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R-Geo "Toronto" F1 chassis, updated - July 2016 version


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#1 JimF

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Posted 06 October 2014 - 09:40 PM

The R-Geo "Toronto" F1 chassis (part one)

Introduction:
 
This build in itself is pretty simple so there will be a little more explanation and theory in this article. Naturally, if you are bored by that part... just scroll to the pictures.
 
So... maybe ten days or so ago Rick B tipped me off that he had a new twist on the ubiquitous tuning fork chassis in F1 format. His theory was that the majority of F1 frames are built too stiff in twist flex so he had come up with a simple frame that was showing a lot of promise. He described his design and requested that I do a pictorial when he could get me some parts.
 
This was really interesting to me because I had built something with the same goal about a year or so ago. Mine had proven enormously successful in its first race but shortly after that it also showed that it could be easily destroyed. After I wrecked that first one beyond repair, I sort of forgot the concept and moved on. Then when Rick mentioned what he was up to, it sounded better and more durable than what I had done.
 
So... while waiting for the parts, I built these two up as a test bed and to make sure that I was on the same page as he was. The one in the foreground is the closest to the description that Rick gave me and it has been tested and tweaked a bit. The one in the background has yet to be tested so it is an unknown and is just shown for reference. 
 
Foreground car:

  • R-Geo .050" x 1” nosepiece and bracket.
  • .062" tuning forks free in the front tubes.
  • Single .047" frame rails.
  • .062" x ¼” pans, total weight with body shown and lead wires in place = 88.4 grams.
  • Arrow... in the initial build, this ‘V’ shaped stop was two single bits of .047".
  • After testing, there was some gear clash sound so I placed the ‘V’ shaped stop of .032" and it was much improved.

On Track:

  • In testing on two different speedway tracks in NorCal, this car was very fast.
  • This was .015-.020 faster than my best prior speedway cars.
  • Surprisingly, this car did not have a “touchy” driving feel like many very light cars.
  • I tried it on a flat track and... yeah... it was too light but it was still faster than my standby flat track chassis. It was a little hard to drive... but fast.
  • This was pretty inspiring so while the parts were in transit, I tried...

Background car: (not yet tested)

  • This car was built to be heavier to start with in order to have a test bed for flat tracks, and will be initially tested without the ‘V’ stop.
  • Bracket brace is .062" brass, nosepiece in .062" brass. Pans and rails are the same.
  • Total weight all up for this one is just over 95 grams.
  • This frame also has a flex stop between the fork rails and main rails just forward of the bracket. This is completely experimental, just something I’m thinking about.

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24f275dc-3bd0-4159-a42b-dd24d9da6301_zps
 
So... on we go...
 
Here are the pre-made parts as you will get them from Rick. You get bracket and nosepiece of .050", pans of .062", bracket brace of .032", and a pair of .062" forks. I have to say that I’ve built a lot of tuning fork chassis and bending and squaring the forks is a serious PITA for me. These forks came very good with very little tuning or squaring required.
 
Parts:
 
9813bff3-0ae7-4db8-8eb8-fef6ed5d86d9_zps
 
Baby steps:

  • Your first steps should be to detail your bracket and make up your fork tubes.
  • Sand or file the bracket face and bottom flat and also the sides if needed.
  • Square up the sides to the face, then screw in a test motor and check it again.
  • Cut a slot at the bottom of the face as shown for the fork rail to pass through.
  • Fork tubes. Two bits of 3/32” box tube soldered up then squared off at about 5/8”.

1a2a06a8-f3ea-4051-bf2d-c7ae34a98ee1_zps
 
Your guidelines... (the template)

  • This is drawn up just to give me some guidelines.
  • This one shown here has actual numbers on it and is a reference that I’ll keep.

b594a1f8-a883-4e7f-9cf4-9054a1a40c51_zps
 
The template in action:

  • This template had some mistakes in dimensions so ignore those. I’m just using this one to check angles and alignment.
  • This will show how the template is used to lay out your parts and check the lengths.
  • Trim your fork wires accordingly and use the template to check parallel.

89e7d2cd-d3ca-4220-bf68-296e1c40c903_zps
 
More template work.

  • Lay your forks on a flat surface and make sure they are flat.
  • Lay your fork wires on the template to check that the fore and aft legs are parallel.
  • Lay your pieces together on a flat block or jig, and check for fit.
  • This step is where you’ll find how square your fork rails are.

a6befec0-3c69-4ec6-8a1b-d356057bdec7_zps
 
Template gone... all on the flat block:

  • Now, lay all your parts in place with the forks in the tubes and the bracket brace in place. Check to see that the forks lay as flat as possible while square around the brace.
  • Lay the bracket over the sub-assembly. Make sure it slips in place without interference.
  • The bends in the wire will want to move things around. Make sure nothing binds.
  • If all looks flat and square, lightly tack the tubes in place (arrow).
  • It is more important for the forks to remain flat at the apex than it is for the tubes at front.
  • If the forks are trying to lift the tube assembly a little... that’s OK let it be.
  • Remember that in a tuning fork build, the forks should not be forced into a position... let them sit where they want to sit.

244cbeee-540b-48c3-9ae5-c55cf97feee0_zps
 
4af02b44-a6b0-4588-99af-9f8580c9411c_zps
 
Into the jig:

  • Place parts in the jig and square up the nosepiece with the guide pin and front axle.
  • The axle slots are a little oversized but if you slip a JK 3/32" retainer in the slot, it all fits tight.
  • Use a square to align the bracket face square to the chassis.
  • Note that there are alignment pins all over the place at this point. Use them a lot.
  • Get your bracket at the right spot for your wheelbase (4”).
  • I don’t use jig wheels and bearings at this point. It’s more important to square up the bracket face than it is to align the bearing holes perfectly.
  • Don't let your bearing holes dictate the accuracy of your bracket face. Align your bearings later.
  • When it all looks right, tack your bracket plate and fork rails at the very rear of the bracket (arrow).

62efb86d-a434-46b2-be3f-d5f4a6994617_zps
 
Still in the jig:

  • Each frame rail is a single .047".
  • You can see that I’ve got guide pins all over the place here.
  • Your jig and your guide pins will keep you square.
  • Lay frame rails in place against the nosepiece, guide pins and bracket.
  • Quadruple check the alignment and tack solder the rails at front and back.

4322e972-d904-4e58-bd4a-77807d3a80fd_zps
 
Out of the jig... on the flat block.

  • Here is where you lay your frame on the flat block to check for flatness.
  • Clean your chassis up so you can see all your solder joints. Check each one.
  • Check each spot with a blue arrow for flat on the block.
  • The apex of your forks may not be perfectly flat but you want very, very close to that.
  • Naturally, the forks will be up a little where they go into the tubes, can’t help that.
  • Douse the thing with flux, turn on your fan and complete the solder joints.
  • Let it cool, then more flux and this time use a torch or a really hot iron and remelt each joint. As you do, check to see if anything moves.
  • It’s a good bet that one or more of the joints will “settle” a bit.
  • Don’t worry unless something moves dramatically.
  • Settling the chassis is key to having a build with no binds in it.
  • Don’t be surprised if your tubes (red arrow) move a touch. If the tubes lift a few thou... that’s OK. That is just taking stress or binds off of the forks.

48ad4808-82ea-422c-80bc-83504d285b05_zps
 
OK... good place to stop for now. Will finish up part 2 tomorrow or the next day.

  • Finishing the rear end with a little theory involved.
  • Front end, axles, and pan pivots.
  • Pan spacing and stops.
  • Added weight for minimums or for flat track use.

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Jim Fowler




#2 macman

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Posted 07 October 2014 - 04:38 AM

Where can I get one of those little squares???


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#3 Dominator

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Posted 07 October 2014 - 05:37 AM

Another great looking build Jim. What I have found when adding the "V" to the forks is that it slightly stiffen's thr rear and still allows the front to flex freely.

A motor is only as fast as the chassis it's in.
 
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#4 Craig

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Posted 07 October 2014 - 09:18 AM

Ben, Micro-Mark has that square.  The Item # is 82147


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#5 JimF

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Posted 07 October 2014 - 11:42 AM

Where can I get one of those little squares???

 

This little thing is almost indispensable for me. I use it constantly. Google "Zona Steel Square" and you'll find 'em all over the place. I wouldn't be surprised if your local hobby store has 'em.


Jim Fowler

#6 JimF

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Posted 07 October 2014 - 11:46 AM

Another great looking build Jim. What I have found when adding the "V" to the forks is that it slightly stiffen's thr rear and still allows the front to flex freely.

 

Exactly. I'm going to put a fair bit of theory discussion at the beginning of part 2 and will discuss several bits relating to the situation of wheel hop or gear clash in some tuning fork frames.


Jim Fowler

#7 Danny Zona

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Posted 07 October 2014 - 04:59 PM

This little thing is almost indispensable for me. I use it constantly. Google "Zona Steel Square" and you'll find 'em all over the place. I wouldn't be surprised if your local hobby store has 'em.


It is one damn good square with an awesome name. Ha-ha.


Test, test, test and go test some more.
You're never fast enough!!! 💯

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Be a fountain not a drain.

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#8 Tim Neja

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Posted 07 October 2014 - 10:02 PM

Well, I use a "Zona" saw when I"m building my R/C planes!! :)


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She's real fine, my 409!!!

#9 Rick

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Posted 07 October 2014 - 10:12 PM

Here ya go, Neja. Git to building a 90 gram F1 and kick some a$$ at BP...


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#10 Tim Neja

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Posted 07 October 2014 - 10:40 PM

If you send it I will build it!!! :)


She's real fine, my 409!!!

#11 JimF

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Posted 08 October 2014 - 12:48 AM

Part two... wrapping it all up

Rear end parts:

  • Rear weight tabs of .062" brass about 1" long.
  • These also provide placement for pan retainer/stops (3/32" box tube).
  • Small bits of .055" wire will support the solder joint between bracket and frame rails.

e528a9c1-3ec5-4934-a913-f4d686022abe_zps

Finished rear end:

ff2ca5aa-6da2-40d7-822e-05bc4fd7a4d0_zps

Right at the finish of part #1 I warned ya'll that I had some theories about the rear end set-up. This is no big deal and certainly not worth a call to NASA but here’s what (I think) I think about tuning fork motor boxes/rear ends.

 

Look ​out!!... incoming theory

  • It seems fairly common to hear about a gear grinding or clashing sound and/or wheel hop from some tuning fork frames... sometimes... sometimes not... and not all of them or all of the time.
  • Most times, when this condition showed up for me, it was in lower traction situations where there was some wheelspin during take-off (like Wonder rubber tires sometimes do).
  • I have had some that have exhibited this and some not.
  • The ones that didn't, seemed most often to have fairly stout main rails in addition to the forks.
  • The ones that did exhibit this seemed to be ones with fairly soft/thin main rails.
  • With the ones that did exhibit this wheel hop, it could usually be mitigated and sometimes eliminated by a soldered flex limiter at the apex of the forks.

WHY???... I dunno... but...

  • (I think) that I think it has to do with excessive torsional flex which the flex limiter can mitigate.
  • It might also be a more complex situation of the torsional flex plus some “rear steer” due to the thin frame rails not controlling this phenomenon (IMO rear steer is undesirable with inlines).

SO...

  • We build with tuning forks to get that big flex to give us bite and cornering speed.
  • But... sometimes we get that chatter/wheel hop/gear clash.
  • So then we surround the forks with stiffer main rails... but we lose some of that bite we were trying to get.
  • Pic below shows another little thing I’m just now messing with which may not help at all... but it might.

This is a small bit of .062" wire dropped between the main .047" rail and the fork rail. When soldered up to the rails and the bracket, this will mitigate the rear steer from the flex of the thin main rails to some extent while not changing the flex at the apex of the forks much if any. This bit is very small but of course could (probably will) be made longer.
 
2974035c-a372-4ae6-94a7-7457d7d4ef1c_zps
 
OK... back to the real subject...

  • Pans are placed next to the frame and trimmed to length as you see fit.
  • I have set these so the rear body mount is about 1-1/8" forward of the rear axle.

3fee1886-1e84-4a73-a42c-ce21b95b285f_zps

  • Pans are cut to size and placed.
  • Pans are side to side spaced with .008" paper on either side (double arrows).
  • Pans are spaced fore and aft with .015" card stock at the rear of the pans (blue).

082baef7-9ab6-4196-9877-852eca19cf54_zps

  • Front pan hinge rod (.039") with one side bent, sitting by the front.
  • Hold the pans snugly against the spacers and solder pin tubes into uprights.
  • Spreader bar (.032") is in place and soldered to pans just fwd of the fork apex. Pan spacing is now held securely.

e8de98f9-289d-4a61-9054-3e30ffcd7a02_zps

  • Front pan hinge is slid through the hinge tubes, bent on the far side and leveled, soldered in place.
  • At very rear of each pan is a bit of .015" brass that levels the pan to the stop tubes.
  • When the pan stop rod goes in place it will now be level with the bottom of the stop tube.

b5108966-58b8-404e-85bf-f307056be4e8_zps
 
A lot of finishing details here...

  • ‘V’ shaped stop in place at the fork apex. This will rest on the pans and be soldered to each fork angle.
  • This will act as a flex limiter and also limit upward pan movement. Fore and aft slide is still free.
  • Also shown are two bits of .047" that could replace the ‘V’. They would be soldered to the angles, resting on the pans but obviously, not connected over the fork apex.
  • If I were using the two independent stop rods, I'd probably use a soldered flex limiter just forward of the spreader bar. There is one dropped in place here for illustration.
  • Front axle with JK retainers, ready to jig up and solder in place. The retainers will snug up the axle slots and make the axle more solid as well as easier to get square.
  • Rear pan stops in place (.047") inside the rear stop tubes. Could be any size you want.
  • Do these final details, jig up your bearings solder it all up and almost done...
  • We are looking at about 94.8 grams all up with all running gear and body.

4b773d40-6939-4d31-8ebc-ab0d37d2cfb7_zps
 
Last thing... running weight:

  • My testing so far has shown that for our NorCal speedway tracks, I’d keep the ~ 95 grams or even go lighter (as in the example shown in the beginning).
  • But for the East, the 100 gram minimum has to be met.
  • So... two little brass center weights are cut. They are soldered to the spreader bar and floating in front and there is a .032" downstop bar across the front of them.
  • These weights are .340" wide and about 1” on the long side. Each is about 2.7 grams.
  • Roughly in the middle of the chassis and down as low as reasonable is where I like to add weight.
  • With the parts and body I used to check weight, this car will complete at about 100-101 grams.

I think this frame will end up being a great general purpose racer. One very key thing is that this is the easiest to drive car of this weight that I've ever driven. The fact that it can run well on at least one flat track at this light weight is very surprising.

  • If you wanted more weight like for a flat track, these center weights could be made longer.
  • However, this frame runs so well with the light setup, I’m unsure as to whether much additional weight is needed.

893a1516-78f4-4284-abff-dbc756612f88_zps


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Jim Fowler

#12 bluecars

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Posted 08 October 2014 - 06:31 AM

:) Very cool. :good:


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#13 John Gorski

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Posted 08 October 2014 - 10:40 AM

Sano build, Jim.

 

Some very valuable info for scratchbuilders new and old.  :good:


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#14 Dominator

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Posted 08 October 2014 - 11:32 AM

Jim, did you leave any space between the ends of the V and the pans?
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#15 JimF

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Posted 08 October 2014 - 12:11 PM

Dom:
 
I didn't. I followed Rick's original concept which was that the limiters would rest on the pans and keep upward movement basically nil. You could put a piece of paper with the desired thickness under the tips when you soldered in the V, and then you'd have whatever you wanted.
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#16 Danny Zona

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Posted 08 October 2014 - 03:40 PM

Jim, very nice build. I love how you explain your builds. It helps me out a ton.

I can't wait to build a few myself.
Test, test, test and go test some more.
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Be a fountain not a drain.

It's not about being right, it's getting it right.

#17 Tim Neja

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Posted 08 October 2014 - 03:43 PM

SWEET!! I love all the thought and pictures you've used as well!! Makes it easy for those of us the "Copy" rather than "design"!!! Always appreciate your work and racing with ya!!! You should try to make it down for our "Boola Bash" at the end of October--racing on BOTH the flat track AND the King!! :)


She's real fine, my 409!!!

#18 JimF

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Posted 09 October 2014 - 12:14 PM

Jim, very nice build. I love how you explain your builds. It helps me out a ton.

I can't wait to build a few myself.

 

You'll be able to do a number of them easily in not that much time. I spent more time on text and pictures than usual here b/c the build was pretty easy and that gave an opportunity for more explanation and theory. The writing and picture editing and all that took longer than the build did.

 

I think that this could be one of those great starting points where you can try several versions for different applications in a short time. I know that the very light version will go well on our speedway tracks. I'm anxious to work more with the heavier versions as more dedicated flat track cars.


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Jim Fowler

#19 ejgehrken

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Posted 10 October 2014 - 10:55 AM

What wheelbase did you use?


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#20 JimF

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Posted 10 October 2014 - 11:31 AM

Eric:

 

This one is going home to Rick's house and he asked for 4". The two initial test cars were longer than that.


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#21 Rick

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Posted 10 October 2014 - 12:04 PM

:)

 

It's here and it's beautfiful!!!


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#22 ejgehrken

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Posted 10 October 2014 - 01:28 PM

How long were the initial test cars?


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#23 JimF

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Posted 10 October 2014 - 01:33 PM

The light one is 4-1/16", the heavier one is 4-1/8".


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#24 Tim Neja

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Posted 10 October 2014 - 01:39 PM

Oh, regular "limos" huh!??? :) :)


She's real fine, my 409!!!

#25 JimF

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Posted 10 October 2014 - 02:20 PM

Limos?... Yeah, I guess although I haven't built an F1 under 4" for quite a while and usually like 4-1/8". Those are just normal lengths for my tastes, although this lighter Toronto at 4-1/16" might change my tune on that (at least for that particular car).

 

Heck, most of my general purpose Can-Ams are 4-1/16".


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