7/23/2019 Model Solar Car http://slidepdf.com/reader/full/model-solar-car 1/31 - 1 - Table of Contents Table of Contents..................................................................................................1 What Makes a Model Solar Car go Really, Really Fast ? .....................................3 The Bits and Pieces of a Model Solar Car ............................................................3 The Model Solar Car Shell ................................................................................4 The Model Solar Car Chassis............................................................................5 The Model Solar Car Motor System ..................................................................6 The Model Solar Car Power System .................................................................7 How Fast Can a Model Solar Car Go ?.................................................................8 Let’s calculate it !!!.............................................................................................8 Speed of the Wheels .........................................................................................8 Speed of the Car ...............................................................................................8 Elapsed Race Time ...........................................................................................9 What Determines the Top Speed of the Car ? ......................................................9 Inertia of the Model Car.....................................................................................9 Friction ..............................................................................................................9 Loss in Power Transfer ...................................................................................10 Car Acceleration and Top Speed ........................................................................10 Acceleration Rate ............................................................................................10 Worst Case Acceleration ............................................................................. 10 Better Case Acceleration ............................................................................. 11 Best Case Acceleration ............................................................................... 11 Measuring the Effect of Choices and Changes ................................................... 12 How and When ? .............................................................................................12 The Wind Tunnel .............................................................................................12 The Inclined Plane...........................................................................................13 The Race Timer...............................................................................................13 The Dynamometer...........................................................................................13 Let’s Build a Model Solar Car ............................................................................. 14 Getting Started....................................................................................................15 How do We do This? .......................................................................................15 Project Launch.............................................................................................16 Prototype Car Build......................................................................................16 Production Car Build....................................................................................16 Car Selection ...............................................................................................16 Race Team Selection ..................................................................................16 The Model Solar Car Project Calendar ........................................................17 Tools Required................................................................................................19 Materials Required ..........................................................................................19 Rules in the Model Solar Car Garage.............................................................. 20 A Little bit of Planning Goes a Long Way ........................................................20 The Car’s Shell ................................................................................................... 21 Designing the Car’s Shell ................................................................................ 21 Building the Car’s Shell ...................................................................................21 The Car’s Chassis...............................................................................................22
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Table of ContentsTable of Contents..................................................................................................1What Makes a Model Solar Car go Really, Really Fast ? .....................................3The Bits and Pieces of a Model Solar Car ............................................................3
The Model Solar Car Shell ................................................................................4The Model Solar Car Chassis............................................................................5The Model Solar Car Motor System..................................................................6The Model Solar Car Power System .................................................................7
How Fast Can a Model Solar Car Go ?.................................................................8Let’s calculate it !!!.............................................................................................8Speed of the Wheels .........................................................................................8Speed of the Car ...............................................................................................8Elapsed Race Time...........................................................................................9
What Determines the Top Speed of the Car ? ......................................................9Inertia of the Model Car.....................................................................................9
Friction ..............................................................................................................9Loss in Power Transfer ...................................................................................10
Car Acceleration and Top Speed........................................................................10 Acceleration Rate............................................................................................10
Worst Case Acceleration .............................................................................10Better Case Acceleration .............................................................................11Best Case Acceleration ...............................................................................11
Measuring the Effect of Choices and Changes...................................................12How and When ?.............................................................................................12The Wind Tunnel.............................................................................................12The Inclined Plane...........................................................................................13
The Race Timer...............................................................................................13The Dynamometer...........................................................................................13
Let’s Build a Model Solar Car .............................................................................14Getting Started....................................................................................................15
How do We do This?.......................................................................................15Project Launch.............................................................................................16Prototype Car Build......................................................................................16Production Car Build....................................................................................16Car Selection ...............................................................................................16Race Team Selection ..................................................................................16The Model Solar Car Project Calendar ........................................................17
Tools Required................................................................................................19Materials Required ..........................................................................................19Rules in the Model Solar Car Garage..............................................................20
A Little bit of Planning Goes a Long Way ........................................................20The Car’s Shell ...................................................................................................21
Designing the Car’s Shell ................................................................................21Building the Car’s Shell ...................................................................................21
The Car’s Chassis...............................................................................................22
Designing the Car’s Chassis ...........................................................................22Building the Car’s Chassis ..............................................................................22Tweaking and Adjusting the Chassis...............................................................23
The Car’s Motive Power......................................................................................25Designing the Car’s Motive Power System .....................................................25
Building the Car’s Motive Power System.........................................................25Tweaking and Adjusting the Power Train ........................................................26Gears...........................................................................................................26Pulleys.........................................................................................................27
What’s a Model Solar Car without a PV Panel?..................................................28Installing the Shell on the Chassis...................................................................28The Solar Panel...............................................................................................28
Designing the Solar Panel Support..............................................................28Building the Solar Panel Support.................................................................28Tweaking and Adjusting the Solar Panel .....................................................29
Model Solar Car Build Check List .......................................................................30
Chassis ...........................................................................................................30Motor and Transmission..................................................................................30Body Shell .......................................................................................................30Solar Panel......................................................................................................30
• The chassis is the main platform of the car.• The functions of the chassis are to provide
o support for the drive and non-drive wheels and axles
o support for the motor and transmissiono a way to attach the body shello a way to support the photo-cell panelo a way to attach the guide-wire “hooks”
! transfer the rotation from the motor to the axle! change the direction of the motor movement! transform the speed of rotation of the engine into an increase of power to
the axle! Considerations
o meet the requirementso power
! maximize the power to speed ratio of motor! minimize friction in transmission
o weight! should not add significant weight to the car
o performance! should not slip due to shock to the car! ease of alignment
! Provide electricity to power the motor! Only the solar panel provided with the kit can be used! The solar panel must be removable and attached with the provided Velcro
strip! Position the power source in such a way that it captures the maximum sun
rays! The wiring from the solar panel must be removable, but sturdy enough so
it does not accidentally disconnect! Considerations
o We can only use the panel provided with the kit, therefore thedimensions and power output are fixed.
o The solar panel is fastened with a strip of Velcroo The electrical connection from the solar panel to the motor should
be sturdy but removable
o It is recommended that these connections be alligator clipso The connections should be labeled in order to avoid connecting the
• so the elapsed time is 20m / 8.8 m/s =2.27 seconds ! WOW ! is that reallypossible ?
• Unfortunately not, our calculations donot account for the loss of energy dueto friction and the amount of energyused to overcome the inertia in the car.
What Determines the Top Speed of the Car ?• The potential top speed is limited by the amount of power produced by the
solar panel and the power that the motor can generate from it.
• These are constraints. We have to use the SolarQuest’s solar panel andmotor.
• So let’s look at the other parameters that we can control and see how wecan measure and minimize their effect.
Inert ia of the Mod el Car
• The total car’s inertia is the sum of – the inertia due to the resting mass of the car (dead weight) – the inertia due to the wheel’s size and weight (rotational) – the inertia due to the gear’s size and weight (rotational) – the inertia due to the axle’s size and weight (rotational)
• The total inertia of the car can be minimized – by proper material selection – by using building techniques that minimize the weight of
the materials used
Fr ic t ion
• There are numerous sources of friction in the car – Friction of the air against the shell (called drag) – Friction of the wheels against the race surface – Friction of the axle against the bearings – Friction of the transmission components – Friction on the guide wire
• The friction of the car can be minimized by – using bearings on axles – lubricating rotating components – minimizing the friction surface areas – using materials that provide the least amount of friction – ensure that components are properly aligned
• The motor does not develop sufficienttorque to directly drive the wheels
• We must use mechanical advantage to
multiply the torque available to thewheels. We use a transmission toachieve this.
• Let’s look at scenarios on how thetransmission power transfer ratio willaffect the maximum speed of the car.
Car Acceleration and Top Speed
Accelerat ion Rate
• At the starting line, when the race switch isreleased, the motor turns on.
• The car will move forward and will graduallyaccelerate to its top speed.
• The acceleration rate is greatly dependent onthe power transfer ratio of the transmission
Worst Case Acceleration
• This occurs when the torque to the wheels is too low• You will need to change the gear ratio to provide more torque• The acceleration is so slow that the car accelerates throughout the race
• This occurs when the speed to the wheels is too low• You need to change the gear ratio to provide more speed
• We have rapid acceleration, but it bottoms out before the car reaches itstop speed.
Best Case Acceleration
• Excellent acceleration rate• We are reaching the maximum speed very early in the race• The gear ratio is just right, the balance between torque and speed is
• An easy way to determine the level of friction of the car is to put it on aninclined plane and see at what angle it starts rolling and measure how farit rolls off the inclined plane
• Incremental improvements can be made to the bearings, axles and wheelsand the car can be retested on the inclined plane
The Race Timer
• Once the car is essentially completed, itsracing characteristics can be determinedwith the MSCRT. (Model Solar Car RaceTimer)
• The MSCRT reproduces the real racingconditions but also times the raceaccurately (to 1/10 of second)
• The car should be run on the 20 meter
track 3 or 4 times and an average racetime calculated
• Note: The race time includes the time forthe car handler to release the car at thestart line.
The Dynamom eter
• We could use the MSCRT to see if the caris using the best possible power transferratio. But the MSCRT requires the car tobe completed
• A better approach is to test the car whilestill in the build stage.
• The dynamometer simulates the inertialweight of the car and accuratelymeasures the wheel’s speed.
• This allows the teams to experiment withthe ratios and determine the best one fortheir car.
The teams will meet once a week, after school, for an hour. The sessions afterChristmas are typically extended to two hours in order to provide morecontinuous work time on the production cars. The teams will be asked to keep a
journal of their weekly activities.
The first session launches the project. We get the students to form teams andelect captains. We go through the contest rules and car’s specifications.
Prototype Car Build
This year we are using a different approach. The teams will first build aprototype car. By building a prototype, they will learn about the various aspectsof designing and building a model solar car. The teams will go through severalcycles of build-testing-refinements until the car is ready to race. The teams mustcomplete their prototype cars and have it evaluated before they can begin towork on the production version.
Production Car Build
After the Christmas break, the teams will use their acquired experiences andknowledge to design and build a production car. These cars will go through aselection process and only two cars will be chosen to compete at the annualSolarQuest meet in May at the Sciences and Technologies Museum.
Car SelectionThe final selection process is designed to offer every team the same chances tohave their car picked. The cars are evaluated using the same criteria as duringthe SolarQuest challenge. In addition to these criteria, each team will berequired to have designed and produced a web site meeting the SolarQuestcompetition requirements. The team participants will be asked to vote for thecars that they believe best meet the criteria and best represent the school.
Race Team Selection
The race teams, 10 students, will be selected by the supervising teachers. The
selection is based on the team member’s attendance, participations, contributionand conduct during the project.
• Presentation of the project process, rules & analyzing requirements
Building & Racing prototype Cars, October 13th to February 2nd
! The intent here is to provide hands-on learning of what makes a solar cargo fast.
! The teams will each build a prototype car with the kits that we will providethem.
! They will follow specific instructions, so we can keep the teams movingalong at the same pace.
October
- SolarQuest rules- What makes a car go fast- Playing the solar car game- Handing out the Solar Car Prototype kit
November - Drawing a 3D view of the car- Building the prototype car shell- Testing the shell in the wind tunnel
December - Building the prototype chassis- Attaching wheels to the chassis
- Testing the chassis on the inclined planeJanuary - Building a prototype transmission- Testing the transmission with the dynamometer- Building a prototype solar panel support- Wiring the prototype car
February - Racing the prototype cars
Building & Racing the Race Cars, February 9th to May 4th
! The intent here is to provide the teams with the opportunities to design acar from scratch.! The teams will each build a racing car from scratch materials, no kits this
time.! The teams focus should be on build quality and making a "fast" car.
• Use Styrofoam to make the shell• Use your drawings to
– Determine the location for mounting points for the shell onto thechassis. These mounting points will serve as support for the shell.
– Ensure that the shell will allow space for the motor, pulleys, gears,axles and battery holder.
• Velcro strips make a good fastener that can be used to attach the shell tothe chassis mounts.
• Your shell should be easily removable or provide access hatches foradjustments or repairs
Bu ilding th e Car ’s Shel l
1. Transcribe your 3 view diagram onto a block of Styrofoam.2. Starting with the side view, cut the foam to the shape of the drawing. A
hacksaw blade cuts the Styrofoam quite nicely.3. Hollow out the shell. This is required to make space for the motive power
and this will lighten the shell.4. Test your shell in the wind tunnel and note the drag created by the shape.5. Use sandpaper to smooth the shape of the shell and see if it reduces the
shell’s drag.6. Compare your shell’s drag index with other cars and see if you can apply
any of their designs into yours to further reduce the drag of your shell.
• Use your overall shape/dimensions and picture to design your chassis – Determine the overall shape and size of the chassis – Determine the location of the wheels and axles – Determine the location of the wheel bearings – Determine the location of the transmission – Determine the location of the motor on the chassis
– Determine the location of the battery holder• Overlay a new sheet of paper over your previous plan (the exterior view of
your car). Trace the contour of the car on the new sheet of paper. Thendraw your chassis design.
• Your chassis drawing should incorporate – the overall shape and size of your chassis – the location of the wheels, axles and bearings – the location of the motor – the location of the transmission – the location of the battery holder
Bui ld ing the Car ’s Chassis1. Using your chassis diagram, measure and using an Xacto knife to cut the
various pieces of foam core to make your chassis/frame.2. Assemble and fasten the pieces together with low temperature hot melt
glue.3. Measure and cut the axles to length with a triangular file. Make sure that
all burrs are removed.4. Mark where the pulley fits onto the drive axle.
5. Using cyanoacrylate glue, fasten the pulley onto the drive axle.6. Mark the position of the axle onto the chassis. Take care in aligning the
axles properly to the chassis.7. Mark the position of the axle pulley onto the chassis, and then remove the
chassis material to provide proper clearance for the pulley.
8. Construct the front and rear axle bearings from aluminum tubing.9. Install the pulley on the drive axle.10. Slip the bearings onto the axles.11. Fasten the bearings to the chassis with hot melt glue. Double check the
alignment of the axles with respect to the chassis.12.Temporarily attach the wheels to the axles.13. Test the axles.
1. lubricate the axles and bearings with light oil2. ensure that they rotate freely, with minimum force required3. ensure that the car moves in a straight line
Now you have a chassis with 2 axles mounted on bearings. One of the axles has
a gear or pulley attached to it.
Tweaking and A djust ing th e Chassis
• Some tweaking may be necessary to make the axles run smoothly andwith minimum friction...
– Double check the alignment of the bearings. Their centers shouldbe aligned!
– You may consider lubricating the axle and bearings with a very lightoil. Make sure that the lubricant is compatible with your materials!
• If you find the car is not traveling in a straight line... – double check the alignment of the axle with respect to the chassis – The axle must be at 90 degrees off the center line running through
• If you find that the car “pulls” to the left... – the distance between the axles on the left side of the car is shorter
than the distance between the axles on the right side of the car
• If you find that the car “pulls” to the right... – The distance between the axles on the left side of the car is longer
than the distance between the axles on the right side of the car.
• If you find the car wobbling... – double check the alignment of the wheels with respect to the axle – The wheels must be at a 90 degrees off the center line running
through the length of the axle
You are now ready to test your car on the inclined plane to measure itsoverall coefficient of friction. You will need to temporar i ly attach theshell to your chassis.
• Use your chassis drawing to design your motor/transmission assembly
– Select the size of pulley that you will use on the motor – Determine the best location of the motor to provide the bestmechanical coupling to the drive axle
– Capture the location of the motor onto the drawing• Considerations for pulley ratio
– the higher the ratio the more torque you will get at the wheel – the lower the ratio the more speed you will get at the wheel – the heavier the car the more torque you will need
• Use the following diagram to wire your car
Bui ld ing the Car ’s Mot ive Power System
1. Attach the drive pulley to the motor. Be careful, the pulley is pressed fit
onto the motor’s axle. Support the axle against the surface of a tablebefore pushing the pulley onto the axle on the other side of the motor.
2. Position the motor onto the chassis.3. Ensure that the motor is parallel with the drive axle.4. Ensure that the pulleys align properly.5. Attach the motor to the chassis with hot melt glue. Be careful not to
6. Using a 1.5Vdc AA cell, identify the polarity that makes the motor rotate inthe proper direction for your car.
7. Mark the appropriate polarity on the leads of the motor.8. Ask the mentor to demonstrate how to solder.9. Solder the negative lead from the motor to a small alligator clip.
10. Solder the positive lead from the motor to the middle terminal of the raceswitch.11. Solder a wire from the normally closed (N.C.) terminal of the race switch to
a small alligator clip.12. Connect the alligator clips to the battery holder terminals.13. Glue the battery holder to the chassis with hot melt glue.14. Test the motor assembly using two 1.5Vdc cells.15. Ensure that the race switch works properly and that the motor rotates in
the proper direction.
Tweaking and Adjus t ing the Power Train
Gears
• Some tweaking may be necessary to make the gears engage properly... – Double check the alignment of the motor in respect to the axle.
The motor should be parallel to the axle. – You may consider lubricating the gears with very light grease.
Make sure that the lubricant is compatible with your materials!
• If you find that your axle is not moving or moves very slowly... (motorstraining)
– The contact between the gears is too tight – Slightly move the motor assembly away from
the axle in order to increase the distancebetween the gears.
• If you find that your axle is not moving or moves veryslowly... (gears are grinding)
– The meshing is improper. The contactbetween the gears may be too loose
– Slightly move the motor assembly towardsthe axle in order to decrease the distancebetween the gears.
• Fasten the car’s shell to the chassis with small rectangles of Velcro.• Ensure that none of the moving parts make contact with the shell.• Test the race switch to ensure that it moves freely and turns the motor on
and off.
The Solar Panel
Designing the Solar Panel Support
• Use your chassis & shell drawing to design a mount to support your solarpanel
– Determine the best location for your solar panel – Decide whether your mount will be fixed or provide an adjustable tilt
for the panel – Keep in mind that the panel MUST be removable – Design a lightweight panel mount
Building the Solar Panel Support
1. Measure and cut all the pieces to construct the panel mount2. Assemble and fasten all the pieces for your panel mount3. Attach the panel mount to the chassis or shell of the car4. With a voltmeter, determine the polarity of the leads from the solar panel5. Mark the polarities on the leads of the solar panel6. Attach and install the solar panel on the mount
7. Connect the alligator clips from the motor to the solar panel.
Tweaking and Adjusting the Solar Panel
• Very little tweaking should be necessary at this point, unless there is no
sun. – provided you have a source of light – make sure that the surface of the solar panel is clean – connecting the solar panel with the alligator clips will power the
motor – if the car does not move, verify that your connections are good – if you have an adjustable solar panel support, adjust the orientation
of the panel to obtain the most output – verify the output of the panel with a voltmeter – note that the panel may produce voltage but may not produce
sufficient current to run the motor (low light)
You are now ready to retest your car in the wind tunnel. This will tell you howmuch drag is created by the solar panel and its support. Once you havefinalized your support, you are ready to race the car and capture the race timewith the Solar Car race timer.