Engineering tips for Space Derby
 

Ok. I may be a little over competitive but I come about it honestly. My dad had a history of crushing the competition in PineWoodDerby and I have continued this.

This year, the Cub Scout Troop is doing the Space Derby - and I need tips. Here is what a Space Derby racer looks like:

http://forums.pelicanparts.com/uploa...1321503187.jpg

It is a tube of balsa, some rubber bands, and a prop. It slides on some 50# monofilament for 40 -50 feet. I have read tips online and understand to lube the rubber bands and that weight is a big deal. That is simple. I want to up the ante a bit and do something cool like a ducted fan. Any thoughts?

Thanks,
Larry

Check the rules, you'd hate to have your kids racer Dq'd.....

For the pinewood derby, we always had the races that followed the book, and then an unlimited anything goes class for the dads.....

We also had a rocket powered truck, but this is OK, and its not a public gathering if something doesn't explode/catch fire....

Well. The thrust does have to be from a rubber band powered prop. The rubber bands and prop are supplied. I am just thinking that reduction of weight is one method of increasing acceleration and increased thrust is the other. I am open to ideas. (Not that the above was completely out of the question!)

Larry

Please post the rules as they are actually written so we can see the wording to find some loopholes that can be exploited to give that little extra edge ;)

Since this is our first go at Space Derby, there aren't any. It is implied that the supplied prop and rubber bands are to power this. I think if I went outside that I would be perceived as a little too competitive.

Lets assume I need to use the provided hardware. How to increase thrust?

Thanks,
Larry

Here is a thought, let your son do it. I had the pleasure of helping a kid with an absent father with a pine wood derby car this spring. Told him to draw me a profile on the block of what he wanted it to look like and I cut it out for him. Showed him how to sand and paint it, sent the wheels and everything back home with him. His mom and him put it all together and took second place. They sent me a pic from the event, one of the high points of my year was helping the boy, not doing his project.

Perhaps do what Sid said, have an all out class for the dads.

sand down the prop to shed weight

use a dry powder to lube your rubber bands, instead of oil.

if the prop is used for sustained propulsion, is there a rule against getting to top velocity faster via a spring loaded launcher, like a mouse or rat trap neck-whacker bar launch assist to the butt end of the rocket? Lots of stored energy in a cocked/loaded rat trap.

Minimize cross-sectional area. Don't worry about fins, etc. Make sure the hanger is as thin as possible. Make the nose areo dynamic. Consider dimples like a golf ball. Put a solid lubricant in the hanger area, like a thik pencil lead, in the hanger to minimize friction.

Refrigerate your rubber bands in an airtight container. They do deteriorate quickly. Use a dry lube on them just before use.

See if the rubber bands will allow doubling without any stretch. If so, do it.

Is the propeller plastic? If so use heat to alter the pitch so that max rpm is reached at 50% of the distance to be covered.

Smallest cross section, lightest weight possible. No extra drag caused by protrusions.

Can you lube the wire it travels on? A ceramic bearing in the guide tube will minimize friction.

i've done this race, back in the day. the bolded idea sounds like it has the most promise to me.

also, if you were able to build some sort of simple venturi, just in front of the prop, you might get more thrust and less loss off of the tips of the blades.

The drawing looks like the propeller will hit the wire....unlikely, but certainly a problem if it did.

Bringing over principles from the Pinewood derby, where we have achieved some , cough, cough, success .... Air resistance is minimal at this scale although because the propeller provides thrust any protrusions would obstruct the flow.

It will be easier than Pinewood to set up a test race. The weight of the rocket will likely have a sweet spot - I would optimize this. Since it self-acclerates lightness is helpful for starting and having less friction on the hanger, BUT - if the rubberband power runs out before the end you will want some mass to maintain momentum. The critical item is friction and alignment aqnd fore and aft position (balance) of the hanger tube - there are likely rule limitations to modifying the hanger with bearings etc - ceramic would work well if allowed. Make sure that the dynamic axis of movement does not cause even slight binding in the tube. The rotational and off-axis thrust forces make this a dynamic/kinetic situation. A tail fin/rudder could help with that.

I found that with the Pinewood Derby, Rain Gutter Regatta and likely this activity that alignment to minimize friction losses is what puts boys on the podium.

Test, test and good luck.

Have your son do the homework, then have him do the work. Guide don't do.

I may be speaking out of turn, but there was a point in my son's relationship with me, and it was very early (4/5 years-old) when Dad doing the work was not productive or desired.

Kids know. You're being both competitive and intrusive. It your son's race to win or lose. He'll know who did the work and who really won.

CO2 cartridge.... ;)

Do this.

We did the Space Derby when I was a Scout, along with the Pinewood Derby and the boat race(don't recall the proper name), and all were alot fun. However, I remember the ill feelings towards the scouts who brought in "ringers" which were obviously not built by them.
Scouting is about fun and fairness--just remember that there may be some scouts in the competiton who don't have the resources(either financialy, or the presence of a parent) that would allow them to fully exploit the potential loopholes in the rules for the event.
There is nothing wrong with being creative, but the point of these events is fairness, sportsmanship and fun.