Designing new MBS Matrix motor mount

Hi, I’ve previously built motor mounts for these Matrix Pro ii trucks, as you can see in the build log here, but they failed on me after 20 or so rides. The zinc angled brackets both cracked and fell apart, and I decided rather than sticking with that design, I’d make totally new mounts, and also make a new drive train with much shorter 15mm HTD5 belts instead of the unusually long 9mm XL belts I was using.

So I’m designing the new mounts, and thought I’d ask to see if anyone had any ideas before I start building. I have two aluminium bars, one 1/2 inch thick and one 1/4 inch. So I thought I would do something like this, half inch thick on the left, 1/4 inch on the right (rough sketch):

The left piece would be clamped on to the truck with the two M5 bolts, and then the right would be bolted to that with M5 bolts in the two slots, top and bottom.

The center truck hole would be filed as close as possible to the MBS truck profile. The right piece would have a larger hole, to allow for adjustment for belt tensioning.

Seems like it might work?

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So I took no feedback as meaning no problems and went ahead, and it’s looking good.

As always it was hard to get a good profile of the MBS truck. This time I took a high resolution photo of the truck along the axle, traced around the profile in photoshop, then printed it on to wax paper at the correct dimensions. I then rubbed the ink on to the plate, and traced carefully around the edges with a sharpie.

Here’s the photoshopped truck profile:

The result was accurate enough, but my issues then were with filing through the 1/2 inch thick bar accurate to the markings. At one end it looked great, at the other, ¯_(ツ)_/¯. One of my mounts is angled a bit as a result, but it’s OK enough. The method worked as a guide, not sure it was worth the effort.

I enlarged those truck holes first, enough that the truck could just fit. Then cut them in to squares, then drilled the clamp holes either side in the drill press, then cut through the sides with a hack saw.

I drilled the larger holes in the motor bracket using hole saw bits in a drill press. I managed to yet again measure everything a bit wrong, but it worked out OK. The saturn rings were created by drilling with the drill press, then using a hand drill to wiggle back and forth to enlarge them, and a little filing and aggressive wire cutter tooth pulling.

The mounting bar is adjustable for belt tension pretty easily, tuns out I can do that without removing anything, with a hex screwdriver through the hub.

Happy clamp

Took it for a quick test burn tonight, might need to tighten the belts a little, but it’s looking good!


What about using the motor holes for the belt tensioning instead of where it attaches to the other piece. Since you have four for the motor and only to on the other.

This Truckprofile is really hard to meassure. I break my neck by this (-; Really appreciate your hand work on this, i can only imagine how hard it is to get it matching.

It takes me 5 trys with a CNC to get it in shape:

In my opinion you dont have to split the part which is mounted on the Axle, if the shape is good you can use two big setscrews to push it in the prism:

Thumps up again for your work.


@DilatedPupilsI do quite like that idea. My reasoning was that two screws would be easier than 4 to adjust, however that was wrong, because the access is harder, and they need nuts on the other side. I’m struggling a little to get the belts tight enough, so might try that, thanks.

@Nowind I wish they had a simpler profile, because other than that they are great! For my next build I’m going to try some other trucks just to avoid this problem. Good idea on the set screws, though I really hate tapping threads, so it’s probably 50/50 which would be easier, and the two bolts provide a really secure fixing.

Cheers :slight_smile: