30 replies to this topic

[Michael Rigsby]

This is actually a very good design. I built one very, very similar playing around one weekend, but ended up using .062" outer perimeter wire after finding the .047" too soft for our Hillclimb. I used an R-Geo bracket in the back with no crossplate, and the outer pans were all .047" wire. All brass was .032" except the motor bracket. A very fast chassis and very easy to tune. Probably the only tuning fork I ever built that really worked on a Hillclimb, which are the predominant tracks down here.

 

Of course, my builds are nowhere near as neat as Jim's, as his are works of art in cleanliness.

 

This would make a good basic kit to put into the hands of novice builders as it's not that hard to build, and wire sizes can be changed for track tuning quite quickly (hint, hint).

[A. J. Hoyt]

Jim,

 

I had a similar "chatter" character in what became my "go to" chassis design three years ago. I cut a vertical slot for some .025" wire to mount flush (or slightly below) into the face of the motor bracket such that the wire, after being soldered in, gets sandwiched between the motor mounting face and the bracket (trapped so it can't go anywhere or even flex to weaken or fail the solder joint).

 

This wire went "up" and then had a 120 degree bend that took it to the mainrail, another 30 degree bend so that I had a land about 1/2 inch long to solder it to the mainrail ahead of the but along side the motor. This was quite a bit lighter than the .055" wire "L" you show but seems absolutely stiff in gusseting up that cantilever zone from the motor bracket to the mainrail.

 

Like yours, the chatter went away but, much more importantly, the chassis ALL really hook up off the corners allowing me to just glide the car into the corner and punch it out very early. Extremely forgiving and very fast for every lap because it is not driven as a straight, then a turn, then a straight - it just strings the whole lap together as a smooth "rhythm" kind of driving. Just as important, when pushed, it will allow you to step up your laps to chase someone down!

 

Also interesting is that it did not seem to change the twist stiffness from front axle to rear axle at all - just stiffens up the longitudinal flex where it needs it. Actually, I think it changes the "resonant" frequency of the rear axle torque "wrap up", kind of like traction bars on a leaf spring 1:1 car. If the stiffness of this area matches the torque/bite, it seems to get on a "resonance", the source of the chatter.

 

I really like your outside the box thinking and watch your threads with great interest. Not enough people experimenting out there with new things that are completely within the spirit and letter that the rules allow, in my opinion. Glad to see you are and that you choose to take time to share with well thought out and written articles with nice, clear pictures.

 

Keep it in the slot,

 

AJ

[JimF]

AJ... Thanks for the feedback. I wonder if you have a pic that you might share that shows your idea???

 

OK... the X-1 raced to a comfortable win in its first outing yesterday. I honestly didn't expect this light frame to be very good on a surface with varied bite and conditions... but it was really good. The biggest advantage seemed to be that it could gain one-three feet in the donut on the very dirty King at Eddie's Slot Car World. Even racing against young gun Justin Colvin (who I cheerfully admit is a better driver than I am) I could gain ground in cornering in these highly variable conditions.

 

The pic below shows the frame as it raced. Right below the the frame itself is a fork in tube setup ready to drop in. I didn't try it over the race weekend once it became evident that this was the car I was going to race. That will be the next step. I want to see what effect it will have to drop in the forks in tubes. Then, it may be time for the next version, incorporating what I've learned so far.

 

[Tex]

Very cool... love the development of the tuning fork.

[JimF]

OK... some further testing today still at Fast Track Hobbies in Rocklin. Testing today was primarily about the tuning fork and determining the effect of the forward chords going into tubes. The track had been cleaned since my last test and the surface condition was much better than in the prior test. This time, I was running a JK 8713T slightly narrowed just as I raced it last on the King at Eddie's SCW in Vallejo. The results were even faster than the prior test here and still easy to drive fast with it. The F-7 motor had laid down a little in the race last week, yet I was still able to run comfortably in the 4.82 - 4.89 range. I got a few laps in the 4.7s which is as fast as I've ever gone on this track before... and this even with a modest motor.

 

Then, I tried the pre-fabbed forks in tubes setup as shown above in post #28. I just dropped out the fixed forks and dropped in the little setup as shown and went right back to the track. The car was still good but not quite as hooked up as before. Best times were in the 4.94-5.05 range. This is still good, but just not great like the previous test. I then tried some different tires looking for a little more bite and although some full width untreated tires 'felt' better, the times didn't show any improvement. 

 

I then tried this 95 gram car on the flat MTT with just a gear change. I kept the 9t pinion and went from a 27 to a 30t crown. Later, I went to an 8t pinion. Unfortunately this track was pretty dry and loose and I never got any good results. Of course, this weight is definitely too light for a flat track and for sure, most of my 100 (ish) gram cars were not much to write home about either. After some tires and then a sort of half-hearted attempt at some additions of weight, I left it for what it is, and went on to a bunch of other cars that I had to test on this day.

 

So.... so far, this car has been great on higher speed tracks at the 95 gram original build. I'd also say that it prefers a track with some bite on it but it still was good here at FTH on the Purple Angel when it was decidedly loose. As far as a flat track car, I don't have a great feel for that yet but I have any number of other cars that work great on flatsters so I'm not feeling pressured to make this a go or at least not at this weight. Next steps I think are to build up another one and then work one against the other and also try the general concept on a 4.5" stock car.

 

So far... this is the first car I'd reach for on any high speed track that we run on here in NorCal.

[SlowBeas]

I think I had the same experience as AJ, although I have no pics of it, either.

 

Basically, I bent a short "L." The shortest leg of the L was soldered to the face of the motor bracket, and the longer (maybe 1/2") piece was soldered up the inside of the main rail – in this case, of the tuning fork as it moves forward of the motor bracket.

 

I found this small reinforcement stopped all chatter and the made the chassis much more responsive for me.