50 replies to this topic

[JimF]

I have some bits and pieces and a nice R-Geo kit to use in building a tuning fork chassis. Problem is.........I don't really know what it does. After looking at the various pictures and reading postings regarding the tuning fork......I still don't know enough. I had a general idea of what the concept does of course but just not enough to go on for a serious build attempt. Sooooo..........I took some bits and built one figuring to just slap it on the track and see. I didn't take a lot of time or effort for a super sano build and I didn't use up any of my favorite components, because I think I'll be hacking and slashing on this thing.

 

This frame was built up with a pair of forks in .062 supplied by 'R-Geo' Rick. The rest is an old JK nosepiece, JK bracket and 1/4" X .062 pans.

 

Some details:

• Forks twist freely in the 3/32 tubing bits. Thus, nothing is holding the front and back halves together.
• To tie the ends together without changing the character of the fork concept, I added secondary rails of .039 wire.
• Pans are hung on a bit of .032 wire and form a fixed plumber arrangement.
• At the mid-rear, there is a bit of 3/32 soldered only to the fork rail. A bit of .047 goes into this to form an up/down stop.
• The longitudinal flex is more or less as one would expect but the torsion is ridiculously soft.
• This car is stoopid-light @ 84 gr as shown.

 

 

 

Here is how the car will get tested today with weight added as shown to hit 96 gr. Still really light for me.

 

 

Development thoughts:

 

 

• Actually, my first thought is that this car won't work at all......but a lot of good builders are using the concept so.......????
• Brass weights are soldered to the center forks. No effort was made to create any 'suspension' system for the weights.
• The extreme torsional flex may make the car really tippy and 'bitey'
• The torsion can be stiffened by soldering the forks into the tubes or tying the fork to outer rails in various locations.
• The outer rails could also be made of larger gauge wire (like .055)
• I'll be testing today @ Fast Track Hobbies and this is always a mixed bag due to highly variable conditions.

 

[SlotStox#53]

Whether first attempts building & exploring tuning fork chassis or not it looks a class build!

One very clean & sharp looking F1, hope the test goes well & answers some of your questions/concerns . Will definitely look forward to reading your results

-Paul

[Tim Neja]

Take the weights out Jim---be LIGHT and FLEXY!! For some reason--it works!!

[MantaRay]

Nice Buils as Allways........Did you make and coin the nose piece?

[JimF]

Dang.....gonna have to back to work to close up tonight so.....testing is stalled for the moment.

 

 

Timmy.....I hear ya and that's why I built this the way I did for starters.........but 84 gr.? I don't think I could drive an 84 down there let alone up here on our flatter tracks. Still, after some tuning, those weights will drop right right out at the touch of an iron.

 

Ray.....The nosepiece was hacked out of an experimental JK kit build that uhhhh.......didn't work out.

[Tim Neja]

Well Jim---the guys down here are getting 84 gram cars around on the KING track---then it seems we've still gone up to 90 some grams for the flatster!!! The super light--has worked on the King only so far--but who knows?? Obviously the lighter Can Am cars have been going faster too!  So it's inevitable that F-1 is going to move in that direction!!  

Nice build Jim!!

[Jim Lange]

Don't be afraid of the LIGHT! I have made many nay sayers....Believers!

[Rick]

Very intersting, I like the idea for a test. Car should be able to use a harder tire, now to see if it sucks HP or not? I think Jim is correct with changing the propertes with several options, tacking the fork together, torsion wires to pans etc. Can't wait for his test results! The .039 rails should not change the fork characteristics any..................now we wait.

[JimF]

Development thoughts:

• Actually, my first thought is that this car won't work at all......but a lot of good builders are using the concept so.......????

 

 

OkaaaaySoooo......................don't necessarily go with one's first thought.

 

Got some track time today @ Fast Track Hobbies in Citrus Heights. My first laps were done on the fast Purple Angel track. We don't have a target time for F-1s on this track as yet but it's safe to figure 5-6 tenths slower than a good Can Am and a standard fast time for a very good Can Am is ~~ 5.0 so I'm targeting 5.6 as good and 5.5 as really good. Today, my F-1 that has won on the King @ Eddies the last two time out was @ 5.58 ....so that's a fair guess. Track conditions were poor as even the normally fast orange lane was slick and maybe a tenth or two off.

 

• Started as shown in the OP with weight in place and Alpha Wonder rubber. Car was loose but reasonably stable and easy. Time was a 5.78 best.
• Went through the tire options and ended up with JK 8713 untreated. At this point, the car was running a 5.55 best and felt quite forgiving. Still a touch loose and maybe a small amount of wheel hop on turn exit.
• First modification was to solder a small 3/32 tube bridging the front part of the fork rails (blue arrow). This didn't do much either way. Still easy, maybe a tad less wheel hop.

 

 

 

• Solder joint on the short tube cracked pretty quick so a second tube was added at the location of the red arrow. Again......not much different.
• Almost immediately, I dropped all the weights as shown here. Now the car was running a best of 5.47 and was still forgiving. By this point, I'm pretty surprised.

 

 

• Next step was over to the flat track, change the 9-27 for a 9-30 and add back all the weights. Target time would normally be 4.95 but my regular cars weren't that fast today.
• Best time was 5.05 and the car was much more forgiving than I thought a 97 gr car would be.
• Next, I dropped the weights. I expected the car to be really jumpy and it was notably quicker off the corners but not as hard to drive (@ 85 gr) as I thought it would be. Best time was 5.00 and the tradeoff here was not worth it. The heavier car was a better race car.
• Last step was to solder the forks solid within the front tubes (red arrow below). At this point, the character of the car changed notably. The car was much quicker off the corners but also tippy like I thought it would be from the start.
• I took it back to the Purple Angel to verify and got a similar feeling.....it drove like a light car.

 

Conclusions and speculations:

 

• The tuning fork makes the car softer on turn exit as long as the forks are free within the front tubes.
• With the forks in this setup, the car does not feel light or tippy or nervous. It is not terribly punchy as I thought it might be.
• Solder the forks into the tubes and this changes for the worse as the cars exhibits the feel of a car that's too light.
• I think the fork twisting in the tube softens some of the torque transfer from front to back making the car more forgiving.
• I think surrounding the fork with more conventional chassis rails might negate some of the effect of the fork. (for example, if I had made the rails on this car say 1X .062 or 2X .055 instead of the 1X .039)
• I THINK, that I think that a lighter and more flexy chassis could make a good combination that you might normally think wouldn't work. (such as maybe a multi rail can am with far fewer than normal rails (like say 4X .039 + a fork vs. say 7X .039)

Uhhhhh............I THINK!!!

[John Streisguth]

I recently built a tuning fork F1 with 055 center rails (soldered in front and rear) and started with 4 rails of 039 on each side.  It seemed way to flexible torsionally, so I ended up with 6 rails of 039 on each side.  No room for pans anymore so I used an 063 wire on each side as the "pan".  The car works really well on a fast king, not quite as well on a more "standard" king.  I would just add a second 039 rail and uncouple those forks again. 

 

Great seeing your experiments Jim!

[JimF]

I will change the rail setup to a 2X .039 or a 1X .047 but there are some other things that I want to try first. For sure, the forks are going to be unsoldered....that didn't seem to offer the effect that I was looking for. I'll finish version 1.2 today. The rail change will be version 1.3 or 1.4.

 

The goal for these experiments isn't necessarily to make this car a final form. Rather, it's to see if I can figger out the effects before transferring the findings to a more finished product.

[John Streisguth]

Absolutely...that's why I like your build reports.  One step at a time to see what does what...very informative!

[MikeC]

If you think these reports are thourough, you should see his notebook and note keeping. 

[JimF]

Version 1.2

 

 

Following up on what I learned from the first test round. Goal for this go was to get a slightly tighter feel without losing the forgiveness of the fork design.

 

I put a bit of .047 wire about 1/2" long between the main fork rail and the .039 secondary rail. This is to place a stopping point for the enormous amount of twist that results from the fork design. Forward of this block, there is still plenty of twist flex.

 

 

 

All hinges and stops are removed from the pans and they are soldered directly to the .039 frame rail. The .039 rail has so much flex that the pans flex totally separately from the center section.

 

The solder joint between pan and rail stops just forward of where the flex block is (between the arrows). At first, I soldered all the way to the back of the bracket but this stiffened up the entire structure pretty dramatically.

 

 

This won't get tested now until Friday or Saturday. The whole structure is now slightly stiffer than the original version and some reinforcement has been added in case I decide to race it this weekend.

 

 

 

[JimF]

OK......quickie update.

 

I ran last night @ TNT raceway in Modesto with the 'Forker'. I'm still shaking my head but no longer a disbeliever. With the configuration shown in the last update above and back to the basic weight of 85 gr (no body) the car was stupid fast on the full tuck hillclimb. It needed no additional weight and the pans soldered to the main rails seemed to eliminate the last bit of pan rattle. On the twisty little Korkscrew road course, it was surprisingly good for an 85 gr. car. In this case it needed weight to settle it down but was pretty good the way it was/is.

 

At this point, I can't wait to build up a test mule in Can Am form and an additional F-1 geared more to flat tracks.

 

Reports in this thread as I get those going.

[team burrito]

You still have to renforce those axle tubes; those will bend for sure in race conditions. Just pointing it out.

[Duffy]

Thanks so much for this narrative. We don't see nearly enough of this sort of analysis & thinking out here in the trenches, and it's where lots of us oughta be in our own race programs.

duf

[SlotStox#53]

As Duffy so eloquently put it thanks so much for taking the time and effort to put this much time and description into testing the chassis/ideas.

There really isn't any substitute for doing your own testing such as this.

-Paul

[JimF]

Thanks guys. I find that doing something like this helps my own thinking about this particular frame concept. I think this is a case where I think the jury is still out. These frames have been in use, some with great success. However, I'm not sure that any of us know precisely what the 'fork' does. I don't know precisely myself but I do know a lot more than I did a couple weeks ago.

 

What I have learned so far will help a lot in trying this concept in other forms such as a Can Am or as a more flat track oriented F-1. I'll be sure to report the ongoing developments as I learn more.

[redbackspyder]

Russ, why do you need axle tubes at all ? ? ?  The axle tubes add weight up high, and simple ball bearings with aluminum axle spacers will prevent any bearing blow out.....   Don't take my word for it, check out numerous Retro Chassis in the SCRRA,  ball bearings without axle tubes......

[JimF]

FWIW.....Russ didn't build this, I did and I used some sorta "disposable" components such as a JK bracket that needs tubes. (you'll notice BTW that the tubes are very short) The reason was that I sorta thought this wouldn't work and and didn't want to use up one of the "good ones" that I ordered from Bryan which are set up for no tube. I'll probably do the same with the first experimental Can Am as well.

[redbackspyder]

Beautiful Chassis Jim, Bryan and I have been running the tuning fork F1's very successfully on our King Track.....I was 2nd TQ at the Checkpoint Cup with mine...

[JimF]

Mill, I knew that you have had good results and was really the impetus for me to start this project. I just didn't really "get it" about this chassis concept until I started messing with it a bit. This one won pretty handily today in it's first outing so now I have enough to go for the next few stages.

 

I hope to make it down there for the first Retro race @ the "cave" but not sure yet if it's doable.

 

 

[endbelldrive]

Hi Jim, I used to use 3 small pieces of .063 OD tube and a length of .032 piano wire on my old cheap and cheerful tuning fork sidewinder scratchbuilds from the dark ages.  I used the middle tube to tune the dampening effect.  Maybe worth a try?

 

 

[JimF]

Bob:

 

Thanks for those pics. This application of the concept would violate the universal interpretation of the "no center hinge" clause that is present in most national rule sets. Your two main forks are offset to either side of the centerline and thus avoid the current rule interpretation. (plus) they aren't hinging in a tube anyway so it would be OK regardless. However, it looks like the 1/32 wire is actually turning within the three tubes and is on the centerline thus, this would be a "center hinge"

 

Honestly, I wouldn't be surprised to see some re-consideration of the current rules interpretation. My design and the ones that I used for guidance (like the Warmacks) are legal by virtue of the center rails not being precisely on the centerline but are actually fractionally offset to either side. I'm not 100% sure either way that this should be legal or not. However, currently it is......and so I'm going to continue to play with it for a while.

 

The car shown in this thread was an easy winner yesterday in it's first race outing. I don't know that it will be a game changer in other applications or not. If it is, then I'm going to have to address the situation as to whether to allow the concept or come up with a ruling to outlaw it. I'm also cognizant of all the national organizations and their interpretations. While I'm a little more restrictive than IRRA in some areas (for example bodies), I do pretty much follow what they and So-Cal do for chassis regs. While the jury will be out for a while, it wouldn't be a total shock that some form of this design might be a game changer and thus, might be something that we want to re-consider vs. the original concept of retro racing.

 

Back to your pic, that gets me brain spinning again. I have a lot to do in experimenting with the F-1s and starting to play with the Can Ams but I hadn't thought far enough ahead to the anglewinders yet. (or geeeze....the 1/32nd) I really like your design there and will likely try to get one similar going before our next coupe race.

 

Thanks for the brain teaser....awsome work as always.