Solar Power Cube v17.10

The solar power cube is driven by a solar panel to pump hydraulic fluid with the initial purpose of powering an autonomous tractor for agricultural use.

Specifications

Solar Panel

 
 STC Power Rating 290W
 PTC Power Rating 263.07W 1
 STC Power per unit of area 13.8W/ft2 (148.2W/m2)
 Peak Efficiency 14.82%
 Power Tolerances -3%/+3%
 Number of Cells 72
 Nominal Voltage not applicable
 Imp 8.02A
 Vmp 36.4V 
 Dimensions: 77.6in (1,972mm) x 39.1in (992mm) x 1.6in (40mm)
 Weight: 50.7lb (23kg) 
 Hanwha Solar Panel

DC Motor

 
 450W 36 V DC electric motor MY1020z gear reduction
 Input Voltage:		36 V
 Base RPM:		450
 Wires:			12 Gauge
 Efficiency:		78%
 Full Load Amps:	16
 Current Type:		DC
 Gear Ratio:		6.67:1
 Shaft Diameter: 	20 mm (13/16")
 Motor Body Diameter: 	4 1/4"
 Motor Body Length: 	5 1/4"
 Total Length: 	8 1/4"
 Total Height: 	5.65"
 Mount screw spacing: 	4" x 2 1/4"
 Roller Diameter: 	0.3in
 Roller Width: 	0.16in
 Reversible
 EBAY MY1020z $67.05

Hydraulic Power Unit

 
 Power 5 HP 3600 RPM
 Flow 2 GPM max.
 Pressure 2500 PSI max.
 Reservoir 1.1 gallons
 Shaft 1/2" dia. x 7/8" w/keyway
 Rotation CW
 Ports 3/8" NPT pressure
 Return 3/8" & 3/4" NPT
 Orientation Vertical
 Size 10" x 10" x 10"
 Shpg. 13 lbs.
 Surplus Center Hydraulic Power Unit $109.95

Timing Belt and Pulleys

Hydraulic Motor (for reference)

 
 45.6 cubic inch / revolution
 Max RPM: 150
 Max fluid flow: 30 GPM

Calculations

Power

 Max Motor Input: 290 W * 78% * 100 = 226.2 Watts
 Motor Output: 226 W / (746 W/HP) = 0.303 HP
 Motor Torque @ 450 RPM = 4.54 ft-lb
 
 Torque (ft-lb) = (HP * 33000) / (2 * pi * rotational speed) = (.303 * 33000) / (2 * 3.14159 * 450) = 3.54 ft-lbs
 Torque (NM) = Watts / (2 * pi * rotational speed) = 226 W / (2 * 3.14159 * 450 RPM) = 0.08 NM
 
 These numbers are for the electric motor and will be used to determine pulley and belt specs

RPM input/output

 Max electric motor RPM: 450
 Max Hydraulic Pump RPM: 3600
 Max Hydraulic Motor RPM: 150
 
 Estimated Max Wheel RPM: 1

Hydraulic Fluid Flow

 GPM required for 1 RPM @wheel: 45.6 cu in/min or 45.6 / 231 = 0.197 GPM
 Max Pump Output: 2 GPM @ 3600 RPM => Pump CIPR = (2 GPM * 231 cu in/Gal) / 3600 RPM = 0.128 CIPR (Cubic Inches Per Revolution)
 RPM required from pump for 0.138 GPM output: (0.197 GPM * 231 cu in/Gal) / 0.128 CIPR = 355 RPM

Pulley and Belt Sizing

The RPM of the electric motor at 36VDC is 450 RPM and must drive the pulley on the hydraulic pump at 355 RPM, so the ratio of pulleys is 450:355 or roughly 1:1.27.

The smaller pulley must accommodate the motor's 20 mm shaft, so its "OD" must be 20mm + 2 * 5mm to allow 5mm thickness to allow for a set screw. According to PolyBelt.com (http://polybelt.com/5mb.php), the smaller pulley must have at least 20 teeth.

Applying the 1:1.27 ratio, this gives us 20:25.4 teeth (round down to 20:25).

The larger pulley goes on the pump and the smaller on the electric motor.

The shaft on the electric motor is 13/16" and the shaft on the pump is 1/2". Both pulleys must be machined for their respective shaft sizes and allow enough material for set screws. The smaller pulley requires an OD of about 30mm to allow for machining, making it a 19 tooth pulley. Applying the pulley ratio, we calculate the size of the larger pulley in teeth:

20 teeth * 1.27 = 25.4 teeth (round down to 25 teeth)

Looking up the pulleys on the vendor webpage shows the following part pages:

 20 Tooth Pulley with flanges
 25 Tooth Pulley with flanges

They don't seem to carry a 20 tooth pulley without the flanges, so we can purchase the bar stock instead, which we can cut and machine to our specs:

 20 Tooth Pulley Bar Stock

This will be better for the smaller pulley, as we need more height to make up for the sort motor shaft.

This yields pulley pitch diameters of 31.83mm and 39.8mm.

The approximate distance between shaft centers is 5.1" (129.54mm)

The "formal" calculation of belt length with different size pulleys is rather complex, but as our pulleys are close and we have an adjustment, we can use a simple approximation for the belt length (d = 5.1" = 129.54mm):

pi * (d1 + d2)/2 + 2 * d = pi * (31.83mm + 39.8mm)/2 + 2 * 115.9mm = 344.3mm (13.55")

Calculate the belt length in terms of 5mm teeth: 344.3 / 5 = 68.9. This is roughly 69 teeth in length of a 5mm pitch belt. Looking it up on vendor's page: Polybelt Timing Belts

We see that the 69 tooth belt has the following web page:

 Polyurethane Steel Timing Belt 69 Tooth

Power Cube Working Document

 ["https://docs.google.com/spreadsheets/d/1KNVP2O3KogC6jyxMuRALWTxrYjyCJ4ChjeZsJVdqHsg/edit#gid=1"]

Files

 File:Solar Power Cube V1.0.skp
 File:Solar Power Cube V1.0 BOM.pdf