Welcome to Making with Technology!
Transcript of Welcome to Making with Technology!
Mens et Manus
Welcome to Making with Technology!
These notes are posted on our website http://mit.edu/6.a01.
Click “Slides” for the week of October 28.
Also see our “Overview” document (separate tab at top of page)
and our complete “Parts” list.
October 28, 2019
Brushless Motor Project
Brushless Motor technology is the leading motor technology in a
wide range of applications:
• high precision: e.g., computer peripherals,
• low cost: e.g., hand-held power tools, and
• high power: e.g., electric and hybrid automobiles.
Brushless Motor Project
We will build a brushless motor using
• a modern microcontroller (Teensy 3.2) and
• parts constructed with modern rapid-prototyping techniques
− laser cutting
− 3D printing
Great project for all skill levels:
• intro level project for students with no previous experience
• many opportunities for optimizations to develop existing skills
How do electric motors work?
Electric motors rotate due to the interaction of magnetic fields that
are fixed to a rotor that rotates and a stator that is stationary.
N
S
S
N
NS
NS
How do electric motors work?
Electric motors rotate due to the interaction of magnetic fields that
are fixed to a rotor that rotates and a stator that is stationary.
N
S
S
N
NS
NS
How do electric motors work?
Electric motors rotate due to the interaction of magnetic fields that
are fixed to a rotor that rotates and a stator that is stationary.
N
S
S
N
NS
NS
How do electric motors work?
Electric motors rotate due to the interaction of magnetic fields that
are fixed to a rotor that rotates and a stator that is stationary.
N
S
S
N
NS
NS
How do electric motors work?
Electric motors rotate due to the interaction of magnetic fields that
are fixed to a rotor that rotates and a stator that is stationary.
N
S
S
N
NS
NS
How do electric motors work?
Electric motors rotate due to the interaction of magnetic fields that
are fixed to a rotor that rotates and a stator that is stationary.
N
S
S
N
NSNS
How do electric motors work?
Electric motors rotate due to the interaction of magnetic fields that
are fixed to a rotor that rotates and a stator that is stationary.
N
S
S
N
NS
NS
How do electric motors work?
Electric motors rotate due to the interaction of magnetic fields that
are fixed to a rotor that rotates and a stator that is stationary.
N
S
S
N
NS
NS
How do electric motors work?
Electric motors rotate due to the interaction of magnetic fields that
are fixed to a rotor that rotates and a stator that is stationary.
N
S
S
N
NS
NS
How do electric motors work?
Electric motors rotate due to the interaction of magnetic fields that
are fixed to a rotor that rotates and a stator that is stationary.
N
S
S
N
NS
NS
Controlling the Electromagnets
In a brushed motor, currents are switched mechanically using a
commutator, which has parts on both the rotor and stator.
Controlling the Electromagnets
In a brushed motor, currents are switched mechanically using a
commutator, which has parts on both the rotor and stator.
Controlling the Electromagnets
In a brushed motor, currents are switched mechanically using a
commutator, which has parts on both the rotor and stator.
Controlling the Electromagnets
In a brushed motor, currents are switched mechanically using a
commutator, which has parts on both the rotor and stator.
Controlling the Electromagnets
In a brushed motor, currents are switched mechanically using a
commutator, which has parts on both the rotor and stator.
Controlling the Electromagnets
In a brushed motor, currents are switched mechanically using a
commutator, which has parts on both the rotor and stator.
Controlling the Electromagnets
In a brushed motor, currents are switched mechanically using a
commutator, which has parts on both the rotor and stator.
Controlling the Electromagnets
In a brushed motor, currents are switched mechanically using a
commutator, which has parts on both the rotor and stator.
Controlling the Electromagnets
Electromagnets are activated based on rotor angle. now is a good
time for all commutator
Controlling the Electromagnets
Commutator in an electric drill.
commutator plates
brushbrush
Mechanical switching generates sparks, excess heat, and power loss.
Controlling the Electromagnets
Sensing rotor position and controlling current flow are separated in
a brushless motor.
Sensing is accomplished with a solid-state device.
Currents are switched electronically.
Hall Effect Sensor
Magnetic fields divert the motion of charged particles.
By
Ix
Ix
fv
e−
Current in x direction results from flow of electrons in −x direction.
Magnetic field B in y direction generates (Lorentz) force f in z
direction,
f = qv ×B
were q is charge on electron and v is it’s velocity.
Lorentz force pushes electrons upward, making conductor more neg-
ative at top than bottom.
Sensing Rotor Position
Two (or more) sensors are usually required to determine the angular
position of the rotor.
Controlling the Electromagnets
We will use electronic switches to activate the electromagnets.
This configuration is called an H-bridge. It consists of two half-
bridges that each control the voltage on one side of the coil.
V
X1H
X1L
X2H
X2L
By opening and closing four switches, one can set the voltage across
a coil to be +V , −V , or zero.
Controlling the Electromagnets
We will use electronic switches to activate the electromagnets.
This configuration is called an H-bridge. It consists of two half-
bridges that each control the voltage on one side of the coil.
V
X1H
X1L
X2H
X2L
Closing X1H and X2L causes currents to flow left-to-right through
the coil.
Controlling the Electromagnets
We will use electronic switches to activate the electromagnets.
This configuration is called an H-bridge. It consists of two half-
bridges that each control the voltage on one side of the coil.
V
X1H
X1L
X2H
X2L
Closing X2H and X1L causes currents to flow right-to-left through
the coil – reversing the magnetic polarity of the coil.
Brushless Motor Project
Make a brushless motor:
• using laser-cut or 3D printed parts,
• with electronic sensors and actuators, and
• controlled with a microcontroller.
You can choose
• the configuration of the rotor and stator,
• the number and configuration of coils and magnets,
• the placement of sensors, and
• timing and choreography via a microcontroller.
No previous experience is assumed.
Brushless Motor Examples
Four magnets and four coils.
Brushless Motor Examples
Six magnets and three coils.
Brushless Motor Examples
Twelve magnets and six customized coils.
Brushless Motor Examples
Two magnets and two coils, vertical design.
Brushless Motor Examples
Rotor surrounds stator.
Inrunner and Outrunner Configurations
Electromagnets are (almost) always rigidly attached to base plate.
inrunner outrunner
Inrunner: Disk-shaped rotor spins inside electromagnets.
Outrunner: Annular rotor spins outside electromagnets.
Parts
We have distributed bags of parts for your motor.
Take some time to familiarize yourselves with the parts.
Motor Design Issues
Attaching the rotor.
The simplest kind of axle is a bolt.
For most purposes that is fine.
Motor Design Issues
Ball bearings are better.
You could use a ball bearing that fits into a 1/2” hole and provides
a freely rotating attachment to a 1/4” shaft.
Motor Design Issues
After assembly.
Rotor
The rotor should firmly attach to the shaft so that the shaft turns
with the rotor.
This can be accomplished using a ”D-shaft” with a corresponding
D-shaped hole in the rotor.
Electromagnets
Coils for electromagnets can be wound on plastic bobbins or by
wrapping wire around a bolt with washers.
An all-metal design better withstands heat produced by windings.
Magnetic force depends on voltage, wire diameter, and number of
turns. We will discuss designing coils at a later session.
Electromagnets
Coils can be attached to a base plate using angle brackets or inte-
grated into the design of the base plate.
Hall Sensors
Wires can be connected to the hall sensors using a wire-wrapping
tool.
They should be held in place with some sort of fixture, which can
be 3D printed or laser-cut acrylic as shown above.
Finished
Here is an example of a fully assembled motor.
Elevation
Maximum force results when coils line up with rotor plane.
stator
rotor
sha
ft
bearings
spacer
spa
ce
r
collar
collar
Hall sensor
coil
• Two bearings help stabilize the shaft.
• Two collars hold the rotor assembly together.
• Small-diameter spacers are needed to prevent collar and rotor
from touching outside of bearing.
Electronic Control
The electronic parts are contained on a single printed circuit card.
We will discuss these parts in a later session.
Important Practical Considerations
Magnetic forces diminish rapidly with distance.
0 2 4 6 8 10 12 140
0.25
0.5
0.75
1
no
rma
lized
forc
e
distance d [mm]
d
coil
magnet
Force at 2 mm is only half that at 0 mm.
Very little force is exerted at a distance of 20 mm.
→ stator coils can only exert significant force on magnets if distance
to magnet is <10 mm.
Important Practical Considerations
Ferrous cores increase magnetic force but also add static force.
You can hold coils in place with steel screws (highly magnetic) stain-
less steel screws (slightly magnetic) or nylon screws (not magnetic).
Ferrous cores increase magnetic force by concentrating flux (good!).
However ferrous cores are attracted to permanent magnets in rotor
regardless of whether the coil is energized (bad!).
For most designs, the extra force using ferrous cores outweighs dis-
advantages of static forces.
Important Practical Considerations
Build a plan for mounting Hall sensors into your conceptual design.
Most designs use one sensor to control each pair of electromagnets.
2 electromagnets → one sensor
4 electromagnets → two sensors
6 electromagnets → three sensors
· · ·
Important Practical Considerations
Avoid overly symmetric designs.
What’s wrong with the following design?
NS
S N
NS
SN
Important Practical Considerations
Avoid overly symmetric designs.
What’s wrong with the following design?
NS
S N
NS
SN
None of the electromagnetics exert torque on rotor in this position.
Important Practical Considerations
Less symmetry: different number of permanent and electromagnets.
NS
SN
NS
SN
NSSN
If permanent magnets have left-right symmetry (as illustrated), we
can still use the horizontal coils will generate torque.
Important Practical Considerations
Avoid overly symmetric designs.
What’s wrong with the following placements of Hall sensors?
NS
S N
NS
SN
Important Practical Considerations
Avoid overly symmetric designs.
What’s wrong with the following placements of Hall sensors?
NS
SN N
S
SN
If one sensor detects a north pole, the other will detect a south pole.
→ the second sensor provides no new information.
Important Practical Considerations
How about this placement of Hall sensors?
NS
SN
NS
SN
NSSN
Important Practical Considerations
How about this placement of Hall sensors?
NSS
N
N S
SN N
S
SN
If first sensor sees north, use vertical coils to make clockwise torque.
Important Practical Considerations
How about this placement of Hall sensors?
NS
SN
N SS N
NS
SN
If first sensor sees north, use vertical coils to make clockwise torque.
If second sensor sees north, use horiz coils to make clockwise torque.
Schedule
Five weeks to design, build, and debug.
Week 1: 10/28 Conceptual (paper) Design
Week 2: 11/4 CAD
11/11 Veterans Day (no class)
Week 3: 11/18 FAB
Week 4: 11/25 Coils and Assembly
Week 5: 12/2 Programming and Debugging
12/9 Motor Presentations
Today: Conceptual (paper) Design
Each student should design their own motor.
However, it’s easier to work with a partner with whom you can
discuss ideas (yours and theirs).
Today: Conceptual (paper) Design
Focus on high-level goals (lasercut vs. 3D printed, geometry, . . .).
We will refine technical aspects in subsequent sessions.
Before leaving today, get a checkoff and upload your sketches:
• Go to our home page: http://mit.edu/6.a01
• Click on “Conceptual (paper) Design”
• Get a Checkoff: discuss your design with a staff member
• Upload pictures of your design sketches.
New Week: CAD
Next week we will use Fusion 360 to make CAD files for your parts.
Download Fusion 360 (free to students) to your laptop before class.
If you’d like to use a loaner laptop, send email to [email protected]