Parmodels.com going down end of June

[9600baud]

Hi all,

I just saw that parmodels.com, the wonderful site of Paul and Ralph Bradley goes down end of June. That's a real pity.
It has a ton of beautiful plans, No-Cal and full sheet models. If you haven't already, maybe head over there and save your favorite plan before it is gone.

I have many plans from there on my todo list and built already two of them.

Cheers
Alex

[Spiros]

It seems there is a problem with the site, concerning the protocol.

Any ideas?

[9600baud]

My bad!
It's http, not https, which any modern browser assumes.

Please try http://parmodels.com/

You may see an alert because the site does not use https, but it's fine.

Cheers
Alex

[lincoln]

Fortunately for us, the site is at least partially backed up. I was able to look at an all sheet Cessna 180. It came up blank at first, but then I switched to an eaelier date.

[OZPAF]

They will be missed - thank you Paul and Ralph for providing all that info for 20yrs.

John

[lincoln]

I poked around here:
https://web.archive.org/web/20260314022122/https://parmodels.com/
I found at least one plan. You may have to try different dates to make a plan show up.

Thanks Brewster!

[Jmk89]

Maybe someone who knows them could suggest that they upload their material to HPA Plans Gallery?  That way the stuff won't be lost and it will be easier to access than through the Wayback Machine

[Jmk89]

Today I downloaded from PARMODELS before the website disappears and printed out the 3D pieces for the external winding torque meter.  I just have to wait for the ball bearings to arrive (Temu purchase so a bit of a wait) and then I can start putting the device together.

I think I will recalculate the torque readings to newtons/mm and print out new dials.

I'll add photos when I come to the actual build.

[Spiros]

I poked around here:
https://web.archive.org/web/20260314022122/https://parmodels.com/
I found at least one plan. You may have to try different dates to make a plan show up.

Thanks Brewster!

not sure if it works for you. It still does for me. Here is the link with all the FF plans

https://web.archive.org/web/20260308031846/http://www.parmodels.com/free-flight-models.html

[Jmk89]

Today I downloaded from PARMODELS before the website disappears and printed out the 3D pieces for the external winding torque meter.  I just have to wait for the ball bearings to arrive (Temu purchase so a bit of a wait) and then I can start putting the device together.

I think I will recalculate the torque readings to newtons/mm and print out new dials.

I'll add photos when I come to the actual build.

I forgot that I was going to take photos when building the meter, but here are a couple of photos of the finished meter.


(Sorry about the camera shake in the second picture)

A few points:
1.  I printed all parts using PLA CF so that there was a good chance of them being strong enough to cope with larger motors.

2.  I used metric fasteners - M3 for the 4-40 screws specified and M6 for the 1/4-20 screws.

3. I did recalculate for N-mm instead of OZ-in.  I generated the dial face using excel and printed out onto self-adhesive white vinyl. 

4.  I worked out the torque bars for 3 kinds of motors
     a. 100 N-mm for motors up to four strands of 6 mm x 1 mm  (i.e standard modern tan rubber)
     b. 240 N-mm for motors from four up to 8 strands
     c. 720 N-mm for motors from 8 up to 16 strands.
    The torque bars are:
     a.  62 mm of 0.635 mm (0.025") piano wire
     b.  63 mm of 0.79375 mm (1/31") piano wire
     c.  52.5 mm of 1 mm piano wire.
In each case, I have worked on the basis that the max force to be measured will twist the bar 270° as ISTR someone saying that beyond that angle, piano wire will deform and get a permanent set, but that up to that angle, it should spring back to zero.  We will see.

I will see how this goes in the 240 N-mm version when I start trimming the Tyra Cd'H - which I must get on to soon so I can put a score into the postal comp.

I have downloaded the files that were on the Parmodels.com website.  I don't know if those guys would mind if I put those files up in the HPA Plans Gallery with an acknowledgement to them.  I can add the dials I have generated as well, if that would help as well as explaining how to get from Oz-in to Gm-cm to N-mm.  However, we do still need to allow .stl files to be uploaded to the Plans Gallery before I can add them to the Gallery (unless I convert the files to .zip).  I prefer not to zip the files - the fewer transformations that we ask a computer to do to a file, the less the chance of something going wrong - that's not cynicism, it's experience!

[lincoln]

That looks great.

I hope you're not depending on the nominal diameter and the length to give you the right tolerances. Since the spring constant is proportional to the fourth power of the diameter, you could be off by as much as 5 percent that way. You can, of course, adjust the spring constant by grinding away a bit of metal (best if not all in one place) or shortening the wire. Per ASTM A228, .025" Ø nominal wire is allowed to vary +/- .0003". Come to think of it, in some cases you could be off by more than that.

BTW, the mysterious "Thanks, Brewster" was for Brewster Kahle, one of the founders of the Wayback Machine (archive.org ). I just found out, according to Wikipedia, that there was another founder as well, Bruce Gilliat. I don't think I ever met him, but I should thank him as well.

https://en.wikipedia.org/wiki/Wayback_Machine

Speaking of P&R, I think at least one of them is either here or on RC Groups, participating in a discussion of parmodels.

[Jmk89]

You are quite right, Lincoln.  The calculation of N-mm (or any other torque measure) is really a kind of false precision.  But so too are our calculations of the torque that a rubber motor will take.  They depend on either testing each batch of rubber you buy (and assuming that it is homogeneous in its characteristics) or relying on an assumed capacity. 

However, I'm not really looking to determine the actual N-mm at which a motor will burst or that I want to wind to, but rather trying to determine a number (which in a sense is non-dimensional) where burst happens and then work out how close to that number I can wind motors to get a predictable and repeatable torque result that gives the best performance that I can actually use.

Really all I have used the length and diameter calculation for is to try to ensure that the meter is in the right ballpark for motors of the kinds of cross-sections that I use.  The numbers themselves could be anything so long as they show the relative torque.