Another RC model side project

[crueby]

Wow, take a few days off to attend son #2 graduation, and the elves go nuts!

Hopefully you have plenty of that kevlar string handy, I'd not want to have to splice the stuff (though you'd probably just hand it off to the apprentice elf?)

 

One way to keep an apprentice  busy!  Its braided kite line, very strong, but I have to  put a drop of superglue on it and let dry before cutting or it frays out. I recall seeing an article about splicing it, use a large needle to feed it back through other side rather than the old 3 strand rope weaving. It comes in a variety of diameters, more strands stronger but thicker, so I have  several spools of different  sizes. The bigger one I have is  500 pound breaking strength, should be plenty for the elves to excavate the swarf pile!

[crueby]

Spring is finally here!  (great looking latch Chris!)

Thanks  Jeff!  Been nice the last few days, lots of outside  time. Hope its good this weekend,  we have our first pond run of the season with the subs.

[crueby]

Did a little on the shovel this evening - made up the yoke block, which the dipper boom slides/rotates in - its the brass fitting where the two booms cross:

Still need to make more brackets for where the bucket connects to the boom, and a stop plate at the inboard end to keep it from sliding out of the yoke block. Also the pulleys/cable connections for the ends of the dipper boom for the crowd cable to connect to. But, before any of that, I want to make up the drum assembly for the hoist cable, to test out the movement and make sure the motors I am using will do the job - strength and enough speed. If any changes are needed there, want to get that sorted before more work done on the crowd movement.

Slow but sure, this project is inching forward in spare time...

[cnr6400]

  Looking great! Hope the drum / drives work goes well. 

[crueby]

I started laying out the bar stock to make the shafts for mounting the winch drums onto the motor shafts, plus the limit switch setups. All good there, but I was not really happy with the worm gear plus arm for the boom tilt mechanism. It works, but didn't get quite the movement on the boom I wanted, and it was struggling to lift that much weight when the dipper/bucket was on. The cabling on the original, which I'm following, gives a 3:1 reduction in movement on the boom. That means the cable needs to move a couple of feet for the boom movement it should have. The arm, limited in length due to the height of the cab, only gives about 8" movement, so I had to add another pulley to double the cable movement, halving the effective strength of the winch. Also, the worm gear and shafts add some friction losses.


So, long story not much shorter, I got out another sail winch servo thats been in the drawer (identical to the one I've been using, but without the worm gear/arm addition), and tried it with just the sail winch drum it comes with, and tried that. It alone has the travel needed on the cable (since I have a servo travel adjustment on the radio so I can get up to 8 turns on the servo output), and it has the strength needed to pull the cable in even with the dipper/bucket extended.  So, So, I'm going to pull the worm gear/arm assembly back off and mount the plain winch drum in its place.

Not much to show photo-wise till that happens, and by then I'll likely have the first of the drums hooked up to the bucket hoist cable. Maybe in another week...
 

[cnr6400]

  Standing by. I'll listen for the first "make sail" command.  The RC sailboat habits are so hard to break! 

[crueby]

Standing by. I'll listen for the first "make sail" command.  The RC sailboat habits are so hard to break! 

Reef the mains'l ye scabby bugger!

[cnr6400]

 Aye aye sir!

[crueby]

A little time on the shovel side-project - did a little drawing in Fusion and fired up the boiler on the 3d printer (ooooh! That would be really steampunk!) to print out a new bracket to hold the sail winch servo to replace the one with the worm gear/arm on it.

It had to be angled to wind up the cable without jumping the rim - not enough room to turn it sideways with the spool vertical, since the crowd cables will be running past on that side. In the picture its just held on with clamps to test it, need to get some holes drilled/tapped in the floor to hold it for real.
Ran a test with it, and it gets lots more travel on the boom, so happy with this arrangement. The base servo gives about 3.5 turns, but I picked up a servo travel tuner from ServoCity. Its a little box that plugs in inline to the servo cable, and has a couple of adjustment pots on it to set the total travel - works by expanding the timing on the control pulses. The tuner and servo are a set made for robotics use, its a variant of the Hitec sail winch with extra travel and heavy duty gears and ball bearings, rated to 11 inch-pounds or so at 6 volts. Perfect for the boom tilt, but the big gearmotors you can see in the background to the left in the picture will give many times that in power for the main hoist and crowd. I'm using Kevlar braided line rated to 500 pounds, so no worries there unless the shop elves try to lift their bar tab!

[cnr6400]

  Glad to hear the sail winch is working out well!   

Re the elves' bar tab - might need to call for a semi truck recovery tow rig for that one! 

[Kim]

That's very cool, Chris!   
Are you going to leave that bracket as a printed part?  Will it be strong enough to take the stress of the boom winch and all?  Probably, just wondering...

Kim

[crueby]

That's very cool, Chris!   
Are you going to leave that bracket as a printed part?  Will it be strong enough to take the stress of the boom winch and all?  Probably, just wondering...

Kim

Yes - that holder is printed in PETG, 3 extra layers on the perimeter and 40% infill. The walls are .315 thick at the ends and .154 thick down the sides. Quite strong. The sail winch servo itself is about twice the size of a standard servo, so it makes the holder look smaller.

[crueby]

Got the shafts made for the winding drums on the big gearmotors, and two winch drums mounted on them to test out the motors and drums. No limit switches yet, so I have to be careful not to jam them up at the end of the travel. The crowd cabling is not hooked up yet, so the dipper stick has a couple of clamps on it to keep it from shifting in and out.


Here is the larger diameter drum running the bucket up and down. Too fast, even when I changed the battery from 12 volts down to 9.6 volts. In this test, I was only using 1/2 to 3/4 throttle, its too twitchy on position. Also, with the large drum, it has so much leverage on the drum that when the motor is off, the weight of the bucket when extended out on the boom is enough to make the motor turn and creep the bucket downwards.

<a href="https://www.youtube.com/watch?v=XhwUmncoTy8" target="_blank">http://www.youtube.com/watch?v=XhwUmncoTy8</a>

Now here, its running with same motor type/speed, but with a smaller diameter drum winding the cable. Much better control, and it cannot pull the motor around when the power is off. This looks like the combination I'll use. This was done with the 9.6v battery again, if I want more speed I can up it to the 12v one.

<a href="https://www.youtube.com/watch?v=LIuytIkABAw" target="_blank">http://www.youtube.com/watch?v=LIuytIkABAw</a>

[Kim]

That's mighty cool, Chris! 

Kim

[cnr6400]

  Motion looks so much better in the second video! Very nice Chris.