RA car questions - Side rail design

[CallMeChris]

My 2 sons race in the Royal Ambassador races at our church...this will be our 4th year to race. Our first year my wife would not allow me to spend any money on the car so the construction was dismal...I missed the race because I was at work but my wife took the boys and got to leave with them crying since their cars didn't even cross the finish line. There was another race a couple weeks later with a couple churches and we had a chance to rework the cars. With mom's approval this time I was able to dive into the internet and learned a LOT, had no idea there was such a science to these little wood blocks! After all was said and done they both won 1st in their age group and took 1st and 2nd overall. They were so proud! The next 2 years my boys have been the team to beat so every year the bar has been raised. We have been able to pull off 1st place wins in their respective age groups and 1st and 2nd overall in all of the church races and the "district" races have been the same results...until last year. There is a new church that has joined in with the district races last year and WOW, these guys are good! My boys ended up pulling off 2nd and 3rd in their respective age groups last year and 3rd and 4th overall. The cars a couple of these kids brought were unbelievably fast! With this being the last year my oldest will get to race we have pulled out all the stops. I have ordered a bunch of the pro tools to be help his car and we are trying out the tungsten cube weights. One of my major questions right now is about the camber for the rear wheels. We build 3 wheel RR style cars but the tires are different than the BSA tires. With the BSA tires the rear is cambered 2.5 degrees for obvious reasons but I have seen to NOT camber the razor wheels. The RA wheels are narrow already...would you think it better to camber the wheels normally or would it be better to use a less of a camber just to make sure the wheels ride out to the axle heads....or not camber at all like we have done in the past? Here are a few pictures of our cars from last year so you can see what our level of building is and what the tires look like for those that don't know...

My youngest ones car:





My older sons car:







Any other words of wisdom or advice for the RA style cars?

[Speedster]

Hi Chris. What are the rules? I'm going to suggest you build it like a BSA car. Think THIN to WIN ????? I'd like to know more about what the Royal Ambassador's are.

[sporty]

I use to have a few bags of those wheels. Use to cut the wheels to thin them back in 2007/2008.


I forget if this is the kit tho, that has the round doll rods. At one time I had gotten a few of the different kits out there, and there is royal rangers and royal ambassador and i get the two confused sometimes.


I just recall, that I noticed allof the wheels were out of round pretty good and certainly removing the burs and mold marks on the wheels was key.

Not to mention some of the wheels had a solid wheel bore and some I found were hollow in the middle. I felt the solid wheel bore wheels worked better. This could h ave been a mold defect on why some of them were hollow in the middle versus not.


Sporty

[pgosselin]

Hi CallMeChris,

I have no experience with RA, just Cub Scouts Pinewood Derby, but I bet some of the same principles apply here. A safe center of mass is usually about an inch in front of the rear axle. Balance the car on a ruler with all wheels and weight on it, then measure from the balance point to the rear axle to calculate it. Best to do this before you glue all your weight in. Just tape it on temporarily.

Now if you want to go more aggressive, 5/8" is as aggressive as you want to go. 3/4" is a nice split-the-difference spot. However, the more aggressive you go with the center of mass, the harder the car is to align. You're alignment has to be spot on otherwise you get death wiggle down the flat portion of the track.

I can't speak to the proper degree of negative camber for your rear wheels or positive camber for your front wheels because of the differences in wheels between RA and PWD. Maybe one of our other members will come by and shed some light. For that reason, I might tend to go a little more conservative with about -1 degrees for the rears. Introducing camber into your car has both good points and bad points. The good: less tread area touching the track can speed your cars up, I find some negative camber on the rear wheels also makes them a little easier to align because you're always trying to get the wheels to roll to the axle heads, both forwards and backwards, instead of balancing in the middle of the axle. The bad: if you don't drill your axle holes just perfect you can add more instability (death wiggle) into the car and end up in an alignment nightmare.

Also, looking at your designs, there's a lot of wood still on those cars. You could try a design that has less wood, which gives your more weight for tungsten on the back of the car. Sporty has a nice photo tutorial of how he builds his, and I can speak from personal experience, they are very fast. Just make sure you leave enough wood over top of the front axles to keep the front end from becoming unstable.

So bottom line, you're on the right track to more speed. Both a more aggressive COM and canting the wheels can give you a speed edge, but your cars may be trickier to align. Know that going in. Also, reduce the amount of wood in your designs if you can.

My advice is to build more than one for each boy and try some of these aggressive tricks, but also do a couple with a less aggressive COM. You also might try a few without any canting at all.

Paul

[CallMeChris]

The rules are very loose and we race on an old wooden rickety track. I don't remember all of the rules but pretty much has to have 4 wheels, be 5 oz or under, and use dry lube. The Royal Ambassadors are a church group for young boys, the girls in our church are GA's. Here is a link to the main site if you want to learn more. http://www.royalambassadors.com/" target="_blank

The car this year we are leaning towards a 1/4" - 1/2" thick wedge with all the weight being the tungsten squares surrounding the rear axle. 2 rows behind the axle, remaining weight in front. We are shooting for a COM of 3/4". I don't know what the COM on the other cars was, I never even checked before. I figure with the old wooden track I wouldn't want to go any more extreme than that. I plan on checking on the other cars when I get home and get to actually start working on the cars to see what the COM is. The cars in the pictures above are being weighed with lead fishing weights drilled into the car and wood putty filler before paint.

[pgosselin]

BTW, welcome to DerbyTalk!

Paul

[CallMeChris]

BTW, welcome to DerbyTalk!

Paul

Glad to be here!

While this will be the last year for my oldest son, I still have a couple years for the younger....and I'm still holding out hope they will let the dads start racing in an outlaw style race! Starting out I had no idea how addictive this would get!!!

[FatSebastian]

Chris!

I'd like to know more about what the Royal Ambassador's are.

The Order of Royal Ambassadors is a long-standing program for boys operated under the Women's Missionary Union (WMU) of the Southern Baptist Convention. It is actually [url=http://royal_ambassadortx.tripod.com/harmonybaptistroyalambassadors/id1.html]older[/url] than Boy Scouts of America. GAs ("Girls in Action") is an analogous program established much later for girls. The program creates awareness of Christian missionary work and emphasizes scriptural familiarity (like AWANAs) as well as crafts and outdoorsmanship with a system of ranks and awards (like Scouts). Or at least it used to.

The official kit is Royal Racers and the event usually called "RA Racers". This is the closest thing I have found to RA national rules, but rules vary regionally and locally just like PWD. Here's a related topic.

Here is a link to the main site if you want to learn more. http://www.royalambassadors.com" target="_blank

Actually that is not the main site for RAs. See their disclaimer.

[CallMeChris]

I've not had any dealings with a bsa race but I just made a major discovery.....our track is a side rail design, not a center rail design. When I said we have been making a 3 wheeled RR car I might have been completely off base with the way a bsa car....I have to think about this. We have done them in the past where the raised wheel rubs the outside rail. This is completely wrong from what I'm learning now. With that said, should I set it up where my DFW rides the outside rail and inset the rear wheel 1/16" to keep it free of the wall?

[FatSebastian]

our track is a side rail design, not a center rail design.

Paul recently offered some sage advice that applies to "side-rail" racing. Is your track a plastic Supertrack (which interestingly, comes in RA colors!)?

[CallMeChris]

Track is wood. Looks just like the one advertised in the Royal Racers link you provided above....that's actually what got it through my thick skull there were actually 2 types of tracks.

http://www.royalracers.com/main1.htm" target="_blank

[CallMeChris]

THANK YOU FS!!! the links you have posted have had a lot of food for thought for me to chew on. The wood track I'm running on doesn't have the low guide rails the supertrack is plauged with so I shouldn't have to worry about jumping out of my lane. After reading this is the setup I am considering this year.

A very thin and light wedge design
narrow the rear 1/16" on both sides
3 wheel
Straight runner
COM 3/4"
straight rear axles
1.5 degree front axle on DFW


Anything I'm missing from the people that have experience with this style track?

[rpcarpe]

Looks like you've got it mostly figured out!
Any chance you can simulate the track for your tuning board and/or test runs?

[pgosselin]

Yep, all that is the right way to go. Make sure you polish the outsides of your wheels where they will rub against the track edge, too. Your wheels will probably hit the side at some point and you want the contact point to be as slick as possible.

Paul

[CallMeChris]

Good idea, I will polish the outside of the wheel...also plan on shaping the car so the wheel does not make contact with the body. Would it be worth rubbing graphite onto the outer wheel also?