So we had an old motor on a positioner finally die, I'm guessing the motor was at least 35 years old and we had issues with it wandering in rpm. Our maintenance engineer said he could get a "good deal" on a new DC motor. Since this was a repair task we let him go about the grunt work of spec'ing a motor with the right HP and torque etc. a shiny new motor arrived in our shipping doc for a good price and a maintenance guy fabbed a new bracket and installed the motor.
well he never checked the output RPM:
The old motor's output was 1200 rpm
the new motor was 18 max
When the tech finished hooking it up to the gear box he thought a keyway had been stripped away. You could see the input shaft spinning, but at a 5000:1 reduction ratio the output rpm was about 0.0036... OR 1 revolution every 4 hours and 27 minutes. Hey that's no big deal I suppose we can just turn down our amperage and WFS.
Well then someone got a great idea of pulling the old gearbox and using a new single gear reduction from the motor to the positioner final drive. That's when I got involved as I was ordered to "do the math and buy the #^#% gear already". I entertained the idea did some math and found we needed a 78:1 reduction ratio. well... The final drive was 5" O.D x 78 that only leads to a drive gear that 35 feet in diameter....
Long story short that "deal" on the motor turned out to be a major hassle and wasted a lot of man hours fabricating new gear boxes, mounts and couplings to work with our "cheap" motor. Check your numbers folks, simple math can save a lot of head aches
Why not settle for a drive gear, say 17 feet in diameter? This way you wouldn't have to adjust the amps and WFS quite so much...you do have 17' + ceiling clearance don't cha???
that would work, but then we would have to mount the motor 8.5' above the ground at the center of the hub. I wonder if a 1/2 HP motor could turn such a big gear...
Sorry Metarinka, LMAO!! 35' drive gear! Wow!! I know what you mean though, people lately seem to forget about forthought and planning, it's like it's a dying art and would rather spend a ton of money taking the long road instead of using the K.I.S.S method.
Sounds like the blind leading the blind :) Never seen a good deal on DC motor or speed controller yet they always cost something more.
You did say maintenance engineer didn't you??? Because it reads like the job was given to a janitor apprentice still wet behind the ears!!! ;) ;) ;)
I wonder why nobody in purchasing even bothered to ask questions prior to ordering... was it because he didn't have to submit a separate PO (Purchase Order) since their department already had a standing PO with the supplier? I also wonder why nobody did a check on what he was ordering just to make sure he got it right. You know, like the person who threw some expletives your way even though it wasn't your call to make??? Is this person who made the mistake usually dependable otherwise?
Respectfully,
Henry
Maintenance engineer?????
WOW yall hand out titles loosely eh? I rekon I could be a welding and mechanical/electrical engineer without a blink?!?! Sorry bud just ribbing a bit.....ya got to be carefull who you let req stuff and if you had a maintenance planner worth his salt he would have caught it. Sad to say but any planners that know anything beyond SAP are hard to come by it seems.
One thing I have gathered from working around engineers is they are some the most intelligent, technically , by the book minded people. But they don't have enough common sense to fill a thimble.
I wonder why engineers are that way. I also worked with many engineers during my 18 years at Dow Chemical as an employee. And as stated they are some of the most intelligent people to be found,but out of all those that I worked with{probably about 100}only 2 had any common sense,and that wasn`t just my observation.
Too many engineers have no or too little hands on experience.
Years ago I met a guy who had learned mechanical engineering from the rail road in England prior to WW1. The beginning of His training was 1 year working in the machine shop - without pay. Following that the classroom training started.
hope you all got a chuckle out of this story.
Sometimes something very simple can get very simple like a motor swap can become a big deal if people don't do their homework.
The solution was to use a worm gear. Which can practically achieve reductions up to 80:1
All this time, and purchasing, not to mention the fabrication of the mounts mean this "cheap" motor will end up costing more. However that being said the old motor was crap so I can't complain too much.
perhaps engineers seem to lack common sense because numbers and blueprints are so removed from the actual shop floor it's very easy to overlook things that don't stand out in calculations. That's why as an engineer the very first thing I do is go to the floor and talk to the personnel who run the machines, and the maintenance guys and the welders because 100% of the time they will have further insight and have a better feel of the situation than I can ever get sitting in a desk chair.
Boy do I wish all eng. had your attitude. No telling how many times I've gone to look at a project and had to have the preliminary drawing revamped because the engineer didn't go out and walk through the job with the maintenance super before having the prints printed. I mean all it would've taken was about an hour of his time to do the leg work and get it right the first time. Instead of me pointing out clearance and code violations on my first walkthrough with the maint. super. Then waiting two weeks for the revised prints to show up( just to be wrong again!) Thank goodness I didn't just order parts from the prints and show up to do the job and end up with my butt twisting in the wind because I didn't do my job and do my little walk through. Never take for granted anything an eng. puts on a print. Always over order your parts, add 30% to your labor and take a minute to look over the job twice before you do that. Thats why I just do my little pipeline job now and don't do that other stuff anymore. To much wear and tear on my a$$.
again sounding off thanks for your patience.
Bare in mind that the fact of the matter is "The only people that don't F*&%$ up are the ones who don't do any thing."
I never said I didn't screw up. I was only saying that you need to put alittle effort into your job! Take nothing for granted. that's all
By RonG 
Date 12-14-2009 12:50
Edited 12-14-2009 12:53
That was not intended as blast to any one.
I was just pointing out that we all make mistakes. Politically correct "We gain experience through our efforts". Alas; no effort no experience (wisdom). Its hard to fault a person who is trying like hell to move forward in new terrain.
