Coelacanth wrote: ↑Thu Nov 04, 2021 2:02 pm
How do the mounting posts & standoffs hold up with 3D-printed material compared to the original plastics, as far as self-tapping threaded parts go?
The first car that i remade in Fusion 360 was Ultima ST EP Type-R. In the first chassis that went to use was the same PETG/CF material that i use now and in design there were lots of self tapping screw points and plastic 3D printed (integrated to chassis) body posts. They held "kind of fine", but after some serious bashing the screws started to loosen up. The PETG really isnt ideal for this kind of use. I have Nylon/CF which would be perfect material for things like this, but it doesnt adhere to my printer bed and theres some serious warping issues as i dont have enclosure for the printer. Thats why i use PETG/CF, because it never warps and it attaches to bed like crazy. This is the easiest material i´ve ever printed.
The first chassis damaged badly on full speed, head on impact to icy snowbank in about -20c (4000kV brushless motor, 60A ESC + 3S LiPo). I broke the integrated front chassis body posts, original Kyosho shock upper mount and original front lower control arm in that impact, but otherwise the chassis was still okay. Thats when i swapped to 5mm od/M3 ID aluminum posts and designed nice pockets to chassis for those. Pockets prevent flex and they also look nice. I use minimum 3mm of printing material between the screw head and the aluminum posts. For 5mm post, the plastic that surrounds it is either 7 or 8mm diameter.
After swapping to those + use of brass M3 inserts in the screw points (that are going to be affected by some kind of force) that i install with soldering iron, i hadnt had a single problem with the parts.
You can see the 2 brass scew inserts that i already installed to chassis in this picture:
Rear chassis plate is one example where these kind of inserts are going to be needed. Expecially when there is so little space (original design is aluminum and there really isn´t space because laydown spur gear eats all the space thats there).
Heres the current rear motor layout with newly designed rear chassis cradle. It stiffens up the rear chassis and ties gearbox, main chassis and rear chassis plate neatly together. I also drawed the rear bulkhead. Some minor work still to be done before printing (removing need for major supports/making it pretty, adding some ribbing for reinforcement etc).
Theres lots of things going on when designing these kind of things. The original design cant be usually just copied, as theres always going to be problems either with printing the part (lots of supports needed) or then the layer area is going to be too small, which will cause failure etc etc.
Edit: I actually realized that i dont have a perfectly clear clue how far i should go with this concept of designing an 3D printed a highly adjustable, mod-friendly and nicely performing rc car chassis. I mean, it would be nice if it had 3D printed gearbox cases etc. Im also fiddling around if i should do a rev 2 from my 3D printed oil filled shock cases. I had an idea of using a copper pipe joining shim or maybe something like a Kar 98 shell inside the 3D printed shock case as a liner to get more smoother shock than just purely 3D printing the whole shock case. I just think that i cant get the shells, because they might be regulated here were i live and even if they werent, im not gonna buy a pack of 100 shells to make 4 shock absorbers, so probably have to look other options.
But yea, I dont know, have to think about this.
Just assembled the upgraded RB6/RB7 style front end to it, which also fits nicely. From now own it _should_ be smooth sailing and just designing and printing the smaller and easier parts. Cant wait to test it!
