23 replies to this topic

[crazyphysicsteacher]

Alright, fast tracks is over and done.  The car I ran was, well a whale.  156 grams.  It was the heaviest at the track.  So time for some changes.  I have since removed the shaker and look to make it much smaller and and out of 032 instead of 064.  I am also looking to make some other changes.  Please peruse the phot and give some ideas.  I may use some or just go crazy and do something entirely different but I am looking for the a path to start on.  As to the car, it started with a D3 nose, cut down and had a 064 brass guide added.  The rear is Rgeo and I have Slick 7 bushings in the rear.  I know about bearings but they work for me right now and did not seem to wear after the weekend. the pans are 062 and the rails are 062.  I will be moving the pin tubes to further out on the rails to match to my normal scale chassis and to get the most out of the body on the car.  The problem I had with the car was a lack of rear grip and it was really squirrely coming out of the donut.  You see it as it was raced so the lead did not change places.  I think it needs longer thinner pans and maybe more flex in the twist, but not sure if that would help.      So, as I said, any and all suggestinons, please.  And Thank you in advance. 

Attached Images

• 

[Samiam]

Remove the square tubes that hold the shaker pan and split the ones that hold the bite bar. This will give you more flex. And definitely use thinner pans. 

[Brinkley47]

The car needs a major diet. I would shave weight everywhere possible and then test again.

[James Grandi]

I would start in the front, and work my way back. Those big front wings on the nose piece, cut 'em. Don't need a lot of weight in the nose, even on a stock car. You can remove that center weight and replace it with one of a much thinner material - I'll assume this one is of .064 brass, you could do .032, .025, .015 even. I have a feeling that the vast majority of the extra weight is in that center. You can also trim the pans shorter and take a few grams out there.

Now, to address the handling issue - aside from playing with tires, the amount of pan movement in the car is likely playing a big factor. It's a .063 rail tripod design car, which a number of racers have used very successfully, so the main rails and design aren't the problem. From what I can see, I'm guessing there is a lot of pan movement forward and back, and a fair bit of up and down. First thing I would do, cut the existing bite bar out of the car. Replace it with one that is either .047 or .055 wire, and solder it down flat inside the square tubing. Then, remove the wire loops that capture the ends of the bar. Figure out the spacing/shimming that you would need to make everything sit level and flat with the bite bar captured by a piece of 3/32 square tubing.

When all is said and done, you'll still have independent pans, but the movement up/down and fore/aft will be limited to roughly .015 - my experience has been that this will tighten the car up significantly

[John Streisguth]

100% with what James said.  This is part of the fun (huh??  LOL) with retro racing, build a chassis, try it, then see what small modifications do.  Some of the chassis I build I get lucky and they're good out of the box, some require work to improve.

 

And what tires were you using?

[crazyphysicsteacher]

Thanks a lot. Yeah, the shaker is gone and the car weighed about 138. It has found the parts bin. I had bent the hangers for the bite bar on the land just before tech and it was a direction I was going to head in the future. I now have confirmation I was on the right track.
For those of you at the race this weekend, I saw how Jerry Herbert got rid of the brass uprights and used wire for holding the front axle. He also wire braced the front wings like in a stamped steel car. I may cut mine up and do that in the future to get rid of weight and better protect those front wheels during a race.
But first, cut out the bit bar, thin it down and get rid of a lot of the pan motion. Tighten then thing up.
Thanks Gents.

Sent from my DL718M using Tapatalk

[crazyphysicsteacher]

John, tire wise I tested both Kelly retros and jk treated. I found the retros seemed to hook the car better and wore very little during the race. Don't even think they really lost any thing at all.

Sent from my DL718M using Tapatalk

[Samiam]

.
But first, cut out the bit bar, thin it down and get rid of a lot of the pan motion. Tighten then thing up.
 

If you are making new pans you may want to get rid of the bite bar completely. Use the pan control like that on many of the kits that use an extension off the rear of the chassis. 

[crazyphysicsteacher]

First, I am going to cut the tubing to give the chassis more flex. Then I will will shrink the bar to and work from there. I definitely need to get back to work on this.
As to the pans, that will have too wait until I can get my hands on a block so that I don't make the car too wide and I can really get better results. No reason to make changes that don't work because it went together wrong.

Sent from my DL718M using Tapatalk

[Dominator]

If you are still looking for more rear bite, solder a preice of 3/32 brass rod on both sides of the motor bracket along the rails. I would place the rod from the rear most point to where the wire starts to bend out. This will add about 2 grams to the rear.

For your pin tubes, here is a trick I use when trying different chassis designs. Measure from the center of the front axle to the center of where you want your front tube to be. Then measure the distance from the front tube to where you want the second one to be. This way you can use the same body on different chassis. If you like to switch between. 032 and .064 brass pans simply add a .032 spacer under the pin tube when using .032 pans. This method works for all classes.

[Half Fast]

Also change the lead wires to those on the second place car in Noose's report.

 

Cheers

[slotcarone]

Joe as you can see your chassis is a replica of one of my builds. I never have any problems with rear grip. You should try removing the weight on rear of the pans first. You don't want too much flex/bite on a stock car anyway. I always use alpha wonder on mine and works well.

Attached Images

• 

[crazyphysicsteacher]

Mike, do you have the bit bar fixed solid or can it float side to side? The one on mine was fixed with no play. I think some of the solder joints also failed in the bit bar so that could have caused some odd behavior. Now do you recommend 064 or 032 pans? And how far back should they go?

[JerseyJohn]

Chris Mike uses a floating bite bar as I do. If you use .032 pans you probably wont make the 125 minimum . For a center weight I us a .064 x 3/4 wide 1.250 long it ways 10 grams . RTR with no led the car is around 140 which is pretty much where you want it. The chassi bare weighs 84 grams

I also bend my outer rails farther up the mains . It adds alittle more flex

 

 

 

Attached Images

• 

[crazyphysicsteacher]

And I have now found part of the problem. The solid bar stopped the flex but since I had a bad joint it flexes randomly. That would explain why it would just fight me at times.
As to the weight, John, mine needs a crash diet and I would rather need to add than to be so overweight again. Besides, I will then have some brakes.

[slotcarone]

Joe My bite bar is floating in the tubing but not much as it is .063 stainless rod in the 3/32 square tube so there is not much movement. Side to side really doesnt matter. I use two pieces of insulation stripped off of lead wire as a retainer. You can see them in the picture.

[James Grandi]

Interesting to note the differences of preferences, floating bar vs fixed bar, diameter of the bar, how much pan movement there is, etc.

It is perhaps one of the most interesting things about building these cars, that the various builders have a number of ways in which they accomplish the same goal of building a car - and they all work

[crazyphysicsteacher]

Mike, this is Chris. I'm one of Joe's buddies that raced the last weekend. I had managed to pull off second in the D main. I am the usual one who asked lots of questions and tries the odd choices that usually work, sometimes. I really appreciate the help from everybody and can't wait to be able to test some changes the next time I get to my local track. I have retweaked and flowed the wires to straighten some stuff out. I found some more broken joints last night and fixed them. I will be testing both the fixed bite bar and a floating bar to see which works best with the car at this point. I find that my drive style causes most cars to tricycle throughbthe turns so testing is going to be needed. The car is still going to be put on the Atkins plan and it gets no more carbo loading prior to a race. I will update all this weekend once I get to test on Friday night.

[James Grandi]

Chris,

Out of curiosity ( and I forgot to ask before ), do all 4 tires sit planted on the block with the guide height set for the correct braid depth?

[crazyphysicsteacher]

Yup. One of the first things I checked. Guide is at the right height and the chassis was square. It is now really square and flat. The guide us also not twisted to one side or the other.

[Joexemm]

Kurts car was screwy too. But max's car same as the other 2 was fast. So maybe the characteristics of the car are better for one driver and not the other two? Jerry also seemed to be fine with a car slightly different. Having said all they there are a ferw things i will be changing. 

[crazyphysicsteacher]

Alright, so I tested. Tried the replaced bar and movement. The car was really loose. So I tightened it up by soldering the bar in and it got much better. I am on the right track. I still need to diet the car and loose about 10 grams to get it below 130 without a shaker pan to allow me move and place it where I want. Thank you all for your help and I will update as I am able to modify and test some more.

[wicked01]

Chris ,                                                                                                                                                                                                                                                                     I would either cut off the front ears in front of the tires or use thinner brass for the center weight . I have tested a lot of cars and when i cut the front ears off it really helped with corner speed .

[crazyphysicsteacher]

That is next on my list of mods. Just need to go one change at a time.