Day 3

Our Top, side and Back Views of our Preliminary Sketches.

Good news! We finally got the specs for our servos:

Control System: +Pulse Width Control 1520usec Neutral

Required Pulse: 3-5 Volt Peak to Peak Square Wave

Operating Voltage: 4.8-6.0 Volts

Operating Temperature Range: -20 to +60 Degree C

Operating Speed (4.8V): 0.23sec/60 degrees at no load

Operating Speed (6.0V): 0.19sec/60 degrees at no load

Stall Torque (6.0V): 56.8 oz/in. (4.1kg.cm)

Operating Angle: 45 Deg. one side pulse traveling 400usec

360 Modifiable: Yes

Direction: Counter Clockwise/Pulse Traveling 1520-1900usec

Current Drain (4.8V): 7.2mA/idle

Current Drain (6.0V): 8mA/idle

Motor Type: 3 Pole Ferrite

Potentiometer Drive: Indirect Drive 

Bearing Type: Single Ball Bearing

Gear Type: All Nylon Gears

Connector Wire Length: 12"

Dimensions: 1.6" x 0.8"x 1.4" (41 x 20 x 36mm)

Weight: 

1.3oz. (37.2g)

Will we have enough torque to lift the object? This has concerned me since we started designing it, but Brandon assured me we will have more than enough power. Time to find out:

Assumptions: The wood weighs .23oz/cubic inch, the arm has dimensions .5" by .5" by 10" (I will explain how we arrived at this approximate length later); 2.5 cubic inches, it weighs .575 oz. The object we're lifting weighs, at most, 1.15 oz.

First, we calculate the center of gravity using this equation:

WRONG: UPLOAD NEW PIC
DENOMINATOR SHOULD BE M1 + M2

m1 = .575oz

m2 = 1.15oz

x1 = 5"

x2 = 10" + Radius (assuming to be 4"; Brandon has the data at the moment)

Xc = 28cm
Total Mass = 1.725oz
           

Now calculate the torque needed to lift the object: 

T = F * r * sin(θ)

T = Torque

F = M * a = total weight (in this case 1.726 ounces)
r = distance to center of gravity, because this is the point on the object gravity can actually be thought of as acting on. In our case 28cm, or 11 inches

θ = angle between the lever arm and the force (in this case, gravity) being applied to it. The torque from gravity will be strongest θ = 90 degrees (the or the horizontal. Sin(90) = 1.

T = 1.726oz * 11 = 19 oz * in of torque