout problem, I decided to check the rest of the connection and start labeling the pins for each connector. As I was checking, I realized the pins of the Bluetooth module connector were also flipped. The pin was in reverse order, so I had to de-solder the pins of the Bluetooth module and invert the pins, so the pins were in the reverse order like the layout of the PCB.
With the correct alterations to conform to the layouts of the PCB, we hooked up the components and the power supply, and paired it with the Android device to start the uplink to use the Arxterra Control Panel. We were able to connect to the Arxterra server after a few tries with the S2 but was always able to connect with the S4. However, to go along with the requirements, we wanted the use the Samsung Galaxy S2 as our selected Android device. When we were able to get a good connection to the server, we tested the motors going forward, backwards and turning left and right, from a low speed to the higher speed. During our testing, we did notice that one of our motors was running at a different speed. When connected to a power supply, we noticed that this was the same situation, which made us conclude that the motor was either faulty or damaged during our initial test of stall current and load. However, after making use of Arxterra, the RPM of each motor was not as severe as we saw with the direct connection to a power supply. As for the servo, before connection to the Arxterra App, there was a current problem, which made the servo vibrate instead of rotate. However, with the Bluetooth connection made, and the Arduino Micro connected to Arxterra, the shaking halted. We believe this to be a current problem, due to another team’s observation and our testings of our servos.
After completing the PCB layout and connection test, we decided to move onto the chassis build and assembling all the parts. For our motors, for instance, we wanted to mount them directly onto the wall of the chassis. We did this by using an R/C hobbyist glue to attach the motors to the wall of the chassis and the wheels to the shaft of our micro motor. However, due to complications in the 3D printing, one of the openings of the wall of the chassis was printed too big and we attempted to use glue to create a tighter fit. Unfortunately, the glue was too heavy and we ended up stripping off one of our motors. Luckily, with the help of a spare motor from MicroSegbot, we were able to find a solution to this problem. Next, we moved onto the pan mirror system, which gave us trouble on the viewing system. Unfortunately, for our Samsung Galaxy S2 layout, we could not get a full field of vision on our Arxterra Control panel. We were able to get the mirror to display on half of the available screen of the control panel. This could have been resolved if we had more time with the 3D printed chassis and adjusting the pan system’s height.
Finally, we were ready to test it on the test course. However, when we got the chassis assembled, we ran into a few problems with the wheels. One major problem that we ran into was the friction caused by the free-spinning wheels of the Micro Rover. We tried to solve the issue by pushing the wheels further out, but that caused the rover to be unbalanced and did not create enough traction to move. We attempted to increase the voltage of the power supply, hoping it would create more torque to push the rover, but that only helped in the short run.
Overall, we were able to perform a handful of the verification tests. But with the requirements dealing with the movements of the rover, we were not very successful. For future reference, to the next Rover team:
1. Use bushing to avoid friction caused by the wheels against the chassis
2. Design the chassis with the angle of the mirror system already figured out
3. Create a wheel that will directly hook onto the wheels – note that the motors you use may have custom mounting equipment by the vendor
4. Make sure components of the 3D printed parts have some room in case of the printing material is overused