The chassis can be thought of as the biggest bracket on the solar car; everything else has to attach to it. The chassis needs to be designed to support the weight of the driver and battery
Welded Tube ChassisEdit
Teams have built solar car chassis out of tube steel, aluminum, and even titanium for decades.
- At the moment, this wiki is entirely the product of University of Minnesota alum. Our team has never built a tube-frame chassis before, so have really have no other information, or even tips, to put here. Someone should populate this section.
Composite Monocoque ChassisEdit
The alternative to a welded tube-frame chassis is to build the chassis out of composite panels. You can choose to either use prefabricated panels from companies like Teklam or Hexcel, or alternatively choose to mold your own panels. Prefabricated panels have a much better strength to weight ratio than most teams have the resources to manufacture, but then you are limited to building the chassis out of flat panels. On the other hand, while molding your own chassis will allow much more flexibility with packaging the chassis within the shell of the car, it will probably end up heavier than a chassis built out of professionally manufactured panels.
There are two major concerns with a composite chassis: How is the chassis bonded together, and how are components like the roll cage and suspension attached to it.
- Chassis bonding: You have two basic options for bonding the chassis together: glue the joints, or do a wet-fabric layup over the joints. You can also do both. The strength depends entirely on your glue, fabric, and resin system. There are very few hard and fast rules for what works and what doesn't, but keep the following in mind:
- Surface prep is important here more than anywhere on the car. Use some low-grit sandpaper to lightly rough up the surface of any composite you are going to be applying glue or resin to, and clean with with alcohol afterward. Dust from the sanding or grease from your hands will greatly reduce the strength of your joint!
- Make a whole bunch of small test articles using different adhesives and test them to failure. This will A) Give you experience in the method of manufacture, and B) give you a good idea of both the failure mode and how much force the entire combined glue/resin/fabric composite system can withstand.
- Bracket attachment: Todo: discuss metal inserts vs. fiberglass plug (like how cirrus does it) vs. aluminum or plastic aircraft floor grommet.
The Minnesota MethodEdit
The University of Minnesota Solar Vehicle Project has been building their chassis out of prefabricated composite panels since 1995, and over the course of 8 cars, has refined the process considerably. For a detailed discussion on the UMNSVP's thoughts on chassis design, see this page.
The suspension protects a vehicle from the impact of driving over bumps and pits in the road, and increases the driver's comfort. If a car is rigid, then the frame (and thus anything attach to the frame) takes the full force of an impacts the car encounters due to debris, holes, ect. However, a suspension is designed to allow the wheels to move and absorb the impact. This movement mainly involves a vertical component of wheel movement, but usually involves some hortizontal and forward/backward movement as well.
Double Wishbone - Most common type, a type of four-bar linkage
MacPherson Strut - Not really used in solar cars, but nonetheless interesting to learn about
Swing Arm - Most common and simple type of rear suspension
Double Wishbone - Sometimes people want adjustability, or steering, in their rear wheel as well.
Aluminum wheels can be bought from NGM for approximately $600. These wheels tend to have fatigue problems. Carbon Fiber wheels can be bought from GH-craft for approximately $1300. GH-craft is a Japanese company, so it helps to have someone who can speak Japanese. The Northwestern Solar car team likes these wheels.
Changing Tires (Iron Man Style)Edit
Changing tires without tire irons makes it much easier to seat the tires on the wheels. If you are attempting to seat a tire with a tube it is very important not to damage the tire with tire irons. Damage to the tire makes it very difficult to seat. The following technique is not reliant on the users’ strength. It relies on body weight. 90 lb. girls can change a tire in this manner.
You will need: KY-jelly, valve stem tool, and an air compressor, (and a tire and a wheel)
- 1. Place a piece of foam core on the ground this is your pad,
- 2. Place the wheel flat on the pad
- 3. KY jelly to the bead of the tire, get a good film on.
- 4. Hook the tire on the wheel and kneel on it until it goes on (be sure the valve stem does not interfere)
- 5. Place a ratchet around the circumference of the tire and tighten.
- 6. Remove the valve stem with the valve stem changing tool
- 7. Inflate the tire until it seats: you should hear 2 pops.
- 8. Quickly, before it unseats, screw the valve stem back in
- 9. Inflate to proper PSI.
- 1. Remove the valve stem (air hisses out fast)
- 2. Break the seating seam of the tire on the wheel
- 3. Making sure the valve stem does not interfere, do #4>>>
- 4. Position the wheel so the tire is resting on the ground and the flat of the wheel is parallel to your chest
- 5. Lift the tire relative to the wheel, with your thumbs, until you can see light coming between the tire and the wheel
- 6. Push the tire forward relative to you chest
- 7. Lean Straight down on the tire, until it pops off
they dont help you go fast so just dont bother my dude