Kodiak AEV 3 Armoured Excavation Vehicle

[wibblywobbly]

Sometimes I just want to weep.... take a look at 3:22, as well as everything else in this video...

Edit - Found the model, over £5300??
http://www.cg-modellbau.de/epages/62183 ... 2FK-16-108



and then I find this....at 17:22, this is the last time I try and build anything that no one else has built...sob sob sob....

[wibblywobbly]

The excavator arm has proved to be one huge headache.

I bought some 1" C section alloy, and my brother got me some free 3/4", but trying to cut 1/8" thick alloy out with a hacksaw very soon became an impossible task. Dremel disks weren't accurate enough either. Add to that the weight of the alloy and I admitted defeat.

So back to jolly old styrene. The way I have done it is to use the alloy as a former, and build the three sections of the arms around it. The tapers etc are a pain, but it is going together ok, and not only are the arms square, they are straight and in alignment. Its not to scale, it would have been well nigh impossible to cut the styrene to perfect shape and keep it all in line, plus I went for strength over anything else. That is a long 3 section arm, and if it all works there will be a bucket full of earth dangling at the far end.

Once I know that it all works manually, I will brace the arms internally with alloy bar that I will be able to get for £zero, so it should in theory be as strong as an ox. The styrene is fixed with industrial strength superglue, and when dry I run a squirt of plastic weld along the seams.

The excavator bucket hasn't arrived yet, so until it does I can't complete the last section of the arm as I need to know how I am going to mount it, swivel points etc.

Once that is all done I have to decide how to motorise it. The turntable at the front is easy enough, I have a 90 degree drive motor on its way from China.

Emulating the arm hydraulics is still up for debate.

1. Lego Technics Pneumatics? - Would work except the pump would need to be in the hull, and I can't see any way of getting 360 degree rotatation.

2. Lego Technics Linear Actuators? - Would work except I haven't seen any with inline motors, which is the only way to fit them inside the jib arms.

3. Geared electric motors from China? - Seem ideal, and they have threaded armatures so work as an actuator, but they only have 0.1kg of torque.

4. Other Linear actuators are silly money so they are off the list.

So...I still sit and stare at it.

[Bogeyman]

Rob, looking good, let's hope something turns up on the power front.

Have you thought about air operated rams, the ones used in r/c aircraft, just a thought.

John

[wibblywobbly]

Yup looked at rc aircraft ones, the problem with air is the hoses, the arm needs to rotate 360, though having said that the motors would need wires that rotated 360 too.
I wish I knew someone with Lego Technics experience as looking at the things that have been built on You Tube I reckon that there must be a solution somewhere. Eg if I could mount the compressor motor in the turntable platform then it would allow me to use pneumatics?
Linear actuators are my preferred route as they will offer a lot more control. Pneumatics tend to be on or off.

Rob

[wibblywobbly]

Starting to look like it is supposed to now...

[Bogeyman]

Rob,

That looks amazing mate.

John

[AlwynTurner]

Hi Rob, my thinking may be a bit off-the-wall, but what about using remote shutter release cables linked to micro servos in the hull:
http://www.harrisoncameras.co.uk/Camera ... tAod_yEA3A or some similar gadget.
I'm not sure if they would be up to the stress of working the mechanism, but it should allow for a lot of flexibility. It probably wouldn't give you 360 degrees but may give you some of what you need?
Oh by the way the build looks awesome - great job!
Cheers
Alwyn

[wibblywobbly]

I was having similar thoughts about either using bicycle brake cables (they are called Bowden Cables I think), but there is no way that three or four of them will rotate freely. I will await the slow boat from China with my motors, as the sort I am getting will be ideal for making linear actuators. I may even buy some Lego Technics kit as there is a 'brick' that allows inline motors to be used.

I have been priming/sanding/priming/sanding, and smoothing down the joins, it is getting there. Still need to do some hatches, vents etc. The eagle eyed may notice that one of the rear bins should have an open top. I have covered them all for no reason other than to retain box section strength. The stuff on the rear is only placed there as I need to paint the rear deck before I cover it with the storage bins.

[wibblywobbly]

I was amazed that this morning the three motors that I thought were on there way from China turned up on my doorstep, with a UK return address. I lashed up a test rig on one of the excavator arms, and my theory worked. The motors are tiny and will fit inside the arms quite easily, will lift and lower an arm section, and they are totally controllable running off an RX18, so I have high hopes that the whole arm will work when I eventually get around to completing it. I am now rather glad that I made the arms from lightweight styrene rather than alloy, as the weight saving is considerable. The motors weigh nothing at all.

My Lego rear bucket also arrived, and it looks just about the right size. That saves me making one, I now have a perfectly formed one, complete with hinge mounts moulded in, so it should be a doddle to get that working.

Woz offered to test my 3D printer code writing skills, so I sent him something to feed his printer with. It sounds like it worked, and he has printed the two small parts and is sending them to me, so a huge thanks to him for that kind gesture.

Pics will follow when I have things glued together.

RobG

[PainlessWolf]

W.W.,
Almost nothing is beyond your skill set with the services of a 3D printer. Very good news to hear that this one will have full functionality. ;o) Following along.
regards,
Painless