Q & A from Kat and Hai-Yue

Here is a section where Kat and Hai-Yue answer questions from the team!

Driving
Question: during high speeds the phoenix shakes back and forth. What amount of wiggle is 'tolerable" when drivers are going at high speeds.

ANSWER:

There are several reasons why the Phoenix wobbles back and forth, and it's important to understand why to in order to determine the safety tolerance. The Phoenix generally wobbles for a few reasons: backlash in the steering system and its linkages, high sensitivity of the steering wheel, wheels misbalanced, and a low caster angle.

Backlash in the steering system can cause the wheel to move independently to the steering wheel. That is, if you hold the steering wheel straight, the wheels still wobble. Backlash can come from a variety of sources, including: the steering wheel to steering shaft coupler, rack and pinion gearbox (spur gear against spur rack will have a small amount of play, guarenteed), rod end (http://www.metasys.net.in/images/rod%20end%20bearing.jpg) backlash on steering knuckles, and rod end slop of the A-arms. To minimize slop, make sure that all the jam nuts are tight against the rod ends (this is something you ought to be checking anyhow), and that's pretty much it. I tried my best to find a helical gear rack and pinion that'd fit our car, but I just couldn't find one. Helical gears have a clean engagement and have very little or no backlash, which is nice. You'd have to custom make a rack and pinion, which is not too hard, but we didn't have time to do it for the 2012 race.

Steering sensitivity is probably your primary issue. Here's the problem: the car needs to pass the U turn test, pass slalom, and figure 8. All of these tests argues for a vehicle that's got a tight turning radius. Now, if you have a tight turning radius, you'd nominally want the steering system to be such that two or three full rotations of the steering wheel makes you have that range of motion (look at your gas cars, for example). However, it has been difficult to find a rack and pinion system that allows two or even three full turns from lock to lock that'd fit in our solar car. Our car only has I think a turn and a half from lock to lock. This is where the steering wheel sensitivity comes from - on one hand the car is constrained by the need to make a U turn in a 16 meter lane (which we passed I think at 14 meters, so pretty close!), and the other side we're constrained by the steering racks available for go-karts, dune buggies, and SAE Formula cars. Steering sensitivity is the reason that I told the team that they should take the rack and pinion gearbox and remachine the rack or swap out the pinion to give more turns from lock to lock.

Our wheels could also be out of balance. There nothing to be done about that - we don't have the resources to properly baance a wheel every time a tire is installed, but it's at least good to know that the wheel might be wobbling up and down might be coming from the wheel being out of balance.

A low caster angle (http://www.ozebiz.com.au/racetech/theory/align.html - scroll down to caster ) can also give straight line stability issues. Our caster angle is about 2 degrees, which is typical for solar cars. Our caster angle can't be changed - it is machined into the A-arms. The two of holes on the A-arms that hold the rod ends are machined off center on purpose - they make the upright lean such that we have the 2 degree of castor. Make sure the castor is in the right direction - that is - the wheel should lean the same way a bicycle or motorcycle wheel leans forwards. If the A-arms are installed wrong, then you might have the wheels leaning the wrong way, and would definitely cause stability problems while driving!

So, the answer is still whatever is comfortable for the driver. Holding the steering wheel tight will reduce steering wobble. Reducing steering backlash will the car stay stable also. But now, at least, you know where the wobbling is coming from, and if you have excess wobbling while the car's steering wheel is held straight, you know that something may be out of whack and you know to check the car now!

Canopy
Question: We have a problem with the canopy unlatching. We put some velcro on it and it holds down for 90% of bumps but still pops open occasionally. Do you have any suggestions for keeping the canopy latched during big bumps?

ANSWER:

Canopy latching is a challenge - we need the canopy to close when we want it closed, and open when we really need it to open. Sounds easy, but it's actually quite tricky

Having the canopy close when we want it closed is easy: we just get a latch that positively locks the canopy down, and we're done. However, with this design, a faulty latch (think: accident) can trap a person inside. The Odyssey had a positively locking latch that worked 90% of the time (meaning, it opened 9 out of 10 times when we wanted it), and I had personally fixed the latching mechanism until it work 95% to 98% of the time (1 in 20 would get stuck or better). I still wasn't satsified, and was intending to fix it when the car burned down. Luckily, the latch and egress worked. If it hadn't, things would have been very bad.

So, how do you make a latch that closes, but doesn't positively lock? The velcro strips was a great idea! The current spring and ball latch works good too, but the pin that latches needs to be re-machined out of steel so that it doesn't wear down as much, and the screw that holds the spring in needs threadlocker so that it doesn't come out.

What I was thinking that could additionally help was a magnetic latch. A magnet works great to hold down the latch. A magnetic tool holder with a on/off switch is even better: http://smile.amazon.com/NOGA-Magnetic-Holder-Bed-Dimensions/dp/B006LLQ65K/ref=pd_sim_sbs_hi_6?ie=UTF8&refRID=00KXW38XTMJ6YAGXKVYG

The on/off magnetic tool holder is a brillant piece of hardware: it works by having two sets of magnets that are either aligned to have it turn on (N-S:N-S) or counter aligned to have it turn off (N-S:S-N). The tool holder is defintely strong enough to hold the canopy down (72 lbs with the one that I found), yet in an emergency, the latch could be opened. You can also make the steel plate smaller than the size of the holder to reduce the holding force. I had left the team two magnetic tool holders from my garage for this purpose! :)