41 replies to this topic

[Larry Horner]

In an earlier post, Martin and I created a new interpretation of the iconic Starship chassis that combines classic brass and wire construction with modern 3D printed parts: https://slotblog.net/topic/105188-something-borrowed-something-new. It was a very fun collaboration but I wanted to push the boundaries a bit further. Specifically, the choice of a sidewinder layout meant a minimum of 7/8” rear tires whereas modern flexi chassis are running much smaller tires. So I embarked to return to the original Starship’s anglewinder configuration.  The first step was to widen the rear triangle from the sidewinder’s slim 20 degree angle to 24 degrees which I think is pretty much in the ballpark with the original Starship. I also dropped the rear axle to allow .050” clearance with .720 tires.

Now the elephant in the room is that the motor can’t be soldered to the motor box hence I had to engineer a way around what Pablo calls the dreaded bunny hop. The solution begins with an inset left rear bearing so that it lies under the plane of the motor box exterior. And this allows the use of not one but TWO motor mounting bolts as the rear one simply rides over the bearing. I’ve provisioned the chassis with holes for the motor’s top and bottom screws as well but I don’t think this belt and suspenders approach is really necessary.

 

 

I also designed a cap to lock down the endbell. The end result is that the motor is firmly locked at both ends with absolutely no movement so I’m confident the demon bunny hop has been exorcized.

 

[MSwiss]

Could you solder the bearings in a brass tube, and then glue that bearing/tube assembly into the rear?

 

You could then solder a wire from the back of the can to the axle tube.

[Larry Horner]

Expoy bonds extremely well to PA12 plastic so that might work. But the melting point of PA12 is around 360 degrees Fahrenheit so you'd need a way to protect the plastic from the heat of soldering. But with the above design, the motor is very rigidly mounted so I want to test it first to see if the problem hasn't already been resolved. But it's an interesting idea if the problem still persists.

[mreibman]

Could you countersink the screw holes and use flat head screws? These screws just bother me a bit.

 

But looks good otherwise.

[Pablo]

With the EB secured like that, no way it can bunny-hop 

 

Also, it looks like your axle and shaft centerlines are exactly same height.

The gears will thank you for that. A sidewinder wouldn't care, but an anglewinder will.

Looks like the beginnings of a happy drivetrain to me 

[Martin]

With the EB secured like that, no way it can bunny-hop 

 

Also, it looks like your axle and shaft centerlines are exactly same height.

The gears will thank you for that. A sidewinder wouldn't care, but an anglewinder will.

Looks like the beginnings of a happy drivetrain to me 

Could not agree more. Thank you Pablo for recognizing a good design when you see one.  

Thank you Larry for inspiring me to get back to my full sidewinder build. Easy for me to get sidetracked.

Great job Larry for simplifying the construction too.

 

Mike R,.My side winder build does have flat-heads as space saving was necessary to keep the width to 3.25 with .9'' wide tires.Thanking Pablo for those. 

 

 

 

[Brian Czeiner]

I am guessing the advantage of an angle vs sidewinder is better gear options with smaller tire combinations?  Is it still an advantage with todays smaller canned motors? 

[Martin]

Exactly Brian, the sidewinder is limited to 7/8" o.d. tires and we had to use drag race spur gears. So yes limitations to get the symmetrical design. The sidewinder does move more weight over those tires, it will be fun to test and compare the 2 designs at some point. 

[Larry Horner]

Good eyes Pablo and yes, the height of the pinion and axle are within a few thousands of each other!

 

Mike, as Martin pointed out, we did use flatheads on the sidewinder to allow the spur gear to ride inboard. But unfortunately they won't work on the anglewinder (well not in back anyway) as the head needs to ride over the top of the left axle bearing.

 

Brian, our earlier sidewinder does use a minican motor but is still limited to a 7/8" minimum tire size.

[Larry Horner]

Building the plumber rail pan assembly for the sidewinder Starship was a bit fiddly and I also thought the finished chassis looked a little busy. So I was wondering if I could simplify things by making the plumber rail do double duty as the pan pivot too. To do this I would have to notch the bottom lip surrounding the central  chassis section but hey, the original Starship had notches too. It was back to the drawing board and here are the results.

 

 

The notches are .500” and the tabs on the pans are .460” so the pans can slide .020” forward or backward. The next step was to have the new parts manufactured and I made a couple of discoveries. One is that OSH-Cut can cut parts in .032” brass. Second is that Shapeways can now print PA12 in black which I think will look uber cool and is in keeping with the look of the original Starship’s tempered steel. But it will take several weeks to get that back from Shapeways so in the meantime,  here is my original chassis manually notched with the new pans. Time to get to work…

 

[Alchemist]

Excellent craftsmanship!

 

This project is so inspiring, thank you for sharing Larry.

 

Ernie

[Larry Horner]

Glad you joined us Ernie. And I loved how your 930 turned out!

[Larry Horner]

The first step in building the new pans is to file the tabs from .032” down to .024”. And when the .024” is added to the .016” wall thickness of the 3/32” hinge tube, the inside bottom of the tube  is perfectly flush with the .040” height of the chassis rim. Here is a shot after filing down the tabs.

 

 

Now the pivot tubes can be soldered onto the tabs and they need to be soldered .010” out from the inside edge of the pan. So I clamp them with their inside edge flush with the top of my vice, lay  a .010 shim on top of it, lay the tubing on top of the shim and soldered it to the tabs … easy peasy. The .008” drop at the edge of the tab yields a linear look to the inside edges of the pans which I think is a nice optical delusion. Here is a shot of the pans with their freshly mounted hinge tubes.

 

 

Here is a test fit with the new pans installed. I still need to solder on the rear plumber rail crossmember but once that is done, the pans won’t be able to come off. So I am going to figure out a way to mount the pin-tubes to the pans first. But my goal was achieved as this was way easier to build and I think the finished look is much cleaner. Onward…

 

[Pablo]

Ultra-SANO 

[Larry Horner]

The new design for pan pivot requires a new design for the pin-tube mounts as well. One solution would be to just solder the pin-tubes directly onto the pans but I like to have the pin-tubes higher up on the body. So my first attempt was to cut some ¼” strips of ¼” angle stock, drill some 1/16” holes in both sides and solder them into the pans. This worked out ok but was time consuming and was a bit flimsy as the angle stock is only 1/64” thick.

I talked this over with Martin and he suggested the pin-tube mounts could extend from the edges of the pans and then be bent upwards. I’ve seen this used in chassis kits and it is a very simple and effective solution. But it requires the brass to be milled along the bend lines and I don’t have a way of doing that. So instead I borrowed from the woodworking world and opted for a box or finger joint. While it looks very minimal, the fingers actually provide substantial surface area for the solder joint. Here is a CAD drawing showing it from the underside.

 

 

Here are laser cut pans and pin-tube mounts with fingers after a light sanding to get rid of the laser flash. I’ve also cut some fingers in the middle of the pans to play with later.

 

 

Here is a bottom view of a pan after installing the mounts and pin-tubes. I love how the box joint virtually disappears once it fills with solder. It seems to be quite strong too so I’m going to be using this trick again.

 

 

Here is a top view of a pan with mounts and pin-tubes. I decided to add some 1/16” tubing to reinforce the inside of the box joints but unfortunately made this decision after I had already installed the pin-tubes. This made it impossible to solder in the supports so they had to be epoxied instead. Next time I will solder them first.

 

 

[Bill from NH]

Larry, .032 piano wire could have also been used to reinforce those box joints. Those joints could have also been cut as dovetails, but box should be strong enough,

[Larry Horner]

Bill .... dovetails??? 

 

And now we’re going into uncharted territory or at least a design I’ve never seen before. I was wondering if something might be done to simplify the bite-bar too so I came up with a design in which the bite-bar goes through the central chassis beams .020” above the plumber rails. This allows the bite-bar to also function as the plumber rail up-stop. But there is an important caveat … when the plumber rail goes up, the inside of the pans go with it but the outsides don’t. This causes the pans to arch upwards as opposed to the usual dead lift. At first this seems like less movement but it’s actually not. Instead the vertical movement at the outside is being converted to rotation movement hence will still be absorbing energy. Will it work? I don’t know but if it doesn’t, the design can be easily converted back to my prior bite-bar arrangement. Here is a CAD drawing to show the concept (sans plumber rail crossmembers). And now you can see why I added finger joints in the middle of the pans. The bite-bar will run through snippets of ⅛” tubing soldered in the hangers. This will allow 1/32” of wiggle room and the circular shape will also help to center the pans like the more conventional V shaped hangers. Unfortunately the new design is still in Shapeway’s product queue so this may be the last post for a bit… 

 

[Martin]

I like that the pans are more independent, only held by the front cross bar. Does it even need that?

 

The subject of rigid vs floating came up many years ago see below Tony P's response. Now if only there was a way to make it adjustable, similar to a sway bar on a 1/1 race car.

 

[Bill from NH]

Tex (Richard H,) built a couple slot car chassis that he controlled chassis flex with set screws on the rails. Perhaps they could be applied to other chassis parts as well.

[Martin]

The more adjustments you can add to a chassis design the more you will learn what does what. In earlier conversations Larry and I had an adjustable front axle flex and height adjustment. 

 

[Mark Onofri]

Optical delusion: when you have looked at something for so long you have become delusional
Optical conclusion: when you look at something and come to the conclusion that it's FUBAR'D

[Larry Horner]

Over the weekend, my black anglewinder chassis with notches for the pans and holes for the bite-bar finally arrived! I think it looks pretty awesome but I will let you judge for yourselves. I threw in the optional center pan too to show off the contrast between the black and polished brass.

 

 

After a quick test fit to check accuracy, I was able to finish up the plumber rail / pan assembly and here is a shot of the results. The rear plumber rail crossmember is still present for strength even though it no longer needs to function as the up-stop. But it is positioned such that it could if I decide to return to a conventional bit-bar design. I will try and finish up the roller tomorrow.

 

[Brian Czeiner]

It's tomorrow. I'm waitiiiing. 

 

I've been enjoying this build with great enthusiasm. When I first discovered 3d printing, I knew it could be a game changer for the hobby in both performance and scale appearance. I'm so glad others with more computer savvy had this same vision.

[Dave Crevie]

. 

 

I've been enjoying this build with great enthusiasm. 

 

Me too. Or should I say, with great interest.

 

Just out of curiosity, have you ever been able to run the design for the center section through a stress analysis program, more to see how the tortional stiffness might compare to a stainless steel center section? Just wondering if there might be something that could be changed in the current design of slot cars. Of course, the final question I have will have to be answered after the finished prototype can be tested on the track. In any event, there is room for 3D printed chassis as their own class. Personally, I see them as more a product aimed at the home racing crowd. 

[Larry Horner]

Brian, glad you're enjoying the ride. Sadly, I had to help a friend install a dishwasher today so no time for the roller. But tomorrow is wide open so I'm hopeful.

 

Dave, you need a full blown AutoCAD license (or equivalent) to do any finite element analysis and as a retired guy, that's out of my pay grade. But the pans have as much freedom of movement as any of my classic plumber hinge cars. And the main points of contact are the brushes and the back tires so I'm expecting this car to handle somewhere between a modern flexi and retro anglewinder ... we'll see. For me, the main thing is having fun combining new and old art forms together ... but it would be sweet if it ends up with great handling too!