Go to Post After this trip, a person might want to change their underpants. - Andy Baker [more]
Home
Go Back   Chief Delphi > Technical > Technical Discussion
CD-Media   CD-Spy  
portal register members calendar search Today's Posts Mark Forums Read FAQ rules

 
Closed Thread
Thread Tools Rate Thread Display Modes
  #16   Spotlight this post!  
Unread 26-10-2005, 10:11
KenWittlief KenWittlief is offline
.
no team
Team Role: Engineer
 
Join Date: Mar 2003
Location: Rochester, NY
Posts: 4,213
KenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond repute
Re: Mechanical Reliability

Quote:
Originally Posted by Alex.Norton
...Also, I would like to ask what a "tie rod bearing" is ...
a tie rod, you know, it ties the piston to the crankshaft :^)

good catch - I meant the connecting rod bearings (this is why Im not a M.E.)
  #17   Spotlight this post!  
Unread 26-10-2005, 10:15
KenWittlief KenWittlief is offline
.
no team
Team Role: Engineer
 
Join Date: Mar 2003
Location: Rochester, NY
Posts: 4,213
KenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond repute
Re: Mechanical Reliability

Quote:
Originally Posted by mechanicalbrain
...It's no fun to watch the robot you spent many all-nighters working on start spewing "magical electrical smoke" in the middle of a match.
its equally distressing when your robot spews all of its magical noise all at once

because mechanical parts are pumped full of noise in a machine shop. If the noise leaks out all at once, it stops working

sometimes you can force a little noise back into mechanical parts by wacking them, but usually it has to go back to the machine shop, to be refilled with all the noise it can hold.
  #18   Spotlight this post!  
Unread 26-10-2005, 10:24
sanddrag sanddrag is offline
On to my 16th year in FRC
FRC #0696 (Circuit Breakers)
Team Role: Teacher
 
Join Date: Jul 2002
Rookie Year: 2002
Location: Glendale, CA
Posts: 8,515
sanddrag has a reputation beyond reputesanddrag has a reputation beyond reputesanddrag has a reputation beyond reputesanddrag has a reputation beyond reputesanddrag has a reputation beyond reputesanddrag has a reputation beyond reputesanddrag has a reputation beyond reputesanddrag has a reputation beyond reputesanddrag has a reputation beyond reputesanddrag has a reputation beyond reputesanddrag has a reputation beyond repute
Re: Mechanical Reliability

Quote:
Originally Posted by KenWittlief
a tie rod, you know, it ties the piston to the crankshaft :^)

good catch - I meant the connecting rod bearings (this is why Im not a M.E.)
LOL, I was trying to figure that out for the longest time. I'm studying to become and ME and I'm like "there is no way 10 tons of force is exerted on the tie rods." For the connecting rods (and bearings) it makes perfect sense because the pistons have a respectable amount of mass to them and at the top and bottom of each stroke, it goes through an extremely massive acceleration because it is a very large change of velocity that happens in the blink of an eye and because F=ma the force will be very large.
__________________
Teacher/Engineer/Machinist - Team 696 Circuit Breakers, 2011 - Present
Mentor/Engineer/Machinist, Team 968 RAWC, 2007-2010
Technical Mentor, Team 696 Circuit Breakers, 2005-2007
Student Mechanical Leader and Driver, Team 696 Circuit Breakers, 2002-2004
  #19   Spotlight this post!  
Unread 26-10-2005, 10:35
KenWittlief KenWittlief is offline
.
no team
Team Role: Engineer
 
Join Date: Mar 2003
Location: Rochester, NY
Posts: 4,213
KenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond repute
Re: Mechanical Reliability

its not just the force that is being transferred to the driveshaft, its the angular acceleration as well, because it is spinning at 4 or 5,000 RPM in a 6 or 8 inch diameter circular path, with all the weight of the connecting rod and piston attached.

you tie rods should not see too much force, unless your name is Joey Chitwood

but even there, when you turn your wheels on dry pavement, with the car stationary, Ill bet there is a lot

Last edited by KenWittlief : 26-10-2005 at 10:37.
  #20   Spotlight this post!  
Unread 26-10-2005, 20:33
Alex.Norton's Avatar
Alex.Norton Alex.Norton is offline
Fidgetting
no team
 
Join Date: Apr 2005
Rookie Year: 2003
Location: Ft. Collins, Colorado
Posts: 190
Alex.Norton has much to be proud ofAlex.Norton has much to be proud ofAlex.Norton has much to be proud ofAlex.Norton has much to be proud ofAlex.Norton has much to be proud ofAlex.Norton has much to be proud ofAlex.Norton has much to be proud ofAlex.Norton has much to be proud of
Send a message via AIM to Alex.Norton Send a message via MSN to Alex.Norton
Re: Mechanical Reliability

actually the force in that part of the engine is still not that large. The moving parts of an egine weigh almost nothing because that engine will turn faster if it is lighter so the rotation of the engine alone isn't going to cause the largest force in the engine. I mean if they actually weighed a lot then the engine would need a fly wheel in the sense of keeping the engine turning (the starter would have to turn the engine in a different method).

The largest force in an engine will come from the expanding gas in the piston causing the engine to turn. In my fathers car the engine is a 4 piston engine meaning that the torque put out is constant and only one piston is firing at a time. the engine has 205 ft lbs. of tourqe so that is the amount each piston puts out while firering. The distance traveled by each piston is 3.042 inches. divide that by 2 to get the radius. So the piston is pushing on a 1.701 inch lever. then divide 12 by that and mutiply by 205 to get the number of pounds on the be 1446.208 pounds.

Also just think that if the force exerted by the pistons of the bearings was 10 tons then engine would take a very long time to reach red line and most engines only take seconds.

Alex
  #21   Spotlight this post!  
Unread 26-10-2005, 21:29
KenWittlief KenWittlief is offline
.
no team
Team Role: Engineer
 
Join Date: Mar 2003
Location: Rochester, NY
Posts: 4,213
KenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond reputeKenWittlief has a reputation beyond repute
Re: Mechanical Reliability

Alex, what is the angular acceleration of the connecting rod bearing journal, when the engine is spinning at 5,000 RPM, assuming your crankshaft is what? 1.5" radius (that sounds pretty small, I think an old VW crankshaft had a 3" radius)

and what is it at redline RPM?

another way to calculate it, the piston accelerates towards the crankshaft, then slows and accelerates the other way, at 5000 rpm, what is the force just moving the piston back and forth?

Edit: I did some quick calculations.

for an engine with a 4" piston throw (a 4" crankshaft diameter at the center of the bearing journals)

at 5,000 RPM, the piston and connecting rod are accelerating back and forth with A = 37,036 ft/S^2 (1157 g's)

and the angular (centripetal) acceleration of the connecting rod where its attached to the crankshaft is A= 45,654 ft/S^2 (1426 g's)

If your piston and connecting rod together weigh 1 pound, the force for the linear motion is about 1,100 lbs. The centripetal force depends on the weight of the connecting rod held by the bearing. If its a half pound then the force is 710 lbs - so we are close to one ton, and this is only with the engine spinning freely (not supplying any torque to the wheels).

the forces increase by the square of the velocity, so at 10,000 RPM (a high performace engine) you are looking at 4 tons of force on that one bearing, again, just to spin the engine parts themselves.

Last edited by KenWittlief : 26-10-2005 at 22:13.
Closed Thread


Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Mechanical vs. Software Engineering. JoshL General Forum 13 01-03-2005 00:23
Mechanical Wheel Encoders? Jaine Perotti Electrical 15 04-12-2004 22:46
Where can I learn some mechanical before build season John JediMaster General Forum 7 23-09-2003 20:27
Mechanical Engineering archiver 2000 0 24-06-2002 00:04
Max mechanical power of motors, how is it useful? Ken Leung Motors 1 09-11-2001 14:15


All times are GMT -5. The time now is 03:44.

The Chief Delphi Forums are sponsored by Innovation First International, Inc.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Copyright © Chief Delphi