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Author Topic: 3D Printed Digital Torque Meter Build Thread  (Read 1229 times)
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dslusarc
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« Reply #25 on: September 20, 2017, 11:38:56 PM »

I have a feeling that on these cheap scales they give slightly different values depending on where the load is applied to the load cell and that the precise centre is not necessarily,consistently the best.

If you look at the photo before I take off the 2 screws holding the load cell to the bottom of the pan, the stamping has a smaller rectangular section that touches the load cell. I found that if a weight was added to the load cell anywhere in that width (about 3-4 mm on either side of the screw centerlines) the weight was the same, as I got closer to the center of the cell, about 6mm from the centerline it changed .01gr. So there is a pretty wide range for the load to be applied. On this design, the transfer washer at the 1" arm length is right at the centerline of those tapped holes.
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Tapio Linkosalo
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« Reply #26 on: September 21, 2017, 12:30:49 AM »


Maybe use rechargeable NiMh cells and charge them in-situ?
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Hepcat
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« Reply #27 on: September 21, 2017, 08:01:27 AM »

Response to #23.

Thank you Andrew,
Of course I immediately opened my scale to prove you wrong. I had a convenient bottle that weighs about 20g.  I put it on each corner (to be honest overlapping a little) of the platform. I was amazed that the only difference was an occasional flicker in the second decimal place (20.12 or 20.13). Education can be embarassingly quick with the right teacher!
John

 
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jakepF1D
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« Reply #28 on: September 21, 2017, 11:50:26 AM »

These are pictures of a newer prototype, but as you can see, it's not difficult to remove the batteries.
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dslusarc
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« Reply #29 on: September 24, 2017, 11:09:19 PM »

I printed out the new version that uses a fiber supper for the thrust load and it is not completed. The new design required a new enclosure to be printed as well an  new cover (slide on and off cover) , and the new collar to hold the thread fiber.

First photo is the load cell and battery holder transferred to the new enclosure.

Second photo, I also installed two rulon J bearings into the new case then used a single edge razor to slice off the excess.

The new shaft is only 1.75" long for this revised design. A short piece of .047 wire about .35" long is needed to hold the thread, in this case spider wire brand fishing line. I cut about a 12" long piece of spider wire and I feed the two ends through the new collar. I drilled a .047 hole in the collar for the thread to come out. You put the short piece of music wire into the new collar so that the loop of the spider wire goes around it. Then press the music wire into the groove on the collar to hold it into place.
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dslusarc
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« Reply #30 on: September 24, 2017, 11:18:16 PM »

Then the rubber hook was installed as well as the torque arm assembly and the new collar to hold the spider wire. Make sure the torque arm is positioned so that the transfer washer does not touch the front of the case.

Cur a piece of .047 wire about .65" long, this will hold the thread to the back of the case. Press the wire into the hole until flush with the top of the case.

Thread the the two ends of the spider wire through the hole on the back of the meter. One thread end needs to be on one side of the music wire stop and the other thread on the other side of the music wire stop. Pull the thread ends and then tie a knot making sure the knot goes down into the hole. Then I tied about 6 or 7 more knots to ensure the knots don't slip when winding when the rubber is pulling. I then used a scale and pulled on the hook on the front to about 8 pounds to make sure nothing slipped.
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dslusarc
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« Reply #31 on: September 24, 2017, 11:23:25 PM »

Here is how it looks all tied. Again make sure when pulling on the hook that the transfer washer does not hit the case anywhere, or the collar holding the thread. When I tied mine I pulled until the hook collar was rubbing on the face of the meter, after it was tied there was a little slop so the hook collar cleared. You may need to do this step a few times to get it tied just right.


The last photo is the finished product with the new case cover slid in position. This meter when I pull on it now with a rubber motor there is no longer the friction from the pull on the front sleeve that was in the earlier version I did at the beginning of the thread.

Don
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« Reply #32 on: September 25, 2017, 03:09:57 AM »

How do you attach this winder to your tripod  winding stooge?
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jakepF1D
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« Reply #33 on: September 25, 2017, 01:48:51 PM »

I wind on top of my model box, and I use 3M dual lock to attach it.  It's basically Velcro on steroids and I've never had my torque meter come loose, although I'm only winding F1D motors.
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jakepF1D
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« Reply #34 on: September 25, 2017, 03:09:33 PM »

Then I tied about 6 or 7 more knots to ensure the knots don't slip when winding when the rubber is pulling. I then used a scale and pulled on the hook on the front to about 8 pounds to make sure nothing slipped.

I used a simple overhand knot, and adjusted the length until it was just right.  Then I added a square knot behind the overhand knot, and put a drop of thin CA on it.  I've pulled as hard as I'm comfortable with, and the knot hasn't slipped at all.
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Skymon
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« Reply #35 on: September 25, 2017, 03:36:17 PM »

Some really great development work happening here. It's turning in to a very nice product.
Had you considered putting it on shapeways or does Thingverse off the same type of printing service??
Could you look to reduce the wall thickness to reduce the cost and time of printing??
Best regards
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jakepF1D
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« Reply #36 on: September 25, 2017, 04:12:07 PM »

Some really great development work happening here. It's turning in to a very nice product.
Had you considered putting it on shapeways or does Thingverse off the same type of printing service??
Could you look to reduce the wall thickness to reduce the cost and time of printing??
Best regards

Thingiverse does offer a printing service, but I'm also about to announce availability of complete torque meters.  I'm selling them as a fundraiser for the junior F1D team.  I haven't figured out how much to ask, but they cost me about $15-$20 each to build.  Anything beyond that will go as a donation to the junior team.

The file versions I plan to post tonight will be the final version.  I can reduce the wall thicknesses a bit, but it honestly doesn't make a major difference in regards to print time.  With my printer and slicer settings it takes about 6 hours to print a complete torque meter, and reducing the wall thickness might drop that by 20-30 minutes.
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jakepF1D
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« Reply #37 on: September 26, 2017, 11:16:09 AM »

I posted what I think will be the final version of the files last night on Thingiverse.  Most of the changes are cosmetic, but I did thin out the walls a bit to reduce print time slightly.
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