Magnetic Downforce Scale Apparatus - Adjustable

prusaprinters

<p>This is a simple concept that has been used by many over the years, usually using various bits of wood and other hardware. I designed this to be as simple as possible to make using your printer and minimal tools and hardware. Using the Fusion 360 (f3d) file, you can easily change the parameters to change the models for your own scale and slot car track rails. The provided STL files will only work properly for Scalextric Sport (½ straight) track rails and an electronic scale like the one shown in the photos. The height of that scale is 30mm, so if yours is the same height from the table to the top of the scale pad, then these models should work with your scale.&nbsp;</p><p>While this version allows you to tune the readings by adjusting the height of the rails, the numbers you get from this apparatus are for comparative purposes only. If you race in a club with a downforce limit, you will want to adjust your MDSA to match the readings on their device as closely as possible, and then note the difference that can't be eliminated. This is not meant for club use, unless this IS the club scale. This is meant for the average user to have a simple device with which to compare his cars for racing on his track under his own rules. The number itself is not necessarily accurate to the real magnetic downforce of the car, or important in any way other than to see which cars have more or less downforce, and to hopefully group cars in a way that encourages even and fair racing. Good? OK, then let's go…</p><p>The first step of the process is to get a spare piece of the kind of slot car track you have. You're going to cut away the track surface, keeping only the rails and the plastic that holds the rails in place, including the slot between them. Most track can either be cut with a sharp knife (aka Stanley knife), or scored and then snapped apart at the score line. See photo for example using Scalextric Sport track.</p><p>Once you have cut out the rails, you'll need to measure the total length of the rails (remove or cut off any pins at the ends), as well as the width of the piece and the height/thickness of it. This will determine the size of the pockets that hold the rails in the apparatus as well as the channel in the plate. If you prefer, you can find a piece of flat steel bar that can serve the same purpose as the rails and cut to an appropriate length (about 175mm). These measurements go into the following parameters in Fusion 360: raillength, railheight, and railwidth.&nbsp;</p><p>Once you have your rails (or steel bar), you'll need a small scale such as for baking or postage (See image) and grab measurements from it. Scalepadlength and scalepadwidth are for the actual scale pad surface itself. This shape is centered under the floating plate the car rests on to pull against the rails and therefore press against the scale. We want this to be as centered as possible, so only measure the actual pad of the scale. Scalepadextension is how far the scale extends from the pad, where the buttons and screen usually are. Finally, scaleheight is the measurement of the scale pad off the surface the scale sits on. Be sure to account for any feet that may be on the bottom of the scale.</p><p>Plateheight is based on the railheight and raildown parameters, plus 3mm to ensure a stiff/strong plate. Raildown is how much downward motion you think is necessary for adequate adjustability. The default of 2mm should be sufficient for most users. There is an intentional gap of 2mm between the bottom of the rails and the top of the channel in the plate. This is to ensure that the car wheels are the only thing pressing down on the plate.</p><p>Width is the final parameter to set. This is based on your track lane width, or at least the width of your widest car. This is currently set to 77mm, which is the lane width of Scalextric Sport 1/32 size track.</p><p>There is also an intentional 1mm gap between the legs and the plate, as well as between the rails in the sides of the channel in the plate. This is to ensure that the plate floats freely, so that all the magnetic pull is transferred to the scale.</p><p>After you've made your edits, export the models as STL files, or the whole thing as a STEP file, and then import that into your preferred slicer program to print. Note that the legs are designed with support bridging and should be printed upside-down with the rail slot nearer the build plate. The STL is provided in the appropriate print orientation.&nbsp;</p><p>The legs are held to the base using 4 m3x10mm socket head cap screws, but whatever works will do. The rails are held in by friction, but you could always slather some glue in the pockets if you felt the need.</p><p>The railcarriers are adjusted using an M6x1 40mm socket head cap screw in each leg, held in place on top with an M6x1 nylock nut. You will need to insert the screw from the bottom of the leg, then insert the rail carrier and thread the screw through it and through the top of the leg. Secure with the nylock nut and tighten down to the top of the leg. It should be just loose enough to allow free rotation of the screw and not deform the top of the leg. You should be adjust to adjust the rail carrier by tuning the screw or by turning the nut (which is locked to the screw).</p><p>The precision and repeatability of the MDSA will depend a lot on the quality of the rails you use (new versus used and all bent up) as well as the quality of the scale you use. A scale that has a loose/wobbly pad won't get repeatable readings compared to a scale with a fairly solid pad. Don't skimp too much on the scale if you have to buy a new one.</p><p>To use the MDSA, place your car on it's side, OFF the rails, on one side of the plate, and tare your scale to eliminate the weight of the plate and the car. Then, place the car on it's wheels above the rails. This will provide a measurement of how many grams/ounces of downforce is being created by that car over those rails. If you want the readings to match those of another device, turn the screws or nuts as needed to raise or lower the rails. Raising the rails will increase the reading, and lowering the rails will decrease them. Change a small amount at a time and test the scale by starting from zero again.&nbsp;</p><p>Remember, magnetic downforce is only ONE of many factors that impact the performance of your slot cars. Don't ignore the tires!</p><p>If you can't do the changes yourself, feel free to message me with the measurements needed, and I'll put up a remix for you.</p>