I have a Tekno MT410. First kit I've ever built, which I started in late spring '19. I went a route with several components that aren't common insofar as these monster trucks go. I installed a MGM TMM 14063-3 X2-Series Pro ESC and a Lehner LMT 1950 motor, which required a custom printed ESC mount. I also added a VG Racing roll cage that is designed for a E-Revo Brushless V1. I designed some cage mounts and printed them in PLA (not the best choice, especially in hindsight). Everything seemed to be good as they secured the cage to the shock towers well enough.

I've been messing around with a GPS unit and cameras for the truck, which at first didn't seem like a big deal, but after you start wiring everything it gets to be busy. I have ideas for the V2 approach on how I can clean things up a bit for the wiring, although it's not visually bad as I put wire sleeves on it and ran plastic conduit down the center of the truck.

Finally, I was tired of the wiring thing, and just wanted to get the truck done. I got it to a state where I could take it out for a test run last Saturday. A friend suggested a place where we could go. Upon getting there it wasn't as wide open as I was hoping (which isn't common in NY but there are a few places I'd prefer over this location) There was too much stuff to run into. Park benches and highway supports for the elevated FDR Drive among other things.

There are problems with my design, too. The placement of the camera in the front doesn't leave any room for the bumper to pivot up, or not enough. When I ran into a few things -- not high speed or anything, but more along the lines of what you might expect in a normal experience, the bumper was forced into the camera, which broke its mount and then was forced up into the cage/head light mount which split the cage mount. The camera and lights seem to be fine, so no harm there. Just need to rethink how they're mounted. With the camera where it was, it was a situation of having 10 lbs of crap in a 5 lb bag as the saying goes.

As for the part itself, I believe there was poor extrusion adhesion, especially on the sidewalls. That could have been better, and in the time since I think I've improved my print quality to the point of which that shouldn't be a problem. However, brittle PLA isn't a particularly good choice for this project. I'm thinking that TPU might be a better solution. Strong, but some flexibility as well. Might push the infill up to 35 to 40%. Not sure at this point, though.

Running into stuff, while fun, is hard on your vehicle. I'm hoping that I can solve this problem in order to have a reliable roll cage. I have other ideas on what to do with the cage mounts, such as integrating the camera/light mounts into them as well as possibly a quick release for the cage to remove it. It's difficult to access anything on the truck with that cage in the way.

The truck itself is fine. There were a few minor issues such as the pinion gear loosening itself on the motor shaft. Probably have to grind a flat on the shaft as there isn't one now. Seems like a fairly stout vehicle.

Looking at your broken part, it looks like your printer is under extruding and the print temperature might be a little too low or your print speed is a little too fast. Nice truck though. Always liked Tekno products.

It's been a long time since I printed those cage mounts, and I don't remember what the particular settings were then. Above all else, PLA is a terrible choice for a part that will require durability where shock/impacts are involved.

I've since done some work on redesigning the whole cage mount setup and came up with a design that has a hinge allowing access to the truck. Something I found to be a PITA was trying to do anything to the truck through that cage. Changing batteries was a bigger challenge than I care to experience.

I came up with two designs, actually. This is the first one. Worked well enough, but I decided I wanted to lower the cage as far as possible, and the way I'd designed the rear mount that wasn't really possible, although there was definitely room to do it. The design didn't allow for a quick design change.

I had added holes for tail lights and the brake lights. This is TPU. I never really cleaned up the parts when I was done, so it looks pretty ratty, but is more or less a prototype. I didn't want to use a light gray color for the finished piece, and this was the only TPU I had at the time. This is also the first piece I had printed with supports. They weren't too difficult to remove, but left some remnants as you can see.

The hinge pin is a piece of carbon fiber tubing I had. I used a 'tongue' as a key to help keep both pieces in alignment when closed and also to provide some additinal resistance against shearing forces.

I had to figure out a way to lock the front cage mount pieces together, and decided to use a quick change pin to do it along with an interlocking design.

I don't really like the design. I think it's bulky. The mount on the shock tower is too thick, but in order to use the quick change pin I needed it to extend beyond the shocks in front. I have another idea on what I can do to change that, but this will do for the time being.

This is printed with the spiffy new roll of TPU I received. These pieces printed well enough, but along the way I manged to bend the heatbreak on my hot end while removing the nozzle to clear a jam. I bought titanium replacements and have an extra on hand. I believe I have everything on hand to go to higher temperatures, up to 360C or so with the thermal compound I'm using -- does anyone know what the thermal compound being used on hot ends that can go up to 500C? That's about the only restriction I have at this point. Although I don't have any filaments that require temperatures that high presently. Having the option is good if something interesting comes along.

This is the final design for the rear cage mount. Printed in TPU. I managed to add a spot on top for the brake lights.

This lowers the cage roughly .75" (18mm).

The main problem I had when trying to lower the cage with the previous design was that the holes that mount the assembly to the shock tower overlapped the holes that held the cage on. I also had to have the hinge below the point where the cage attaches otherwise it would pivot into the shocks. The hinge had to move anyway, so that wasn't a problem.

The TPU seems to allow enough flexibility but also is strong. I don't have to worry about it shattering like PLA. It seems to be tough enough and doesn't seem like it would tear easily.

Hinge pin is a solid carbon fiber rod. Bought a set of varying diameters, so I'll have some available for projects like this.

I had to drill a few holes on the face of the base that attaches to the shock tower for clearance of a few nuts. I forgot about them. Need to add that clearance to the design.

So that entire hinge assembly is TPU? It's not too "rubbery" and flexy? Looks good though.

@babblefish

I've found when printing TPU it's definitely flexible when printing thin parts, but the thicker ones can be flexed a little, but not much. That front cage mount assembly isn't really flexible at all, and I think it's at 25% infill. The rear assembly isn't as thick but it's still very solid. It's going to some force to deform it. I'm more worried about the screws pulling through the mounting holes than I am the TPU tearing. I made the screw holes and clearances large enough to put washers under the socket head cap screw heads. Thought that would help disperse the pressure from the screw.

As above , TPU when printing thicker parts is like a very hard rubber , I've made buggy wing mounting posts of dense TPU that are virtually indestructible , its a good choice for the cage mounting .

Interesting use of TPU...never seen it used that way before, but it does make sense for that application.

In defense of the original part, it's certainly a little under extruded/printed too cool as the wall thicknesses have separated, but ye gods that was a hell of a whack to break it like that! Did you build that truck or steal it? Because it looks like it was driven like a stolen one lol.

How's the TPU hold up at mount points where something is bolted onto it?

Ohla RC/DC!

Heh. Yeah, it took a head on into a ship mooring bollard. I found out later that my braking was compromised due to the set screw in the pinion gear getting loose and allowing it to spin on the motor shaft. Well, acceleration and braking were compromised. I'll have to cut a flat on the motor shaft and use a stronger thread locker.

I knew that the heads of the screws might compress the TPU to the point that they could pull through the hole or deform the part in a negative way. While TPU can be strong, its elasticity can be a problem like that. I printed the various clearances and holes for the screw heads to allow for a washer to fit underneath the screw head. That helps reduce the probability the screw head will pull through the hole. The way the cage mounts are designed it would take something rather catastrophic to allow that to happen, like a shock tower breaking or ripping off its mount point. Could happen I suppose. I have braces installed and also have aluminum diff cases to replace the composite ones at one point, which is what the shock towers are mounted to. The cage mounts are mounted on the front of the front shock tower, and the rear of the rear shock tower as well, so the forces applied are distributed at several points.

Originally Posted by devzero

Ohla RC/DC!

Heh. Yeah, it took a head on into a ship mooring bollard. I found out later that my braking was compromised due to the set screw in the pinion gear getting loose and allowing it to spin on the motor shaft. Well, acceleration and braking were compromised. I'll have to cut a flat on the motor shaft and use a stronger thread locker.

I knew that the heads of the screws might compress the TPU to the point that they could pull through the hole or deform the part in a negative way. While TPU can be strong, its elasticity can be a problem like that. I printed the various clearances and holes for the screw heads to allow for a washer to fit underneath the screw head. That helps reduce the probability the screw head will pull through the hole. The way the cage mounts are designed it would take something rather catastrophic to allow that to happen, like a shock tower breaking or ripping off its mount point. Could happen I suppose. I have braces installed and also have aluminum diff cases to replace the composite ones at one point, which is what the shock towers are mounted to. The cage mounts are mounted on the front of the front shock tower, and the rear of the rear shock tower as well, so the forces applied are distributed at several points.

Well it certainly can take a knock. I'm going to have to try some flexibles, I've not bothered yet.

Whenever you're using allen/button head screws or any screw with a small head and it's going through plastic or anything soft such as TPU, use a flat washer. It'll help spread the load and prevent pull through. Bugs me every time I see people using allen/button heads in something soft in high stress situations and not use a flat washer.

^^^^Agreed^^^^

SteveT.

If you like TPU, check out cheetah.