Super Track Pack Race

[Tony_in_NYC]

Howdy everyone!
We had our PWD for the pack on Friday and it is run on a SuperTrack. I was around here last year asking some questions, not sure who recalls. Last year, we came in 4th. Our best time was 3.14 seconds. I found this forum a bit too late to help me for last year race, but this year, we came in second. My son picked another difficult car to carve, but it came out ok. Here is a pic
2015_57Tbird by bighead421, on Flickr

So, running on a Supertrack, this is what we did:
DFW on the left, steering to the left 2.5" over 4'. On the first pass, we ran straight until we hit about 8 feet from the end of the track in lane 4, then we zig zagged until the finish. Ran a 3.073 in lane 4.
Here are our times for the 4 passes:
Pass 1- Lane 4 - 3.073sec
Pass 2 - Lane 1 - 3.1654 sec
Pass 3- Lane 2 - 3.1364 sec
Pass 4 - Lane 3 - 3.1567

My results were typical. Lane 4 was the fastest for everyone. Now, in lanes 1, 2, and 3, my car was wiggling from shortly after the transition until the finish. I thought maybe the steer had gotten messed up from the crash box finish, but it is still the same 2.5 inches over 4feet that I set it at before the race. I think the wiggles came from bad joints.
My question is, would more steer help stop the wiggles after they start, and if so, would more steer also slow me down before the wiggles begin when I hit a bad joint?
Or, since this is a SuperTrack, that nobody seems to have much experience on, would less steer, tring to go straight as possible, stop the car from banging side to side after hitting a bad joint? I think the banging happened because it was trying to correct itself back to the left side after being pushed to the right by the bad joint.
Also, thanks for sharing so much info here. Helped me to get into the top three for my son's age group. He was so upset last year when he didn't get a trophy.
Any thoughts would be appreciated. Probably should have gone out for a beer with Laserman before this years race.
Thanks,
Tony

 

[Kinser Racing]

With really bad joints as high of a degree of bend as possible on the steer axle is best. It helps the wheel roll more easily over the joints because the radius of the wheel in front won't touch the joint and as the wheel rolls over the joint it'll transition more smoothly as the bottom of the wheel passes the bad joint. It will however make it harder to fine tune the steer. 2.5" is not enough steer IMO, 4"+ would be better. I have never been able to get away with as little as 4" of steer on a big wheeled car. COM will be a determining factor on steer. The more aggressive the COM the more steer it mat require.

 

[Tony_in_NYC]

Thanks for the quick reply Kinser. My COM is about 1.5 inches in front of the rear wheels. Due to the design my son chose, which if you can't tell, is a '57 Thunderbird, I had to hog out the bottom of the car just to get to 5 oz. It started out at 6 oz because of the full fenders and the roof. So the joints that were the issue were the guide rail joints. They were off by a tiny, tiny bit, but enough to push the car to the right. Then my car would steer back to the left and bounce off the rail to the right again. I suppose more steer wouldn't hurt. I ran negative cant on the rear wheels and negative cant on the DFW per another thread on here.
One thing I am still confused about, should I steer towards the DFW so that the DFW runs against the rail, or steer towards the NDFW? I am currently steering towards the DFW so that the DFW runs against the side rail.
Unfortunately, I don't have a test track so I can't test if any adjustments affect my times. So 4" or more of steer over 4feet?

 

[Quicktimederby]

Super Tracks can be very difficult to tune for. The inconsistency in the lanes can kill you, if the CRASH BOX(stop box) doesn't get you first. Some of the key things is to have your DOM wheel on a neg. cant, not a positive. Also narrow the DOM side rear of the car to keep the rear wheel from dragging. Also put more steer in it, like Kinser said at least 4 inches. There drop is much more agressive than the Best Track 27.1 deg.
The Car looks AWESOME!! You should post more pictures of it in the photo section.

 

[ngyoung]

You are doing the right thing steering into the DFW. The goal is to convert as much potential energy into kinetic energy as possible. You only want have 3 wheels touching the track and it takes less energy away from the car when a spinning wheel is along the rail then a non-spinning wheel. If you steer into the NDFW you are essentially running a 4 wheel car since all 4 wheels will be using up rotational energy to get up to speed and taking away from your kinetic energy.

As for amount of steer listen to Kinser and QT.

 

[zigzag]

First of all - nice looking car. I suspect the COM cost you a little time.

Do you happen to know if you were running on a 35 or 42 foot track?

My daughters troop raced on a 42 ft track - and I had the car set up to run straight. For the most part it appeared to run clear of the rails out of the transition. Next time round - I may change that up and will get one of the wheels off the ground (although we are required to use the pre drilled axle slots).

I am new to this so the other guys responding are certainly the ones to listen to....

 

[Kinser Racing]

So, does the Super Track have a center rail or no. From QT's post, I quess no. Sorry I didn't realize that.

 

[zigzag]

So, does the Super Track have a center rail or no. From QT's post, I quess no. Sorry I didn't realize that.

The Super Track does not have a center rail.

 

[Vitamin K]

So, does the Super Track have a center rail or no. From QT's post, I quess no. Sorry I didn't realize that.

The Super Track does not have a center rail.

I was starting to wonder...I think perhaps y'all are thinking of the Derby Magic track?

So...probably want go with a straight-runner car, correct?

 

[Quicktimederby]

You still want the car to run the rail. You just have to reverse a few things. As far as the track imagine looking at a over sized Hotwheels track and you'll get the idea.

 

[Tony_in_NYC]

Yup. Its an oversized Hotwheels track. I will add more steer and see what happens at the district races. Thanks for the help fellas!

 

[Tony_in_NYC]

Thanks for the compliments fellas. My son worked his ass off sanding that car. I used double stick tape to put sandpaper onto shaped blocks and drew lines on the car where he had to sand to make the fins. I basically cut out the main block for him, then we glued on the fenders, then he sanded the shape. He sat for 5 hours sanding that car to get it to look how it does. I sat and supervised. I am really proud of his hard work. Two parents at the races recognized the car as a '57 T-bird! Turns out, they had recently sold their '57, so they were very familiar with the shape.

Zigzag, why do you think the wiggles might have been caused by the COM? Was it not far enough back? It would take a lot of work to move it further back.

Here is a pic of the car we made last year (I did pretty much all of the work on it. My son didn't want to do anything to ruin it and refused to work on it for more than 10 minutes at a time)

Here is the bottom. I had to do the same thing to the T-Bird to get it to make weight.

I covered the hole in the bottom of both cars with clear packing tape.
I will add some more pics of the T-Bird later.

Again, thanks for your help. I appreciate all of the info you guys share. We got a trophy this year as a result.

Tony

 

[ngyoung]

It seems like at the pack level that you are in reach to take first regardless of having a automobile body style that isn't aerodynamic. At districts you have a higher chance to run into more cars that may be doing some of the same things you are to gain speed but using typical flat or wedge PWD bodies. For this year I think just adding more steer like QT suggested is about all that you can do to improve your times on a track with rough seems.
If you are using those slot covers on your current car I would consider removing them and take their weight to put in the back. You have a pretty conservative COM so anything to move it back should contribute to your wiggling problem. Most of that seems to be track relative vs alignment issues.

In the future I would consider making a thin 5/8" ladder style chassis with the pine block similar to the the majority of the cars you see in the league and adding any design features like the fenders and cabin using basswood or balsa. You can use thin super glue to stiffen and harden up the balsa when shaping and sanding. Basswood is a little heavier than balsa but less fragile and may be easier to work with for small pieces. That will at least get the body weight down to be able to get more weight moved to the back. If the level of competition remains the same this change to building up the body may be enough to get your scout's car to the top in the pack.

 

[Tony_in_NYC]

Yeah...I wanted to make a thin car but the kid wanted a T-Bird. I didn't use the axle retainers. Thanks for the tips, but I am confused a bit. You say moving my COM back will contribute to my wiggling problem? As in, make it worse?

 

[ngyoung]

I was saying that you are far enough forward where any more weight that could be cut out of the body and added to the back is unlikely to get it into the aggressive CoM range. The CoM that you stated is on the conservative side and I doubt is a major factor in your current wiggle issues. Stability issues from CoM don't really become a problem until you start going under 3/4". For league there are many that push close to 1/2"

It is OK if your son wants a realistic car design. Aero counts but is much lower of a priority then alignment and wheel/axle prep. The balsa or basswood suggestion is just an alternative to build the same thing but much lighter. Having just a thin slab of pine to hold the weights and axle while building up the body using the lighter wood will help you not have to hog out all that pine later when your car is done. You will be able to get a lot more added weight at the back vs only removing weight from the front to get under 5oz. Think of a real car's strong frame and light body paneling.

 

[Tony_in_NYC]

Thats a good idea. If he wants another real car next year, I will do as you suggest and use balsa or some light wood. I have a bunch of really light cedar off cuts from my other hobby that are not quite as light as balsa, but very strong and stiff.
Thanks again for the help.

 

[Tony_in_NYC]

We had the district races yesterday and we took first place for the wolves. Our car was also the third fastest car out of 106 cars!
I added a bit more steer, 4" over 4'. Unfortunately, we had an event at church and were not able to watch the races so I don't know if the wiggles were stopped by the added steer. I also pulled the axles and used pledge on them which I did not do before the pack race.
I wanted to say thanks to everyone for your help. We are going to be racing in Times Square for what they are calling the Pinewood derby world championships. My son is over the moon happy with his first place finish. We arrived just in time for him to hear his name announced as the winner for the wolves. He was in shock but ran out to get his trophy with the biggest smile I've seen.
Thanks again!

 

[Kinser Racing]

Congrats Tony!

 

[Tony_in_NYC]

Congrats Tony!

Thanks Kinser!

 

[DEW36]

Congratulations!!!