Ok, I’m going to give as many ideas as I can in this post and make a few requests as I’m not 100% certain as to what you are asking about.
First, my understanding is that you want to make something that could be generated by using the coil tool on a rectangle about one of it’s sides. Is this accurate?
Second, 83" diameter? That one rotation won’t fit in your robot limits. Please post your math or at least check it.
Third, when drawing an abstract curve that follows a mathematical path, use your dimensioning tools to set up individual points and then polyline to make the curve along it.
Fourth, most people look at a helix and think, circles. I see triangles. Think about it, if you uncurl your edge of your helix it is going to form a slope with a length of the circumference in the 2D plane. This slope is your hypotenuse. The base of your triangle is the circumference of the circle once it is curled and the height is the pitch of the helix. Refer to below image.
|\
| \
Circumference of helix | \ Circumference in your 2D plane
when it is curled |
| ____
Distance between revolutions
Example: Lets say that you want the outer edge of the helix to be 24 inches diameter. We are going to make a 6 inch space in between revolutions. Ok, given Pythagorean theorem we know that the circumference in your 2D plane=sqrt(6^2+24^2)=sqrt(36+576)=sqrt(612)=about 24.75 inches. Ok, now lets do it with an 18 inch interior, we know that the 6 inch space will be the same. Now the 2D circumference=sqrt(6^2+18^2)=sqrt(36+324)=sqrt(360)=19 inches. Ok, now we know the difference in diameter is 6 inches.
So, given these calculations…We can find the outer circumference and the inner circumference and that the offset is 6 inches. Not sure, but I believe that you can use Inventor to solve the rest. Draw two circles with the same center. Now, draw two lines. Then, use the coincide tool to make the points on the lines line up on the circles.(These will be the two lines on the picture you posted). Now, we will trim the parts of the circles between this points. Now, I think there is a tool to measure arc length. Now you should be able to put in your circumferences you solved for. Also, input your six inch difference. Now all you should have to do is find the angles to make the lines at. Ok, now if you were able to follow the above, you should be able to handle things from here.
I apologize for the confusion above, but the math involved is kind of conceptual geometry and the tools necessary a bit unique to such a need. I’ve done something like this before so I know the math is true, however the application of it is a bit different. Lucky you, you got the Official Inventor Guru of 1766 (title given to me by a few of my friends and one of the head teachers). Any questions you have with the math or the commands, I will try to explain to the best of my ability. I’m sorry if this a bit more then you expected, but there really isn’t an easier way to do the math. If you go back and check your numbers, I’ll be glad to run them through for you if you get stuck somewhere along the line.
