Alignment mysteries

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Jeff Piazza
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Alignment mysteries

Post by Jeff Piazza »

Oldest son and I are working on alignment for this year's car. The car was a disappointing 6th in the pack race, but we're hoping to help him defend his district championship (for rank) from last year.

On Saturday we had gotten to a point where the rear wheels stayed where they were placed (in or out) going forward, but when placed "in," the car wanted to steer to the left. We eventually concluded that there must be something right at the body that was increasing the friction on the left rear wheel. To test/confirm, we cut off the "tails" of the shims on that wheel (there were three), and, sure enough, the car then ran straight (and the wheels stayed put) with the wheels moved "in". (So that's one mystery, along with a solution that worked for us.)

Our second, and current, mystery is that now the rear wheels stay put rolling forward, but both move firmly "in" when the car rolls backwards. In previous years we've seen cases where a wheel stays put going forward but has a slight tendency to move going backwards. The wheel movement this year is more pronounced, and it seems to be happening about equally vigorously to both rear wheels. I'm at a loss for how to interpret this, or how to proceed.

Some details that may or may not bear on this:

Our rear wheel alignment is being done with the DFW off the car, and the raised front wheel shimmed so the car rolls straight. The raised wheel is a little higher this year than the Pro Body Tool would put it. (He initially mis-drilled that hole, resulting in such a strong camber that the raised wheel intermittently touched the track. We filled that hole with white glue and re-drilled just above. This car has fenders, so there was not a lot of freedom here!)

I had thought perhaps there was an answer in the axle's reorientation during the switch from forward to backward rolls. We do our alignment on a 4'-long kitchen table, with a book under one end of the table top. The book's perhaps 3/4" thick, so the incline should be about 1 degree. Switching from forward to backward means only about a 2 degree change in where the wheel meets the axle; I have to think that's too small to be meaningful.

My other thought was that perhaps the axles are slightly loose in their holes, and are shifting around during testing. Subjectively I don't feel any real movement when gently trying to deflect the axles. When I tried securing the car (again, gently) in a small vice and putting a dial indicator on the axle head, I could read a deflection on the indicator of perhaps one one-thousandth, but the pointer seemed to return when I stopped pressing. (The spring on the DI seems to be pretty strong relative to the finger force I was applying on the axle, so I'm not sure how meaningful this last observation is -- the DI could be pushing the axle enough to influence the reading.)

Anybody have any insights or suggestions? Similar experiences? Anything?

Thanks in advance,
/JEP
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Stan Pope
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Re: Alignment mysteries

Post by Stan Pope »

Jeff Piazza wrote:Our second, and current, mystery is that now the rear wheels stay put rolling forward, but both move firmly "in" when the car rolls backwards.
Assuming no forces other than axle orientation, this suggests (strongly) that there are two errors at work: Rear axles heads tipped down and back. The errors cancel when rolled forward and combine when rolled backward.

This is not to say that other forces are not at work ... but this, I think, is the most likely and the easiest to eliminate.

Your results so far are why we run the cars both forward and backward.


On the "tail cutting" ... I don't pay any attention to direction changes that happen after the wheels migrate to extremes They just make unproductive work.

If you complete the alignment, including removal of shim tails, but find you have such direction issues, then there are some prep issues that should be reviewed and, probably, corrected.
Stan
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Pinewood Daddy
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Re: Alignment mysteries

Post by Pinewood Daddy »

Bending the rear axles 2.5 degrees and angling them upward (negative cant) will reduce or eliminate your rear end alignment issues. A 1.5 degree positive cant on the Dominant Front Wheel with a minor twist to steer into the rail makes front end alignment easy. I gave up with the shims 3 years ago. Lost too much hair!!! :mrgreen: Keep the other front wheel from touching the track.
Jeff Piazza
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Re: Alignment mysteries

Post by Jeff Piazza »

I actually did have an "aha" moment last year about camber and toe canceling each other out in one direction and combining in the other, but somehow blocked it out this year in thinking about the question.

Thanks to Stan's reminder, we found that the right rear wheel was, indeed, down and back. It aligned very quickly after that.

The left rear wheel was another story. For whatever reason, I couldn't get alignment even after adding eight or nine shims. We tried swapping axles and wheels, but with no change in the outcome. Eventually I noticed that the axle had discernible (by feel) movement in the hole, so the shims really didn't stand a chance. (I can't say whether the hole enlargement was caused by too many shims, too many axle removals and re-insertions, or something else.)

We ended up trying to fill the hole with epoxy and re-drilling, but weren't very successful. The Pro Body Tool wouldn't fit with the fenders installed, so we tried drilling on the drill press with a carbide bit. Drips of paint on the bottom of the car probably kept the hole from being coplanar to the (original) car bottom. The result was a strong negative camber. Axle insertion required less force than we would have preferred, too. After applying three shims to try to move the axle down, we chose to accept the camber rather than risk more damage to the hole with a lot more shims.

On race day, during check-in, there was also a lot of handling of the car by the boy scout inspectors (the fenders were a hair wider than their jig), including more contact with the rear axles than we would have liked. On the track, the car had a respectable, but not amazing, time for the first heat, while the other three heats were substantially off the pace. That one good heat let us at least come away feeling like we'd truly tried our best, even if we couldn't quite overcome all our compounded errors.
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Re: Alignment mysteries

Post by PWD_addict »

Live and learn. You can "Do your best" even better next year (assuming your boy didn't cross over this year).

Once I switched to bending axles, I never thought of going back to shims . . .

Don't forget that with wood holes you can moisten them with water to help them swell a little tighter.
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Re: Alignment mysteries

Post by quadad »

One of the things that I am slowly learning, thanks to people on this web site, is to move the alignment task up much earlier. I plan for us to do it as soon as the car is basically cut out (rough) and you can place weight in the basic body.

We rejected one car out of four this year because it was taking too much work to align and it was quicker (with the tools I have) to cut out another body and get it to that same point, perhaps with more carefully drilled axle holes or a straighter block. Heck, we are used to doing that (or more) when the kids accidently destroy one at a not much earlier point. :roll:

I will add that our cars have either been fairly simple or we have made the "fancier" parts out of added on balsa or foam insulation. When the kids want a special look, I am really liking the foam insulation "topper" approach as it provides such minimum weight influence and you can separate the basic car build/tune from the artistic part (which my wife helps with !). YMMV

Finally, we step through the alignment process and attempt to isolate wheels as much as possible so we know who is causing the problems.
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Re: Alignment mysteries

Post by Pinewood Daddy »

quadad wrote:Finally, we step through the alignment process and attempt to isolate wheels as much as possible so we know who is causing the problems.
When using bent axles (2.5° rear & 1.5° front) alignment can be done in a few minutes with an alignment board and a board with a 1 5/8" rail on it. If the rear axles are accurately marked on the head to show the true position of the bend, rear alignment is done. Then rotate the front axle to get your desired drift and the car is finished. I think I might be able to build a top 3 in the Pack car in an hour (from scratch, but no paint) using this technique.

Previously I was afraid to clean up and retune a car before the District race, re-aligning a straight axle car could take hours. Now it's no brainer.
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Stan Pope
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Re: Alignment mysteries

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quadad wrote:... we step through the alignment process and attempt to isolate wheels as much as possible so we know who is causing the problems.
Interesting comment ... how do you go about isolating the wheels?
Stan
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Re: Alignment mysteries

Post by quadad »

Stan Pope wrote:Interesting comment ... how do you go about isolating the wheels?
Following a tip from Sporty, with straight axles I go about the alignment in four steps:
1) High board incline, rear wheels only and tape on the front bottom;
2) Low board incline, rear wheels plus one front wheel;
3) Low board incline, rear wheels plus the other front wheel;
4) Low board incline, all four wheels.

The car goes down the board in Fwd/Rev in all four steps. The typical guidance applies about how to tell if an axle is too high/low/fore/aft.

Its more time consuming that what Pinewood Daddy is suggesting, but I think it was a nice way to start learning about alignment and to get pretty direct feedback. Most often after drilling with the ProBody Tool or Jig, our rear wheels have the car travelling straight on their own. This way we never are attempting to fix a rear wheel problem by adjusting the fronts. At least that's what I believe.

Looking forward to trying out canted axles and RR. Just didn't have the knowledge (or new tools) last year, and not enough time this year to be confident we could do it succesfully. Will try all of that out, and Stan's new alignment method for canted axles, before next season. I like to do everything myself before trying to lead the kids on it.
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Stan Pope
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Re: Alignment mysteries

Post by Stan Pope »

I see. Thank you. Was hoping for more isolation, especially between the rear wheels! :)
Stan
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