SOLAR CAR

MOTOR AND MOTOR

CONTROLLER

WHEEL MOTORS

Discrete Bridge circuits

Torque Calculations

Program to Demonstrate

H-bridge

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 ResistanceGR [lb] = GVW [lb] x sin(α)

Where:• GR = grade resistance (lb)• GVW = gross vehicle weight (lb)• α = incline angle (degrees)Example

GR = 35 lb x sin(2°) = 1.2 lb

• Step Three: Determine Acceleration ForceFA [lb] = GVW [lb] x Vmax [ft/s] / (32.2 [ft/s2] x ta [s])

Where:• FA = acceleration force (lb)• GVW = gross vehicle weight (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 TorqueTw [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 circuitsSome 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.

DARLINGTONS H-BRIDGE

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 ' Motor-speed "accumulator."SYMBOL motDir = bit0 ' Motor direction: 0=fwd;1=reverse.SYMBOL spd = b10 ' Motor speed, 0 (off) to 15 (full on).SYMBOL cycles = b9 ' Number of loops at a given speed.SYMBOL A_ = pin0 ' Controller A input.SYMBOL B_ = pin1 ' Controller B input.dirs = %11 ' Set pins 0 and 1 to output.again: for cycles = 0 to 255 ' Turn 255 cycles at each speed. gosub motor ' Output to motor. next spd = spd +1 ' Increase speed. If spd <= 15 then again ' If speed is > 15, then.. spd = 0 ' ..turn motor off.. motDir = motDir ^ 1 ' ..and reverse direction.goto again ' 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_ ^ 1return

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