This week: Testing and data acquisition

It’s a few weeks after the 2013 competition, and we are already on our way to designing the 2014 car.  We held elections and all the new system leads are designated.  This coming season, I will be in charge of the steering system, as well as take on the new position of technical director.

The technical director has two main responsibilities: keeping the full car Solidworks model and being in charge of the team’s new data acquisition system.  Last year’s full CAD model is shown below.

Having an entire model of the car helps immensely with the integration of all the subsystems.  Being able to measure a distance in the computer model, then use that to locate your parts rather than some arbitrary placement means that we will actually build the car that we designed.  It also helps us figure out issues with packaging (fitting all the parts in) early, while still in the design phase.  In the past, these sorts of issues have been solved with on the spot design changes, which often result in a “thrown together” looking car.

This past year, we discovered just how important testing data is.  Our testing told us to shorten up the car, increase the turning radius, and to change our shock settings for different events.  All of these together definitely made a better car, as we scored better than Cal Poly has in the past nine years.  Testing data helps us confirm (or disprove and change) all of the assumptions we make during our designs.  A senior project of two of the older members left us with a data acquisition system to help us refine our testing techniques in the coming years.  The system can measure: speed, shock travel, front and rear wheel speed, engine rpm, overall accelerations, and steering angle.  Individual wheel speeds, when compared to the speed of the car, give us data about slipping of the tires, a very important aspect of off road racing.  Steering angle and shock travel both are very important for the design of the steering and suspension.  Engine rpm can be used to try to optimize our use of the competition’s regulated engine.  By tuning our CVT (Continuously variable transmission, Blog Entree #1) to maintain the maximum engine rpm at any speed, we can pull as much power out of the engine as possible.

I look forward to the coming year of Baja, acting as the technical director and steering lead, and thank you for reading my blog.  This will probably be my last entree since I was only doing this for my technical writing class, but who knows, maybe I will feel the need to chronicle my adventures as the technical director.  Until then, thanks for reading.

This week: Ergo

When hurdling along at 30 mph, bouncing off of rocks and logs and whatever else the trail throws at you, driver comfort must be taken into account during design.  There are many things about a car that effect driver comfort.  These include several aspects of the steering wheel, pedals, and shock settings.

As far as steering is concerned, wheel position, steering force, and steering range are all important.  The wheel position and angle are mostly personal preference, so we just check the placement with numerous experienced drivers before finalizing it.  Steering forces and the range of steering angle have more significant implications while driving.   Steering force is the amount of strength it takes to force the wheel to turn.  Modern automobiles have power steering to keep steering force low.  For our smaller vehicle, we don’t have to go to this extreme; in fact we have to make sure that there is sufficient steering force for the wheel to give some feedback to the driver.  The range of steering is important, since hand over hand steering, shown in the image below, is not preferred for off-road driving.  When you are being bounced all over the place, the last thing you want is to take your hands off the wheel.  Additionally, this type of car uses its full range of steering much more often than a road vehicle, as it must make tight corners and rapid steering movements.

Source: http://www.nzta.govt.nz/resources/roadcode/gfx/steering-hand-over.gif

Shock settings can greatly affect the comfort of the driver, but potentially at the loss of performance.  The opposite can also be true, for instance, we discovered that very stiff shocks in the rear were good for maneuverability as it made it much easier to slide the rear around tight corners.  The stiff shocks, however, made for a very rough ride on longer drives.  As a result, we had to compromise between performance and comfort for the endurance race.

The positioning of the pedals, as well as the distance they must be pushed, both play important roles in the feel of the car.  Touchy gas or brake pedals can make a car jerky to drive, so the throw distance of the pedals should be designed accordingly.  Additionally, the pedals should be positioned in a way that the driver’s feet and legs are comfortable when the pedals are not being used.  Following this logic, the driver’s leg should be comfortable while not putting any pressure on the brake pedal, as that is the most common position for that leg.