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Post by CycRunner on Apr 9, 2011 21:20:58 GMT -6
I am trying to tune my Mills Craft Stock for this month's race. I have a big problem with the rear of the car moving to the right as I run it slowly down the slow portion of my track. It moves far enough to make the left rear rub the rail - you know what that does!
I am using MV Precision Max-Velocity wheels reworked as allowed and bores polished to 12K (really bright). Grooved rear axels 0.092 dia. polished to 12k. Using Krytox 100. Positive camber on RF with LF raised. Rears negative camber 3 degrees. Front axel bent for drift - rears straight.
Rear wheels run to axel head going forward and back. Left drift set to 3" at 4' and 9" at 7' very smooth arc. So, now how to eliminate the movement of the rear of the car?
A little history: I first used the as drilled rear axel holes. When the problem of the rear of the car moving right I thought the rear holes might be the culprit so I removed the wheels/axels and filled the rear holes with epoxy and redrilled (3 degrees camber) and slightly lower for better clearance. In my test of this new and supposedly better set up I see the same problem - the car rear moves right on the track! What a surprise! Now what - what am I missing here? Any ideas?
Car stats: Wt.= 5.02oz. COM 0.9", Wt. on rears = 3.99oz, front=1.03oz. 56% of the rear wt is on the left side, 44% on the right. I biased the tungsten weights the best I could to get the rear weight balanced as close as possible. So, there it is folks - what's my next move to fix this?
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Post by Lucky 13 on Apr 9, 2011 21:31:39 GMT -6
Have you tried a different set of wheels ?
How did you drill the rear axle holes ? Is it possible your drill press table is not level and when you drilled the rear holes you ended up with a slight toe-in on one side and toe out on the other ? It sounds like a toe-in/toe-out problem on the back.
Lucky 13
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Post by Evolution on Apr 10, 2011 10:19:37 GMT -6
I agree with Lucky, have you tried any other sets of wheels. I would also try different axles on the rear. If you have eliminated the axle holes as the problem, them I would try those two other things. I also wonder if maybe your weight placement could be causing this, if you weight if to far over to one side it could cause it to drift.
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Post by CycRunner on Apr 10, 2011 19:12:44 GMT -6
Well, I have been working hard to solve this problem and no joy so far!
I have switched to another set of MV Precision wheels and to BSA machined wheels and see no change. My drilling is a precise as I can make it and I drill all my cars the same way. I use my Shopsmith in the horizontal mode with my cars clamped against my table fence witch I square up to my drill spindle. I tilt the table to get my camber drilling angle and use a digital level to verify the degree setting. I rechecked and all looks good. With the rear wheels installed I have checked the toe in/toe out and found a little LR toe out which tends to steer the car to the right (according to Stan Pope's papers). So, I created a slight LR toe in to supposedly correct the problem. The RR had zero toe. Retested and the rear of the car still moved right! Surprise! Next, tried toe out of the RR to help make the correction -still no good!. So, made a drastic toe in of the LR and this was no good either, actually made the problem worse. Hmmm- maybe I have this backwards - so I tried LR toe out and had the same problem! When I made these changes I adjusted the drift accordingly but I cannot get the wheels to stay out in both forward and backward mode. They always move in when I get them to stay out going forward. BAD, I know! I have also changed from wide to close gaps and back again with no help. The car runs down the track and I can hear the noise it makes as the left rear wheel rubs the rail. To verify that my track is OK I ran my Spec/Tuner and it was great, clean straight runs. Evolution brought up the weight distribution issue. My Spec/Tuner has the rear weight 42% on the dominant side, and 58% on the other side. As I said earlier my Mills Craft is more equally distributed with 44%, and 56% so I don't think this is causing my problem. My Mills Craft COM at 0.9"is very conservative and I don't think this is a problem either. So, there we are- I have one more day to work on this - not sure what I will do next! Too bad we have only one month to race there Mills Craft Stocks!
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Post by Lucky 13 on Apr 10, 2011 19:52:27 GMT -6
If the rear of the car is shifting right, then you either have a toe-out problem on the passenger rear or a toe-in problem on the driver rear....or a combination of both. I know you have drilled canted holes, but have you tried putting a slight bend in each axle to rotate the toe-out/toe-in out ?
The problem has to be in the rear axle holes. You have a lot of cant on the rear wheels already, which is emphasizing the problem, so that will make adjustments very touchy, but adding a slight bend to each axle may be the only quick way to fix it ??!!
Lucky 13
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Post by CycRunner on Apr 10, 2011 21:12:50 GMT -6
I agree with what you say - I am using bent axels for tuning - that is how I have been changing my toe. Also used straight axels but could not get enough change to make a difference in the results. As you say the bent axels when rotated not only change the toe but change the camber and the movement of the wheel in and out on the axel. There has to be a solution to this but I am not there yet!
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Post by ProQuest on Apr 10, 2011 22:42:36 GMT -6
Hey CycRunner,
This is only a guess, but here are a couple of ideas to consider:
1. Some part of the chassis is contacting the rail and the unwanted contact is affecting the steer. I haven't seen the Mills Craft chassis you are working with, but my impression is that most of the Mills Craft chassis are made to extend below the rail on the sides. could some part of the chassis be coming into contact with the rail?
2. Another thing to look at is whether the wheels are all clearing the fenders. If any of them, even the raised wheel is rubbing inside the fender-well, that might cause the problem you described.
I would have seconded what Lucky said, except that you seem to have tried just about every possible combination of alignment options.
I have a philosophy -- when the answer is not where you think it should be, look where you don't think it should be. Actually, that is how I find lost socks, but the theory applies here as well. Let us know if any of these ideas work. Good Luck,
ProQuest
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Post by CycRunner on Apr 11, 2011 1:12:16 GMT -6
Hi ProQuest,
On your point no. 1 - No, none of the chassis is contacting the rail, none of it extends below the rail. Your point no. 2 is an issue but the wheels do clear, but just barely. I raised this issue with Lucky 13 when I first started working on my car. I solved the raised wheel concern by leaving it as is and actually lowering the dominant front wheel as he suggested. I have finally made the car run without the rear moving over to the right. However, I am getting the wobbles after the track transitions from the curve to the flat and I can hear the wheels hitting the rail. I am surprised at this because my COM is 0.9 inches which should result in a stable run. I am getting huge variations in run times as a result. I have a few runs on my 39' track of less than 3.03, several between 3.03 and 3.04 but then I will get following runs of 3.1 and greater! I have never seen great time differences like this before. Times bounce all over the place! My good running cars have standard deviations of around .002 to .003 seconds. One thing I have noticed about the Mills Craft and the rules, is that we cannot use washers between the inner wheel hub and car body. If this was allowed there could be more space between the inner wheel rim and the track rail - a little more forgiving and less chance of hitting the rail! I usually do this and use most of the allowable maximum width of 2.750". If I had more time maybe I could solve the "wobble' problem. Oh well, I will send it in and see what happens! I have named the car "Cyc's Factory Special"
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Post by Cutter Racing on Apr 11, 2011 7:00:28 GMT -6
I wish you guys the best racing the mills-craft stock. I couldn't get the c.o.m. right on mine. It was driving me crazy! The build wasn't fun anymore so I CHUCKED IT!!!  I'll be racing a new pro-mod and extreme instead. My spec/tuner won't be racing either this month. I'll let someone else be first this month........on the bottom. lol!! CUTTER |
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Post by Evolution on Apr 11, 2011 8:52:03 GMT -6
Cutter,
Sorry to hear that. I find them very fun to build, but I treat them like no other car and so the general rules for other cars don't apply. There is always the extreme Mills-craft class, you really can do almost anything to them and it is 1 gram wheels. So dont pitch the one you have, just modify it to the other class.
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Post by CycRunner on Apr 11, 2011 11:16:47 GMT -6
Cutter,
What was your COM when you decided to give it up? I agree, it is difficult to get it far back! I did all I could to get it to 0.9" in front of the rear axel, and was hoping to get it further back. Even so, I am getting the wobbles late on my track . With this conservative COM I don't know why this is happening. The race will be interesting. Wonder how many entries there will be. Well, I am off to my workshop to get my cars ready to ship today. Still tweaking my Mills Craft and HR66. Spec/Tuner is ready to roll again.
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Post by Cutter Racing on Apr 11, 2011 16:09:43 GMT -6
CycRunner,
Sent you a p.m.
Thanks, CutterRacing
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I'll be racing a new pro-mod and extreme instead. My spec/tuner won't be racing either this month. I'll let someone else be first this month........on the bottom. lol!!