1.0 Purpose

To reinforce the chassis of MSXIV the team is looking into the adding sheet metal to gain the extra structural support needed. This page seeks to find all possible consideration to this addition to the car. Considerations such as relevant regulation from the American Solar Car Challenge (ASC), different sub-assemblies within MSXIV that may interfere with the addition, and ways to go about adding it to the car.

2.0 Relevant Regulations

This section will list the important regulations that will be relevant to the attachment of sheet metal.

9.3 - Ground Clearance

The fully-laden solar car must have a minimum ground clearance of 50 mm such that he solar car can be driven over a 50 mm object and no part of the solar car except for the tire may make contact with the object.

10.3.D - Belly Pan

The cockpit must be equipped with a full belly pan to isolate the occupants from the road. The belly pan be strong enough to support the full weight of each occupant. Each occupant’s torso and limbs must be above the lower element of the structural chassis.

10.4 - Fastener

All fasteners must be of suitable type, strength, and durability for their application. Friction, glued, or press fit assemblies will not be accepted in critical areas (as defined in 10.4.E) as the sole means of retention. For glued of press fit assemblies a pin is required. The pin diameter shall be 1/4 of the tube’s outer diameter. A press fit roll pin is acceptable for this application. Set screw intended to transmit torque of force will not be accepted.

10.4.A - Bolts

Bolts used in critical areas (as defined in 10.4.E) must at minimum meet SAE grade 5, metric grade M*.* and/or AN/MS specifications. Bolts must be of the correct length, and extend at least two threads beyond the nut. Bolts in tension must not have shave or cut heads. All fasteners should be a properly torqued. U-bolts are not allowed in critical areas.

10.4.B - Securing of Fasteners

All structural and other critical fasteners (bolts, nuts) must have an acceptable form of securing such that the fastener cannot loosen of be removed unintentionally. Acceptable methods of securing are:

(1) Bolts with flex-loc type nuts or other nuts that use flexure as the means of locking and are re-useable.

(2) Bolts with pre-drilled shafts and castle nuts with cotter pins installed to prevent loosing.

(3) Bolts with pre-drilled heads and/or nuts properly safety wired with stainless steel wire from 0.024” (0.6 mm) to 0.032” (0.8 mm) diameter conforming to Mil Spec MS20995C. The safety wire between fasteners and anchor points must be twisted to prevent rotation of the fastener.

(4) In blind hole applications, bolts with pre-drilled heads properly safety wired.

(5) Other methods of securing fasteners may be deemed acceptable at the discretion of the Inspector.

Securing methods that are not acceptable are Nylon lock nuts, “lock” washers, Loctite, or lock nuts that use thread distortion as a means to secure the nut. Lock nuts with thread distortion are not considered to be reusable. Other methods of securing fasteners, where the above methods are not appropriate may be considered at the discretion of the Inspector. Non-critical fasteners need not be secured with lock nuts.

10.4.E Critical Areas

For application of the above critical areas are defined to include: steering, braking, suspension, seat mounts, safety harness, drive train, battery box, and ballast carrier.

3.0 Potential Sub-assembly Interferences

As this project was started from changing the bottom panel from a structural member to a non-structural one, there will be a focus on the assemblies that will be near the bottom panel.

Sourced from the Chassis Mounting Reservation Slide Deck

4.0 Sheet Metal Mounting Designs

During the manufacturing process the final product may not match the original design as intended; the product will not match the CAD perfectly. This section will look at different ways to secure the sheet metal to the chassis while following different regulations and passing simulations.

Some thoughts:

To prevent stress from accumulating on certain chassis members, it might be worth looking into increasing the surface area the sheet metal will be attached to the chassis with. Specifically, look into attaching the sheet metal to multiple sides of the square tubing.

Spacers or shims can be added to fill in gaps from CAD inaccuracies, but the chassis would need to be cut if an intersection becomes apparent. Better to design with the intent of adjusting the amount of gap; leave room in the current CAD between chassis members and sheet metal.

Concept 1 has a strong base idea, but lacks the adjustability to fill the gap between the chassis and sheet metal.

Open

Concept 1

Concept 2 improves on Concept 1 by introducing a degree of freedom - a linear movement in the X-axis. This is achieved through the extending rods. In the concept sketch it shows rods, though I think the best course of action would be to use square tubing. In assembly/manufacturing of the mechanism we would join the two plates to the chassis and to the sheet metal. Then, on a square tube mark the gap that would need to be filled and weld everything together (square tube to chassis plate, and square tube to sheet metal attachment plate).

This manufacturing process would allow for gaps between sheet metal and chassis to be rectified and allow for potential rotations in the Z-axis. As a side note, some of the adjustments to ensure a good fit can come from cutting the sheet metal correctly.

Open

Concept 2

A flaw with this method would be the lack of space to put a welder in to bond the joints, assuming the gaps are very small. This would be fixed by removing the chassis plate and welding the square tubes directly to the chassis. If the gap would still be too small, the square tubes would be welded to the chassis and a slotting mechanism would be made between the square tube and the sheet metal attachment plate.

I believe Concept 3 to be the best solution to attach sheet metal to the chassis. In the manufacturing process we are able to allow deviation from CAD to still accommodate sheet metal. In the case steel sheet metal is used, it can be directly welded to the additional tubes.

In the case where aluminum sheet metal is used, a steel attachment plate can be welded on to the end of the additional tubes, something similar to the place for sheet metal in Concept 2. Then the aluminum can be fastened to the attachment plate. However, as discussed in Concept 2, this will create a gap that a welder might not be able to access.

Though I will be moving forward with Manufacturing Process and Materials, any suggestions would be great!

5.0 Materials

With Concept 3, all there’s needed is addition chassis tubes, and if aluminum sheet metal is used some steel sheet metal would be needed.

Ideally, there would be scraps left over in the bay, that way there are no additional costs. Otherwise, more tubes would need to be sourced. The best place to start would be where the original chassis tubes were sourced. So I would need to get into contact with people on the team to look into where to begin sourcing.

The same thoughts apply to the steel sheet metal.

6.0 Manufacturing Process

1. With a gap between the sheet metal and the chassis, a tube would marked to transfer the exact geometry needed to bridge the gap.

2. The shape in the additional tube needs to be cut.

3. The cutout of the additional tube would be welded onto the chassis.

4. The sheet metal or the attachment plate would be attached to the chassis.

   1. If there is enough room, welding would be ideal.

   2. Otherwise, a slotting mechanism or mechanical attachment would need to be made.