Year 3 in the books - excitement, mystery, technology

General discussions for car and semi-truck racers.
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ironband
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Year 3 in the books - excitement, mystery, technology

Post by ironband » Mon Jan 22, 2018 5:54 pm

We had our Pack Pinewood Derby this past Saturday.

I was rolling out the new instant replay system as well as my computer integration. There were a few glitches, but for the most part, everything went pretty solidly.

My son wanted to focus on getting a shiny finish this year, so we applied multiple coats of primer, paint, and clear coat, sanding rough spots in-between. He wanted a technology themed car, so I found a stencil with some circuit lines and helped him cut them up and tape them down to make a fun design.

Initial stats on his car:
Tungsten Weight
0.75" COM
2.5 degree bent axle rear
1.5 degree bent axle FDW
3 wheel rail runner
2" drift over 3 feet
Axles polished to 2500 grit followed by Mibro #6
Wheel Bores prepped with [no advertising for this vendor] 3 step wheel polishing kit
Modified Curvy wedge shape

I say initial stats because we got to the derby early so I could help set up the track. As I was working, I heard the unmistakable sound of a pinecar hitting the floor. I turned to see my son picking his car up. He had gotten a little antsy while showing off his car to a friend and dropped it. We checked for cracks, did a quick check to see if the rear wheels were migrating outward, quick check to see if we were drifting. First roll, didn't drift. Second roll, drifted. That was odd. Third roll, drifting. OK. I explained that we had no way of knowing what was up with the alignment since I didn't bring the board, and there wasn't really time anyhow to make any big changes, we'd have to race it as it was and see what happened. I finished helping to set up the track then worked with him to check in.

I knew that the official scale we have used for the last two years was only accurate to the nearest 0.05 ounce, so at home I had weighted both of our cars to 5.02 ounces, knowing that they would show as 5.00 on the official scale. I was a little surprised to see a brand new scale at the check in table, and darn if he didn't weigh in at 5.02 and I didn't weigh in at 5.03. It is amazing how much wood you have to remove to loose 0.02 ounces :) After a few minutes with the drill, we applied graphite, cleaned the wheels off, and checked the cars in.

I went back to my set up work, getting all the electronics squared away. Tested the integration with the computer and it appeared to be working ok. Set up the instant replay to find that my ancient monitor with the VGA to HDMI didn't want to play with the splitter I had gotten. We had to go with a single replay monitor, but we only had a field of 17 cubs, so I figured it would be sufficient for this year.

With everything set up, projecting, showing, and clicking, we finally started with opening ceremonies followed by the adult/sibling/den chief race. I took that competition handily with my car, similar in build to my son's, but with lead internal weight and stacked zinc weight on top. I was disappointed to find that the replay was giving a lot of speed blur we hadn't seen in testing, and realized it was because we tested outdoors in sunlight and we were indoors in a dimmish hall. I made a mental note to add LEDs to illuminate the finish for next time. Even so, folks really enjoyed the instant replay!

I attached my phone to the top of the finish gate to capture more footage and gave my shutter clicker to our den chief, asking him to record as many races as possible. It gave out after about 6 heats and I had to dig out a charger to continue, so my video misses a few heats.

It was on to the main event. We race on a point elimination (ladderless) system, zero points for first place, 1 point for second, 2 points for third. We set the system to 10 points as we only had 17 racers.

In the first race, my son's car beat last year's second place winner by about full car length. That car had a pretty serious case of the wiggles coming off the curve as you can see in the video. He was feeling pretty confident. Next heat was a pretty easy win, and he started to figure that the drop hadn't had any real effect on his car.

Third heat, he lost to a fast looking car with a quick start bar by 0.012 seconds. After a win in the fourth heat against two other cars, he went up against this car again. This time he won by 0.006 seconds. Because of the way the ladderless elimination works trying to pair the faster cars with each other, he went up against this car for most of his remaining heats. It was really thrilling because they jockeyed for position back and forth. A loss by 0.006, another loss by 0.024, another loss by 0.019, but then 4 consecutive wins by 0.004, 0.007, 0.012, and 0.005. Then two losses by 0.010 and 0.017. Three wins by 0.001, 0.001, and 0.004 and it looked like he might take it. But then the other car took the last four races by 0.021, 0.013, 0.012, and 0.007 to win 1st place and solidify his 2nd place finish.

This car got a huge jump on the downhill, but on the straight my son's car always gained. It really depended on how far behind he was at the end of the slope - if it was somewhat close, he'd catch him. If not, he wouldn't.

We have a manual start on our track. I had never given any credence to the concept of the quick start front end, and originally was trying to figure out how he was getting off the line so quickly. The other dad and I talked (we're friendly) and I asked about his wheels. To my surprise he told me he had tried shaving the box wheels, but didn't like the way they came out, and wound up going with the Revell wheels from Lowes. That explained why they were so shiny, but didn't explain why his car got off the line so quickly.

It wasn't until I went back and looked at video that I realized it was indeed the quick start front end that did the trick. With the manual start, if the cubmaster opened the gate more quickly, the cars got off at the same time. If a little more slowly, this car would get off the line and build a decent lead.

Now, there was a terrible coding error in my arduino code that made the elapsed times useless (I used a serial read command that waits for a full second, so when you opened the start gate, up to a full second could go by before the timer started), while preserving the integrity of the differentials. It was very interesting to look at the differentials between my son's car and the 3rd place car, which covered less than 0.01 seconds regardless of lanes etc, vs. the differentials between my son's car and the 1st place car, which spanned 0.036 seconds with a standard deviation of 0.0109. Since, on average, his times were 0.0056 seconds faster than my son's, the race truly could have gone either way.

Nothing in our rules against it! Well done to that dad and his son for sure! It was super exciting to have the first and second place trade spots and made for a thrilling race. And, honestly, it was good to have my son get 2nd place this year. It was good to see him cheerfully shake hands with the other scout, and then sit down to talk about how they built their cars and give each other speed tips for next year.

Did the drop affect things? Hard to say. After the race he played with his car a lot. When we got home, drift was definitely not at what we had set it. He asked me if I thought he might have won if he hadn't dropped his car. I told him honestly that we'd never know, and that was ok. The important thing wasn't the place - it was the time we spent and the fun we had! Still, next year he'll be more careful, I wager.

During exhibition racing, I raced against my son's car and beat it handily. Near the end, the first place winner tapped me on the arm and asked if he could race me. I wasn't going to suggest it, but since he wanted to, we passed the cars up to the cubmaster...

Was the gate opened quickly? I don't know, but he was a little shocked to see my car beat his by a pretty fair margin. I shook hands with him and his father and congratulated them on a race well run. I told the dad I hoped to see him in the adult race next year too... :D

Next year, though, I'm building a solenoid gate for our track...to ensure that the elapsed times we get are consistent. No other reason. Seriously. ;)

If you read this far, please enjoy this recap video I put together using the footage from my cell phone and the raspberry pi instant replay. At one point, a car looses a wheel as it comes across the finish line. That was fun :)

https://youtu.be/wE1gGdM31gc

So, this off season, I need to fix my code, build a solenoid gate, add another camera angle, add a button to replay the last instant replay (we had one finish disputed, but it turned out to be that the camera got knocked on an angle), illuminate the finish line, and do some other cool stuff. I'll keep you posted :)

For next year's car? I'm thinking don't drop it will be the first improvement. This year we did bore prep, but I'm thinking we could do that better than the [no advertising for this vendor] kit with some Novus 2 and perhaps some wax (I suspect that the step 2 polish in the kit actually is Novus 2). I think next year we'll drill canted holes for the rear instead of bending axles, and then maybe...I don't know? Fenders?

We'll see...

Andre
Last edited by ironband on Tue Jan 23, 2018 10:01 am, edited 1 time in total.



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whodathunkit
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Re: Year 3 in the books - excitement, mystery, technology

Post by whodathunkit » Tue Jan 23, 2018 7:38 am

Cool video enjoyed it!


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What type of automobile can be spelled the same forwards & backwards?

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