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R-Geo Samurai (unhinging the fork)


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#1 JimF

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Posted 06 July 2013 - 12:01 PM

I've been staring at this nice kit from Rick for a while... trying to figure what to do with it. This kit is .030" brass except for the bracket which is thicker. The factory cut-outs are set up for several building options.
 
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I've built five-six new 'tuning fork' cars in the last ten days or so. Those have all been two-hinge or four-hinge cars and they have given me further direction. Here are some starting ideas... Top pic shows how the car would set up as a standard 'micro rail' frame with seven rails of .039"/side. Bottom pic shows the addition of a tuning fork.
 
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All the cars that I've done up lately are hinged forks... meaning the forks twist freely in central tubes. Those are great and offer an extremely soft twist flex. However, this nosepiece has a cut-out for wire only with no room for the tubes so rather than modify it at this point, I'm going to run with the stock configuration for the forks.
 
This car will be a hybrid of the micro-rail and the tuning fork. I don't see the need for seven rails/side of wire when I have the central fork so I'm going to get started and see what fits. I'll be looking for a cross between the twist flex of a 2-4 hinge "forker" and a more standard frame.
 
Next steps tonight...
Jim Fowler




#2 John Streisguth

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Posted 06 July 2013 - 12:09 PM

Jim:

I built a similar design for an F1 chassis. I used .055" fork rails, and started with four rails of .039" on each side.  I ended up with six rails on each side because I felt the flex was better (i.e. stiffer) for the high speed tracks I run on. I haven't raced it but it has tested very well.
"Whatever..."

#3 Tim Neja

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Posted 06 July 2013 - 12:11 PM

Always interesting to follow your builds, Jim!! Go for it!! :)
She's real fine, my 409!!!

#4 JimF

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Posted 06 July 2013 - 12:33 PM

This car is actually done but rather than type and photo edit... I'm going to scamper down the hill to Fast Track Hobbies in Rocklin for some testing. All the gazillions of other new 'fork cars' need some exercise, too.
Jim Fowler

#5 JimF

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Posted 06 July 2013 - 02:01 PM

I'm going to scamper down the hill to Fast Track Hobbies in Rocklin[/u][/color] for some testing.

 
Wellll... THAT... was a really bad idea. An hour and 15 min. and I didn't even get eight miles from my house. So... the rest of the build recap soon, the testing... another time.
Jim Fowler

#6 SlotStox#53

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Posted 06 July 2013 - 02:40 PM

Sorry the traffic scuppered your testing plans... Looking forward to seeing another one of your builds. Always plenty of info and all noted for later use. :good:

#7 Tim Neja

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Posted 06 July 2013 - 03:23 PM

Wow---sorry your testing plans didn't work out!!! I headed out to The Cave today to try my two new builds and discovered it was closed when I got there?? They had a race on the schedule so I hope there wasn't some kind of emergency medical or otherwise that caused the closing!!  Looking forward to your summary and PICS Jim!!! 


She's real fine, my 409!!!

#8 JimF

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Posted 06 July 2013 - 06:10 PM

OKAYSO......................here's the rest of the build.

 

 

Chassis plate in the jig, forks in place. Using a popsicle stick as a hold down right at the bend in the forks......tack the forks front and rear. Notice a little wire bit extending from the front of the forks. This is a bit of .032 that lies in the valley between the forks and extends out over the front plate.

 

 

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Forks are now in place and tacked fore and aft. Here's another look at that little bit of .032, not yet soldered in place.There is a scrap of oiled paper between the fork rails right at the front. This will keep the solder from flowing back along the rails and locking them up.

 

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Nosepiece more or less done and pans cut off, Note there is now a bit of .055 on either side of the center. This corresponds to the thickness of the .055 forks that staddle the motor bracket. This allows the rest of the rails to lay in parallel to the center line. Guide tongue brace and the .032 wire support are also in place and the new spacing dimensions that we are working with are now marked.

 

 

 

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Here's the rail layout.....sorta spread out so's you can see it. We have (4) main rails of .039 with a .062 spacer front and rear. There is also a .062 rear guard in the pic that will go in place as the rails go in.

 

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Here we are soldering in the main rails, the spacers, and also solidifying the connection from the rails to the bracket and the nosepiece. There is a scrap of notebook paper that is well oiled between the fork rails and the main rails. I personally think that isolating the fork/bracket assembly from the outer main rails is one key to the benefits of the various "forkers".  Again IMO, but I think you do not want the fork rails soldered solidly to the outer "main rails" much forward of the bracket. Note that all the various spacer rails are held forward about .090 from the trailing edge of the nosepiece. This is to allow clearance for the 'shaker' rail that will follow.

 

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Starting to look like something (I hope). All main rails are now in place and flow soldered. Rear guard is in place, we are getting close.

 

 

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This little bit here is the front "shaker" tube. This is a bit of 3/32 sq. tube, inside of a bit of 1/8 sq. tube. The goal here is to get a little moe "lift" off the deck of the noespice so that the shaker rail has clearance over the main rails and the "fork" rails. This is made up in one piece and then cut in two. The dimension of the tube is not critical but these will each be about .200" long.

 

 

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Here we are in the jig with the front and rear shaker tubes in place. Front tubes are as described above, rear are 3/32" sq. tubing.

 

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Really wrapping it up here. Front shaker rail is .055. A little dogleg is bent into the outer edge so as to lay flat on the pans. A bit of .062 wire is in place to reinforce the solder joint. The tie bar is .032 but could be about anything. Rear shaker rails are .047 wire and placed within the tubes for free but minimum movement.

 

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Bottom view.

 

 

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And all set up with running gear including Samson BB fronts. This goes 101 gr as shown (no body) probably about right for a one of our speedway tracks but probably a little light for a flat track.

 

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As always.......more to come.


Jim Fowler

#9 SlotStox#53

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Posted 06 July 2013 - 06:31 PM

Excellent build as always Jim :good: 

 

Looks like it really came together nicely..



#10 John Streisguth

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Posted 06 July 2013 - 06:51 PM

Nice...


"Whatever..."

#11 Rick

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Posted 07 July 2013 - 12:58 PM

Very kool build Jim, as always your design will stir the creativity in others that follow along. Can't wait to hear how it works for you. For those of us the race in IRRA(s) the weight is great. Should be 106 RTR....................... 


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#12 JimF

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Posted 07 July 2013 - 01:10 PM

Thanks guys. Just about to dart out the door and try the 90 mi drive to FTH again. I suspect that this car will be great right off. This is firmer in flex than all of the two-four hinge cars but softer than the Speedwagon so it should fit a nice little niche in the quiver.

 

Hoping that the holiday traffic from Tahoe (where I live) to Sacto has calmed down some. If not........I'm going fishin'


Jim Fowler

#13 Tim Neja

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Posted 07 July 2013 - 06:16 PM

I'm not sure we need weight on the flat tracks anymore with these wishbone chassis Jim!! The original wishbone I built for the King did not come in as light as I thought it would--104 grams--and trying it on the BPR MTT track today the car was VERY good!!! Very smooth--lot's of bite with treated tires!!! We usually run non-treated on the flatster!! So I'm busy putting the same pans on my new wishbone to lighten it up more--and going away from the shaker pans back to hinged pans with very little movement!! It works on the first car---the Gen II car in the pic has heavy pans as a shaker I'm removing.

Enjoy your testing.

T

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She's real fine, my 409!!!

#14 JimF

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Posted 08 July 2013 - 10:21 AM

Here's a quick update before I head off to work.

 

I tested yesterday @ FTH on both the Purple Angel and the Flat track. The Samurai was great on the Angel just as shown. Eventually, I tuned it a bit with tires and a little weight and ended up with 2 gr each side at the rear of the pans and Koford Wonder softs. Body chosen was an O/S lola 163 (medium downforce)

 

On the flat track, it was a different story. The light car was just overmatched. The track conditions were spotty in that there was very light glue and inconsistent rubber build up so the bite was inconsistent. On this day, the better cars were heavier and stiffer than this. I had so many new cars to work on today that I just didn't spend a lot of time with this car on the flat track. Since I planned it as a speedway car anyway.....no worries.

 

This design works like a conventional frame with a very soft flex like maybe a 1 x .062, 3 x .047 or something like that. The solid fork connection takes most of the effect of the fork out of the equation so this car does not have the dampening effect of the hinged forks. I'll have to think about this one for a bit and may end up doing a retro-fit of some tubes in the front......not sure yet.


Jim Fowler





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