RC Tank Warfare community hobby forum

Fantastic build Rob.
Stevie

Hi Rob, just back from the french tunnel fiasco and wow what a brilliant job you've done on the Kodiak!!
brilliant piece of engineering and modelling. Alwyn

After hitting numerous problems with the electrics and the excavator arm, I decided to cut the wiring out months ago and leave the arm static. However things like that grate on me every time I look at them, so seeing as winter is around the corner I decided to have another go.

My original choice was three RX18's using the various motor controllers to operate the numerous motors on the arm and dozer blade. This was 'ok', but it meant no sound, and a handful of tx's.

Since then I have bought a 6 channel radio, and also acquired a Tiger SLU, so I just let ideas waft around my brain, and then set to work.

I designed it all so that I could disassemble it without breaking anything, so I stripped out all of the motors and tested them. One of the arm motors was duff, so I replaced that. I also redid the wiring using smaller gauge wire to reduce friction. All three motors now work off the turret rotation and elevation circuits. The SLU has two-way elevation so it can be used for two way motor control on the digger bucket. The other two motors are wired together so that they turn the same way, this means that the middle two motors can run off the turret rotation circuit.

I had a spare full size servo, so modified that for 360 degree rotation, and it will marry up with the existing turntable perfectly as it has a hole in the drive that takes an M3 bolt. It also fits without interfering with the operating arms for the dozer blade. It will operate at proportional speed off one of the tx pots on channel 5 of the rx, so it was fairly simple solution.

The arm lift was where the problems all started, the mini motors that I used on the rest of the arm weren't beefy enough to lift the arm reliably, so I bought some mini servos with steel gears, and I am now designing a holder for one that will allow it to lift the arm on a linked pivot. I will see if 90 degrees will lift the arm, but if not, then that will get the 360 treatment as well. Channel 6 will take care of that.

This leaves me with the dozer blade to operate, but I have already used all 6 channels. When I installed the original electrics I installed two switches, and two batteries. I am guessing that if I take the elevation circuit and the dozer circuit and wire them to a standard HL 3 way on/off switch, I can manually switch between dozer and excavator.

Just to add to the fun, the SLU has multiple lighting options, all controlled via the tx. I intend making some spotlights to go on the roof.

The Tiger sound is absolutely deafening, the SLU's and an FRS7 work really well, and sounds quite meaty, so it suits the tank.

When it is all up and running again, and repainted, I will post up a video.

For Pete

This is how I did a spring assisted servo. I use a peg in the hydraulic ram to get the tension right, it needs to be pushing enough to assist the servo when it lifts the arm, but weak enough so that the weight of the arm will collapse it back down when the servo is run the other way. I can get it to lift ok now, but its getting it all the way back down that needs adjustment. Might need to add some weight to the arm? It took several attempts to get the design right, but I think its about as efficient as it can get now within the available space.

It destroyed one of the new steel geared servo's I bought, I am hoping that this one lasts.

Rob, you can do it, just leave it for a while, think, then get stuck in!!

John

Hi Rob looks an interesting solution, Also with a small mod you could use these as recoil units . Hope it works out O.K. looks to be a good way to get fast moving rams, which is what you need for the excavation arm.


regards pete

Took me a while to get it working right, I thought I had failed but the one thing that is crucial is the preload on the spring, it had to be mm perfect or the arm wouldn't lift. It was trial and error with a pin through the rod to compress the spring that found the magic tipping point.

Hi Rob take a look at these photos found them here http://www.forum-rc-panzer.com/t3951-Sherman-dozer.htm

they look like they are bought off the shelf, had a good look round cant find them . Could be ideal for making a arm work , looks like they operate by pulling then release by spring . Might need to alter the servo so it doesn't self Centre.

regards pete

I can see how it works now I have had a look. Servo arm connected to a wire, the wire runs through a sleeve and is connected to the inner cylinder. Activated the servo and the arm pulls the wire, the wire pulls the inner piston into the outer one. Release the servo and the spring pushes the piston back out.

My guess is that he made it, as I have never seen this set up anywhere before. If the servo forces the blade down it would make more sense as the unstressed position would be up?

It's pretty much what I have done, though my big problem is the lack of space. Not only does the mechanism have to be powerful enough to lift the arm, the whole thing has to be compact enough to spin around and face forward, under the arm, whilst avoiding the front of the upper hull. It also has to be controllable as the arm is in three articulated sections, plus the bucket.

Hopefully mine will all remain working once it is all re-assembled....

As good as I can make it. Not perfect, cables snag a bit, and the end of the arm is held down with a neodyne magnet to stop it moving while the AEV is in motion. Electronics are an SLU (need to disable the gun recoil), powering electric motors, with servo's running directly off the receiver. Need one more channel set up to operate the bucket motor, but that would need a small esc and run it off the last empty channel on the rx.