Improved Steering Knuckle Mount for Tarmo4

prusaprinters

This is an improved steering knuckle mount (part 18B) for the Tarmo4 RC car by KrisCubed. The original can be found on Thingiverse.ChangesFor me, the original design would always come apart quite quickly, with the screws rattling loose and the threads in the plastic getting worn away fast. My take has the following changes:Square nuts hold the screws connecting the control arms.Upper control arms now attach using M4 screws.The M3 screws connecting the steering knuckle are locked in place by the M4 screws.The updated cad model is available in Onshape.PrintingPrint in the orientation of the STL file, note that it's different from the original version of the part.Use supports, but add support blockers around the captive nut pockets and the M3 screw holes. See the cover photo.Bridges in the ceiling of the pockets were designed with a 0.2 mm layer height in mind. If you print with a different setting, ensure your slicer preserves them.AssemblyDrill out the hole in the upper control arm (19B) that attaches to the knuckle mount to 4 mm. Ensure an M4 screw fits snugly but without threading into the plastic.Test and drill out the M4 holes in the knuckle mount if necessary. Again ensure a snug fit while still being able to push screws through the holes without threading into the plastic.Now flatten four M3x16 screws 2.5 mm below the head using the “Screw Template” part as a guide.Insert a screw with the head toward the narrow side. See image.Lock the screw in place by adding a nut so that it won't rotate in the guide.File down the exposed thread in the channel.Mark the screw head so that you know where the flat spot is.Turn the screw over 180 degrees and file down the other side too.Mount the steering knuckles (18C) using the prepared M3 screws, turn them so that the flat spots face the M4 screw holes.Insert square M4 nuts into the pockets. The pockets are sized for 6.8x6.8x3 mm nuts.Attach the upper control arms (19B) using two M4x20 screws, and put some blue threadlocker on the screws as well. Ensure they are seated against the M3 screw in the middle. Don't over tighten, or you risk cracking the plastic.Repeat for the lower control arms (17A), use two M4x18 screws. Don't forget blue threadlocker!The M4 screw heads will extend a bit from the control arms, but that's fine. You can add a washer or use slightly shorter screws for better looks, but it's important they are properly seated against the M3 screws while not pinching the control arms, preventing smooth movement!