Let's Make Robots!

Ignoble Idiocy

"Those who cannot remember the past are condemned to repeat it." - George Santayana

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Nobody's perfect, least of all me.  Here I intend to record some of my roboting mistakes for my own good.  Perhaps you can learn from my errors, or even contribute your own.

Latest Update: 2010-02-04

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Picture the scene:-

"LoMoR" experimental Sonar scanner, full gas lets "push it some more" impulse.

Lets connect my only sharp and try infra red probe instead of ultrasonic - quick scan of internet to get the pinouts ....easy

Wired up and noticed the Display dimmed a little (hmmmmm strange i thought) lets turn up the brightness of the display.....fine display good.

Measure the current i thought.... mmmmmm 300ma must be the nice blue display take-ing the current...........

.......... "Sniff sniff" lift IR module up to nose and chin ..... a faint heat was detected on my chin and the whiff of carbonising SharpIR lose-ing its life force and finally kicking the bucket.............

Moral:- never trust the internet for pinouts and test new circuits with low current batteries.........

thank you TinHead and Ignoblegnome for respecting the 1 minute silence , all collections,flower etc will go to charity.

Sharpkick_the_bucket.jpg

I can almost smell it... wait, that's my 5 year old cooking marshmellows in the microwave.

I'm trying to make some couplers so I can connect the Mr. Basic drive shaft to a short length of steel cable. The goal is to create a flexible drive shaft.

Here's the problem, I have so far consistently failed to get a hole drilled straight through the axis of a 1/4 inch steel rod.

Update 2009-09-28: Success! I had another blunder and then finally got it. I added pictures too.

Attempt #1:

  • Used a Dremel to cut off and clean up an 8mm piece of steel rod.  No problem.
  • Center tapped "by eye" the end of the rod.
  • Used a 3/32 inch drill in a drill press, with the rod held in a vice.

Coupler_try__1.jpg

Result: The hole was visibly off-center.

Attempt #2:

  • Used a Dremel to cut off and clean up a 5mm (which is too short, I forgot to double-check the required length) piece of steel rod.
  • Tried a cute idea I read about on the web for a center tap jig. The result was WAAAY off center, so I went back to just visually centering and taping the end of the rod. I had to Dremel down the originally off-center tapped hole.
  • Used a 3/32 inch drill in a drill press, with the rod held in a vice.

Coupler_try__2.jpg

Result: The hole was off-center. The rod was too short.

Attempt #3 (a bit better):

  • Cut and center tapped the piece as before.
  • This time I really watch the drill as it started to cut, and I saw that even with the center-tapped hole, the bit tended to wander.
  • I REALLLY slowed down the downward pressure, and let the hole establish itself in the center before pushing through.

Coupler_try__3.jpg

Result: The hole was centered on ONE SIDE, and off-center on the other.  GRRRRRRR!

At least I'm learning. Next time I'll be 100% sure I have the piece in the vice vertically. I'll go slow all the way through the cut, and i'll try using some oil to lubricate the drill bit before cutting. I'll also double check the speed I'm running the drill press at.

Update!

Attempt #4 (Oh! The humanity!)

  • Tried another one. It was still off-center, but at least the hole went straight through.
  • Decided to try the two side holes for the set screws. Tight fit since the piece wound up about 7.5 mm long, and each hole is 3/32 (almost 2.5mm).
  • Two side holes center-tapped, drilled, and threaded. OK!

Coupler_try__4.jpg

Result: Put in the set screws, but one got stuck and wouldn't back out. One half of the slotted head snapped off, and I can't get the f***er out even with vice grips. I ALMOST had it.

Attempt #5 (Busted drill bit!)

  • This time I thought I had it.
  • Everything was going so well.
  • I got as far as drilling the hole for the last set screw and BAM! The piece went flying.
  • I didn't have it clamped down well, and the tip of the drill bit snapped off!

Coupler_try__5.jpg 

Result: Busted my nice shiny drill bit and had to substitute an old, not so sharp one.

Finally! Success!

  •  I was able to salvage the piece from attempt #5.
  • Pausing only long enough to document my disaster, I got a new bit and this time rigged a good clamp.
  • Everything came out swell.

Coupler_success.jpg 

Result: Set screws are holding in the steel cable. Now I just need a 2.5mm drill bit so I can widen the center hole for the Mr. Basic drive shaft.

Oh, yeah... and build like seven more of these.

Learn well from my mistakes, oh reader.

Now with pictures to document my inability to center a hole on a metal shaft.

I was talking to a friend of mine yesterday who works with machinists. He said the best way to get a center drilled hole on a shaft is to start with a square rod, drill the hole, and then use a lathe to round out the rod around the center hole.

Nice for him. He has a metal lathe.

Alright so I ordered these servos http://www.pololu.com/catalog/product/1040. I had the intent of modifying them in the usual way. I opened the case and took the first three gears off. I couldn't find a stop so I put the gears back on in their proper places. I reassembled the whole thing and when I rotated it by hand it rotated continuously. This happened for both. I hooked it up to my board and used 0, 90, & 180 for full speed one way, neutral, and full speed other way. The first servo just sorta spun in one direction full speed, and stopped and twitched, then spun full speed until one of the gearshafts broke and took a few gears with it... :(. So I thought I'd try the second servo. I hooked it up and it spun way with 180, and was nuetral at 90. When I entered 0, the gears stopped moving and only the pager motor was spinning. It got really hot and just went caput. So yeah, I think part of the problem was that these servos were just pieces of crap and poorly built. So I recommend you don't buy these... Anyone know of good reliable and relatively cheap micro servos?
How do they compare to the DAGU mini servos?
I haven't used the DAGU servos... Have you? I'm looking for another good tiny servo. Mine that broke were pretty noisy but were very small as a plus.
I used them here on my pan/tilt mount.
awsome, I shall visit here regularly. I had the feeling that my general impatiance and hence incompetance in construction was an isolated case. It's good to know that for other people naturally choosing the correct method is also hard won! :D
Glad to know you like it. I've promised myself to post my mistakes, and not be embarrassed by them. I will learn from them. Others will be amused, disgusted, or entertained as is their wont. I'm cool with that.