Week 5: 7/31/2017 to 8/4/2017

Progress this week (more details below):
-DC motor issue research
-Battery charge no longer lasts as long on the bogie research
-Now able to control bogie with a Virtual Device uploaded with mobile application on Android Studio
-Soldered 2 pairs of hall effect sensors
-Tested new hall effect sensor brackets, no longer need to use glue




DC MOTOR

Issues with DC motor on 1/12th scale Bogie:
-Particles (dirt, metal shavings from gears, etc.) get stuck in the gear assembly.
-A few motors (so far 3 out of 6 tested) do not work at all
-Initially a total of 8 motors that cannot rotate
-Motor output is 4.6 volts using volt meter while battery output is 6.3 volts. This could be possibly due to the efficiency that brushed motors provide, a lot of energy lost due to heat.

Since the DC motor gear assembly is covered with a bracket, I am lead to believe that the gears are deteriorating or the bogie is too heavy and applying too much load on the gears causing extra wear.

Figure 1: Black bracket with two screws cover the gear assembly

Short Term Solution:
-Took out the metal gear shaft assembly and:
       - Sprayed Carburetor cleaner on the metal gear assembly to clean
       -Air compressor to dry gears and make sure all dirt is removed
       -Applied oil to all the gears in the assembly and rotated the shaft to allow oil to evenly spread


Summary:
We are currently using brushed dc motors and over time the metal brushes and commutator inside the armature wear out. Brushed dc motors have a small lifespan and even worse when they are continuously running. Brushed dc motors prove two advantages, that is, they can easily be wired directly to DC power and they are not expensive. The alternative to brushed motors would be brushless motors and these provide a great deal of advantages such as; longer lifespan, quiet running time, 90% efficiency and not effected by heat. But, they do come with an expensive price tag, and a motor driver or controller would need to be implemented.


BATTERY

We are currently using NiMH 6V 5 cell batteries that as of this week only are able to last 10 minutes or so running on the track with the bogie. These batteries are not expensive making them an easy buy, but they only last a few months and significantly decrease power output when exposed to heat.

In the 2016-2017 SSW 1/12th scale solar team's report, they mentioned how the 5 cell NiMH batteries only last 20 minutes running on the bogie and take 55 minutes to charge.

General Future/long term:
There are multiple ways to address the motor and battery issue and all depend on how we plan to present the 1/12th scale to people. For example, if we want to take the entire 1/12th scale to an event and plan to have the bogies continuously run while the audience can interact with the bogies or use it as a visual showpiece while running the mobile application and bogies a few times.

These two different scenarios are important to know because it will ultimately be the deciding factor on whether we should do a full motor and battery overhaul or use the parts we have and try to rebuild them instead of replacing them.

Either way the batteries do need to be replaced soon since the new rotary encoder design for bogie positioning uses two Arduino's (one Mega and one UNO).

Figure 2: Old hall effect sensor bracket, but we are using zip ties instead of glue.
                                          This will allow us to easily replace the brackets without damaging the hall effect sensor.

Figure 3: Soldering the wires onto the hall effect sensors.
         Using cardboard to avoid damaging sensor. 

Figure 4: Guide to use when soldering hall effect sensors. The shaded dot/circle indicates the label part is facing down.