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  • Carbon Fiber

    I have been experimenting with custom-fabricating lightweight chassis for 1/32nd cars. Mostly that has been by 3D printing chassis components for monocoque construction -- using the body of the car as a structural component.

    But I have also tried replacing the traditional steel front axle with a carbon-fiber rod. The rod material was sourced from McMaster-Carr. That rod turned out to be oversize, and did not have a smooth finish. But I was able to sand the ends small enough and round enough to be a decent fit to the ID of some ball bearings. With independent front wheels the axle doesn't have to turn.

    The resulting axle is stiff and light, as would be expected. So it reduces the high CG mass of the car by a few grams. If the car needs more weight in the front that can be added lower. But I am hoping the power-ramping feature of my SlotIt controller will make that unnecessary. Or less necessary.

    And yes, I am aware I could dispense with a solid front axle, mounting the front wheels on stub-axles. That is a design I have played with in the past.

    Instead I have elected to integrate a front axle into a rigid assembly that includes the front wheels and guide shoe, all of which is mounted to the body so that the assembly can pivot in the 'roll' direction. The ability to pivot is intended to keep the whole front 'sub-chassis' square with the track surface. Including -- critically -- the guide.

    It will be a while yet before I can test out my lightened designs in competition. There's a good chance I will use that carbon-fiber front axle.

    I don't see any other uses for carbon-fiber components at the moment. I don't think the material I've got would be good enough for a rear axle.

    But things might change.

    Ed Bianchi

  • #2
    Ed, carbon fiber by alone won't cut it. If you remember, many moons ago, I was making carbon fiber filled axles and helicopter main shafts using very thin-walled stainless steel tubing and then filling said tube with a carbon fiber/resin matrix. I modified a RCBS reloading press, machined sets of dies, and developed a pull-trusion process were I could reliably get a 100% fill of 3" or 1 meter long tubes depending upon the tube size. I would then slice the axles to length. I stopped doing said axles after a party bought 1,000 of them from me and I'm reasonably sure that said axles ended up on another supplier's web site as their own product. I made HO axles in 0.0595" and 0.063" as well as 3/32" and 1/8" axles for the larger slot cars. The R/C helicopter main shaft products had a longer life, but eventually all the major heli brands went to much better solid and/or hollow main shafts.

    Comment


    • #3
      Gerry you are a god.

      No, I don't remember that story, but I have no trouble believing it. In my case, however, I am not looking for ultimate stiffness or fatigue life Just a much higher flexural modulus to mass ratio. (See there, technish bafflegab I'm good at. I can't compete with you on actual technical accomplishments.)

      Pulltruding composite stainless/carbon tubes should have resulted in wonderful flexural stiffness and strength. Could the work-hardened stainless tube approach the tensile strength of piano wire?* We wonders we does.

      But getting all those carbon fibers lined up axially might not give so much torsional strength, which I'd think would be the primary concern in your prop shafts. Ideally they'd be wrapped on a bias. Dang near impossible to do that small.

      I'm still curious if there'd be other applications for carbon fiber. Maybe bodies, especially for monocoque cars, if you can make it thin enough. Chassis pans not so much. A chassis pan is where flex and extra mass is often appreciated.

      Maybe wheels.

      Ed Bianchi

      * Piano wire is incredible stuff. A tensile strength of 400,000 pounds per square inch? Yikes!

      Comment


      • #4
        Originally posted by HO RacePro View Post
        I have been experimenting with custom-fabricating lightweight chassis for 1/32nd cars. Mostly that has been by 3D printing chassis components for monocoque construction -- using the body of the car as a structural component.

        But I have also tried replacing the traditional steel front axle with a carbon-fiber rod. The rod material was sourced from McMaster-Carr. That rod turned out to be oversize, and did not have a smooth finish. But I was able to sand the ends small enough and round enough to be a decent fit to the ID of some ball bearings. With independent front wheels the axle doesn't have to turn.

        The resulting axle is stiff and light, as would be expected. So it reduces the high CG mass of the car by a few grams. If the car needs more weight in the front that can be added lower. But I am hoping the power-ramping feature of my SlotIt controller will make that unnecessary. Or less necessary.

        And yes, I am aware I could dispense with a solid front axle, mounting the front wheels on stub-axles. That is a design I have played with in the past.

        Instead I have elected to integrate a front axle into a rigid assembly that includes the front wheels and guide shoe, all of which is mounted to the body so that the assembly can pivot in the 'roll' direction. The ability to pivot is intended to keep the whole front 'sub-chassis' square with the track surface. Including -- critically -- the guide.

        It will be a while yet before I can test out my lightened designs in competition. There's a good chance I will use that carbon-fiber front axle.

        I don't see any other uses for carbon-fiber components at the moment. I don't think the material I've got would be good enough for a rear axle.

        But things might change.

        Ed Bianchi
        Why not bodies ?
        Do a resin body mold of your favorite body, use a very fine weave cloth.
        You may not get windshield wiper fine detail, but the loss in weight above the rocker panel weight would be worth not having door handles or windshield wipers.
        I'm sure that there is basic carbon fiber cloth fine enough to do this. We did some pretty fine detail work where I worked (Aerospace) before my retirement..!

        Mike

        Comment


        • #5
          I started with thin-wall Stainless Steel tubes, 0.005" wall thickness, then using carbon fiber starter strands, pulled the carbon fiber up through the tubes while saturating the the strands with epoxy resin, using the pressure generated by the RCBS press to pressurize the matrix up through the tubes. I have to check my records, but I don't remember if I used 304, 314, or 316 Stainless Steel. I did achieve 100% fill, and never had one break or bend. I bet it was all of 20 years ago when I made them. My how time has a way of slipping by.

          I started making these axles when I was racing 1/24th scale wing cars. The rear axle was very near the motor, and I could demonstrate that the axle was being slowed by the motors magnetic field especially in the classes that allowed cobalt and neo magnets. I could demonstrate both on the track and on the chassis dyno that the cars were faster with the non-magnetic axle.

          As for the unasked question of why didn't I just use carbon fiber rod? Believe it or note, it fractured relatively easily with a wall-shot.

          Comment


          • #6
            Huh. I also had noticed that the attraction of motor or traction magnets could cause drag on the rear axle in HO cars. Mainly due to added load on the bushings, but perhaps a bit due to eddy current braking. I first saw that back in the 1960's in T-jets, believe it or not.

            There are not a lot of good non-magnetic materials that could be used for axles. Aluminum and brass are too soft. Hard-drawn 304 stainless steel tubing comes close, it has very little ferro-magnetism, but bends too easily. Your trick of filling it with carbon fiber was a good way to improve on that.

            You can buy 1/8" diameter hard-drawn precision stainless steel tubing with much thicker walls -- as thick as 0.015". McMaster-Carr sells it.

            As anyone who watches Formula 1 or IndyCar knows, carbon fiber just by itself shatters like glass on heavy impact. So, like you said, a solid carbon fiber axle won't survive wall-shots. Your composite axle addressed that.

            Doing a little research just now I discovered that you can buy tight-tolerance (+/- 0.001" diameter) alumina ceramic rods as small as 1/16" diameter from McMaster-Carr. Ceramics are not magnetic.

            "This ultrahard ceramic can also be used in applications that require superior strength."

            The stuff is pricey. A 12" length of 1/8" diameter costs US$43.39.

            No straightness spec or impact strength numbers are given. And the diameter tolerance could be better. But it might still be interesting to see how well a ceramic axle would perform.

            Ed Bianchi

            PS - As for time slipping by, yeah, it would be great to tap the brakes. I'm working on that.
            Last edited by HO RacePro; 04-14-2021, 05:45 AM.

            Comment


            • #7
              Alumina ceramics will have a relatively high Modulus of Rupture (strength) as well as a high Young's Modulus (stiffness). MoR is typically measured in compression, with the tensile strength being WAY lower. The high YM means that the material will be very resistant to bending, and the low strength in tension would indicate that an axle would fracture easily in even a relatively minor wall shot. How do I know such things? Having been a refractory ceramics engineer for much of my working career, both in R&D and for practical (field) applications, I had access to a wide range of materials and process with which to experiment. Yes, I tried alumina rod, as well as alumina tubes filled with my carbon fiber matrix. I had the best results with Yitteria stabilized Zirconia, but even then, the results were not satisfactory.

              Comment


              • #8
                Why didn't I remember your refractory ceramics background? I'm impressed that you took the time to explore ceramic axles. Thank you for sharing your experiences with same.

                Your last two posts contain some really valuable information on exotic materials. Unfortunately the way SCI is organized it will quickly get lost unless a moderator chooses to salvage it and make it sticky.

                I believe you and Rich deserve your own channel. Rich's authoritative posts on basics like power supplies, T-Jet and 1/32nd car tuning and setup and your test reports should jump out at all SCI newbies and remain easily accessible to all subscribers.

                Ed Bianchi

                Comment


                • #9
                  How about forged titanium? How would that compare to your hand strewn axles of years past?

                  Comment


                  • #10
                    Titanium is supposed to be very mildly magnetic. How that varies by grade and hardness, dunno. My favorite toy store, McMaster-Carr, offers titanium rods in 3 different grades -- 2, 4, and 5 -- with no indication of how magnetic they are. Their diameters are toleranced to +/- 0.003 inches, so, kinda sloppy for axle service.

                    Ed Bianchi

                    Comment


                    • #11
                      There are several HO suppliers that sell Titanium and Tungsten axles. These are typically used to fine-tune the front end weight of Fray type T-Jets. I did experiment with Titanium axles years ago but was unhappy with the hardness, surface finish, and above all dimensional tolerances.

                      Comment


                      • #12
                        Originally posted by gmcullan View Post
                        There are several HO suppliers that sell Titanium and Tungsten axles. These are typically used to fine-tune the front end weight of Fray type T-Jets. I did experiment with Titanium axles years ago but was unhappy with the hardness, surface finish, and above all dimensional tolerances.
                        Were those Forged? I know regular isn't up to par...

                        Comment


                        • #13
                          The forming method for the materials I tested were unknown. However, at the sizes I was testing I would presume that they were drawn/extruded. Granted, forging could result in a better grain alignment. But drawing is much more reasonable for a 0.0595" or 0.063" rod. Especially when you factor in the variance of +/- 0.003".

                          Comment


                          • #14
                            The drawing process pulls a wire of material through a hole in a 'die'. Usually drawn materials are produced to tighter tolerances than +/-0.003 inches. But then drawn materials are usually soft metals like copper. On the other hand there are hard-drawn materials such as piano wire, which is steel, and super-duper hard. Also tightly toleranced.

                            For extremely tight tolerances in hard pieces that are shapes of revolution there is a process known as centerless grinding. The work piece is spun between two grinding wheels -- commonly one fixed, one movable. Tolerances in the tenths of thousandths of an inch are routine.

                            Ed Bianchi

                            Comment


                            • #15
                              I suspect that the Titanium rod that I had was probably drawn and then centerless ground. The surface texture was quite rough and didn'r respond well to attempts to polish it.

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