STEMobile (A design/build electric car)

Students studying Mechanical and Electrical Engineering will be designing and building an electric car during the Spring semester. The car will be based off an electric golf cart chassis which will undergo major modifications. Students will design an entire new car body using Fusion 360 CAD software.  A frame for the body will be laser cut, filled with foam, and then covered with fiberglass.  The new body will be mounted to the chassis and all mechanical controls will be removed. Accelerating, braking and steering will be controlled through small Arduino computers taking inputs from a single joystick.   Students will program the control systems so that preset performance modes can be selected from a touch panel control display.  Additional subsystems, such as lighting and sound will be designed, as well as a new “cockpit” environment for the driver and passenger.  

The end goal is a concept sports car which is drive-by-wire.  It will provide a platform where self-driving technologies can be explored and implemented.  We are calling the project the STEMobile.  Please visit this page often for updates.

Phase 1 - Conceptual Design

During the last few weeks of our course "Introduction to Mechanical Engineering" students engaged in a design challenge to create a conceptual design for the STEMobile.  The winning design was created by Sarah Gaddis in Fusion 360 as shown below.  Her design was then sliced in the software to create rib and stringer frames for the front and rear quadrants.

  

Week 1 - Phase 2 Begins (Pre-paint activities)

The STEMobile project is now fully underway!  Three design/build teams have been established from our Mechanical and Digital Systems classes.  The teams are; the Exterior Team, the Interior Team, and the Electrical, Controls, and Instrumentation Team.  The Exterior team is further divided into two Front and Back sub-teams.  The original golf cart has been striped down to its chassis and is ready to be rebuilt.

                                           Golf Cart Chassis

EXTERIOR TEAMS

The Exterior teams have begun construction of the main body panels.  Sarah's Fusion 360 model was sliced into ribs and stringers to create a frame for the body components.  The ribs and stringers were then cut from 1/8 plywood using our laser cutter. The frame is then assembled, and foam is inserted to fill in the spaces.  The following pictures show the progress to date.

 

                         Frame assembly

               Front body frame in progress

                  Back body frame in progress.

 

 

 

 

 

 

 

 

             

  

INTERIOR TEAM

The interior team installed the new seats and began the design of the center console where the joystick controller will be mounted.  They discussed the human engineering aspects of the design and are aiming at a design which accommodates the widest range of drivers.  The original seat under-structure was cutout and modified to allow the new seat assembly to pivot forward for easy access to the batteries. 

                        New seats attached

 ELECTRICAL, CONTROLS, AND INSTRUMENTATION TEAM

The Electrical, Controls, and Instrumentation Team began defining operational modes and sourcing major electrical components.  They decided on selecting the driving modes and controlling the lighting systems using a touch screen panel.  The touch panel will be mounted alongside an audio/display panel on the dashboard.  The team decided on the following driving modes:  

  • Training mode (50% throttle and steering speed)
  • Normal Mode (80-85% Throttle and steering speed)
  • Sport Mode (100% performance)
  • Inverted Mode (Where pushing the controller forward would make the car reverse),

The following components will be purchased:

Touch Panel for Controls

Speakers

Receiver/display for CarPlay and Android Auto

 

The team also began a preliminary estimate of circuit current requirements.  Step down transformers from 48V to 12V and 5V will be required.

 

Week 2 - It's beginning to look like a car!

The second week of the project was very productive.  All design teams made significant progress as the car is starting to take form.  The picture below shows Mr. Lawes trying out the new armrest and joystick assembly.  

 

EXTERIOR TEAMS

The Front and Back Body teams continued to construct the body panels as shown below:

Next week the side profiles will be cut and the process of shaping, filling and sanding will begin.  Each body section will be fiberglassed to the remaining structures from the original golf cart body.  Once completed, no remains of the original golf cart will be visible.

INTERIOR TEAM

The Interior Team completed the armrest and joystick assembly.  White marine vinyl was chosen to give the cabin area a black and white theme. Wrapping the marine vinyl around the structure proved to be challenging, but all in all it came out pretty good.  The joystick is an industrial controller used on heavy equipment.  It was purchased off Ebay and bench tested.  It works great and even provides several buttons that the ECI Team can program with some sort of functionality.

Next week, the team will begin designing a center console that will connect the joystick housing to the front lower cabin and provide a space for many of the new electronic components.

 ELECTRICAL, CONTROLS, AND INSTRUMENTATION (ECI) TEAM

The ECI Team finished ordering long lead time parts and began practicing their skills using wire connectors, soldering, and configuring an Arduino to do simple tasks,  After a few more weeks of learning the team will be ready to focus their attention to the car.  By then, most of the parts should have arrived.

Week 3 - It's taking shape!

The 3rd week of the project was once again very productive.  All teams made significant progress refining the body, designing the interior, and working out the control systems.  Here is the Front Body Team laying out the right wheel well.

EXTERIOR TEAMS

The exterior teams continued to refine the body shape and make decisions about the wheel well geometry and interfaces to existing structures.  Getting symmetric sides is proving to be more an art than a science.

INTERIOR TEAM

The Interior Team prepared floorboard templates that will receive carpeting, as well as completing the center console mold which will be used to create our first fiberglass component.  

 ELECTRICAL, CONTROLS, AND INSTRUMENTATION (ECI) TEAM

The ECI Team completed their training on circuit, wiring, and Arduino tasks, and began the process of programming the joystick.  The main components were wired up and powered for the first time.  The brake and accelerator stepper motors actually moved with the joystick which was cause for celebration.  However, there appears to be some problems in the code as the stepper motor motion is not what was expected.  Next week, the code will be closely evaluated and modified as required. Additionally, the touch display receiver was powered up and tested.  It worked great!  The backup camera was attached and connected with a button.  It's yet to be determined if the back up camera will be activated with a mechanical button or soft button on the touch panel control.  Unfortunately, the touch panel that will control most systems has yet to arrive from China.  We are hoping that the coronavirus is not to blame.

Week 4 - Ahh, The smell of Bondo!

Although this was a 4 day week, a lot of progress was made. The front and rear body sections are nearing completion as the smell of body filler filled the room (or school apparently :).

EXTERIOR TEAMS

Body work continued as the front team began adding and sanding filler, while the back team modified the profile to flow into the back of the seats.  All in all, everyone is liking the new look.  More filler and sanding will need to take place next week, as well as bonding the new structures to the existing components.  The plan is to begin fiberglassing in March.

 

INTERIOR TEAM

The Interior Team made considerable progress.  The floorboards have been completed, speakers installed, the center console has been fiberglassed, and the dashboard has been readied for electronic components.  However, once installed it was clear that the center console sits a tad high and will need to be lowered.  Also, one of the cup holders is somewhat blocked by the joystick housing.  Some thoughtful modifications will need to happen next week.

 

ELECTRICAL, CONTROLS, AND INSTRUMENTATION (ECI) TEAM

The ECI Team continued programming the brake and accelerator control system.  A lot of progress was made as the joystick is now providing the correct response to inputs. Still, a lot of work remains as various buttons need to programmed and the steering system needs to begin development.   The team is still waiting for the touch panel to arrive from China.  Hopefully, it will be here within the next week or two.

Week 5 - Sanding, Sanding and more Sanding

With another 4 day week, and a delayed start for ice, progress on the car slowed a bit.  However, the body, interior , and electronics continued to move forward.  Shown below, Mr. Boyd continues sanding after school to help his team catch up.

EXTERIOR TEAMh

The front and rear body structures have been removed to allow for sanding, filling, and sanding.  The goal is to complete the body prep soon so that fiberglassing can begin in March.

 

 

INTERIOR TEAM

Now that the body structures have been removed, the interior team has room to complete the installation of various components and fairings.  A custom button panel is being created for the center console to provide 9 different horn sounds/melodies.  It was also decided that the center console be lowered and moved forward by a few inches.  This will allow for easy access to the cup holders as well room for the seats to pivot forward for battery access.  A removable fairing will need to be created to connect the joystick housing to the the center console.

 

ELECTRICAL, CONTROLS, AND INSTRUMENTATION (ECI) TEAM

The ECI Team continues to program the Arduinos and bench test the control system.  The driver for the steering system appeared to be defective so another has been ordered.  This will cause a slight delay, however we did receive notice that our touch panel display has been shipped from China!  Still a lot of electrical work remains. Bennet McKinney estimated that we will need roughly 150 feet of wire to install all the systems into the car.  Its appears we need to order some more wire!

 
Week 6 - Almost ready for Fiberglass?

Body preparation continued as more filling and sanding occurred daily.  As a result, the body is nearly ready for fiberglassing next week.  

EXTERIOR TEAM

On top of sanding and filling, the exterior teams designed and began the installation of new headlights and taillights.  

The headlights (left) are 3.5" LED fog lights which proved to be very bright.  The team came up with a cleaver mounting strategy using a 4" vacuum hose coupler.  The taillights (right) will be an LED strip mounted in a slot as shown .  The tail lights will provide running lights, break lights, and white back up lighting.
 

INTERIOR TEAM

The interior team is nearing the completion of the passenger environment. Most components have been designed and are awaiting installation.

 

The center console (left) is almost finished.  It was painted white and the cup holders and horn button control panel were installed.  The horn panel was designed in Fusion 360 and 3D printed.  It provides mounts for nine buttons which will provide nine different horn melodies.  The dashboard (right) was covered in white leather and the glove box was lined with felt.  A bezel for the glovebox is also being designed and 3D printed.  The team will install the audio unit next week.  Unfortunately, the touch panel control display (center of panel) has not arrived.  It is being shipped from China and may be delayed due to the Coronavirus outbreak.
 

ELECTRICAL, CONTROLS, AND INSTRUMENTATION (ECI) TEAM

The new steering stepper motor driver arrived and the ECI Team was able to finish the joystick programming. Although the bench testing board (below) looks like spaghetti, the team has planned out a wiring scheme that makes use of several quick connectors and wiring harnesses.  This will greatly aid in the removal and replacement of parts for maintainability.  The team is anxious to move from bench testing to on-vehicle testing as soon as possible (perhaps next week?).

The team is still waiting for the arrival of the touch panel from China.  The panel will interface with the Arduinos through a serial connection, providing state data for various screen objects.  The touch panel will be used to choose driving modes (which alter the sensitivity of the joystick); provide lighting control buttons; and display an accelerator position indicator.  The shipping delay does pose a program risk that will need to be discussed in the upcoming weeks.

 

Week 7 - Fiberglassing begins!

It took until Friday, but fiberglassing has begun.  All teams worked hard getting body, structural, and electrical systems moving forward.  So far, each team is on schedule.  Wednesday was reserved for a project meeting where the program status and fiberglassing techniques were discussed. Everyone agreed that the car is exceeding our expectations.  Below, the rear body section is receiving some final sanding before fiberglass.

 

EXTERIOR TEAM

The exterior team began the laborious task of fiberglassing the new body.  They plan on using two to three layers of 11 oz cloth on top and one layer of 11 oz cloth on the underside. Once complete, the process of paint preparation will begin.  

 


INTERIOR TEAM

The Interior team completed the horn button installation and is now ready to solder it up to an Adafruit sound board.  They also completed the installation of the horn speakers and amplifier.

 Overall, the interior is starting to look pretty good.  Add some floor mats and trim, install the receiver unit, and maybe add a windscreen, and we might just call call it done.

 

 ELECTRICAL, CONTROLS, AND INSTRUMENTATION (ECI) TEAM

The touch panel has finally arrived from China! It fits well in the dash board and looks good with the black and white interior theme.  The ECI Team has begun programming the Arduinos to receive serial data from the device.  Screen displays will be designed to present the joystick position as well as button objects to change the driving mode and activate various subsystems. 

Additionally, the team has begun creating the final wire harnesses and connectors that will be installed in the car.  Electrical distribution blocks have been installed for the 48V, 12V, and 5V systems and stepper motor assembly shock mounts have been attached.  On-car testing might actually begin next week.

 

Week 8 - Fiberglassing continues!

The front and rear body components have now received one layer of fiberglass cloth on both sides.  There is no longer any fear of the parts being fragile.  The fiberglass composite structures seem very strong.  An additional layer of fiberglass will be applied to all top surfaces.  This will then receive an extra coat of epoxy and then more sanding and sanding before going off to paint.  However, the project has been interrupted due to the Coronavirus.  As school is now closed for two weeks, progress is halted.  It was decided that the instructors would complete the fiberglassing so that project can remain on schedule.  It is our intent to send it off to paint in a few weeks.  When the students return, the body sections will be ready to mount and integrate with the rest of the vehicle.  As a result, a mid-May completion date is still possible.

 

EXTERIOR TEAM

The exterior team continued fiberglassing while designing and installing aluminum attachment brackets on the underside of the body structures.  The front section is taking on sort of a personality with the circular headlight cutouts.  We're thinking that with the right bumper design it just might be smiling at you:)

 

INTERIOR TEAM

The Interior team continued working on the horn system but was given a slight delay by the failure of the soundboard.  Unfortunately, a 9V power supply was inadvertently attached to the board (by Mr. Scripka of all people) which proved a bit too much.  Another board has been ordered.  Meanwhile, horn sound files are being collected and down-selected for final installation.

 

ELECTRICAL, CONTROLS, AND INSTRUMENTATION (ECI) TEAM

The ECI team began the laborious task of wiring the car to distribute 48V, 12V, and 5V power to fuse blocks strategically located throughout the car.  However, a set back occurred when bench testing the joystick control system.  Apparently, there is a short or bad connection in one or more of the wires that  have been soldered to circuit boards or connectors.  Troubleshooting will continue when the project resumes.

 

Week 9 - Coronavirus halts progress!

Well, after three days into the week, we were sent home to practice social distancing.  As we are not sure of a return date, the plan to paint the body during Spring break has been put on hold.  The body still awaits more sanding and additional layers of fiberglass, the interior still has trim and electronic work to do, and the control system has yet to be integrated into the vehicle.  Below is a picture of the STEMobile as it sits all alone in the STEM lab.  We are praying that a return to school is still possible in April.