yep! its this one! http://www.ebay.de/itm/272572660673?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
and update 3!
i changed the design of the mount a bit. extended the area where it boke before and added a another clamp to the other side of the truck to absorb more energy.
worked pretty well so far. i managed to drive arround 14.5 km (1.3 are missing in the log) and still have 45% battery left.
when back home i saw another crack, but i honestly was expecting one there anyway. should be rather easy to fix since i just have to make it thicker there and maybe experiment with the infill a bit.
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Love what you’re doing here keep it up, how are the teeth on the pulley holding out? Previous threads have said 16t or lower wear out kinda fast. Perhaps allowing for some m5/6 bolts to be put in would make it stronger without compromising on cost or easily-sourced parts?
cant say much for the small pulley because i pretty much have to reprint it every time i change the motor mount (sits on super tight so it usualy breaks when i try to pull it off), but the large one isnt showing any signs of wear so far.
printing the mount right now aggain with 100% infill. previously i had 60% honeycomb infill with 6x6x6 solid layers. pretty sure that not going to cut it because PETG usualy becomes way more brittle when beeing solid, but i’ll try it anyway.
Update 4
ok, so the new mount is finished printing and mounted. this time with 100% infill instead of the 60% i used before.
uppon further inspection of the broken part, i figured out that it only cracked the 6 outer layers i used, the infill and the other side is perfectly fine. which means that im probably on the right track with my 100% infill.
(crack outside)
(inside crackfree)
im updating the thingiverse page and add the support clamp there as well
Update 5
OK, the “right track” wasnt so rigth after all
PETG becomes way to brittle when solid. i think ill try less infill and less layers. not giving up yet ^^
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Have you thought about ABS? I haven’t printed motor mounts, but I have half a dozen ABS WHeel pulleys with 100KM on them, they show no wear at all.
How many teeth on those wheel pulleys?
Usually 36, but I’ve used 32 & 40 as well.
thought about ABS yes, but right now i still wanna try it with PETG. im going to try 2 other ideas i have and if both fail, i try ABS.
they pulleys and everything else hold up fine. but the motor is just to darn powerfull and rips the mount appart. i could solve that by just tuning it down, but that would kinda defeat the purpose.
increased the mountplate in width by 5mm now, not sure if i can fit the pulleyxy now but we’ll see
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I think the wall strength on those are way too thin. I’ve had good results with 20-30% infill. 3D printing sorta reminds me of a bone structure. Relatively thick wall strength and inside is the spongy bone mass which resembles the infill. Try different kind of infill structure.
Did you try annealing your part afterwards ? Would be interesting to see 
Have you considered printing in polycarbonate? I’m planning on printing everything in solid PC (pulleys, enclosure and motor mount) for my next build.
Just an idea, but you could try a hollow 3dprint and fill with something like Epoxy
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How thick are the single layers you print? The thicker the layers the less bonds you need and hence more stability. The finish is not getting nicer but form follows function.
@TranxFu @Vaulter92 Wallstrengt is 6 layers at 0.3mm. pretty much the max you can have with a 0.4mm nozzle. no cooling to give it as much setteling time as possible.
Havent tried annealing yet. my last (and first) attempt to anneal PETG was pretty fubar since it compltely lost its form 
but i will probably try that aggain sooner or later.
the new print with the thicker mountplate and 50% infill is finished now. gonna mount it as test it today.
@colin
isnt petg a polycarbonate?
originlay i was aiming to print it with nylon, but the one i need is pretty much out of stock everywhere
I have a bit of different mounting solution for the caliber trucks with a 3D-printed parts.
It’s pretty durable even when printed with PLA, but they still develop cracks after some use, so I’m going to go for metal motor mounts in the future.
For more pics check out this Imgur album:
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update 6
gnah! i think i reached a dead end here.
so the mounting plate now is holding up fine. but the plate is so thick, that the small pulley only is inserted 1/2 of its size which harms the pulley quite alot. also, i took a few extra bumby roads and the clamp holding onto the truck now broke. i cant make the clamp thicker but i could make it wider like SimosMCmuffin did. i was thinking about that before, but decided aggainst it.
never the less. I think i stop here and just buy a metal mount instead. the motor is just to darn heavy and to fix this properly i would need to mod the motor itself which is out of my abilities.
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Just a small comment after looking at your design, and ignoring the conclusion I think you could improve on the geometry to avoid cracks. Use large radiuses where you can, instead of sharp corners and circular holes, not slots. Preferably also without chamfers/countersunk. @SimosMCmuffin’s design looked interesting.
With 3D printed motor mounts, especially FDM, you have to make sure your motors dont get too hot as it will melt your thermoplastic. Although much more work, I believe making from aluminum is the way to go because they are much tougher and absorb a lot of heat from your motor.