push pull geometry question - HeliFreak
Fun, Learning, Friendship and Mutual Respect START  HERE


Unregistered
Go Back   HeliFreak > R/C Helicopters > Aerodynamics, Physics and Engineering


Aerodynamics, Physics and Engineering Aerodynamics, Physics and Engineering Discussions


Reply
 
LinkBack Thread Tools Display Modes
Old 04-14-2016, 10:37 AM   #1 (permalink)
Registered Users
 
Posts: 1,376
 

Join Date: Dec 2013
Location: Alabama
Default push pull geometry question

Attached is an example. Im trying to figure out if push pull rod length will affect the geometry of lever arms. If my servo arms are 18mm and swash balls are 21mm from main shaft. Does the length of my push pull link change the geometry at all?
Attached Thumbnails
Click image for larger version

Name:	geometry.png
Views:	161
Size:	6.1 KB
ID:	646845  
dominator is offline        Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Old 04-14-2016, 01:23 PM   #2 (permalink)
Registered Users
 
Posts: 25
 

Join Date: Oct 2015
Location: CA
Default

Yes but very little.

push pull geometry.pdf
jorj is offline        Reply With Quote Quick reply to this message
Old 04-14-2016, 01:26 PM   #3 (permalink)
Registered Users
 
Posts: 25
 

Join Date: Oct 2015
Location: CA
Default

Ignore the 67.2 dimension at the bottom it snapped to the wrong point.
jorj is offline        Reply With Quote Quick reply to this message
Old 04-14-2016, 02:29 PM   #4 (permalink)
Registered Users
 
Posts: 1,376
Thread Starter Thread Starter
 

Join Date: Dec 2013
Location: Alabama
Default

Thank you
dominator is offline        Reply With Quote Quick reply to this message
Old 04-20-2016, 02:42 PM   #5 (permalink)
Registered Users
 

Join Date: May 2006
Location: Champaign Il
Default

for proper push/pull that doesn't bind you must have all pushrod connections at 90 degrees to the output arm. Otherwise, as pictured in the first post, you'll have binding anywhere but at a single point in rotation. this angle changes depending on the distance appart the two levers are located, and also the difference in length of the arms. The easiest way is to draw two simple circles in cad the diameters you need for the increase or decrease in ratio you need, and then plot two tangential lines between the circles. The point where the tangent lines intersect the circles is where you want the points. Attached is an image showing your arm lengths, with distances between pivot points of 20 and 30 to show the different "offsets" you'd need for the ball locations. i hate that term offset, as it's not offset, it's proper and 90 degrees,.. but offset sort of gets the point across based on the image the third image is of a much smaller wheel to show how the "offset" changes. In other words, you'd have to re-plot to get perfect geometry any time you change the diameter of either bellcrank, or the distance between them. Push/pull with a straight across arm as the first poster shows is just a recipe for advanced servo wear and tear. If you have that sort of geometry and don't want to re-drill some good servo wheels to place the balls appropriately, I would highly recommend running the servo mounting screws very loose to let the rubber servo mount dampers compress in either direction as you move the controls and torture the servos
Attached Thumbnails
Click image for larger version

Name:	pushpull.JPG
Views:	103
Size:	35.9 KB
ID:	648162  
__________________
Gary Wright
Helifreak user # 7001
gwright is offline        Reply With Quote Quick reply to this message
Reply




Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the HeliFreak forums, you must first register.
Please enter your desired user name, your REAL and WORKING email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself. Use a real email address or you will not be granted access to the site. Thank you.
Email Address:
Location
Where do you live? ie: Country, State, City or General Geographic Location please.
Name and Lastname
Enter name and last name here. (This information is not shown to the general public. Optional)
Helicopter #1
Enter Helicopter #1 type and equipment.
Insurance
Please select your insurance company (Optional)
Helicopter #2
Enter Helicopter #2 type and equipment.
Helicopter #3
Enter Helicopter #3 type and equipment.
Helicopter #4
Enter Helicopter #4 type and equipment.

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools
Display Modes

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

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On




Copyright © VerticalScope Inc. All rights reserved.
 

SEO by vBSEO 3.6.1