Goal: Small Scale Prototype

 GOAL

Our team has started the beginning stages of creating a small scale prototype. We should see significant progress by the week of November 14th. Our goal is to create a complete working small scale prototype with 3D printed materials and small UCAPs. 

Figure 1: We are essentially going to be making this diagram without motor controller and motors.

1.) UCAPs

ISSUES CHARGING UCAPs IN SERIES

An issue has risen when charging two UCAPs in series. Two conditions that may cause problems with series connection is: (1) UCAPs do not have the exact same capacitance due to manufacturing errors. (2) If the capacitors do not have the exact same charge when in series, it will cause one to charge faster than the other and potentially over charge a UCAP and cause damage or failure. 

To avoid this issue when charging the SOLAR BANK, it is necessary to "balance.". From Illinois Capacitor Inc,

Figure 2: We will measure and calculate values from steps 1-4

Figure 3: Using two 2.7V 100F in series will be used to charge the "on-board"ucaps (2.7V 25F in parallel) Vpos = SOLAR BANK VOLTAGE and Vvcap2 = On-Board Voltage using a 2.0 Ohm Resistor added to reduce current

  SMALL SCALE UCAPs

Figure 4: Shows Discharging of On-Board Ucaps to a resistor, which we can measure voltage and current from (acting in place of motors). Vcap is on board voltage and Ir2 is current through resistor.2Ohms

 

 This test will be used to validate: (1) LT Spice simulations with real world testing by measuring various currents and voltages (2) Prove series balancing with basic resistors does in fact work. (3) Integrate switching using a relay (QTY 2 Single Pole Double Throw).

We will also be attempting to balance the series capacitors using mosfets using this technique:

From ALD SAB Mosefts: 

As the gate source voltage increase, the gate opens open more, allowing more current to flow.

 

If the top supercap has a higher internal leakage current than the bottom supercap, the voltage VC1(top) across it tends to drop lower than that of the bottom supercap. The MOSFET IOUT1(ON) across the top supercap, sensing this voltage drop, drops off rapidly. Meanwhile, the bottom supercap VC2(bottom) voltage tends to rise, as VC2(bottom) = (2 x VS) - VS(top). This tendency for the voltage rise also increases VGS = VDS voltage of the MOSFET across the bottom supercap. This increased VGS = VDS voltage would cause the IOUT2(ON) current of the bottom MOSFET to increase rapidly as well. The excess leakage current of the top supercap would now leak across the bottom MOSFET, reducing the voltage rise tendency of the lower supercap. With this self-regulating mechanism, the top supercap, VC1(top), voltage tends to rise while the bottom supercap, VC2(bottom), voltage tends to drop, creating simultaneously opposing actions of the supercap leakage currents.

With appropriate design and selection of a specific MOSFET device for a given pair of supercaps, it is now possible to have regulation and balancing of two series-connected supercaps, at essentially no extra leakage current, since the MOSFET only conducts the difference in leakage current between the two supercaps.

(2) MECHANISM

We will also be creating a small scale third rail / mechanism prototype to test the following: (1) Insulator works correctly (2) The appropriate amount of normal force applied by the mechanism on to the rail to not exceed unnecessary forces which yield increased friction to the overall bogie. This will be tested by achieving the greatest current flow through the carbon shoe measured at various applied weights (up to 50N). (3) Observe when the carbon shoe has a velocity how that effects the current resistance