'Tis the season! And my cub and I are hard at work on our cars for next weekend's pinewood derby.
Last year he wound up with a 1.5" COM on an extended wheelbase 3 wheel rail rider set to about 2" of drift over 4 feet. Racing on a wood track in pretty good condition. He took first in the pack, albeit in a fairly small field of 13.
This year, we switched to tungsten and a lower profile car, so we can set the COM between 5/8" and 1" for a little more speed.
One question that has been rattling around in my mind is whether a more aggressive COM has any bearing on the "right" amount of drift. I know that a more aggressive COM means less weight on the FDW, but I can't decide if that means we should use less drift (less weight more likely to jump the rail?), more drift (needs more steer to keep it on the rail since it has less weight riding on it?) or if it just doesn't really matter.
We won't have a chance to tune on the track, and so have to pick our drift and hope for the best.
What say you experts? Is there a relationship between COM and optimal drift on a 3 wheel rail rider?
Thanks in advance,
If someone has 3 identical scales, you might weigh the 3 wheels on the ground, perhaps using tungsten putty to shift the weight, and shift the weight from 1 1/4" COG to 3/4" COG leaving the drift the same. Then reset the drift and see if there is a gain, loss, or the same speed. Maximum Velocity might have already done this.
OK, I can get behind that.
So if at 1.5" we had success with 2" of drift over 4 feet, do you have any guess for how much more drift would be appropriate at say 0.75"?
Or, would it still be 2" of drift, but to get that amount of drift more toe would be needed due to the reduced authority of the fdw?
We always use the exact same model every year. It is a basic simple wedge cut to look a little bit fancy in order to remove as much wood as possible. The CG is always set at 3/4" using tungsten cylinders. 1 1/2 ounces are behind the rear axle slot. Dfw is set with 1 1/2 degrees of Positive cant and toe-in to get a drift of 2" in 4 feet on our tuning board. The tuning board is not moved after we have the drift. The car is then taken to my garage where the car is run down lane 1 of the Best track where it will travel exactly 30'. I have my track set for 30'. The track has a Micro Wizard timer. The best time is found and the car is then taken back to the test track. Always, and I mean Always, the car will drift to somewhere close to 36". Our Pack track and the 1st track at District are both Best tracks where the car will run 29'10". If we are in the top 8 fastest cars on the 1st track at District we then move to a Freedom track where the car travels about 40'. We have never won on the 1st track and lost on the 2nd track. From the records I have from previous District races I know how fast our car has to travel on my track to be competitive.
That's my story. I would concentrate on bore prep. I like the Walgreen's paper cotton swab shaft but that's just personal choice. I also use Liquid Glass after polishing the bores but again, I don't know if it helps. I cover the wood behind the Dfw with thick finger nail polish before applying graphite. We are limited to graphite. I'm not popular with what we do to the nail so I leave that up to you.
Best wishes to your team.
Thanks for the info Speedster - but do you mean 36", as in 3 feet of drift over 4 feet of running? My tuning board isn't that wide...Is this a typo?
We have been very fortunate to win many 1st place finishes and never worse then 3rd. This year my special scout happens to be my neighbor. Her name is Emma. Yep, the Cub Scouts race February 10th and the Girl Scouts race February 11th. It's going to be a Fun weekend.
My daughter's name is Emma - so we'll be rooting for you!
We agreed it wouldn't be fair for us to test this year's cars since the rest of the pack doesn't have access. Anyway, this year's cars aren't ready yet
Fortunately, I am on the set-up committee, so I can make sure the joints are aligned as well as they can be. What we do in our pack is we have the adults/den chief race as the preliminary event, and use that to test the track and make sure everything is good to go prior to the main cub event. That's worked well for the last couple years, and I don't think we've had a single car leave the track in cub racing since we started that practice. Our adult races have no award beyond bragging rights, so if something goes horribly wrong we all just laugh about it and carry on
Do you have an opinion on whether wood tracks really need a more aggressive drift than aluminum? Unless the track is really rough, I don't really see this as being an issue, but I have read elsewhere that wood tracks might need a touch more.