TwitchMX - The Mech of Many Feet

[Gertlex]

I'll just start this one off similar to Twitch's thread -- Look, Ma! No feet!



The mechanical stuff is not even bolted together. I've got lots of turret work yet to do, and leg mounting to re-design. Oh ya, and battery and power switch location are completely TBD.

The electronics are two Wixels (256 bytes of RAM each!!), both on the robot side, and an xBee will go to the Arbotix Commander. If I have time, I'll have a second software configuration where a third Wixel on the Arbotix Commander is used... However since xBee range > Wixel range, the former gets priority. I'll be using a Pololu motor driver board, and a probably a micro servo hopper agitator, as well.

Software is just a matter of doing and testing. Most of the stuff I've not done yet (gun control) I can almost directly copy from Numa's code.

[jwatte]

See you in April! :-)

[Gertlex]

Did some fabrication today. Now that the body is done, I have a better sense of where things go, and so now back to CAD work. Also time for a McMaster order since I need longer 2.5mm bolts for the MX servos...



The turret mounting is two 3D printed parts "welded" together with ABS filament in a dremel at 10 or 20 kRPM. I tacked it in place while the bot was assembled, then sealed the entire perimeter once I removed the parts. There are also a few bolts on the underside that are also holding the pieces together.


And this was nice improvisation to make dealing with the nuts a bit easier...

[jwatte]

The springs to hold the nuts in place are brilliant! I've been using Scotch tape, but that's not something I can leave while running, and I forget to re-tape it when disassembling, and the nuts fall out.

Also: Are the black horizontal bars also 3D printed?

[Th232]

Also time for a McMaster order since I need longer 2.5mm bolts for the MX servos...

Haha, story of my life. I dread to know how many hundreds of screws I have at the moment. I like how you've done the turret as well.

[tician]

The turret mounting is two 3D printed parts "welded" together with ABS filament in a dremel at 10 or 20 kRPM. I tacked it in place while the bot was assembled, then sealed the entire perimeter once I removed the parts.

I've never seen that particular method employed before, though there is something similar called spin welding - where a metal tool spins fast enough in direct contact with the two pieces to soften and blend them together without the really damaging/weakening high heat of 'normal' welding (I seem to recall it being used on some of the later generation aluminum tanks for the space shuttle - hopefully I have fulfilled my daily quota of random crap nobody really needs to hear).

And this was nice improvisation to make dealing with the nuts a bit easier...

Very nice. Reassembling a DARwIn-OP can be a bit challenging when the nuts don't want to stay in their spots on the mounting flange. Should work to hold them in place long enough to get the bolts started, then pop the springs out later to prevent weight distribution problems. I've had to use index cards as filler between the servo case and plastic frames when assembling AX frames to keep the nuts from falling out (not nice knowing it is there, but it is hidden and works well enough when you don't have any extra black plastic wire routing bands from a premium kit).

[Gertlex]

I've never seen that particular method employed before, though there is something similar called spin welding - where a metal tool spins fast enough in direct contact with the two pieces to soften and blend them together without the really damaging/weakening high heat of 'normal' welding (I seem to recall it being used on some of the later generation aluminum tanks for the space shuttle - hopefully I have fulfilled my daily quota of random crap nobody really needs to hear).

In the case of metals, it's called friction stir welding - and yeah, softening without melting is the key (I re-read the wiki article a couple days ago ). Doing this with plastic was something that showed up on Hack-A-Day a couple of weeks ago, and it works great with easy-to-melt ABS plastic. I was going to buy some 1/8" polycarb rod on McMaster to try, but that comes in 8ft lengths....

I'm in the process of dis/re-assembly, putting the wires on the MX servos. A true PITA.

Edit: Hah. I was sure I ID'd all three servos when I got them, but I only did the middle one. So now I need to remove a wire again while I set the outside servos' IDs... Joy

[Tyberius]

All of you complaining about nuts & bolts with the dynamixels... you shush your mouths. I'm not sure anyone outside of Robotis has assembled/disassembled as many Dynamixel based robots as I have in the last 5 years. Ugh.

[Gertlex]

So the path to minimizing communal misery is to have you assemble our stuff, too?

[byi]

nice welding technique. i might use that. im very jealous of the 3d printer. i wish i had the budget/time for one.