It's just a matter of what's sitting on my shelf. The local metal place only has 6061 from 3/16" thick up. The 1/8" stuff is 5052 but I didn't know that until after I bought the sheets. First tool that hit the stuff welded up and snapped in a couple of seconds. By about tool number three I had figured it out, had to be Johnny on the spot with the air and WD-40. You are right though, 6061 is great to cut, and 7075 has to be like the mark of perfection for machineability.
Well, been a long afternoon. After some things were going great in cutting the openings, the new mist system was doing fine in keeping it going unattended. I then started the slots for the drive unit attachments and it went to #$%@ in a handbasket fast. Came close to total spindle bearing failure. I noticed the smell of really hot oiled metal and put my hand on the head.... it was smoking hot!! I e-stopped and the spindle very nearly stopped inside a single rotation. It was entirely too hot to touch... at all. Themo said close to 190*F inside the casting. Not good. Stopped and dropped the whole thing out and let it cool to take a look. I think the bearings are not long for this world. I backed off the pre-load and reinstalled the spindle to finish up but they don't sound good. Way to much noise. The damage may already be done.
Then I discovered an error in the drawing when I went to machine the rear side. The holes were not symetrical as I had thought and I was using them to locate when I flipped the part over to chamfer the reverse side. Tore up the underside good and proper. Took a while to figure out how i went wrong and compensate the program for it. I did not get around to profiling the outside outline like I had wanted to today. I've had enough for the evening. Need to order new bearings and get ready for the joy of breaking them loose from the spindle. I had a feeling that they were installed a bit too tight from the get-go based on the heating I was getting back in the 3000RPM days. Should have followed my instinct on that one. After I backed the load off they were running at under 110*F at 5500RPM.
Sigh..... Long day.
I feel your pain!
I don't want to feel your pain, sounds expensive...
But hey, what you did get machined, looks impressive though.
Yeah, it's going to be a $100 owchie. I just got the bearings all pulled off and they don't look fried to me. Could be a combination of too much preload and crappy china grease. The bearings surprised me a bit. NSK... not shabby really at all, unless they are counterfiet. However in the process of knocking the spindle out I smashed the lower bearing's roller cage.... "She's dead Jim!". So it's a loss. I figure if I am going to replace one I may as well do both. MSC to the rescue. Should have them before the end of the week. Ordered SKF bearings, that have a couple thousand more RPM rating (8500 vs 6500). I also ordered the Kluber miracle bearing grease. Generally it runs closer to what oil would vs grease.
Anyway I'm turning this into a fixing my machine thread so enough. Time to go back to programming for a bit cause metal cutting is done for a while.
Just to keep up the updates in one place, the proto-bots entry to Erco's figure 8 challenge from the other thread. Proving that with hundreds of dollars in machining and hours of programming I can almost do what he pulled off with some stuff from the junk drawer!
It is definately a lot harder than it looks like it will be to follow any defined arc with a diff-drive even when you have decent command over distance and speed.
Last edited by photomankc; 03-08-2012 at 03:16 PM.
I improved the speed syncronization by allowing the Arc function to calculate in RPM vs the 0 to 128 speed level which worked out to about 4 RPM. Now it can get within 1 RPM of the correct speed to syncronize the motors to each other. Obviously the bigger the arc and the longer they are moving the more even a small error can pile up on you. It will be more accurate making small turns than large ones.
I'm close to putting my spindle back in service. All the bearings are here and three of the four races are in place, just need the grease to get here so I can finish up, set the pre-load and reinstall the machine spindle. Hopefully I'll have the deck done this weekend if the grease arrives tomorrow.
The spindle spins again!!! Yay!!! The little robot gets a much needed skeletal transplant from the original fiber board.
The new bod:
Of course I always jack something up on the last operation of an incredibly long and complicated job:
This is why version 1 is always eventually replaced.... I learn what not to do.
Last edited by photomankc; 03-11-2012 at 04:01 AM.
WOW, It's really starting to look Lean and Mean.. I really like the look..
And your last photo shows some clever thinking, in order to shave off a few grams of weight..
Beauteous, really looks professional!
Good looking job! I find the large thin pieces to be the biggest challenges to machine; you can't put them in a vise and you need sacrificial material under them if they are on the table, the clamps are always in the way, and I'm always worried about a g-code problem that cuts through to the table! I've got to machine a piece like that for the HB25 motor mounts, only I need 6 of them!
Is it just me, or does that beautiful multihole chassis looks like aluminum pegboard? I like it...
Makes far more sense than these aluminum wrenches. Can someone please explain these to me...
5 pounds for the whole robot! I've got one leg weighing in at over 20 lbs! Light weight.
@ DriverBob, yeah but I'm betting you have a good deal more that ~200 oz-in of (idealized) motive force..... fatso!!!! :p
Prowler-Bot has it's first sense of the world! Sharp IR proximity detectors allow my demo code to abort when it senses an object in front. Nothing exciting yet, it just forces a hard-stop and a reboot but no more plowing into stuff in front anyway! Now i have just enough to start playing with behavior based programming for this sucker. Probaly will start with little more than patrol and avoid but should be enough for me to learn on. I guess I better start looking to make a PCB for the motor drivers and main power. The breadboard is getting awful full and it's going to be much more likely I fry something by accident.
Great job, sensors are wonderful. Just don't get hoodwinked and go down the "behavior" buzzword path. If I read one more story touting "emergent behavior" and the wonderfully complex and unanticipated actions stemming from "sensor fusion" (more like sensor confusion if people can't figure out why their multi-sensor bot did something), I'm gonna find a new hobby. Sensors "sense" and your code interprets the readings and reacts. Pretty straightforward stuff!
Behaviour in the sense of a defined set of actions and priorities. The last thing I am interested in something that does whatever it likes and I write papers about how interesting it was when it unexpectedly opened the front door and chased the nieghbor kid.
A test of basic roaming and avoiding. Aside from the false triggers I keep getting from one IR sensor it's working OK. The scope shows one sensor keeps having little 5ms excursions to low. I'll see if making the sensor cog sample as best two out of three helps any with that. I remember seeing one sensor that kept blinking a little here and there in testing too.
Other change needed is I'm going to need a physical 'BUSY' line for the motor controller. I need to be able to sample that rapidly to decide if the last move was completed but doing it 10 times per second over the I2C interface starts to interfere with the generation of step pulses and you can hear it. I was hoping to avoid having to do that. Kinda takes away from the '2 wire' thing. But at robot speeds faster than this even checking 10 times per second I can quickly over-run the sensors detection range and I don't want to eat the whole I2C bus with nothing but status checks while moving.
My behavior functions I'm trying to keep re-entrant. They don't block execution so that another higher priority function can get a bite at the apple if needed so it's complicated to get it right. I'm hoping once I get these two working together good then it will provide a template to build on. The main issue I see is how I can deal with the situation where I see an obstacle ahead, I start avoiding but then run into something behind me... but I'm already avoiding this way so how do I prevent it just oscillating back and forth or becoming paralyzed. For now it's easy! I just bash into whatever is behind me.
Last edited by photomankc; 03-14-2012 at 01:45 PM.