Variable pitch helix
Variable pitch helix
(OP)
Hello People
I have searched through some of the preceeding threads relating to this topic but I've had trouble getting any of the tip to work. Basically I need a helix that satisfies the following criteria
2 turns
Start rad = 30
rad at end of turn 1 = 30
pitch between start point and end of turn 1 = 30
rad at end of turn 2 = 25
pitch between start point and end of turn 2 = 20
I then need to sweep a section along this helix, I also tried doing it in 2 using expressions from a sketch to control the pitch however the 2 were not tangential so it failed.
Any help would be greatly appreciated.
I have searched through some of the preceeding threads relating to this topic but I've had trouble getting any of the tip to work. Basically I need a helix that satisfies the following criteria
2 turns
Start rad = 30
rad at end of turn 1 = 30
pitch between start point and end of turn 1 = 30
rad at end of turn 2 = 25
pitch between start point and end of turn 2 = 20
I then need to sweep a section along this helix, I also tried doing it in 2 using expressions from a sketch to control the pitch however the 2 were not tangential so it failed.
Any help would be greatly appreciated.
Best regards
Simon (NX4.0.4.2 MP4 - TCEng 9.1.3.6.c)
www.jcb.com
If it can't be fixed with a hammer, then it must be an electrical fault...





RE: Variable pitch helix
RE: Variable pitch helix
Best regards
Simon (NX4.0.4.2 MP4 - TCEng 9.1.3.6.c)
www.jcb.com
Life shouldn't be measured by the number of breaths you take, but rather how many times it's taken away...
RE: Variable pitch helix
RE: Variable pitch helix
Best regards
Simon (NX4.0.4.2 MP4 - TCEng 9.1.3.6.c)
www.jcb.com
Life shouldn't be measured by the number of breaths you take, but rather how many times it's taken away...
RE: Variable pitch helix
I have created the helix using law curves, hope it helps.
RE: Variable pitch helix
That's pretty cool, but I'm having trouble understanding the math behind it and what to change if you want to alter the pitch or the radius of each turn. Any change you could give a breif explanation.
Many thanks for your help
Best regards
Simon (NX4.0.4.2 MP4 - TCEng 9.1.3.6.c)
www.jcb.com
Life shouldn't be measured by the number of breaths you take, but rather how many times it's taken away...
RE: Variable pitch helix
xt=r*cos(360*t)
yt=r*sin(360*t)
zt=0
similarly for helix
xt=r*cos(360*n*t)
yt=r*sin(360*n*t)
zt=0 or z=f(t)
Where 'n' is the number of turns.
't' is a parameter which varies from 0 to 1.
Here we have to make
(1)'r' as variable (i.e. variable radius) so as to take r1 (=30) or r2 (=25).
(2)'zt' i.e. "pitch" as variable.
Since there are 2 turns in the helix, for 1st turn the value of 't' varies from 0 to .5
similarly for 2nd turn 't' varies from .5 to 1
Let us define
t1=.5-0=.5
t2=1-.5=.5
Now the equations :
xt=(if(t<=.5)(r1)else(r1-((r1-r2)/t2)*(t-.5)))*cos(total_angle*t)
yt=(if(t<=.5)(r1)else(r1-((r1-r2)/t2)*(t-.5)))*sin(total_angle*t)
zt=if(t<=.5)((pitch_first_turn/t1)*t)else(pitch_first_turn+(pitch_second_turn/t2)*(t-.5))
where
pitch_first_turn=30
pitch_second_turn=20
num_turns=2
r1=30
r2=25
total_angle=360*num_turns
if else conditions are used for variable radius and variable pitch expressions.
(1)Variable radius:
For first turn, radius will be r1 from start to end.
For second turn radius should vary from r1 to r2
The rate of decrease in radius is (r1-r2)/t2
For second turn t becomes (t-.5)
the expression for r for second term becomes
r1-((r1-r2)/t2)*(t-.5))
(2)Variable Pitch:
For first turn, pitch varies from 0 (for t=0) to 30 (for t=.5)
So the expression for pitch at any point in the first turn becomes
((pitch_first_turn-0)/(.5-0))*t
i.e.(pitch_first_turn/t1)*t
similarly for second turn, expression for pitch becomes
pitch_first_turn+(pitch_second_turn/t2)*(t-.5)
RE: Variable pitch helix
That's fantastic, thank you so much for your time and effort, it's much appreciated.
Best regards
Simon (NX4.0.4.2 MP4 - TCEng 9.1.3.6.c)
www.jcb.com
Life shouldn't be measured by the number of breaths you take, but rather how many times it's taken away...
RE: Variable pitch helix