Popsicle Stick Wing Car
By Steve Okeefe
This one... is different...
Wing car chassis are traditionally made out of steel, so that they are strong enough to withstand the rigors of high-speed racing. But it is not steel, or any other particular material, that "make them work"; rather, it is the aerodynamics built into the body.
In other words, you could build a wing car chassis out of almost anything (including Popsicle sticks) and it would work.
So, the original purpose of this project was "Proof of Concept"; to demonstrate using Popsicle sticks that the aerodynamic down force wing car bodies generate is so overwhelming that not much else about the design and construction of the chassis makes any difference in its handling characteristics.
Wood is actually a very efficient building material; it has a fairly high strength-to-weight ratio, and is relatively easy to cut and shape. Early ships and airplanes were made of wood, and even early automobiles had a lot of wood in their construction.
But a Popsicle stick wing car will be more akin to an unlimited hydroplane racing boat, a jet fighter or an outrageously overpowered Can Am car (none of which are made out of wood). This is going to be a challenge.
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First, I went out to a craft store and bought a bag of Popsicle sticks. I started with the assumption I would be mounting the motor with screws (because you cannot solder to wood) and that I would use the Popsicle sticks as direct replacements for the front to back chassis rails. Wrong on both counts.
Two things I realized right away was that the standard Popsicle stick is not tall enough (standing on edge) to mount the motor with both top and bottom screws, and too short (lengthwise) to reach from the rear axle to the guide tongue in a 1/24 scale car.
Too short lengthwise meant that there would have to be a glued, screwed or bolted chassis joint somewhere in the middle. The rear body mount seemed like a logical place.
Popsicle sticks not tall enough (standing on edge) meant that I would have to use tongue depressors as rear half-rails, because on edge they are the about same height as the “C” can motor I would be using.
Back to the craft store to buy some tongue depressors.
Continuing, I generated some computer drawings, which allowed me to quickly try out numerous arrangements and configurations. Following common wing car chassis design, I assumed a tapered motor box with a full chassis width cross rail just ahead of the motor.
This cross rail would provide a convenient place for both the rear body mounts and the chassis joint.
In order to mount the rear axle Oilite bushings, I intended to bend the half rails from their tapered motor box angle to square with the axle by boiling them in water and jigging them bent until dry. That idea worked, but not well enough. No two sticks took the bending process quite the same way, and I found I couldn’t depend on the sticks retaining their initial bend.
I decided this method was not consistent or reliable enough to use for axle bushing mounts, a place where alignment is obviously critical. So it was back to straight half rails with angled holes.
Building the motor box to match the computer drawing turned up several more problems.
First, the motor angle needed to be bigger to make more room to get the motor in and out.
Next, the forward crosspiece was going to have to be a tongue depressor instead of a Popsicle stick, because the latter would not be strong enough under torsion (twisting) loads.
Third, hand drilling five accurately located and angled holes for the motor bearing, screws, and axle bearings is an exceedingly difficult thing to do; particularly after the motor box is completed.
Last, mounting the motor with screws simply wasn’t going to work because three holes (one for the motor bearing and two for screws) weakened the gear side half rail far too much.
The only real show stopper was the motor mounting; it was clear I was going to have to glue or solder it in somehow.
It was back to the computer drawing board. Modern angle winders have rear uprights to mount the axle bearings, but vintage angle winders used brass axle tubes, which were part of the structure of the chassis.
Obviously, brass is easily soldered, so I could replace part of the wooden motor box with a brass axle tube, solving both my axle bushing alignment and motor mounting problems at once!
Proportioning and dimensioning the rest of the chassis design turned out to be fairly easy. I took the general layout and dimensions for wheelbase, guide lead and body mount locations from an old steel wing car chassis.
But we're not out of the "woods" yet...
One of the lessons learned from building the first motor box was that Popsicle sticks and tongue depressors are rarely straight or flat, plus a clear reminder that wood splits easily along its grain.
Solving the straightness problem was a simple matter of going through however many sticks it took until I found some straight ones, but the flatness and splitting problems were solved another way.
Just as crossing the grain of the layers when making plywood renders it relatively flat and split resistant, adding cross-grain doublers to the ends of each chassis rail will do the same for our Popsicle sticks!
Other considerations in designing this chassis included keeping the grain of each chassis part pointed along the line of greatest stress, ensuring that each glue joint is large enough to prevent failure under normal loads, and keeping an eye on the overall weight and balance of the finished car.
After thinking about it for a few days, and using my computer to test ideas by making drawings rather than build numerous chassis, I arrived at a finished design:
Time to setup a building jig. Nothing too fancy, just a flat, white Corian block with square corners and edges, and rear axle positioning pins.
I have taken to laying out the critical chassis dimensions on the block surface with an “ultra fine” marker pen. The square corners and edges of the block allow me to place the lines precisely.
Now I have a clear idea of where things are supposed to go, and where they are not. When I’m done building, I simply erase the lines with some acetone (nail polish remover).
Taking a lesson from the construction of the first motor box, I knew I would have to build a jig to drill the axle tube and motor bearing holes in the rear half rails.
In order for the chassis to have the right track clearance, and the motor to be flush with the bottom of the chassis, not to mention keeping the motor bearing hole as small as possible and still getting the gear mesh correct, the holes must be located with great accuracy.
I took a scrap of three quarter inch plywood, checking to be sure it was flat, and glued two straight Popsicle sticks to it such that a tongue depressor would fit snugly between them but still slide back and forth.
Clamping the jig to my drill press table, I could now drill holes at any angle (by tilting the table) and locate them not only accurately, but also repeatedly.
Time to build some motor boxes! I selected the flattest, straightest tongue depressors I could find, and glued down (with high quality CA and spring clamps) some bits of tongue depressor at a ninety degree angle to form cross grain doublers where the axle tube holes were to go.
While the CA was curing, I cut and squared some brass tubing, tinned portions of the tube where the motor mounts would go, soldered the bushings in, and turned down the flanges until they were flush with the tube diameter.
Then I set the glued up half rail blanks in the drilling jig one by one and drilled the holes, square-up for the motor bearing, seventeen degrees for the gear side axle tube and fourteen degrees for the opposite side. I made enough pieces for two chassis and a spare.
At this point completing the motor box was mostly was a matter of assembling the parts.
Following the lines on the jig block and using CA to attach the half rails to the front cross rail, and JB Weld for the axle tube (not only strong but also heat resistant to withstand soldering the motor mounts on), I clamped the whole assembly down flat with a weight and put it in my (scratch built) “Easy Bake” curing/drying oven.
When the CA and JB Weld were fully cured (overnight) I fabricated three piano wire motor mounts, tinned them, and soldered them to the axle tube; two on top and one on the bottom.
The shape and quantity of the motor mounts serve two purposes; first, isolating the motor to minimize heat transfer to the wooden parts, and second, using three mounts forms a tripod so the motor cannot vibrate relative to the axle tube and mess up the gear mesh.
The motor, by the way, does not touch the axle tube, and there are no cutouts in the tube that would weaken this critical structural part. I might have been able to get away with only two mounts, but I wasn’t willing to risk it.
In designing this chassis, I worried a great deal about how much that motor bearing hole in the gear side half rail reduced its structural strength.
Part of my design-tweaking process included extending both tri-angular half rail gussets almost as far back as the axle tube, as shown on the chassis drawing above, but it still didn’t seem like enough!
Eventually, I glued a parallel grain (as opposed to cross grain) doubler plate across the top of the half rail, above the motor bearing hole, to strengthen it further. You can see the doubler plate on the finished chassis.
With the motor box done, the front end was next. I started with the guide tongue (made, ironically, out of a tongue depressor) and cut it to shape with the grain running lengthwise (front to back).
Then I cut and glued on the forward swept arms, following the lines I had drawn on the jig block.
Cutting pieces to shape and fitting them together is not really all that hard!
It helps to have a small, motorized bench top saw and sander, but the parts can just as easily (although more slowly) be made with a razor saw and some sandpaper. A Dremel with a cutoff wheel or grinding point does not work here; it just burns the wood!
The two brass weights you see in this photo were installed later, as required to add weight and balance the chassis (it was too light!). Also in the photo, taken after the car was run, you may notice that the front corners have dirt marks on them where the car tipped in the turns and touched the track.
You may also notice the right side front wheel is severely damaged, apparently where it too touched the track, spun up to some unknown RPM and simply flew apart!
With the bottom half of the nosepiece done, I cut the cross grain doubler to chassis width minus the space the two outside rails with doublers would need.
Then I finished it off with a cross grain doubler for the front tip of the guide tongue, where the guide hole is located.
Now, the completed nosepiece is ready to be attached to the motor box with three fitted and doubled Popsicle stick main rails, notched to clear the nosepiece and motor box cross rail so that they rest (on edge) directly on the jig block.
The fitting and notching is clearly visible in this photo:
Gusseting and doubling the main rails and the half-rails where they come together in the middle of the chassis finishes off the wood construction part of this project.
I then added the klunker style body mounts by drilling holes and gluing in aluminum tube, and then glued on two ear-ring backs (one on each side of the center rail) to manage the lead wires.
Now we add a motor:
Rear wheels, axle, gears, guide, lead wire and laser printed paper front wheels, and we have a finished chassis:
Some logo stickers, scanned from a Popsicle box bought in the grocery store and printed on clear vinyl sticker sheet with an ALPS printer:
Paint up a wing car body in orange, grape and cherry stripes, add wings and stickers:
Install it on the chassis:
And we have a Popsicle stick wing car:
Does it work? It turned consistent 3.95 second laps (and even managed a 3.88) on a 151' Ogilvie Grandstand II on the same day as steel chassis wing cars with the same (USRA Group 12) class motors were turning 3.8 and 3.9 laps. Yes, it works...
Postscript:
Here's a photo sent in by an enthusiast in Alabama.
He likes Popsicle stick construction also.
I have no words...
