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Building the R-Geo "Razzo" Can-Am chassis updated - tuning fork version


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#1 JimF

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Posted 06 June 2017 - 11:25 AM

Yes, it has been a while and boyo am I rusty. Here is Rick's sorta-new Razzo chassis kit. This has been campaigning for a while but my first look at it. Rick sent along a pic of one of the more common builds and I'll follow that but also show some variations. I'm just finishing now. My initial impression is that this will be a high bite car.

 

Here are the parts as supplied. 1" Z-Poid bracket, nosepiece, motor box, pan hanger wings, and pans.

 

DSC02817.JPG

 

Here a couple of center rail vairiations:

 

Two .047" as a fixed spine.

Two .062" set-up in tubes as a tuning fork.

 

DSC02818.JPG

 

Here's another possibility. No motor box and tuning forks for rails instead as generally built by Mr. GVP.

 

DSC02819.JPG

 

Bracket shown here getting the blueprinting treatment. Bracket face is filed until flat as always, legs squared to the face and and filed flat. Of note here is the little undercut on the bracket face. The motor box slips under this and thus, this needs to be checked to see that the box slips under easily. Carefully file until this is so.

 

DSC02821.JPG

 

Bracket with motor box slipped in place. Also shown here is the connector rail of .055" wire. This rail plays a major role in the assembly and assuring that the chassis is legal.

 

DSC02820.JPG

 

I'll do this in a few installments so I don't get too lost (like I just did on this first bit).


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Jim Fowler




#2 JimF

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Posted 06 June 2017 - 12:01 PM

In the jig now and checking to see that the motor box fits easily under the bracket.

 

DSC02822.JPG

 

Here is the rail layout. I'll be using the two .047" fixed center spine and the angled rails are .062". You'll need to file the slots for the spine in the motor box and nosepiece to fit your rail choice and the slots on the nose and the wings to fit your angled rails. A tip here is don't try to be too precise in filing your slots. File the slots a little over the absolute minimum to fit. If you are too fine with it, when you assemble the rails, you'll inevitably get a bind somewhere and then will have to chase around to get the thing flat. 

 

DSC02823.JPG

 

Check your pans against the center section before you affix the wings so that the wings will be in the correct fore and aft location. This is showing the wings in place and the center rails and angled rails in place. It's on the granite block here and checking for flatness

 

DSC02824.JPG

 

Here is a look at the bottom so you can see the bracket, connector rail and wings and how they fit together.

 

DSC02828.JPG

 

Checking the wing placement by putting the pans in place.

 

DSC02825.JPG


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#3 JimF

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Posted 06 June 2017 - 12:16 PM

Just a short installment to cover several little detail bits. A bunch of added braces, connectors etc.

 

There's some important stuff happening here.

 

Motor Box reinforcement does that of course but also ties in to the motor box connector shown in detail earlier in the second installment. By tying in here, it effectively makes this reinforcement an extension of the main chassis rail system.

 

"Tie in" rail. This is a piece of .055 that contacts the reinforcing rail and the angled frame rail. This makes the sequence of motor box connector > motor box reinforcer > "tie in" rail effectively one continuous fore-aft rail system according to rule interpretation. (or.....so I'm told)

 

Stand off pads. This gives a place for a bite bar to rest that will place it on the same plane as the angled rails. This setup was often used on the "Toronto" F-1 chassis to dampen twist flex a little.

 

DSC02831_zpscssy0q94.JPG

 

 

 

 

 

 

 

 


Edited by JimF, 03 July 2017 - 02:43 AM.
Edited to try and recover from Photobucket locking up seven years of pictures.

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#4 Eddie Fleming

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Posted 06 June 2017 - 12:37 PM

Jim I see this kit as a big bucket of worms from a rules standpoint.

 

As I understand it the construction you have is not legal for IRRA rules. 

 

my understanding is you can not have a connector contacting the end or side of a main rail count as a connection.

 

The connectors must have 1/4 inch of overlapping soldered connection to count as connected.

 

At least that is how I understand it.

 

Someone correct me if I am wrong.


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Eddie Fleming

#5 JimF

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Posted 06 June 2017 - 01:05 PM

Thanks for that. I'm not an IRRA guy but was told that an example that I was shown (just like this) was legal. If the butt joint does not meet the rules completely, no problem to fix it. I'll place a simple "L" shaped piece with each leg being at least 1/4" long that will contact both the angled rail and the reinforcing rail.


Jim Fowler

#6 JimF

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Posted 06 June 2017 - 01:32 PM

From the "just in case files"

 

DSC02833.JPG

 

 


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Jim Fowler

#7 JimF

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Posted 06 June 2017 - 03:14 PM

OK, a bit at a time now. Don't mean to drag this out but I'm juggling chainsaws at the moment and can only get to the jig and then the 'puter at irregular intervals.

 

So.....last biggish step is to hang the pans. Near side pic shows pan in place and done. Far side shows the parts ready to go in place. All box tubing is 3/32" sq. the stop rod is 1/16"

 

  • I was a little dubious about this method of hanging and hinging but it actually works very well.
  • I polished the sq. tube after it was cut with 320 paper.
  • Also deburred the insides of the upright loops with a little diamond file.
  • Sq tubes are soldered at the red arrows and not soldered at the blue arrows.
  • The stop rod is 1/16" and limits movement at the forward inside corner of the pan.
  • The pan and nose are different thickness so a little "dogleg" is bent into the stop rod.
  • This setup had very minimal movement but you could get more by using .055 wire or by filing the inside of the loops a bit larger.

DSC02834.JPG

 


Edited by JimF, 03 July 2017 - 02:46 AM.
Edited to try to recover from Photobucket locking seven years of my pictures from the 'net

Jim Fowler

#8 JimF

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Posted 06 June 2017 - 08:26 PM

Last details:

 

This didn't come with a guide tongue reinforcer so I made one up out of a older style R-Geo one that I had. I soldered a steel guide washer to to give a smooth, flat surface.

 

Extra axle uprights are mostly to give me a place to loop the lead wires.

 

Rear bracket brace is .062 wire.

 

Axle soldered in place with a steel spacer inside the upright to give a better joint in the axle slot.

 

This weighs in as shown at 58.5 gr. All up with no body will be about 99.0. This will be a good weight for my usages. If you take out the "windows" on the pans, expect about 6 gr less. Off to the tumbler for cleanup while I paint a body and bend up a set of body clips.

 

DSC02845.JPG

 


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#9 Racer36

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Posted 07 June 2017 - 09:17 AM

Very nice build!


Dennis Dominey

Lifelong half-assed slot racer


#10 JimF

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Posted 20 June 2017 - 02:28 PM

Finally got to run some laps on what passes for a speedway track in Nor-Cal. The 165' Engleman/Hillclimb @ Motown raceway in Modesto Ca. was the venue. This is our fastest track here in NorCal but it's nowhere near a punchbowl. This track has full punch banks at the main straight and the bottom straight as well. However, the rest of the turns are pretty flat and due to the very tight footprint, the gutters are typically about a 9" radius flat turn.

 

I tested head to head against my best car for this track which is a fairly short and fairly light (98 gr) scratchbuilt car. That car has won here twice and also on other tracks as well. The Razzo is longer and slightly heavier in the stock build configuration (as shown). I tested the Razzo with our relatively low downforce TI-22 body. In regions other than the west coast, the higher downforce bodies in use there might skew the results slightly.

 

Test results:

 

Baseline Car ran a best of 4.78 sec. with a good motor. I figured that was about what the track had in it today. 

 

  • Razzo ran 4.98 as shown in the initial tests. Motor was decent but not picked from the "good" batch.
  • First test was with the bite bar @ .032. I thought going in that this was a mistake.
  • With .032 bite bar the car was fast but exhibited slight wheel hop on exit.
  • Changed bite bar to .039 & characteristic improved. Best times were now ~~ 4.92.
  • Changed bar to .047 and basically eliminated wheel hop. Best of 4.86.
  • Tuned tires with no appreciable changes then switched to gutter lanes.
  • In the very tight gutters and it had some nose lift on entry when driven hard.
  • Added 1.8 gr of lead as shown below right behind the guide & calmed down the nose lift.
  • Went back to center lanes and times ran about 4.84 as best.

At the end of the test cycle.........

 

DSC02874.JPG

 

Myself and two other local drivers felt this car was really forgiving and easy to drive. I think the bite bar can go to .055 or .062 with no negative. I suspect that with another 1-1.5 gr of nose weight, this car would handle the tighter lanes better however, the gutter lanes here are much tighter than on any other track in this region. Although this car didn't eclipse my best car for this track it was easier to drive. I also think with a selected motor it might be even better.

 

I intend to test this car on the Purple Angel @ Fast Track Hobbies in Rocklin hopefully this week. I suspect that it will be very good there as shown so far.

 


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#11 zootmaster

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Posted 22 June 2017 - 02:16 PM

Jim Fowler, could you please message me when you get a chance?

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Russ Upton

#12 JimF

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Posted 22 June 2017 - 06:50 PM

Hey Mr. Blast from the past.....................PM sent.

 

BTW..........found this a while back. This was you wasn't it?

 

DSC02877.JPG

 

 


Jim Fowler

#13 JimF

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Posted 13 July 2017 - 01:46 AM

Here's a re-up on the alternate version of the Razzo that I mentioned at the outset. This is the tuning fork version and the kit can be had this way. This one is actually all scratch b/c I didn't want to mess with the original. Concept is identical and main components are the same. Only real diff is the stops which were made from box tube with piano wire stop rods.

 

I tested this car some over the weekend @ Buena Park on the Gerding. This was spectacularly easy and forgiving but granted......it is a 4" car @ 106 gr and the typical stuff that competes here is 3 7/8" or less-less-less and ~~ 90 gr.

 

Then today, I tested on the "Purple Angel" @ Fast Track Hobbies in Rocklin Ca. Again......stupid easy to drive and also fast......very fast. I expect that I'll race this this weekend as is.....no changes at all. I expect this would be a great car in ~~  100 gr configuration on any hillclimb or flatter speedway. Wouldn't be at all surprised if a slimmed down version would shred on a Gerding @ 92-93 gr. naturally, this would be much easier using the tuning fork version of the kit. I just didn't have one ready to go.

 

Here's the overview:

 

  • 4" WB X .925 GL. All up 106 gr with all running gear and a parma Lola T-163 body.
  • Nosepiece is .040, pans are .032 windowed. "Wings" are .032.
  • Tuning forks are .062 as supplied by Rick....free in the tubes.
  • Razzo rails are also .062.
  • No need for weight, bite bars, or other tuning. Good to go as shown.

 

Nose details:

 

  • .040 nose block. Slick 7 guide tongue on a .025 standoff.
  • Front "hinges" (actually a rattler) stops are .047 wire on .025 standoffs to match level on nose block.
  • Body pin tubes are sq. tubes on 1/8" X .032 standoffs.

 

DSC02900.JPG

 

Wing Details:

 

  • Wings cut from .032 brass.
  • Angled rails are .062
  • No need for a connector on this version as the forks are full length rails.
  • Wing stops are .047 wire on .016 standoffs

 

DSC02901.JPG

 

Bracket and fork details:

 

  • Tuning fork rail tucks inside the 1" Z-poid bracket.
  • Filler rail is .055 wire shaved slightly to match the .050 bracket.
  • Spacer wire is .062....doesn't really need to be here.

 

DSC02902.JPG

 

 

 


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