pre cut cars

[doct1010]

Ute,
Do you recall were the advantage took place on track? Was it quickly from pin drop, in transition or in the flat? Were the other cars gaining speed? This will help our diagnosis. Also I did not see mention of allowed lube.

[Utecharger]

Ute,
Do you recall were the advantage took place on track? Was it quickly from pin drop, in transition or in the flat? Were the other cars gaining speed? This will help our diagnosis. Also I did not see mention of allowed lube.

Excellent question and one that I have been trying to disect. I have been racking my brain all day trying to remember what happened and I am fairly certain that we would always have the lead coming out of the drop and into the transition but would always lose it right after that. What dynamics would cause that? That is a weight placement issue is it not?

[Stan Pope]

Lots of possibilities here, and some missing data.

1. Decision to NOT rail guide (RR) costs average time, and the cost increases as the track length. This probably does not move a car from 1st place to 8th place.

2. Long spin time is atypical of new wheels. Their lower rot. inertia reduces spin time and makes it less useful for comparison. 30 seconds sounds long for new wheels, but maybe still achievable? All else well done, old wheels probably don't move a car from 1st to 8th in a pack race unless the pack is full of mech engineers / machinists!

3. Rear wheel alignment errors cost lots of time, and the cost increases as the track length. Small errors may simplly create "bind" as they fight each other and cost a few ms to a few dozen ms. Larger errors can put a rear wheel against the rail (occasionally to frequently to constantly) and cost "big time." (My good experience with the ProBody Tool needs to be qualified with the observation that the PBT needs to be augmented with very true axles or some serious rear end alignment as well as front-end work (e.g. indent) that keeps the rear wheels off the rail.) This easily moves a car from 1st to 8th place!

Since you have "for sure" eliminated #2, my vote is #3, aggravated by #1.

Ute,
Do you recall were the advantage took place on track? Was it quickly from pin drop, in transition or in the flat? Were the other cars gaining speed? This will help our diagnosis. Also I did not see mention of allowed lube.

Excellent question and one that I have been trying to disect. I have been racking my brain all day trying to remember what happened and I am fairly certain that we would always have the lead coming out of the drop and into the transition but would always lose it right after that. What dynamics would cause that? That is a weight placement issue is it not?

Not a weight placement issue! Indicates new wheels, good prep of axles and wheels, good lube. Affirms my alignment conclusion.

[Utecharger]

Stan I have to say that I am honored you replied to my post. I have always admired your knowledge of science and how it applies to these derby cars.

As for how I got the new wheels to spin so long....we pair them up with a nail 7-10 days before the race. Then we put them in a ziplock bag containing graphite and every evening we spin them with our dremel tool and the soft cotton polisher attachment. by the time the race arrives they are no longer "new".

As for doing a RR, I have never been comfortable attempting to build one of those but I think we will have to if we are going to be competitive.

I am going to have to review this site and start over from step one with our construction.

[Utecharger]

Stan-

Also I noticed that the car would "shimmy" back and forth ALOT! It wasn't very smooth as it came down the track. Is this caused by the "binding" you are refering to?

[FatSebastian]

Also I noticed that the car would "shimmy" back and forth ALOT! Is this caused by the "binding" you are refering to?

BINGO! Ding ding ding ding ding ding! What Stan said:

Larger errors can put a rear wheel against the rail (occasionally to frequently to constantly) and cost "big time."

[FatSebastian]

As for how I got the new wheels to spin so long....every evening we spin them with our dremel tool and the soft cotton polisher attachment. by the time the race arrives they are no longer "new".

Ute, we did some before-and-after experiments, and felt that spinning up the wheels too much wore them out. Has anyone else experienced a slow down in spin times after "breaking in" wheels?

[Utecharger]

Thank you all for the advice!

When we would push the car slowly it would track fairly straight. If we gave it a more for forceful push it would track slightly to the left. It would also, ever so slightly, go to the left when we let it coast down our plank. I guess I thought that it wouldn't be a big deal especially since I wasn't exactly sure how to correct it.

So what is the overall opinion on the pro-body tool and am I using it correctly? We drill one side at a time, with a hand held drill while it's clamped to the block. this way never seemed very accurate to me but I thought "hey the bit barely fits in the hole so it has to be straight, right"? I am sure its not.

[FatSebastian]

I thought "hey the bit barely fits in the hole so it has to be straight, right"? I am sure its not.

You can check if the rear axles have any toe with a square. Stan also has posted alignment procedures. For now, we prefer drilling holes by hand with a pin vise.

I am going to have to review this site

If you spend some time searching the board, you will be rewarded.

[Gameday]

FatSebastian,

I have to say, I LOVE your posts. Great info.

My question, "how do you use a pin vise?"

Thanks.

[FatSebastian]

I have to say, I LOVE your posts. Great info.

My question, "how do you use a pin vise?"

A pin vise is basically a jeweler's screwdriver with a drill bit installed. Use it just like a screwdriver then, just twist and push (the Pro-Body tool acting as the guide). With a sharp bit, even my son can do (does) it.

[Utecharger]

Thank you for all the help yesterday. I went home last night and re-adjusted the rear axels and wasn't suprised how much better it ran. I guess you could say I got lazy. We have been winning the last couple of year with great weight placement and tires but horrible alignment. It finally caught up to us with the competition.

Here was our car this year. My son has had a really rough year (diagnosed with type 1 Diabetes) and I was going to build him whatever car he wanted even if it was a bus. Luckily he chose a guitar and we made it work. I think it would have been a lot faster had the alignment been on.

[Teeeman]

If the cars did not have lightened wheels, low COM and good alignment are next to consider..


hope I'm not repeating info above.


-T

[FatSebastian]

Here was our car this year. My son has had a really rough year (diagnosed with type 1 Diabetes) and I was going to build him whatever car he wanted

Ute, the guitar car looks awesome. You and your son did good, and his health is in our prayers.

I think it would have been a lot faster had the alignment been on.

Glad to hear that you may have discovered an issue that can help next time.

[whodathunkit]

If your talking precut cars made by the pinecar brand.. the wood used is sugar pine! it is some what lighter in weight. then the pinewood used for BSA kits!