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WHEEL
MOTORS

Program to
Demonstrate
H-bridge

MOTOR AND
MOTOR
CONTROLLER

Torque
Calculations

Discrete
Bridge
circuits

WHEEL MOTOR
• The wheel hub motor is an electric motor that is incorporated into
the hub of a wheel and drives it directly.

How In-wheel Motors Work
• The internal combustion
engine normally found under the
hood is simply not necessary. It's
replaced with at least two motors
located in the hub of the wheels.
• When power is applied to the
stationary coils on the inside of the
wheel, an electromagnetic field is
generated and the outer part of the
motor attempts to follow it and turns
the wheel to which it is attached

In-wheel Motor Performance
• Protean modified the Ford F-150
EV by removing the engine and
adding four in-wheel electric
motors to the truck.
• . Each of the four Protean Drive
motors are capable of delivering
over 100 hp each, a total of 400 hp
from all four motors -- far more
than produced by the standard
engine.
• Each motor weighed only 31kg

Protean Electric unveiled a Ford F 150

In-wheel Motor Efficiency
• One of the greatest advantages of in-wheel electric motors is the fact
that the power goes straight from the motor directly to the wheel
• Reducing the distance the power travels increases the efficiency of the
motor.
• For instance:
 In city driving conditions, an internal combustion engine may only run at
20 percent efficiency
 An in-wheel electric motor in the same environment is said to operate at
about 90 percent efficiency.

In-wheel Motor Power
• Electric motors produce a high
amount of torque, and since that
force is transmitted directly to the
wheel, very little is lost in the
transfer.
• Each wheel can be equipped with
sensors to determine how much
torque is required at any given
time.

DISADVANTAGES
The 3 main issues are:
• Cost: Two motors instead of one is simply more expensive.
• Torque: A high rpm low torque motor is smaller and cheaper
than a low rpm high torque motor that is required for a
wheel motor.
• Exposure: An electric motor is still a quite delicate piece of
equipment. We want to have it in a safe, protected spot. In
the wheel the motors are exposed to more vibrations and
dirt.

Drive Wheel Motor Torque
Calculations
• When selecting a drive wheel motor for a mobile vehicle, a number of factors
must be taken into account to determine the maximum torque required.
• The following example outlines one method of computing this torque
• Sample vehicle design criteria:
▪ Gross Vehicle weight (GVW): 35 lb
▪ Weight on each drive wheel (WW): 10 lb
▪ Radius of wheel/tire (Rw): 4 in
▪ Desired top speed (Vmax): 1.5 ft/sec
▪ Desired acceleration time (ta): 1 sec
▪ Max incline angle (α): 2 degree
▪ Worst working surface: concrete (good)

To determine max torque requirement of
motor:
• To determine the maximum torque, it is necessary to determine the
total tractive effort (TE) requirement for the vehicle.
TE [lb] = RR [lb] + GR [lb] + FA [lb]
Where:
• TE = Total tractive effort [lb]
• RR = Force necessary to overcome rolling resistance [lb]
• GR = Force required to climb a grade [lb]
• FA = Force required to accelerate to final velocity [lb]

Step One: Determine Rolling Resistance
RR [lb] = GVW [lb] x R [-]
Where:
• RR = rolling resistance (lb)
• GVW = gross vehicle weight (lb)
• R = surface friction
Example
RR = 35 lb x 0.01 (“good concrete”) = 0.35 lb

Step Two: Determine Grade Resistance
GR [lb] = GVW [lb] x sin(α)
Where:
• GR = grade resistance (lb)
• α = incline angle (degrees)
Example
GR = 35 lb x sin(2°) = 1.2 lb

• Step Three: Determine Acceleration Force
FA [lb] = GVW [lb] x Vmax [ft/s] / (32.2 [ft/s2] x ta [s])
Where:
• FA = acceleration force (lb)
• Vmax = maximum speed (ft/s)
• ta = time required to achieve maximum speed (s)
Example
FA = 35 lb x 1.5 ft/s / (32.2 ft/s2 x 1 s) = 1.6 lb

• Step Four: Determine Total Tractive Effort
TE [lb] = RR [lb] + GR [lb] + FA [lb]
Example
TE = 0.35 lb + 1.2 lb + 1.6 lb = 3.2 lb

• Step Five: Determine Wheel Motor Torque
Tw [lb-in] = TE [lb] x Rw [in] x RF [-]
Where:
• Tw = Wheel torque (lb-in]
• Rw = Radius of the wheel/tire [in]
• RF = “Resistance” factor *-]
Example
Tw = 3.2 lb x 4 in x 1.1 = 14 lb-in

Electronic Control for DC Motors
Using Discrete Bridge circuits
Some of the bridge circuits to control the DC MOTOR.
• Dual relay controller.
• Darlington H Bridge
• Half bridge
• Ingenious H bridge

DUAL RELAY CONTROLLER
• This design uses DPDT relays to control
motor direction, and transistor array to
turn the relays and motors on and off.
• This design gangs two Darlington
transistor outputs together for motor
on/off control.
• the transistors inside the ULN2003 are
Darlington’s, they require only a small
control current to turn on.

HALF BRIDGE
• This circuit offers the pleasant
combination of high efficiency
and low parts count.
• The circuit takes advantage of
the Stamp’s relatively high
current outputs to eliminate the
need for an input transistor or
Darlington.

INGENIOUS H-BRIDGE
• each input transistor
transfers current out of
the base of a PNP and
into the base of the
opposite NPN
• The current switches on
both transistors to make
the motor run.

Program to Demonstrate H-bridge
• This program demonstrates the motor controller to control the direction
and speed of a DC motor.
• Connect input A of the controller to Stamp pin 0; B to pin 1; and GND to
GND
• Run the program
• The motor will slowly accelerate to top speed, then stop and repeat the
acceleration in reverse.
• This program uses a carry-the-1 method of generating duty cycle control of
motor speed.
• When you add a number to an "accumulator" (a memory location of fixed
size), the accumulator will overflow if the result is bigger than it can hold.

SYMBOL motAcc = b11
SYMBOL motDir = bit0
SYMBOL spd = b10
on).
SYMBOL cycles = b9
SYMBOL A_ = pin0
SYMBOL B_ = pin1
dirs = %11
again:
for cycles = 0 to 255
gosub motor
next
spd = spd +1
If
spd <= 15 then again
spd = 0
motDir = motDir ^ 1
goto again

' Motor-speed "accumulator."
' Motor direction: 0=fwd;1=reverse.
' Motor speed, 0 (off) to 15 (full
' Number of loops at a given speed.
' Controller A input.
' Controller B input.
' Set pins 0 and 1 to output.
' Turn 255 cycles at each speed.
' Output to motor.
' Increase speed.
' If speed is > 15, then..
' ..turn motor off..
' ..and reverse direction.
' Loop forever.

motor:
motAcc = motAcc & %1111
' Limit motAcc
to 4 bits.
motAcc = motAcc + spd
' Add speed.
if motAcc >= 16 then motOn
' If
carry, then turn on motor.
A_ = B_
'
Otherwise, motor off.
return
' If you look at the table accompanying the H-bridge, you'll
' see that the motor is on only when inputs A and B are
opposite.
' Programming shorthand for this is to set A to the motor
' direction, and make B = NOT A.
motOn:
A_ = motDir: B_ = A_ ^ 1
return

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