3139 replies to this topic

[A. J. Hoyt]

There's a lot of brass but it is all down as low as it can be. It came in at 122 grams. The first one, the F1 car, was 108 grams RTR.

 

There are lots of places to reduce the weight. The CG is very far forward for one of my cars, at 2.050 inches from the rear axle.

 

The "wings" that you can see in the CAD image did not make in into the first chassis. These were intended to prevent the nose of the motor from swinging "down" when it flexes the main rail, preventing a resonant pendulum swing by eliminating one half of the displacement. The other intent was to offer some lateral support to the PD motor can in the case of a wall slapper hit to the wall. I have bent too many PD cans racing here in CO. But now I can't see a good reason to ever race a PD anymore.

 

AJ

[Bryan Warmack]

Beautiful work and unique design but I dont believe it is IRRA legal since it does not appear to have any main rails.

    Mike,

       No problem. It's on its way to the Parma Checkpoint Cup............no main rails needed!!

[A. J. Hoyt]

Mike, I believe if I soldered those tight in the square tubes, it would immediately break the joints. I think soldering it up tight is a very good experiment. Fore-aft movement is constrained in the exact same manner as the Warmack F1 chassis design.

 

To avoid any further controversy, I am going to solder two .016 diameter brass main rails from front bracket to rear bracket.

 

I only want to race cars that conform to the rules. That was one of the reasons for posting, to engage dialog.

 

AJ

[John Miller]

Nice work A. J.

[Samiam]

As far as the main rails the rules say this:

 

3i. Wire or tubing rails must connect the front
and rear sections of the chassis. Using metal
strip for this purpose is not permitted. A rail is
defined as that which connects the motor
bracket to the front of the chassis.

 

 The way I read this it just says "connect". Nowhere does it say solid or without a hinge. The .055 rails look to connect the motor bracket to the nose via the twin center hinges. May just need stops soldered to the ends of the .055 wire to fully "connect" via just the rails.

  But I could be wrong. More dialog to follow.

[Tex]

Very cool, A.J.!

[Tex]

Sam,

 

Good analysis of the rule(s). But it's how the powers-that-be interpret the rules that holds sway. SCRRA says "bring it on"; IRRA maybe not. As long as one understands which way the wind blows at any particular track before you walk in the door, shouldn't be a problem. The internet makes that possible.

[Samiam]

Tex,

 Having this forum to display chassis builds and ideas is a luxury we didn't have back in the day. I remember seeing a build article in a slot rag I bought at a used book and magazine store(1971?). Built my first chassis off it. All I remember about it was the pretty girlfriend assistant. I still have it and race it.

 

A.J.,

 Thanks for posting such a detailed description of your chassis. Very innovative use of what I call the "K&S Chassis Kit" What motor bracket did you use?

 

 Merry Christmas

 

Sam

[A. J. Hoyt]

Sam,

 

I posted recently that the 1" x .031 and 1/4" x .016 brass strips, .055 wire and pin tubing were my "F1 chassis kit".

 

I intentionally did not talk about the motor bracket but, since inquiring minds want to know, I have always made my own brackets. My engineering sense tells me that it should have a shape that mimics the way we triangulate/brace them and that it would house the bearing/bushing without a high CG extra part like an axle tube or steel wire bracing. Therefore, they are very wide to support the bearing where the load is. However, this prevents me from using the collars that facilitates the very quick tires swaps necessary to get the last tenth or two out of tuning the chassis to the track on race day, so the tire swap is slower for me.

 

Also, I can make the bearing holes as tight as I want them. I don't solder the bearings in as I want them to be free to "re-align" a little bit if I take a side shot and it bends a mite. If the hole ever gets loose, I just stake it with a 4 fluted center drill tool to raise some material in the center so the ball bearings are a light press fit.

 

I like the bevel mesh and keeping the motor flange to axle distance constant. Once broken-in, I keep motors with their crown gears and I can move them from chassis to chassis with no additional break-in necessary.

 

The five-sided bracket just makes sense to me and it was an original thought but I have recently seen a couple of Crutchfield chassis made this way years ago so it is not new - credit where it is due - but, lest anyone comment, it IS legal ("...minimum 3 sided..."). My CAD and FEA simulation tells me that it is 40% stiffer (where it needs to be) and 30% lighter than an equivalent material 3 sided bracket (before adding the braces). I form them by hand with the brass clamped between two blocks of rectangular tool steel in a vise (old school, yo!). I can make these faster than the 3 sided brackets now - my last Retro Stock Car crash cemented the deal that I am not going back to 3-sided (unless the rules change).

 

Maybe some industrious Retro chassis parts supplier would create a 5-sided bracket - it would save me a bunch of time if I could buy them! Plus, they would be spot on accurate and square!

 

Keep it in the slot,

 

AJ

[raisin27]

Sam,

 

I posted recently that the 1" x .031 and 1/4" x .016 brass strips, .055 wire and pin tubing were my "F1 chassis kit".

 

I intentionally did not talk about the motor bracket but, since inquiring minds want to know, I have always made my own brackets. My engineering sense tells me that it should have a shape that mimics the way we triangulate/brace them and that it would house the bearing/bushing without a high CG extra part like an axle tube or steel wire bracing. Therefore, they are very wide to support the bearing where the load is. However, this prevents me from using the collars that facilitates the very quick tires swaps necessary to get the last tenth or two out of tuning the chassis to the track on race day, so the tire swap is slower for me.

 

Also, I can make the bearing holes as tight as I want them. I don't solder the bearings in as I want them to be free to "re-align" a little bit if I take a side shot and it bends a mite. If the hole ever gets loose, I just stake it with a 4 fluted center drill tool to raise some material in the center so the ball bearings are a light press fit.

 

The five-sided bracket just makes sense to me and it was an original thought but I have recently seen a couple of Crutchfield chassis made this way years ago so it is not new - credit where it is due - but, lest anyone comment, it IS legal ("...minimum 3 sided..."). My CAD and FEA simulation tells me that it is 40% stiffer (where it needs to be) and 30% lighter than an equivalent material 3 sided bracket (before adding the braces). I form them by hand with the brass clamped between two blocks of rectangular tool steel in a vise (old school, yo!). I can make these faster than the 3 sided brackets now - my last Retro Stock Car crash cemented the deal that I am not going back to 3-sided (unless the rules change).

 

Maybe some industrious Retro chassis parts supplier would create a 5-sided bracket - it would save me a bunch of time if I could buy them! Plus, they would be spot on accurate and square!

 

Keep it in the slot,

 

AJ

 

AJ

Would it be possible to use the axle collars on the inboard side of the bearings?

[A. J. Hoyt]

Raisin,

 

Yeah, Nelson and I discussed this on the phone last night and, due to the wide width, I could flip the bearing flanges to the insides with no problem. Great! You just stole my latest untried speed secret! I thought you were my friend!?!

 

So much for the "martyr sympathy" for my slower tire tuning changes!

 

AJ

[MSwiss]

Would it be possible to use the axle collars on the inboard side of the bearings?

Of course.
 
I've thought of it if I come out with a wide bracket.
 
The negative:
 
Doing a quick gear change would become much slower.

[John Streisguth]

As far as the main rails the rules say this:
 
3i. Wire or tubing rails must connect the front
and rear sections of the chassis. Using metal
strip for this purpose is not permitted. A rail is
defined as that which connects the motor
bracket to the front of the chassis.
 
 The way I read this it just say "connect". Nowhere does it say solid or without a hinge. The .055 rails look to connect the motor bracket to the nose via the twin center hinges. May just need stops soldered to the ends of the .055 wire to fully "connect" via just the rails.
  But I could be wrong. More dialog to follow.

If it's not soldered, then it's a pivot and not actually "connected", since without other pieces acting as forward/backward stops, that chassis would come apart.

[gascarnut]

Nice frame, AJ!
 
I think it would help us all if those who might have questions about the legality of a frame would quote the specific rule that they think might not be complied with.
 
There have been changes made to both IRRA™ and SCRRA rules over the years, specifically with relation to main rails and the "plane" of the frame. A while back, this frame would not have passed the "nothing below the main rails" rule, but that is no longer the way the rule is worded.
 
What stops the rear end of the frame from sliding backwards out of the front tubes?

[MSwiss]

What stops the rear end of the frame from sliding backwards out of the front tubes?

The four pieces of rod that connect the inner triangles to the nosepiece.
 
From A.J.:
The two "mid pans" are, in the F1 cars, the side pans. They are wider here (at the front) and are attached to the front pan (.031 with formed front axle uprights, guide tongue) with a single piece of fore-aft .039 steel wire (for strength and spring) to the outsides and a single piece of fore-aft .047  brass rod (for strong brass-to-brass solder joint and damping) to the inside, alongside the guide tongue.

[gascarnut]

The more I look at the photos, the more it looks to me that the connection between the motor bracket/main rail assembly and the front end/inner pan assembly is managed by the pins on the rear of the inner pans that pivot in the tubes alongside the motor bracket.
 
The way I understand the rules that would make this frame legal in SCRRA but not in IRRA™, although as an F1 design it would be.

[JimF]

A funny thing happened on X-Mas eve…………I got home from a dinner party and a round of visits and realized I didn’t have anything to do the next day. Normally, I go skiing on the 25^th but skiing is pretty weak here right now and fishing season is over so I decided to hit the bench. I do have a couple of customer cars waiting for parts but……they’re waiting for parts. So………I decided to just sit down and build something without really knowing what.

 

A couple months ago a Nor Cal local had asked me to build him a “training wheels” car for the King @ Buena Park. I hand built this nosepiece for the project and then he decided he couldn’t go to the Checkpoint, so I shelved the project at the time. This morning, I rummaged around and found the nosepiece and bracket and decided to finish the project pretty much as I had planned it originally.

 

A training wheels car for BPR would be a normal build with nothing fancy and a little heavier than the standard 90 gram, shortish wheelbase sorta thing. The goal here was to make a car that was reasonably fast but great handling and easier to drive than the really light stuff.

 

This frame is as follows………………..

• Handmade .032 nosepiece, Warmack guide tongue, R-Geo .040 x ¾” bracket.
• 4” X 1” and will go about 102 gr all up w/body.
• 4 x .047 main rails soldered.
• Side pans are ¼” .062 and rear weights are 3/16”  x .062.
• Center tie rail is .032 and is not soldered to the main rails.
• Up stops are .047 and are set up with about .005” free upward travel.
• Up stops are angled outboard to control but not eliminate the upward flex of the tie rail.

 

 

Although this car will be a little heavier than some would run @ BPR, it is probably a little light for most of our Nor Cal venues, but......time to clean it up and slap on some running gear in order to find out....................

[Tim Neja]

Another beautiful build Jim!! I can't believe how clean they are --- and you say you're going to "clean it up" to get it running!!! YOU SUCK!!!

[DCR]

A funny thing happened on X-Mas eve…………I got home from a dinner party and a round of visits and realized I didn’t have anything to do the next day. Normally, I go skiing on the 25^th but skiing is pretty weak here right now and fishing season is over so I decided to hit the bench. I do have a couple of customer cars waiting for parts but……they’re waiting for parts. So………I decided to just sit down and build something without really knowing what.

 

A couple months ago a Nor Cal local had asked me to build him a “training wheels” car for the King @ Buena Park. I hand built this nosepiece for the project and then he decided he couldn’t go to the Checkpoint, so I shelved the project at the time. This morning, I rummaged around and found the nosepiece and bracket and decided to finish the project pretty much as I had planned it originally.

 

A training wheels car for BPR would be a normal build with nothing fancy and a little heavier than the standard 90 gram, shortish wheelbase sorta thing. The goal here was to make a car that was reasonably fast but great handling and easier to drive than the really light stuff.

 

This frame is as follows………………..

• Handmade .032 nosepiece, Warmack guide tongue, R-Geo .040 x ¾” bracket.
• 4” X 1” and will go about 102 gr all up w/body.
• 4 x .047 main rails soldered.
• Side pans are ¼” .062 and rear weights are 3/16”  x .062.
• Center tie rail is .032 and is not soldered to the main rails.
• Up stops are .047 and are set up with about .005” free upward travel.
• Up stops are angled outboard to control but not eliminate the upward flex of the tie rail.

 

 

Although this car will be a little heavier than some would run @ BPR, it is probably a little light for most of our Nor Cal venues, but......time to clean it up and slap on some running gear in order to find out....................

 

 

Wow,,that design looks very familiar?????………………….LOL…………….Nice work Jim,,,I hope everyone is well……….DC

[Dennis David]

Jim,

 

Between you and Russ I can't get over how sano your chassis are. I got to get one of you guys to build me a chassis for my Mercedes C9 Hardbody.

[JimF]

Jim,

 

Between you and Russ I can't get over how sano your chassis are. I got to get one of you guys to build me a chassis for my Mercedes C9 Hardbody.

 

Dude....you gotsta to come out and run with us sometime. Ummmmm.......not with that hardbody though........

 

Russ would be the one for a hardbody build. He's done a mess of 'em but I never have.

[DCR]

……My fleet!………..go to http://slotblog.net/...can-am-chassis/

 

……..DCR……..

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[macman]

Yes Don... there is some similarity... as well as some difference... Great minds think alike??? Happy NY all

[DCR]

Yes Don... there is some similarity... as well as some difference... Great minds think alike??? Happy NY all

 

No problem,,I was just joking……..I think most of the cars we all build are based on something that Tony P built years ago…….I hope everyone has a great 2014,and that 2014 is good for Slot Racing……………………DC

[Duffy]

I think most of the cars we all build are based on something that Tony P built years ago.

 

I just asked him. He says he doesn't mind.