49 replies to this topic

[JimF]

I haven't posted much this year because I haven't really done much of anything new and posting pictures of stuff I've reported on before doesn't seem to make that much sense. But...........part of this build is new, at least to me.

 

This is a pretty standard "GVP" style tuning fork chassis. Components used were an R-Geo "Razzo" nosepiece and R-Geo "Z-poid" 1" bracket.

 

Nosepiece is .040", bracket is .050, pans are .032.

Fork rails are .062, frame rails are .055

Hinges are .062 wire in 3/32" sq. tubing.

Front stops are .055 wire in 3/32" sq tubing.

Weight as shown is 53.5 gr. which is a good starting point for a NorCal Can Am.

 

 

 

 

Here's the "new to me" part. I was discussing building a tuning fork frame for a very good Motown Racer and he suggested this addition. I'm sure this has been done by others but I haven't seen any testing or reports on the concept so here I go............

 

 

 

 

The fork tubes have a tiny block of 1/16" brass on top that is drilled and tapped as shown here for #0-80 set screws. The usage is obvious. With the screws down tight, the forks are locked and don't rotate in the tubes. Back them off a turn, and they are free. The pic shows a couple of the #0-80 set screws on the right with a couple of std. #4-40 on the left for scale.

 

In messing with it, the difference in flex is very noticeable. What it will do on the track remains to be seen but I'm guessing the difference will be subtle. I'm pretty excited to test this. Enough so that I don't think I'll even bother to clean up the solder joints before I put it on the track. Hope to get it on track tomorrow or the next day.

 

 

[Tim Neja]

Should be an interesting tuning idea!! I wonder--once you find the "sweet spot"  Either tight or loose--would you ever change it??  

[JimF]

Should be an interesting tuning idea!! I wonder--once you find the "sweet spot"  Either tight or loose--would you ever change it??  

 

I'm clueless as to how it'll shake out and whether one configuration is "better" than t'other. I think it might be a possible way to compensate for bite conditions or even for difficult lanes maybe. Aside from the obvious, it would also be possible to lock one side and not the other in order to possibly compensate for a particular turn.

 

All speculation at this point..............

[boxerdog]

You never know. Maybe in combination with some tire tuning? Body swaps? Preload? 

 

What I do know is that Jim will test it to death, and that's a good thing. 

[Tex]

cool! the sliding block concept is brilliant. Rick Moore has used screws to change the flex in his chassis' for some years now. I saw what he did and incorporated the concept in my chassis-building for a while, although slightly different than his. but the "blocks" in both of ours were fixed, soldered solidly to the chassis. the fact that you can slide your block up & down the rails makes it widely tunable. I gave up on the concept while Rick still builds "tuning screws" into every chassis(I "think" every).

[slotcarone]

Cool idea Jim!! Use a special body with two holes in it for quick adjustment.for testing!

[chaparrAL]

working on the same thing but in HO scale.

[JimF]

cool! the sliding block concept is brilliant. Rick Moore has used screws to change the flex in his chassis' for some years now. I saw what he did and incorporated the concept in my chassis-building for a while, although slightly different than his. but the "blocks" in both of ours were fixed, soldered solidly to the chassis. the fact that you can slide your block up & down the rails makes it widely tunable. I gave up on the concept while Rick still builds "tuning screws" into every chassis(I "think" every).

 

Thanks Tex but this block doesn't slide, it is fixed to the top of the fork tubes. Funny that you should mention it though because after messing with it more while I was bolting on the running gear, I thought of that very thing. Now that I've done this one, the next ones won't be near as fiddley to do.

 

You never know. Maybe in combination with some tire tuning? Body swaps? Preload? 

 

What I do know is that Jim will test it to death, and that's a good thing. 

 

Guess who is going to help..............

[Dominator]

Another awesome build Jim and great innovation.

[JimF]

Cool idea Jim!! Use a special body with two holes in it for quick adjustment.for testing!

 

One hole was enough...................thanks for the idea.

 

[Ramcatlarry]

...but you cannot 'view the chassis from above'....

[JimF]

...but you cannot 'view the chassis from above'....

 

Correct. However, I don't worry much about that sorta thing in testing or practice since I won't have to pass tech before putting it on the track for the first time. That's a well used practice body and if I decide to race the thing, I'll figger out what it needs and then put on a real body minus the "hatch"

[Bill from NH]

A piece of masking tape on the inside & that body will be legal to run. Or, use a stick-on number over the hole on the outside. More than one way to skin a cat.   

[boxerdog]

Legal??? What's that mean? 

[Phil Smith]

A piece of masking tape on the inside & that body will be legal to run. Or, use a stick-on number over the hole on the outside. More than one way to skin a cat.   

 

Or a lane sticker.

 

I don't understand how the hole benefits you. Once you slide the bracket, it will no longer line up with the hole.

[Tim Neja]

 

Or a lane sticker.

 

I don't understand how the hole benefits you. Once you slide the bracket, it will no longer line up with the hole.

You missed it above--it doesn't "slide"!! It's fixed in place.  

[Bill from NH]

What's moving? According to Jim's first post, the screws locked down keep the fork tubes from rotating. When the screws are backed off, the tubes are free to rotate.

[Tex]

What's moving? According to Jim's first post, the screws locked down keep the fork tubes from rotating. When the screws are backed off, the tubes are free to rotate.

 

yes, I misunderstood the block's placement(I thought "sliding" instead of permanently fixed) and apparently others followed me over the cliff.   LOL

[Greg VanPeenen]

Jim,

 

It has been tried before as has a sliding block.

 

Will be interested to see if you come to the same conclusion as I did. You do really nice work and will probably do a better test then I did.

 

Keep up the good work.  

 

Regards,

Greg VanPeenen

[Tim Neja]

Greg--

What was your conclusion?  Just curios about the tunability and your thoughts!!

[JimF]

OK......I couldn't wait so I went down to Fast Track Hobbies in Sacto today to spin the new "Tuna Fork". I had another new car to test too and also a stack of fresh motors but the new tuning fork was the main focus of the day. For this initial test, I set the car up as follows............

 

• Assorted RH motors @ 9-28
• Ran JK 8703 PP initially
• Tested 8713 pp and 8713 PPP through the course of the day.
• Parma Lola T-163
• Ran 104 gr all day on the Banked Track. (heavier in the brief flat track test)

Test Venue: 165' Purple Angel track with moderate bite on this scorching Sacramento day. Areas called out are todays problem spots (mostly having to do with bite-or lack of same) Conditions were decent but perhaps 2 tenths off optimal.

 

 

"Armenian Section"

• Section #1 downhill entry into a flat lefty.
• Section #2 the exit from #1 but becomes a fallaway so very different than normal flat exit.
• Section #3 dead flat righty. High forces here.

 

"Sweeper"

• A very long sweeping righty. Highest cornering forces on the track (not as simple as it looks)

 

"Leadon Bank and leadon straight."

• This is a blip punch banked turn but timing is critical b/c you can't exit too loose
• Poor or loose exit here will cause the car to "crab walk" down the leadon straight.

 

Running the test:

• Each combo and subsequent variations was tested "locked" and "unlocked"
• Each combo was tested 10-15 laps at ~~ 97% of max effort. (comfortably fast with few offs)
• Fastest laps were noted but not recorded as results unless repeated.
• A one time "hare" lap was not considered as a result.
• I didn't do much with the 4-rail car shown. It was run to help shake out motors but was really more of a "control" on this day.

 

Results on this track, this day................

• Established the 4 rail as control and it ran well as expected.
• 4 rail was modestly loose in the problem areas detailed above.
• "Tuna-Fork" (locked) was somewhat less loose and a bit more driveable on exit in each area.
• "Tuna Fork" (unlocked) was clearly better in turn exit. It exited straighter and with much less "kick out"
• As each combo was repeated, the results were the same. Unlocked was better and faster in every case. The difference when identical components were tested was approx .01 sec. in favor of unlocked.

I was not sure what to expect from this but in these conditions, the unlocked position was clearly better on the high speed "Purple Angel". A brief test on the yellow Dragon flat track was inconclusive. There was not a definable difference between locked and unlocked on the flat track. Although my fastest time of the day came with the "Tuna" unlocked, it was not as consistent as my long standing favorite flat track car.

 

A lot more to do here and particularly when the opposite from today's somewhat loose conditions are encountered.

[boxerdog]

Tuna? 

Something fishy here.  Come on down!

[A. J. Hoyt]

Do the set screws lock down on each rail? If so, there might be an "intermediate" position with one rail locked down. This would be between neither rail locked down or both rails locked down, if I understand your clever mod correctly. (It may not be the case that one screw securely locks one rail.)

 

However, now that this test was done (on the one track on this day), it is clear that keeping both rails unlocked was superior so it is unlikely that there is a "sweeter spot" that can be felt between the two (with only one rail locked down).

 

Jim, as an engineer, I appreciate these tests you do and that you share them!

 

KIITS,

 

AJ

[JimF]

Hi AJ and thanks. Yes, the screws can be independently manipulated. I alluded to that somewhere in my earlier blather. No time to do that experiment on this day and I'm not sure what circumstance it would be used in reference to, but....it can be done. At some point, I'll try it just to see what happens. I've never been a believer in adapting a car for one one particular turn (lead in the inside pan for the donut for ex.) however, locking one screw and not the other would possibly have a similar effect (maybe????)

 

I think there is a bit of an issue with the screws working loose from tight but I suspect that a dab of blue loctite will fix that. There are flats in the screw bearing areas.

 

 

 

[Tex]

regarding those "flats".......

 

make SURE the flats are PERFECTLY flat. when I was building a similar feature into my cars I ran into a problem where, IF the flat was not perfectly flat, the piano wire would twist when tightening down the set screw... this twist then would manifest itself throughout the chassis proper and one wheel or the other would then not sit on the tech block! the "fix" was to not run the piano wire directly into the square tube; rather, insert & solder a piece of round tubing(that the piano wire fit snugly in) into the square tube and THEN drill/tap out the hole for the set screw. once this was done, there was no need for a "flat"... just tighten the set screw down.