[TC17] Aardvark

[howitzer]

For a while now I had the idea to make a MOC of a mine flail, or in more technical terms an Area Mine Clearing System. There are many models, and one in particular that appealed to me is the Aardvark AMCS, as presented for example in here: http://www.aardvarkclearmine.com/wp-content/uploads/2016/07/ACMS-Brochure_HR_Single_Pages.pdf

I had previously made a few tablescraps and bought the parts I need for the flails, but never got further than that until I saw the new contest, which, I believe is the perfect excuse to actually get the MOC finished, so here I am.

I'm not an experienced builder (exiting my dark ages only about year ago) and I'm still a novice with studless construction, with limited parts selection so I don't expect to win the contest or anything, but I hope I can gain some new insights on how to build with studless system and maybe some good advice. I might even write up something akin to a storyline to accommodate the build when it's at least somewhat complete.

Here's what I've finished so far, the drivetrain for the flail spinner is mechanically complete, though it could use some aesthetic touch. I have previously tested that it spins fast enough, but I'll have to build a some sort of chassis before proper testing. I also spent a while trying to make a nice imitation of the tracks of the real vehicle and while it needs adjusting, it'll be something along the lines of my test build.

A closeup on the flail construction:

One problem I'm not sure what to do about is the powering of various functions. There's nothing especially complex, but I'm severely limited on parts so powering the flail, drivetrain and steering seems somewhat problematic. I only have one PF XL and one L motor (no remotes) and two PU L motors with battery box from the app-controlled Batmobile. Steering especially seems problematic, as the vehicle is steered by normal tires (not skid steering with tracks) and I have no PF servo so if I use PU motors for steering I won't have enough motors for the drive (I don't think one L motor can drive the vehicle). I don't think L motor is powerful enough to spin the flails either so I have to use XL for that. Then there's the raising and lowering of the flail boom, but I think that's the least of my problems at this stage.

[Leonardo da Bricki]

Just a couple tips on the motors and such, since you're new to it all:

The PF L-motor most definitely can drive the flail, with the proper gear ratio. It will also need it's own battery box, as I believe the two systems have incompatible plugs.

As the PU and PF systems are entirely separate, the PU must be used for the driving/steering. Again, using the right gear ratio should allow them to move the vehicle fine, especially since it appears to be skid-steer with the tracks?

[howitzer]

On 1/4/2020 at 1:55 AM, Leonardo da Bricki said:

Just a couple tips on the motors and such, since you're new to it all:

The PF L-motor most definitely can drive the flail, with the proper gear ratio. It will also need it's own battery box, as I believe the two systems have incompatible plugs.

As the PU and PF systems are entirely separate, the PU must be used for the driving/steering. Again, using the right gear ratio should allow them to move the vehicle fine, especially since it appears to be skid-steer with the tracks?

Thanks for the tips! I tried the L-motor and it indeed has more than enough power to run the flail. I was concerned that it might struggle to maintain enough speed under the load (which makes the flail pointless) but it seems to perform with no problem.

Mounting two battery boxes isn't a problem, there's plenty of room in the chassis. It should steer on wheels though, like the real counterpart, so I'm planning to have the treads hard-coupled to each other with driving motor geared down to a suitable speed.

A couple of progress photos. As you can see, there's still plenty to do and I think I'm going to be hard pressed to meet the timeline. I propped the flail up with a battery box so it would be a little closer to the final position.

Something that occurred me today though, is if I should have the XL motor driving both the tracks and the flail, with a selector switch to turn the flail on and off? Is there enough power to do that? I guess I'll have to just build and find out. No idea yet how heavy the final model will be, a ballpark guess would be 1kg or so but it could be more than that with all the batteries and motors.

[howitzer]

A quick update: I took apart and rebuilt almost everything. Now the XL motor drives both, tracks and flail, with switch to turn the flail on and off. I also built a basic steering setup with springs to get sense of the dimensions. Next up is finishing the chassis and probably redesigning the flail arm, as the current contraption is pretty flimsy. Then there's the need for height adjustment for the flail which I haven't really thought about much yet.

[howitzer]

Oops, I have almost forgotten to update my progress. The vehicle has come far from what it was in my previous update, so here is some new progress photos

Firstly, these two photos will hopefully show how I planned to do the drivetrain for the two mini-LA's doing the flail positioning, they are driven by a PUP M-motor with 16:24:8:24 reduction. The other PUP-motor will be used for steering.

You can also see here the driving ring for the selector of the flail rotation, which is driven by the PF XL-motor also responsible for driving.

The next two photos show the current situation, as you can see the whole contraption is taking shape. Exterior is of course still not even really started, but mechanically it's mostly complete, save for some bracing. The flail shield geometry has to be adjusted a bit though, as the flail now sits too low. The PUP battery box will be placed on top of the PF box. I changed the previous suspension assembly for a basic double wishbone suspension, but even there I had a really hard time figuring out how to make it work. In the end I think I succeeded, though it remains to be seen how it actually drives. I have never really built a suspension+steering assembly before and with these small wheels you can't use proper suspension parts so it's a bit of a custom build. 

[howitzer]

So, lately Real Life struck me pretty bad and I was left with very little time to finish my build properly. So after getting it functionally good enough, I threw together probably the most half-assed exterior ever to cover it up. I also found out that the single hard spring on either side isn't strong enough to support the weight of the rear side so I made an emergency fix with additional spring to prevent it sagging too much.

I never got around to actually testing the motorized functions until today, but a bit surprisingly, they mostly work as intended. Steering and flail height work perfectly, except there's no automatic centering as I didn't have time to program it into Brickcontroller. Drive also works, but flail doesn't spin as fast as I had hoped, and both of them together make it's movement really slow.

A short video showing the flail and movement in operation: http://www.jousimo.fi/lego/aardvark.mp4

I couldn't film the steering and flail height adjustment in action, as I couldn't take video while operating them on the same phone. You'll just have to take my word that they work exactly as I had hoped for :)

Some day I might try to finish it properly or rebuild it entirely. Or not. We'll see. But here's a few photos of the "finished" entry:

A short video showing the flail and movement in operation: http://www.jousimo.fi/lego/aardvark.mp4

I couldn't film the steering and flail height adjustment in action, as I couldn't take video while operating them on the same phone. You'll just have to take my word that they work exactly as I had hoped for :)