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Building the R-Geo Dragonslayer 7 (update - track test #2)

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#1 JimF


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Posted 24 April 2015 - 05:02 PM

Dragonslayer Seven

Here is a step by step for the new three-piece DS-7 from R-Geo. I have done an article on the DS-6 in standard stock frame rail format so Im going to do this one a little differently.
The standard build is five rails (.047") per side. Each side gets three main rails and a doubled up tripod rail. The new version could be built that way as well and probably most will want to do it that way. This one is two spaced main rails and one tripod rail per side so it will have more flex. There is also an easy way to add frame rails if you try this and it has too much bite.
So... here are your parts out of the bag. These were nicely flat with only a bit of flattening to do in the bracket frame. This is a new bracket from Rick that is non-hypoid and has an angled bracket face.

As always, you want to sand or file the faces of the bracket so they are nice and flat, then youll square the bracket up if necessary. Then, you'll trial fit the bracket frame and may need to file a bit (arrows) so that it fits easily without binding. Then solder in place.


Next, we make up our frame rails into pre-fab sub assemblies. This allows for easier handling. You can see the two main rails with a spacer in the rear. There is also a piece soldered on the outside which takes the place of the inner tripod rail of the more standard build. You may need to file a bit at the arrow to make sure your sub assemblies fit without any bind.
Arrow shows where you may need to file for the sub assemblies. Forward of that, you can see that there is still a space left for the tripod rail to drop into.

Now, we make a rough bend in a stick of .047" wire in order to form our single tripod rail. After making the bend, we test fit the rail into the remaining space and file at the indicated (arrows) spots to make sure the rails will drop in with no binding. Its better to have a little too much space here than for it to be tight at all.

Now we go onto the jig and set our nosepiece in place. The slots for the front axle are a little oversized so we use a JK 3/32 solder-on retainer here so that the front axle is snug in the uprights. We want bushings and jig wheels at the rear so that front and rear axles are parallel. We have locating pins in place to help keep our main rail assemblies straight. Tack solder the main rail assemblies in place, then finish up the angled bends on the tripod rails, filing as necessary to make sure that the tripod rail fits easily with no bind. Notice a couple of little bits of .047" in place as spacers to hold the tripod rails out from the nosepiece a little. When this is all done, fully solder your rail assemblies and tripod rails in place.

Out of the jig for a minute. Clean the frame up so you can inspect all your solder joints. Then place the frame on your flat block and make sure that it sits flat. You may want to douse everything with acid and use a torch or hot iron on one corner at a time to see if anything settles a bit.

Back into the jig for a sec and make up your retainer tubes. The front is a pair of 3/32 square tubes at just over 3/8 long. They are soldered together and then cleaned and squared up. The rear is a bit of 3/32 inside of a pice of 1/8 square tube. The standard build uses the 1/8 with a 1/16 wire pin. I dont care for that much movement, so I use the 3/32 inside to fit more closely with a .047" pin.

Retainer tubes are now soldered in place front and side. Guide tongue reinforcer is also in place here. The GTR is shortened by about .100 in order to have more room for the front hinge pins Trial fit your pans as shown. I am using a longer wheelbase than the standard 4 and thus, I need to grind a little at the spots shown (arrows) in order for the pans to fit properly. The front and side pins are in place to show approximate placement.
NOTE: It was probably a strategic mistake to solder the front tube in place here. After I did it and started fitting the pins, I realized that it was a seriously fiddley process to work them into place to check the bends, then take them out and do it again etc. It is probably best to bend your pins and test fit as necessary, then put the assemblies in place and solder the tube in place.

Here is a pic of the front pin on the flat block. You can see that the tube holds the pin slightly off of the block. If you install it this way, you will get a little pan droop when the pin drops flat to the nosepiece. You will want to make a tiny upward dogleg bend at the spot indicated (blue arrow) so that the pin sits flat on the nosepiece when resting in the tube. This is important because if you do this, you wont get pan droop. Then, youll make a rearward dogleg bend at roughly the spot indicated (red arrow) so that the pin rests fully on the tip of the pan.

Here it is all wrapped up except for finish details. Ill be using body clips on this car so no pin tubes in place. Naturally tubes are more commonly used, but I like clips where practical. Bearings and front axle need to go in yet, but thats about it. There is a piece of .047" wire sitting below the finished frame. This is an extra frame rail that you can put in place if you feel that the car has too much bite. The second pic below shows it sitting in place as a second tripod rail. It could also be dropped into the space between the two main rails.


Ill show a final setup pic once I get it on track. Here is the new frame shown side by side with a stock build DS-6 that I just finished up for a customer. The frame rails on the DS-7 could well be set up this way as well.

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Jim Fowler

#2 Pablo



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Posted 24 April 2015 - 06:07 PM

Sweeeet. I see how you want the rail flex to begin well forward of the bracket face.


Thanks, as usual, for sharing your ultra SANO-ness, Jim. :whistle3:

Paul Wolcott

#3 JimF


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Posted 24 April 2015 - 06:36 PM

I see how you want the rail flex to begin well forward of the bracket face.

You got that exactly right. I even took the little extra bit of reinforcing wire that I always use next to the bracket and extended it well forward of the bracket face for further stiffening in the bracket area. Too much flex at the bracket face was one lesson that I learned from the experimental "X-1" Can-Am frame.

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Jim Fowler

#4 John Miller

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Posted 24 April 2015 - 07:27 PM

Nice build.

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#5 Rick


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Posted 25 April 2015 - 06:28 PM

Excellent tutorial on the build, Jim. The hinges are very much what I had visioned them to look like. As to the rail configuration, there have been so many different combinations used in the DS6 and all have had their good qualities, so that portion of the build is purely the choice of the builder. 


Will be looking forward to the track test and tune session...

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#6 JimF


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Posted 01 May 2015 - 01:53 AM

OK... first track test of the new DS-7 frame. Testing was done on the twisty 'Purple Angel' speedway at fast Track Hobbies in Rocklin, CA, and also on their traditional MTT flat track. Conditions on the Angel were pretty good while the MTT was dry and pretty slidey. The car was set up as shown below. The finished wheelbase is 4.065" and the guide lead is .850". Weight as shown with the Parma body is 103.5 grams. I started with JK 8713 tires.
My first laps on the Angel showed me how quickly this car responds to throttle input. It took a few laps to adapt to the differing feel from my normally longer (wheelbase an guide lead) cars. After conditioning myself, this car had a really forgiving feel at the turn entry and a very fast exit past the apex. I attribute the forgiving feel to the three-piece pan movement. The fast exit, I attribute to the high bite generated by the more flexible than usual frame rails design. In the middle of the turn, this car was a little twitchy in the multiple interconnected turns that this particular track has. I attribute this to the short guide lead (relative to what I normally run). A treated tire calmed the twitchy feel a bit but also reduced the speed on turn exit. Times boiled down to about the same either way.
For this particular track, I'd maybe build it with a longer guide lead and/or stiffen the frame a little as I discussed above.
On the flat MTT, this turned out to be the fastest car I had on this day. I was mostly running my lighter (under 105 grams) speedway cars and this one was the best of the batch on the rather slippery MTT today. In this case, the relatively high bite was the best attribute and the short guide lead was no hinderance at all. This is possibly because I couldn't hammer the middle of the turn anyway. My normal flat track Can-Ams run about 110-114 grams and I think this car might be a little better on a flat track with some weight added at the two points indicated above.
I plan to test this car exactly as shown this weekend on the flattish King track at Slot Car Raceway in Rohnert Park, CA. I'm speculating, but I think it will be very good on the high-bite King there. I also suspect that the multiple, interconnecting turns on their flat track may not be ideal for this light of a car with the short guide lead.
From initial testing... I suspect...
  • This car will be very good on conventional track layouts (King, Hillclimb, etc.)
  • I think that it will be good in both higher bite and relatively low bite situations.
  • There is some possibility that it might need to be a little stiffer for very stuck conditions.
  • This would probably be best accomplished with the more conventional rail layouts that I mentioned.
  • I think that for flowing, interconnected turns, as on a few flat tracks, this car might be better if built a little stiffer or longer.
More to come as I continue to work with it.
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Jim Fowler

#7 James Grandi

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Posted 02 May 2015 - 01:07 PM

Thanks for such detailed build and testing threads, the information is always great to see.


The analytical side always intrigues me. These make it clear to any builder/racer that one needs to appreciate how much true speed depends on economy of motion.

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#8 JimF


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Posted 03 May 2015 - 01:08 AM

OK... a little more.
Tested today (5/2/15) on the rather flat King track at Slot Car Raceway in Rohnert Park, CA. This track has hosted the D2 nats three times and has a smooth epoxy surface. Frank keeps his tracks up and today, I had a typically high bite situation. I was working on a lot of priorities today that relate to our upcoming race this month but got in several passes with the DS-7 and a few of my other intermediate track setups.
Right away, the DS-7 was more comfortable on this rather conventional track layout than it was on the rather odd Purple Angel at FTH. Results today on the King were as fast as most of my best cars that I "go-to" for this track.

  • Throttle response at turn-in is exceptionally quick.
  • This car tends to "jump" off the corner like a car that is even lighter and shorter than it really is.
  • Tire tuning was key today as I started with JK 8713 and it was way too grippy/tippy.
  • Went to JK 8713T and the car was immediately better at turn exit. (Best times were with this tire.)
  • Tried Kelly Purple and Alpha Wonder medium. Car was more forgiving but was too far the other way.
  • I (think) the ideal tire today would have been 8713T slightly narrowed.
  • As is... this car would probably be at its best on the more swoopy King at Eddie's in Vallejo or the fast Hillclimb at Motown.
  • At this point, I'd say this car is "faster" than the standard frame DS-6 but less forgiving for my tastes.
  • This car is very well suited for a conventional track set-up and for a driver that likes a quick car.
  • Response needs to be a little modulated for my old-guy reflexes and preferences.

So... next step will be to re-do with a longer guide lead and then re-test before changing frame rails or anything else.
Even more to come... maybe a week before next test.

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