30 replies to this topic

[JimF]

Here is the first test mule for something I've been thinking about for a bit. I'm calling this experimental because I'm completely unsure as to whether there's much merit in it or not. What I mean is that if I took a current standard build (saaaay.... multi-rail .047") and varied it from 4-5-6 rails per side or changed the wheelbase or guidelead... that's no great experiment. I know that the variations will work, just a question of what track and what conditions. But with this... I just don't know.

 

So... what is it and why?

 

What...

• The what is almost a full perimeter design with main rails and forks that can be changed.
• Handmade .032" nose with an R-Geo bracket and bracket brace.
• Tuning forks are fixed in front and are .047"
• This is version 1.2 with a single frame rail of .055".
• Version 1.1 had single frame rails of .047". I just changed this today after initial testing yesterday.
• Rear brass tabs are for weight placement and to spread the frame rails.

Why...

• Inspired by Rick's "Toronto" F1, this is an experiment with a softer flexing frame.
• Weight placement... There is very little weight in the mid-section of this frame.
• Most weight is concentrated at front and rear corners (mostly rear)

Variability...

• After initial testing, I dropped out the two original (.047") main rails and replaced with .055".
• This was very easy to do and didn't disrupt anything else.
• The forward half of the forks (currently) .047" could also be easily be replaced with .055".
• I could also replace them with fork rails in tubes without disrupting the rest of the chassis.

So... I'll clean this up and then testing will continue.

 

 

[Pablo]

I could look at that for an hour.   Obviously lots of thinking going on as usual.

 

Glad you are back in the groove, Jim F.

[brnursebmt]

Wow!

[Gator Bob]

Super nice, Jim!

Bet it will work great.

 

Is the bite bar soldered to the outer hinged pan rails?

[JimF]

Bob:

 

Yes, the bite bar is soldered to the outer pans. The pan hinges are .055" in 3/32" tubing so the movement is both fore and aft and a little bit 3D. However, not really tippy pans in the normal interpretation.

[Tim Neja]

Very interesting!! Fun trying different stuff!! Love your testing and explanations!!

[chaparrAL]

I like it! 

[robbovius]

That's pretty neat.

 

So, the idea of this frame is to allow the front and rear axles to twist relative to each other, and control the twist by the stiffness of the single outer rails and the central rails of the fork?

[Tex]

Always enjoy seeing your designs... the wheels are turning.

 

Being somewhat "softer", is this meant to be run on a flat track? Just guessing, but I think a not-too-moderate side hit will bend the perimeter rail... not being critical, just feedback.

 

Look forward to a race report on it.

[SlowBeas]

Like Bob, I'm curious about the soldered outer (pan) rails. I've soldered pans to the bite bar in the past and found that it severely limits the ability of the pans to move independently of one another.
 
I'll be interested in your report.
 
As always, your craftsmanship is truly a work of art, and I really enjoy reading about your successes and stealing... I mean "leveraging"... your ideas.

[Jairus]

Wow, lots of variables to test... like moving the rear pan hinge to the fork to see if that improves handling. 

I love the look of that motor bracket.

[JimF]

Thanks for all the comments, guys. The flex is a major compnent of this design but also the corner weighting is possibly as important as well.
 

So, the idea of this frame is to allow the front and rear axles to twist relative to each other, and control the twist by the stiffness of the single outer rails and the central rails of the fork?

 
Yes. Those are the only structural components and they can be changed relatively easily. The general idea came from Rick B via the "Toronto" F1. His take was that many F1 frames are built stiffer than they need to be. The general effect of the greater twist flex is more cornering speed but without the critical nature of high bite designs. It works on the "Toronto" we'll see about this.
 

Being somewhat "softer", is this meant to be run on a flat track? Just guessing, but I think a not-too-moderate side hit will bend the perimeter rail... not being critical, just feedback.

 
Actually, this is meant as a speedway car rather than flat track although almost all of our King, Hillclimb, etc., tracks are relatively flat. On the relative fragility... yes, it might. I built an F1 with this general idea (soft flex) well before the Toronto and it worked great winning easily its first time out. However, in practice for another race, I folded it up pretty badly with one big hit caused by controller weirdness. The hope is that the elasticity of the rail will cause it spring back rather than take a set but that remains to be seen.
 

Like Bob, I'm curious about the soldered outer (pan) rails. I've soldered pans to the bite bar in the past and found that it severely limits the ability of the pans to move independently of one another.

 
These pans work like a shaker rather than a more conventional hinge. The bite bar is .039" and there is enough flex in it that the pans are somewhat independent. One of the planned variables is to switch this bar out for an .032" and an .047" to see if there any notable difference.
 

Wow, lots of variables to test... like moving the rear pan hinge to the fork to see if that improves handling. I love the look of that motor bracket.

 
Hmmmmm... hadn't thought of that. I don't know if Rick still offers that bracket or not. It has been chopped a bit from stock form but the cut-down bracket face is the way it comes.

[old & gray]

Hmmmmm... hadn't thought of that. I don't know if Rick still offers that bracket or not. It has been chopped a bit from stock form but the cut-down bracket face is the way it comes.

 
Rick still lists it on his website, and PCH lists it as "RGEO PRO 1" Brass Motor Bracket - .050 - RGEO-350".

[Gator Bob]

but I think a not-too-moderate side hit will bend the perimeter rail...

 
A side hit impact will be absorbed by the bite bar with the 'dog leg' in the hinge arm forcing the pan rails to go up on impact. 
 

Like Bob, I'm curious about the soldered outer (pan) rails. I've soldered pans to the bite bar in the past and found that it severely limits the ability of the pans to move independently of one another.

 
I have a flat track 4" chassis that has three .032 'bite bars' soldered to the pans... no bar boxes... and you would be surprised how much 3D movement there is. The pans will still move F to R independently and the 'thin' bar flexes and the pans still have hinge 'action'.  
 
If you solder a 'thick' bite bar to the pans it limits all movement to the size of the 'boxes' or tubes the bar and/or hinge tube runs through. It then becomes a 'shaker'.

[JimF]

Here is a closer look at the bite bar setup. This currently has the .039" bar in a 3/32" square tube. Bottom pic shows the ready to test setup at 93.6 grams all up. I may get it on track as early as tomorrow (Wednesday).
 

 

[Eddie Fleming]

Chassis looks super. I am looking forward to a report on its performance.

 

What brand is that Lola body?

[Dominator]

Another sweet build, Jim.

[JimF]

Chassis looks super. I am looking forward to a report on it's performance.

 

What brand is that Lola body?

 

Tested it today in less than optimal conditions. After a tweak, results were very positive.

 

The body is an O/S 407-L.

[JimF]

Can-Am X-1 track test

 

I tested the new frame today at Fast Track Hobbies in Rocklin, CA. The track was their 165' "Purple Angel" which is a unique test venue. This is a very fast track but almost all the turns are interconnected. Thus, the car stays at high cornering speeds but changes direction almost continually. Lightweight and/or high bite cars usually do not too work well here because despite the speeds, the design favors somewhat heavier cars that can roll from one direction to the other.

 

Track conditions today were not perfect. The bite was off and so personal best times were not in the cards today. I also did a lot of motor, tire, body testing today with this new car. I know how to go fast on this track and so the target was set by my historically best car to date here. This is a six-rail .047" at about 106 grams. Today, that car ran a best of 5.02 with a good motor on board. The car was consistent but fairly loose regardless of tire tuning (best with this car in good conditions is about 4.86)

 

The new car was set up as shown above and started with JK 8703 slightly narrowed.

• Right from the first, the new car exhibited horrendous wheel hop. Basically, I couldn't get it off the line at all.
• I couldn't get the car under 5.40 and the bouncing/grinding was making me cringe.
• Slight wheel hop is not unknown with tuning fork designs but this was like a bent axle or blown bearing.
• I checked all the basics (axle, bent wheel, bad bearing, broken solder joint, etc... all good)
• I suspected two things. (1) needed a flex limiter, (2) too much flex in the rear chord of the motor box.

Soooo...

 

First, I applied a flex limiter in the usual place (blue arrow)... absolutely no change at all.

• So then, I applied some reinforcement to the rear chord of the forks (red arrows)... MAGIC!!!
• The two "L" shaped braces are .055" soldered to the bracket face and full soldered along the rear chord.
• From this point on... this was the fastest car in the box on this day.
• Same setup that was running 5.40 was suddenly running 5.05.
• The handling (even at 93.6 gr.) was so good, that I couldn't believe how hard I could drive it.

I continued to test, first going through four new Retro Hawks... the best one ran a 4.98, worst was a 5.10.

Eventually, I put in one of my best F7s and got into the low 4.9s (4.92 best)

I tested the three bodies that I use most commonly (shown below) but no difference that I could quantify.

I tried my usual litany of tires but with the slidey conditions, the only thing that was decent was full width JK 8703.

 

Soooo...

 

I'm not sure what to do next because there wasn't anything I put my finger on to fix. I guess the next step is to try it with the forks in tubes and also to test on different tracks and conditions.

 

Or... maybe just build another one... 

 

 

[Dominator]

What about trying .063" on the perimeter or running a limiter from the fork to the perimeter rail like you did on the Toronto?

[JimF]

Good thinking, Dom. I could try both of those things and either might work.
 
I think the issue here was not too much twist overall but too much vertical flex in the motor box. The rear chords of the forks are .047" and they had a lot of vertical flex forward of the junction with the bracket The thicker perimeter rail would stiffen the torsion but the motor box is so isolated from the rest of the frame that I don't (think) it would have the right effect on the vertical flex. The first laps I did with the car were with .047" perimeter rails. There was some of the chatter and bounce but not much and it was a different track/different day. Switching to the .055" perimeter for this version didn't make any difference.The single limiter that I soldered at the crux of the forks stiffened the torsion but didn't do much of anything with the vertical flex. The add on "L" braces definitely stiffened that area and stopped the problem cold. The "V" limiter might do it where the single wire bit at the crux didn't.
 
I have a race this weekend so I'm going to let it go for now. Then... I think the next step will be forks in tube and see what happens.

[Gator Bob]

Just a guess ...

 

If the forks go in a floating tube or box (unsoldered) the hop may come back.

 

How much space is between the bite bar and the fork rails? They may have been 'bouncing' off each other if the clearance is small and the 'torque wrap' of the motor box rails.

 

It's very cool the two short 'L' rails calmed the car that much. WTG, Jim.

 

Thinner .032" bar? maybe...

[slotcarone]

Jim,

 

I had a similar experience with a F1 Retro chassis. Horrendous hop and chatter and it was cured by adding to pieces exactly like you did. Now very smoothe!!

[JimF]

If the forks go in a floating tube or box (unsoldered) the hop may come back.

Yeah... it might for sure although then it would be a torque wrap which I don't (think) is what's going on here.
 

How much space is between the bite bar and the fork rails? They may have been 'bouncing' off each other if the clearance is small and the 'torque wrap' of the motor box rails.

There is about .015" between the bar and the rails. As it is here... the forward leg of the forks can touch the bar in extreme twist. However, when I put the limiter in place it was just aft of the bar and in that configuration, the forward legs couldn't touch the bar because the twist was so much less.
 

It's very cool the two short 'L' rails calmed the car that much.

Thinner .032" bar? maybe...

 
Yeah... I had one cut and ready to drop in but when the miraculous "cure" happened, I forgot to try it.

[JimF]

Jim I had a similar experience with a F1 retro chassis. Horrendous hop and chatter and it was cured by adding to pieces exactly like you did. Now very smoothe!!

 

You know... I was thinking about this concept a while back and actually put a tiny version into an F1 that I wrote up last year sometime (a Toronto I think). In that case, it didn't seem to do much and I sorta dropped the idea. Now, it makes me think that it was the right idea but just not enough of it.