<a href=showthread.php?s=&postid=13741751#post13741751 target=_blank>Originally posted</a> by dngspot
What changes the degree of rotation are the arms on the motor and the down tube. If you increase the motor to the same arc as the down tube arm you should be able to get 180 degrees but, will also go over center and lock up the motor. This stuff works sort of like sprockets on a bike, the closer you get to the same radius the closer you get to the same amount of movement per stroke. Shorten the motor arm and you move less. As for the down tube arm make it shorter, more movement and longer less movement. The tie rod is like a bike chain if it is too long it will push the down tube arm at it highest point and lock the motor. To short and it will not allow the motor to complete rotation at it lowest point. I set mine up by moving the motor arm to the lowest point away from the down tube arm, then rotate the down tube arm so it is closest to the motor and fit the tie rod to the arms.
I hope this helps.
dngspot,
This is partially correct....
Some vocab first:
Ground = distance between center of motor shaft and pvc pipe and also the 'zero' plane when considering angles.
*Also when talking about the PVC pipe arm, I'm referring to the total distance from the center of the pipe to the attachment point of the connecting link.
"What changes the degree of rotation are the arms on the motor and the down tube."
Actually the PVC pipe arm, the motor arm, ground, and connecting link lengths are all important. The angle between the ground and the motor arm is a very important angle along with the angle of the connecting link to the 'ground' as well.
"If you increase the motor to the same arc as the down tube arm you should be able to get 180 degrees but, will also go over center and lock up the motor."
The motor will never lock up if the shortest arm (likely the motor) and the longest (SHOULD ALWAYS BE GROUND) are less then the connecting link and PVC pipe arm in total combined length.
"This stuff works sort of like sprockets on a bike, the closer you get to the same radius the closer you get to the same amount of movement per stroke."
Agreed...
"The tie rod is like a bike chain if it is too long it will push the down tube arm at it highest point and lock the motor."
To prevent this condition, make certain the motor arm and connecting arm total combined length does not equal the ground and the PVC pipe arm combined length.
I have an Excel spreadsheet if you know the following that may make the design the linkage system easier. You need to know the following to use this spreadsheet:
1)Desired angle of rotation of PH
2)Link lengths for ground, PVC pipe arm, and motor shaft arm
3)Initial angle of the motor shaft to ground.
There is also a image depicting the Free Body Diagram of this system in a more technical approach with rough shapes of the box, motor, and arms for visual sake. Let me know if anyone is interested in the spreadsheet. It should be used for the time I put into it to only use it for 10 minutes during design of my system. I have more time in fine-tuning the spreadsheet than I do in the actual build portion of this project.
I can hear it now:
