Need advice for pinewood derby project

Thread Starter

strantor

Joined Oct 3, 2010
6,782
My company has an annual pinewood derby. It is on April 12. I have the kit & I want to make a record breaker. I will be in the outlaw powered class. That means I can put a motor or whatever kind of propulsion on it. I can't use compressed air, C02, or combustibles. I don't have to use the regular pinewood derby wheels either.
A coworker gave me a decently high powered ducted fan that runs on 5V; I think it was from a PC CPU that he was going to use but now he's decided not to compete. The top performers have usually been ducted fan cars, but I don't think that using thrust against air is the best option, when I can use thrust against the track. I think it would be better to power the wheels - but, since the wheels would be prone to slippage on the slick track, I thought about making a tracked vehicle. May be as simple as cutting a groove in the center of the wheels and stretching a large rubber 0-ring from the front wheel to the back wheel. Also I though it would be an advantage to make it teardrop shaped. Does any of this sound like a good idea? I've never built a pinewood derby car and not sure. just looking for ideas.

'There was a team of engineers a couple of years ago who made one that set the record. I wasn't there, but people who were there said that it had no visible propulsion system and it's internals were some big secret. The only clue was that it had an LED on the front. Rumor has it, it will be competing this year. I want to beat it.
 

spinnaker

Joined Oct 29, 2009
7,830
Make a rail gun car. You will beat everything going.

More practical a model rocket motor. Maybe combined with a maglev system? :)
 

Thread Starter

strantor

Joined Oct 3, 2010
6,782
Make a rail gun car. You will beat everything going.

More practical a model rocket motor. Maybe combined with a maglev system? :)
I actually could make a rail gun car, but I would need a launching base. Launching bases are allowed, but the weight of it counts towards the weight of the car, and the car has a weight limit. I couln't get help on AAC with that too :(. I will have to see what weight I have available for the base.

Rocket motor has combustible propellant, not allowed
 

Thread Starter

strantor

Joined Oct 3, 2010
6,782
I love Pinewood Derby cars!! (Built several, even built a competitive track.)

Do you have the rules in PDF you can post here, or a link?

:) joe
No, it's on the company server, but I can cut & paste:

Each car participating in the HCS powered race category must pass the following requirements:

P1. Measurements: American (metric)

A. Width - Not to exceed 3 inches (7.62cm)
B. Length - Not over 14 inches (35.56 cm) ) including any parts that are left behind at the starting gate.
C. Weight - Not over 8 ounces (226.80 grams) including any parts that are left behind at the starting gate.
D. Height- Not to exceed 4 inches (10.16 cm)
E. Center Rail Width Clearance - 1 3/4 inches (4.5 cm) car must be able to operate on track with the two ridges approximately 1 ¾ inches apart and approximately 1/8 inch wide each. Keep in mind the shut down area of the track is a raised flat ridge that may damage cars without full clearance or may not stop a car with more than 3/8 clearance.
F. Bottom Clearance - 3/8 inches (.95cm) is adequate, but not required. The car must be able to operate on track with the two ridges approximately 1 ¾ inches apart and approximately 1/8 inch wide each. More clearance may prevent the car from stopping in the shut down area and other arrangements to stop the car may be necessary.​

P2. You may not use any car body that competed in a previous year’s event – the car body must be built for this year’s event.


P3. Wheel guidelines for Powered division are as follows:
A. Wheels must be 4 inches (101.6 mm) diameter or smaller.
B. Wheel surface that touches the track cannot be metal or mark aluminum.
C. Wheel hubs may be made of metal, but may never come in direct surface contact with the track.
P4. Wheels may be polished and/or reshaped as long as they still meet the requirements in rule P3
P5. No part of the wheel that comes in contact with the track may be painted.
P6. If the car does not have at least 2 wheels, all surfaces that come into contact with the track must be significantly softer than the track and must be non-marking. If you plan to try this, please consult EARLY with the tech inspectors!
P7. Lubricants must be dry on the axle at race time. Wet, oily, or greasy axles are not allowed. Over-application of lubricant which results in excessive shedding onto the track is not allowed. Approved lubricants include (but are not limited to) graphite, Teflon, and Nyloil.

P8. Body design may be enhanced by adding stable materials such as plastic or metal. All additions must be firmly attached.
P9. When race is staged, no part of the car may protrude in front of the starting peg.
P10. Any axle type is allowed.
P11. The following modifications are PROHIBITED:

A. Propellants, burning material or compressed gas
B. Hazardous materials
C. Glass or fragile parts
D. Paint that rubs off or smudges
E. Exposed propeller blades
F. Anything that will interfere with another car by design or accident.



P12. Cars that do not meet racing specs may be entered in the show category.
P13. Racers may opt to stage their own cars and make adjustments that are designed into the cars. The cars cannot be lubricated or repaired, only adjusted (set, turned on and off, etc.). Changing batteries is allowed.
 

Thread Starter

strantor

Joined Oct 3, 2010
6,782
Pinewood derbies seem to have come a long way since I did it in the boy scouts...
well for boyscouts, it's probably still the same. Keep in mind, this is for a company event; a company that prides itself in it's engineering prowess.

There are 3 classes. This is the most extreme class. The first class is the same as boyscouts.
 

KJ6EAD

Joined Apr 30, 2011
1,581
Way back when I competed the biggest speed killers were wheel wobble on axles and wheel scrub on the track. I wonder if small guide wheels in the undercarriage on vertical shafts would be a good way to prevent wheel scrub. Lot's of people worked hard on aerodynamics but that never seemed to be much of a factor.
 

mcgyvr

Joined Oct 15, 2009
5,394
What about using a wind up spring setup as your "motor"... Wind it up..and let it go.. you're down the track in a few seconds if that.. Traction will be important.

It can't be tough competition if "ducted PC fans" are last years champs. You are right..Thats not the way to go..

How long is the track?
 
What components of the “kit” you obtained are required on the finished car? Can you scrap the kit and build entirely from scratch? If so, I’d look into a custom carbon fiber chassis. As “pretty” as the body can be decorated, it is cosmetic and adds weight. Though, having a “body” can legally get you past the rule “P2. You may not use any car body that competed in a previous year’s event – the car body must be built for this year’s event.” You may then perfect the chassis from year to year, depending on the intent of Rule P2.

How tall are the lane separation guides? If the separation rails are only half an inch tall, “four inch wheels” (P3A) would probably hop right on over. (grin)

KJ6EAD is correct, aerodynamics doesn’t play much of a role at those speeds. One year, a hollowed out Pinewood Derby car shaped and painted like a full sized flat nosed school bus took grand prize. But “sleekness” has its place.

I hope the judges use a real scale for weigh in. One year, the hosting troop used a kitchen dietary scale which was so out of whack most racers spent the pre-race time shaving weight. (We built our car using an extremely accurate balance scale!)

Slightly angled foam glued to the bottom of the vehicle makes for an excellent brake and is very light weight and durable. You'll have leeway in ground clearance.

Are you permitted to attach a tiny magnet to the “starting peg?” (P9) That would give you a trigger to operate a tiny reed switch on the front of the car. I don’t know if I’d rely on a mechanical contact switch. Depending on room lighting, one might consider a tiny LDR against the peg.

How many times does your car race? If only once, running a 1V motor at 5V (windings smoking as the car flies down the track) (grin) may be a consideration. We’re hopping into the complex aspect here, but ramping speed from start may be important. “Givin’ ‘er all ye got” out of the gate may cause ‘er to wheelie and flip over. Semi-rigid rubber tires comes to mind, time to study the R/C parts websites.

You don’t have much time, April 12 is right around the corner. Get a neighbor to build you a single lane test track, you don’t want any unanticipated surprises come race day! Our test track was made from inexpensive counter-top “plastic laminate” scrap from the lumber yard. It goes without saying, our cars were not powered. (grin)

How come none of the places I ever worked had fun events like this? (I ate some fouled potato salad at a company picnic one time, but let’s not count that!)


:) joe
 

John P

Joined Oct 14, 2008
2,025
Do the rules actually allow powered wheels of any kind? I think that's why people use rockets and CO2 cartridges--it's not that they haven't thought of driving an axle with a motor.

I wonder what the brilliant engineers' "mystery drive" was.
 
Do the rules actually allow powered wheels of any kind? I think that's why people use rockets and CO2 cartridges--it's not that they haven't thought of driving an axle with a motor.
I don’t know if I’d bother with powering the axle, instead couple the motor right to the tire and have a solid both-rear-wheels-driven (posi-track type) axle. Battery could counter-weight. Just speculatin'. :)

I wonder what the brilliant engineers' "mystery drive" was.
The confidentiality of “trade secrets.” (grin) Security of that drive train is probably up there with the President’s “football!”

:) joe
 
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