Solenoid Worksheet - MAELabs UCSD

MAE 3 Solenoid Assignment
Understanding the power and abilities of the components in the MAE 3 robot kit
is important for optimal usage. A solenoid consists of a coil of wire, which
creates a magnetic field when energized, and pulls in an iron plunger.
Electromagnetic field Solenoid Components
(from www.solenoidcity.com)
Objective: To measure the relationship between force and plunger distance,
and calculate the power output of the solenoid.
Assignment Details: Each team should complete this worksheet by measuring
values in the lab with the solenoid jig, and performing the analysis. Show details
of work neatly.
CW
Centroid of added weights
When Plunger is
fully retracted
inwards, D=0
CS
1.5 in
Tick marks indicate
distance plunger is
retracted outwards
(mm)
D Plunger
distance

Instructions:
1. Plug the solenoid into the constant 5 VDC power source and turn the
power source on.
2. Set the gap adjustment screw and measure the plunger distance.
3. Add weights onto the lever arm and slide them until the plunger is pulled
out. Note, the lever itself is balanced, so only the added weight contributes
to forces on the solenoid.
4. Measure at least 4 gap distances, and record values in table below.
5. Turn power source off.
6. Calculate force on plunger using the moment balance equations below.
Use the metric system so that the energy and power calculations provides
Joules and Watts.
Variable Description 1 2 3 4
D Plunger Distance (m)
Mw Total mass of added
weights (g)
Centroid of added
Cw
weights (m)
CwMwag Moment of added
weights (Nm)
CwMwag/Cs Force on Plunger (N)
**** cs = Solenoid moment arm = 1.5in = 38.1 mm
ag = Acceleration due to gravity = 9.8 m/s 2
7. Plot Solenoid Force vs. Plunger gap

8. Estimate energy output that occurs in a single activation of solenoid, which
is the area under the curve. Use either a single triangle or the trapezoid
method to estimate this area.
9. To calculate power, estimate retraction time as due to an average force
acting on the mass of the plunger. This is a rough estimate since the
acceleration is not constant, but it will give you a ball park number.
Variable Description Equation
h Maximum Plunger Gap that can
retract solenoid
h
a Average Acceleration a= average force*/mass
of plunger
t Retraction time t= sqrt(2h/a)
*Estimate the average from the plot Solenoid Force vs. Plunger gap.