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Post by pinewoodnewbie on Jan 29, 2012 17:24:06 GMT -6
This was my first Pinewood Derby with my son, and relied heavily on websites like this to complete his car. We were second in our pack and now going to the regionals in 2 weeks. My car's average speed was 219mph. The car was built with the all the weight in the middle and towards the back of the (and all weight was under the car). The car was 4.99oz at weigh in. The weights used are a 1 oz screw in strip, 2 nickels, 4 half-ounce fishing sinkers, and 1 quarter ounce weight super glued towards the back left of the car. My questions are should I redistribute the weight to another portion of the car for more speed? In the Pack finals, the fastest car was 226mph, so I definitely will not be able to compete at my present average speed. Another mod I was going to do is use wet sand paper to make the axls more smooth, the ones provided in the box I noticed had slight ridges. Any help would be GREATLY appreciated! Thanks in advance for your help! Attachments:
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tkp
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Post by tkp on Jan 29, 2012 17:43:28 GMT -6
Congrats on the great race and good luck in Regionals!
Quick thoughts....
Weigh in at Regionals at 5.0- nothing less! Make sure you bring weight to get to 5.0 at weigh in. Many scales don't go to 5.1 until you get to 5.05. So 5.04 is good! Be prepared regardless.
Do you know what CM is? This is going to be key. Appears from the pic that you can get more aggressive here.
For axles- there are plenty of good posts here but if you and your son have time and are ready to take it on...then....
• Axels- sand with file to eliminate flash. Then use 400, 600, 800, 1200, 2000 (Walmart has up to 2k grit), grit- 10-15 seconds each on each axle. Don’t reduce axle size! Some professionals go up to 12k grit. My opinion is that I have not seen significant increase in times and it opens the door for more reduction on axle size which is what you don’t want to do.
• Axles- use good chrome polish- to polish axles completely. Set axles in 91% alcohol for 1 hour then clean/dry with fine cloth.
I'll let others chime in but get to 5.0, prep axles and bores and tweek CM if possible.
TKP
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Post by pinewoodnewbie on Jan 29, 2012 17:56:33 GMT -6
Thanks for the thoughts!!! Any and all help would be greatly appreciated. However, I don't know what CM means. I have scoured the internet for the best place to put weights and the consensus was at the center of gravity. and towards the back. I rolled the car on the round pencil and the car was level underneath the black windshield towards the rear of the car, this is where I started to put the weights. No weight was placed anywhere forward. Definitely I plan on tweaking the axls and polishing the tires. THANKS FOR ALL YOUR HELP, but as a newbie, I will need some hand holding going foward. Thanks!
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tkp
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Post by tkp on Jan 29, 2012 18:21:09 GMT -6
Balance it on a pencil and let us know how far in front of the rear axle that is- measure exactly with ruler- be very specific. We'll go from there. If needed, send me an email, perhaps we can discuss on phone as well. However, we want to keep good info flowing here to the forum so let us know what CM is on your son's car.
TKP
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Post by pinewoodnewbie on Jan 29, 2012 20:29:13 GMT -6
I did as you described, the measurement is as shown in the attached picture. I rolled the car on a round pencil (with tires/axl and weights installed). The black smudge below the tape measure is where the car balanced perfectly on the pencil. I assume the ideal placement of the weights is at the center of gravity/mass? I have also researched and found Tungsten is preferable to lead, is that correct, does it make a big difference? Looking forward to your response. If the picture is not really good, the exact measurement from the center of the axl to the center of mass is 1 to 2 lines short of 1 3/4 inch line. Thanks again for your help Attachments:
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tkp
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Posts: 65
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Post by tkp on Jan 29, 2012 22:22:57 GMT -6
BTW- what kind of track will you be racing on?
How much weight did you add to get to 4.99?
Looks like you guys have done a great job, there is just some speed your still leaving on the track.
1 3/4 CM is very conservative and if you and your son have time, see what you can do to get around 1 inch. This will make you competitive and will keep you on the track with most likely no issues if all else is good.
If you want to be competitive yes, tungsten will help as it allows the center of mass in your car to be smaller/compact and therefore the gravitational pull on that center will allow for greater speed on the track. You and your son shouldn't get too crazy but if possible and not too much work, see if you can replace some of the weight you have now with tungsten- IE- perhaps just in front of the rear axle(closer to the nose).
After looking at your pic- I would just keep the weight behind the rear axle to make it easy. Then I would replace the weight in front of the rear axle with tungsten to make to 4.99 (then on race day- at weigh in-tune to 5.0). How much weight is behind the rear axle currently and just curious, what is the weight on the back right side for?
Lastly, do you need to have all 4 tires on the floor? What did your son do here and what are the district rules?
TKP
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Post by Murph on Jan 29, 2012 22:53:09 GMT -6
Hi PWNewbie,
I agree. You can move some of your weight towards the back by drilling into wood and insert the lead weight in the hole.
Spend the rest of the time on overall alignment of the car.
Alignment will get you speed. If you want to know more about alignment, look through the posts on this forum or ask some questions if your car does not track exactly as you want!
Good luck to you and your Scout!
Murph
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Post by pinewoodnewbie on Jan 30, 2012 1:23:36 GMT -6
Thanks for your help! The single weight on the right rear of the car was added on race day as I originally weighed in as 4.82. The one piece brought me up to 4.99. I will remove the existing weights and try to move em around. I will also try to get some Tungsten weights. If I understood your post correctly, as much weight I could possibly move to the end of the car is preferable? Life further back of the axls into the rear of the car. I am not sure of the rules yet, hopefully I will get them during the next scout meeting. I will keep you posted. Thanks again for your help!
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tkp
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Posts: 65
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Post by tkp on Jan 30, 2012 9:42:54 GMT -6
Sure- just ensure your alignment is good and your CM is around 1 inch. Lastly, I believe you were going to mention doing your wheels and axles again?
On race day for final 5.0, use can use small think tungsten disc to add on or tungsten putty. But keep weight centralized if possible.
And if you can do a 3 wheeler- please do- check rules first.
TKP
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Post by pinewoodnewbie on Jan 30, 2012 16:41:46 GMT -6
Thanks for your help. When you say CM should be an inch, that means what exactly. If I understand correctly, the Center of Mass should be an inch from the end of the car? Would that be alot closer to the rear of the car? I plan on tearing out all the lead weights and getting the Tungsten, so all of that weight should be massed all together, correct? Thanks!
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tkp
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Posts: 65
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Post by tkp on Jan 30, 2012 17:40:51 GMT -6
Generally yes. Get CM- 1 inch in front of "rear axle slot". Since you are a newer builder a 1 inch CM would be perfect.
My suggestions earlier were simply to help you and your son get your car more speed, but not completely re-vamp the car with a ton of work.
If you and your son are willing, you should:
address axles and wheels as I shared earlier- be careful here though
Put in/replace with tungsten
get to 1 inch CM
make it a 3 wheeler if you can
Don't get too much more into it as you already have a good car.
If you start removing weight from behind your rear axle, it looks like your son will need to deepen the cavity etc....which is leading to a bunch more work, dremmeling etc. You certainly can do that but this is now starting to change your son's car significantly and I don't know front end weight, wheel spacing, shimmy potential etc and many things will need to be re-tested, validated etc.
I and all the folks on the board are more then happy to assist in either direction you and your son want to go but....
If you want to quickly improve your cars speed I would do the following- (keep car close to current state and less intrusive and don't open the door for track performance issues- ie- shimmy, sliding etc)
replace with tungsten in front of rears and get close to 1' CM
sand/polish the axles/wheels
align and graphite up!
check into 3 wheel rules
You do these things alone, you will have a much quicker car.
How much weight did you add to get to 4.99?
Do you know what track yet?
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Post by pinewoodnewbie on Jan 30, 2012 19:28:58 GMT -6
Thanks for your quick response.
My sons car originally weighed in at 4.88 and was suggested that I add more weight. That one rectangle weight behind the back axl is the piece I added to bring it up to 4.99.
The track we raced on was a metal track for our troop. We had a pack meeting tonight but they didn't have any details on what the requirements are for the regional race. That will be forthcoming.
Not to sound stupid, but 1 inch of CM is one inch in front of the rear axl. So by moving the weights from where they currently are to the back of the car would move the CM towards the rear axl. My goal is to move the CM about 3/4 of an inch of where it currently stands.
I plan on doing that and as I weight for the Tungsten to arrive I will work on preparing the axls. Thanks again
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tkp
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Posts: 65
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Post by tkp on Jan 30, 2012 20:36:07 GMT -6
Sounds good! Good luck on the CM and let us know if you have any additional questions.
If needed and it's a different topic- please feel free to add a new topic/question to the forum! But definitely want to know what Track you'll race on.
Again, good luck and it sounds like you and your son can UP his speed a bit! ;D
TKP
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