Update third_scale.md

docs/third_scale.md

@@ -19,20 +19,35 @@ Since the last two measurements corroborate each other, the torque specification
 ### Motor Mounts
 
 ## Power and Electrical
+
+### Electronics Voltage Needs
+* [Victron Energy Orion DC-DC Converter 48V>>24V](https://www.amazon.com/Victron-Energy-Orion-Tr-380-Watt-Converter/dp/B07DPZ9G7M) - rated up to 16A (380W) and accepts voltages between 32-70V.
+* [Victron Energy Orion DC-DC Converter 48V>>12V](https://www.amazon.com/Victron-Orion-TR-DC-DC-Converter-Isolated/dp/B07DQ5H3T2) - rated up to 30A (360W) and accepts voltages between 32-70V.
+* The [Flipsky-75100-pro VESC motor controller board](https://flipsky.net/products/flipsky-75100-pro-with-aluminum-pcb-based-on-vesc-for-electric-skateboard-scooter-ebike-speed-controller) accepts voltages between 14-84V. We had considered the [TRAMPA VESC 100V 250A](https://trampaboards.com/vesc-100v-250a-in-cnc-t6-silicone-sealed-aluminum-box--p-28113.html) that is a bit more capable, but we did not need that extra capability and it would be harder to order.
+* The [Onlogic Karbon 804, On Board Computer (OBC)](https://www.onlogic.com/k804/) accepts voltages between 12-48V.
+* The [Docyne motor](https://www.docyke.com/products/servo-motor) accepts voltages between 12-24V.
+* The NVIDIA Orin accepts voltages between 7-20V.
+* The LIDAR operates on PoE sourced from the OBC.
+* The ZED cameras operate on GMSL connections from the NVIDIA Orin.
+
+### Power Requirements
 * The stock motor pulls 16A at 24V, leading to 16*24= **384W**
 * The Docyne motor (throttle) is 5A at 18V --> 5*18 = **90W**
 * The Docyne motor (brake) is also **90W** (although used much less frequently)
 * The On Board Computer (OBC) uses **65W**
 * The NVIDIA Orin + ZED cameras use roughly **100W** (?check this empirically?)
 
-The third-scale vehicle's battery is selected based on the above power requirements, which **sum to 729W** (Watts). If we select a 44.4V (volts) battery, the current draw is 729/44.4 = 16.4A (amps). Thus a 16Ah = 16000mAh battery would last one hour of operation and a 32Ah battery would last roughly 2 hours.
+These power needs **sum to 729W** (Watts).  This informs the capacity of the battery we select (in Amp-Hours, Ah) based on the length of time we wish to operate the vehicle.
 
-The choice of battery voltage is informed by the ability to have step-down DC-DC converters from [48V>>24V (rated up to 16A)](https://www.amazon.com/Victron-Energy-Orion-Tr-380-Watt-Converter/dp/B07DPZ9G7M) and [48V>>12V (rated up to 30A)](https://www.amazon.com/Victron-Orion-TR-DC-DC-Converter-Isolated/dp/B07DQ5H3T2).
-* The [motor controller board](https://trampaboards.com/vesc-100v-250a-in-cnc-t6-silicone-sealed-aluminum-box--p-28113.html) accepts voltages between 14-100V.
-* The [On Board Computer (OBC)](https://www.onlogic.com/k804/) accepts voltages between 12-48V (so this sets the upper limit on voltage, unless we wanted to use another step-down converter to 45V).
-* The [Docyne motor](https://www.docyke.com/products/servo-motor) accepts voltages between 12-24V.
-* The NVIDIA Orin accepts voltages between 7-20V.
-* The LIDAR operates on PoE sourced from the OBC.
-* The ZED cameras operate on GMSL connections from the NVIDIA Orin.
+### Battery Selection
+There is a benefit to selecting a higher voltage battery largely because it enables faster speeds, by driving the stock drive motor at a higher voltage.  There are also DC-DC step down converters that can be used to provide lower voltages for the electronics onboard. Our battery selection considers the following criteria:
+
+* Voltage greater than 24V
+* [Hobbyists](https://www.youtube.com/@ExtremePowerWheels/videos) have demonstrated that the stock motor can handle at least up to 75V and maybe 92.5V.  So we aim for a voltage less than 75V.
+* The vehicle should be able to run continuously for 2 hours.
+
+We found cost effective batteries typically used for golf carts at 48V.  Li Time sells a [48V 30Ah LiFePO Battery](https://www.litime.com/products/litime-48v-30ah-gc2-golf-cart-lithium-battery-gc2-battery-for-club-cart-golf-cart) that has bluetooth connectivity for diagnostics.  The nominal voltage is actually 51.2V, so a step-down converter will be needed for even the OBC.
+
+Given the 48V, assuming no losses in the DC-DC conversion, the current draw would be 729W/48V = 15.2A (amps). Rounding this up to 16A to include losses, a 16Ah = 16000mAh battery would last one hour of operation and a 32Ah battery would last roughly 2 hours. Thus the 30Ah battery should last roughly 2 hours.
 
 ## Sensor Mounts