Help needed for gear connection

[Ramone]

<DIV =wordwrap nd="3">I am able to create a gear connection but I am trying to create a connection between two gears with variable diameters.

I have tried using a cam connection but cannot achieve this, I would like to see the reaction between two gears where the ratio between them varies as they turn through a whole turn.

Could someone tell me if this is possible in Mechanism or if there is another way to model this.

Many Thanks</DIV>

 

[magneplanar]

Ramone,

Can you make a surface that is the same as the pitch circle for each gear? then you can use a cam follower method to have one surface follow the surface of the other gears pitch circle shape ( the circle that is the point where the two gears touch). Each gear then is actually riding on the surface that is the pitch circle. You will need to work out how to position the gear centers.

Did you make some gears that are out of round?

cheers,

M

 

[Ramone]

I can do this no problem but the rotation of one gear will not cause the other gear to rotate, they will just slide over each other and the centres move relative to each other. Is there any way in Mechanism to create the rotation between the two?

 

[magneplanar]

Ramone,

the gear connection does not use the actual teeth so it can't perform in this way. I have a question, if the gears are not a continuous shape, how have you allowed for the inevitable movement? Does one gear move away like an idler? Can you set up a servo motor to power each gear using the following of the cam profile I described? I will do some tests, but I think your main issue is to get both gears rotating and moving closer and farther apart as the profile changes?

M

 

[Ramone]

Magneplanar,


Thanks for your help so far, yes, the centre of the top gear will move relative to the centre of the bottom gear as it rotates but will always be kept in contact as it will be held down by gravityon a heavy axle.


As it rotates it will obviously have to work harder as it will raise against gravity but this is the idea of using Mechanica.


I haven't used Servo motors before so any help in this area would be greatly appreciated


Ramone

 

[magneplanar]

Hi Ramone,

welcome...a servo motor provides the rotation to make a mechanism function on its own instead of you swinging it around. Depending on your pro e module setup you can do alot. Dynamic and static tests, etc...You will need to set up an analyisis to observe the servo in action.

the servo motor is activated by the little swirl icon and gets assigned to an axis. It gets involved so I suggest you check here:
<a href="http://www.stdg.us/Tutorials/Mechanism_WF2/MDX_WF2_Lesson06.htm" target="_blank">
http://www.stdg.us/Tutorials/Mechanism_WF2/MDX_WF2_Lesson06. htm</a>

actually this link is for the servos, the full page has more about mechanisms.

that should hook you up.

I suggest you make a servo for each gear to make them rotate at the speed you expect, and make the surface I described. Allow the one gear to float on the surface of the other as a cam follower. That might work...

not sure how this will all pan out if you are bringing it into mechanica...

cheers,

M

 

[Ramone]

Thanks M,


Do you know if a servo motor can be set up to rotate as a function of the rotation of the other part (i.e. the other gear) or would it have to be set up so to rotate as a function of time irrelevant of the movement of other parts.


To try to explain, the second gear will only rotate if the first (irregular shaped) gear turns. The first gear will only rotate as atorque is applied to an arm from the gear. The rotation of these gears casues a movement in the system to raise against gravity at an incresing rate.


If you're still with me, the more it rotates, the harder it is to rotate, I want to find out with a static analysis where the system will settle when a certain load (torque) is applied and further to this a dynamic analysis to see how the system reacts with a varying load.


I'm unsure if a servo motor will allow me to model the interaction between the two gears causing one gear to rotate at a changing ratio relative to the other and only if the first is turned by the force.


If that makes sense you are very clever


Thanks


Ramone
Edited by: Ramone

 

[magneplanar]

Ramone,

Straight up I have not made a mechanism as you described. You are in for some work to get it set up with all these parameters. I can say that the analysis and motor setups allow non linear speeds changes and variations based on alot of options. I bet the functionality is there. The sequencing should allow you to make them rotate in order as you described. Gravity, friction forces, and lift off are all options you can define. I am guessing you want to find an optimal speed and then run above and below to see the performance. Dynamic analysis is possible, it will take you some time to set up each axis and movement. I think it is there...dig in and see what you come up with.

cheers,

M

 

[Kaz Z06]

Ramone,


Mechanisms will allow you to create a servo based on the state of other joints using kinematic measures at these joints (displacement, velocity, acceleration) of any other joint can be used as input to any other joint axis. You should be able to drive the rotation of one joint based on the rotation of another. You'll need to use a "User Defined" servo. Here's an excerpt from the on-line help:
User-Defined generates the magnitude of a servo motor, force motor, or force/torque with a function you create using sets of expressions and domain constraints.
For servo motors, magnitude must be defined as a function of analysis time.
For force motors and forces/torques, magnitude may be defined as a function of time, or as a function of multiple variables that includes time and one or more existing measures. For example, to define a force that decreases directly as the inverse of the separation between two points, first create a distance separation measure named septn1. Then define the force magnitude with the expression 1/septn1.


I hope this helps out!

 

[Ramone]

Thank you very much for your help, I have had a play around and think I'm on the right tracks.


I've tried to enter a distance separation measurement between points at the centre of the two gears using Anaylsis -> Measures which I think has worked.


Using a Servo Motor with the driven entity as a Motion Axis and selected as the pin connection.


I've then chosen Velocity as the Specification. Under the magnitude I've selected User defined tab.


I now need to define my ratio in terms of the separation between the gear centres, as a default the "Expression" is set to t. Can anyone tell me how to change this to the separation measurement I've set up and how I fill in the "Domain" to vary the velocity of rotation with respect to the separation.


This will be a great help, Thanks


Ramone