Mini-Meg

[johnnydmd]

So this I mentioned in my Dragonoid thread, and originally it was going to be a mini Dragonoid, but I really don't like having two of the same theme trucks, so I changed it up. Last summer I made a 1/10 Megalodon form out of silicone (that was uh, a huge mistake!). It worked, but it came out rather rough, and there's no way to fix it. Although, the mold I made the silicone form from is intact, I could conceivably pour a water putty form and sand it down...maybe one day...maybe.

Meanwhile I still had the 3D model I used for the 1/10 scale, and decided I could use that to make a 3D printed form for the 1/16 version in two pieces. That took a couple of days, but the form came out great using my Ender 3. I ordered up some .040 PETG, but got shipped .060 instead. Oh well, actually this was better anyway, pretty indestructible at this scale. So I went into the garage (yes, it's finished, much to my chagrin, one day I'll rip out the flooring and put in a real garage door, etc), set up the trusty vacuum former and went to work.

As usual, there's some trial and error. The first attempt I let the PETG sag a bit too much, and it wound up with a couple of creases. It wasn't horrible, but I had bought four sheets, so I gave it another shot. Second time was the charm, came out 100% perfect.

Did some cutting, will smooth out the rough spots later, and got it fitted to the chassis.

It's really just about perfect in fitment, somewhat lucky guess on dimensions.

So this thing is using the WPL C14 upgrade chassis. It's a pretty good little chassis, with metal axles/gears throughout. The chassis plates are a little on the weak side, fairly thin CF which I have reinforced with aluminum struts in a couple of places. I made an engine mount plate using CF, that also mounts the gas tank. I cut another piece of CF for the front posts and for the radio and battery to sit on. The radio is just held in with servo tape, and the battery pack is strapped down with ties. There's really not a lot of room to work with at this scale for sure! The transmission is modified, using parts from a Traxxas 1/16 Exeed Blure for the spur and shaft. The shaft is pretty long, and I've put a bearing on the end, and 3D printed a housing for it that bolts to the engine mount plate. I'll get some better pics of all that nonsense. The engine is an SH .07, and I've some concerns about the way the clutch mounts on it. They don't have the tapered shaft collar like larger nitros, it's really just held on with the friction of the screw head/washers. I *think* it'll not slip, but dang, not sure why it's built like that. Then again, this is just a teeny tiny little engine, so I guess that's just how it is.

I got some REALLY nice little micro metal geared servos, and they are beasts! I forget the model, I'll have to update with that. Wheels and tires are from a 1/16 Traxxas Grave Digger, and I had to put adapters/extenders to make that all fit. They are kinda just wedged tightly on the original hex shafts(which were long enough to do this), and I will put some set screws in to hold it, though it's so tight I doubt it could actually slip (had to pound them on). The throttle servo/linkage is some serious hillbilly rigging (but I am, a hillbilly, so whatevs) - it works nicely.

Some stuff needs adjusting/aligning yet to make it really tight and pretty, but it's all functional thus far. I'm probably going to replace the links with something that's less adjustable once I get the lengths figured perfectly. I have a bunch of threaded hollow rods that I was using for the body mount posts that I can use for that. Those stock ones with all of their adjusting nuts have no chance of staying together even with red Loctite!

I'm printing out the molds for the rubber fins as I write this.

 

[johnnydmd]

Well, got this little bugger painted, really happy with the result!

Now just waiting on some new links and shocks.

 

[johnnydmd]

Got my new links and shocks, so I tore the sucker apart, rebuilt it. Now it's at 90% complete I think. Still need to put on the exhaust mounting bracket(bent wire) and the lights, fuel primer bulb, and a better steering servo arm. Overall I am loving this little machine, might be my favorite build yet. I haven't seen many 1/16 solid axle racing events, and I have not once seen a nitro 1/16 solid axle truck, but maybe I can start a trend I will post the build guide/specs on my blog at some point. This is definitely one of those "it might work" kind of builds, I surely have some concerns with the drivetrain, but I do think it's beefy enough to handle the little SH .07 engine.

The little plastic servo arm is getting replaced with an aluminum one. I really wanted to use the servo saver that comes with the chassis kit, but I cannot find a micro servo that fits it, or an adapter. Plus, these servos are serious beasts and I want to keep them. BTW, the make is AGFrc B13 DLM. Really nice all metal servo.

I added a little piece of poly to fill out the sideplates and allow for sponser sticker placement. Also note the throttle servo mount made of .080 poly. This servo mount was really tricky to figure out, there's just not a lot of width here to work with, and not a lot of room. The linkage is quite whacky looking!

Bought these upgraded links cheap, and the color matched the new shocks.

These shocks are great, no leaks, maybe a little on the stiff side but ok. Huge improvement over the stock shocks which were total trash, leaked all over the place, bound badly at times too.

This little 3d printed piece is multi purpose and took a few tries to get right. It serves as a brace and mounting bracket for the engine plate, as well as a bearing carrier for the transmission input shaft. I used the spur and shaft from an Exceed Blur, and just needed an 8x4 bearing for the brace, and a 7x4 flanged bearing for inside the transmission. The rest used the stock remains of the WPL transmission.

And this is how it looks mounted. This keeps the spur tight against the pinion, and also relieves stress on the 7x4 internal bearing. Sometimes things just work out

On a scale of 1-10 of difficulty, this one has been about an 8 so far, mostly because I had to cut CF which I hate doing, but also because of figuring out where to mount stuff and make it work. I'd say working on an MT at this scale is far more difficult than 1/8-10 for sure. It also didn't help that the kit I bought was missing parts, and the transmission was put together wrong, among other things. The links that came with the kit were not correct I think, because the upgrade ones I bought worked much better. I'll detail more of this in my guide. This would certainly be a much easier project the second time around if I ever built another one at this scale.

 

[johnnydmd]

Added some lighting.

Since then I've done a bit of work with the wiring, getting it shrink wrapped and tucked away better. I also have begun breaking in the engine. After a couple of tanks, I drove it around a bit, slowly. However, it seems it had to rev a little on the high side to get the clutch to engage. Pulled the clutch, and it was literally melted. I have some theories as to what's wrong.

For starters, these clutches are el-cheapo plastic. A friend said you need to scuff them up a bit before using, otherwise they slip badly and it heats up and melts. I also wonder if I shouldn't reverse the shoes, as that will also create a better, quicker bite with less slip? I do think that my flywheel may have been slipping some too, but I don't think that would have caused this. I have new shoes(bought 3 sets) and I managed to find a flywheel cone(finally). I really, really want aluminum shoes, but I have not yet found any for this scale. So, I think I might 3d print up some prototypes, make sure they fit, and then have them printed in aluminum. No idea if that'll work, but worth a try

 

[johnnydmd]

Looks like Himoto makes aluminum shoes for this! Ordered a pair. If they work, gonna order every set they have, lol.

As a backup plan, I also ordered an aluminum .12 clutch and bell, as it looks like it's got the same shaft size. It was cheap, so figured what the heck. If the .07 clutch system wears too easily, I'll see if this will work.

 

[D3MON]

this is an awesome build to see come to life, top notch handiwork there , i didnt see it in my reading through, but i might have just missed it, what did you have set up for braking? can't wait to see some video of this, hoping that clutch setup works better with the aluminum shoes! another possibility for the melting clutch might be the gearing? though i can only imagine with the axles that it wouldnt be overgeared.

 

[johnnydmd]

Thanks!

So the brakes I haven't talked about yet - there are none just yet! However, I do have a plan for them, but waiting on the parts. It's probably hard to see from the pics, but there is a second shaft on the front side of the transmission. In fact in these pictures I have some stuff wonked up that is now changed, so the extra shaft is now on the top rather than bottom. This shaft will get the brake pads and rotor, which will be all held together with a new, 3d printed cross brace and mounting for the cam, etc.

I think the gearing is ok, if anything it's probably under geared a bit.

BTW, this little engine is hi pitched and loud as hell! I do have a video (on FB) and somebody was like "you're idling really high!", thinking it was a 1/8 scale truck, lol. Nope, it's just sounding like an angry mosquito because it's tiny!

 

[D3MON]

Ah, ok, very interested to see how you set it up!
i was guessing that it wouldnt be overgeared, but just a though, i know typically on the bigger rigs it is what tends to prematurely wear and melt pads, but given this scale, and the previous problems, that just the cheaper plastic would be more probable.

lol can only imagine the sound!

 

[johnnydmd]

Well, this little project is largely completed

I rigged up a brake system that works flawlessly, required 3d printing out a couple of things, making a few minor changes.

It basically bolts to the chassis where previously I had a brace, and has tabs that slip over the transmission to keep it from rotating any. A hex drive is printed and attached to the top, unused output shaft on the transmission.

I also replaced the stock rod ends with some color matched ones.

Finished chassis:

Been driving it around in my driveway a bit to break it in when it's been warm enough. I also replaced the plastic clutches with aluminum, and they seem to be holding up much better. I installed them reverse for better bite, but I might actually put them back to normal as the truck does want to move a bit at idle, and the engine isn't spooling up at take off for enough power. All in all it handles pretty well, though maybe a bit tippy on hard surfaces. Should be a fun little truck though

 

[BobP]

cool build, keep us up to date

 

[johnnydmd]

I posted on my blog the build specs - this was before I did the brake system - 1/16 Megaldon Nitro Monster Truck final specs and build guide – RC Insanity (wordpress.com)

So far the aluminum clutch has worked well. I took it apart this weekend to inspect, and it's got a little wear, but it's still intact and working. I did however strip the spur gear, and have to refactor the mounting bracket a little to give it a bit more strength, as it looks like it flexed a little under a heavy load and caused the slippage. Got some spurs on the way, and will replace.

 

[johnnydmd]

Spur gears came, and I replaced. Truck is all apart right now, printing out the new bracket today. It appears the problem was that the screws holding the bracket to the engine plate had come loose, allowing the spur to slip. So just reprinting and will be more careful to make sure it's all tight after running.

Overall the little truck is fun to drive, as long as it's on loose dirt, otherwise it rolls pretty easily.

 

[johnnydmd]

Back together.