Bryan's Presto "Tower of Power" servo / belt mod for 8D

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EpicenterBryan
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Location: Eugene, OR USA

Bryan's Presto "Tower of Power" servo / belt mod for 8D

Post: # 39308Unread post EpicenterBryan
Sun Dec 27, 2015 12:33 am

Like usual, I have too many projects going on.

Tonight I thought I should share a few pictures from a several month long project which I am still playing with. I call this project the "Tower of Power". It's an external tower housing a servo drive, to retrofit to my Presto 8D lathe and convert it to a Servo / belt drive configuration. This uses existing grooves on the outer rim of the platter.

Here are photos from 2 of the most promising configurations I've messed with:

MXL belt to rim:
IMG_4230.JPG
Home made NinjaFlex / SemiFlex O-ring with dual idlers:
IMG_4228.JPG
That's all for tonight.

Bryan
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EpicenterBryan
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Re: Bryan's Presto "Tower of Power" servo / belt mod for 8D

Post: # 39325Unread post EpicenterBryan
Sun Dec 27, 2015 8:57 pm

Here are some more pictures of the "Tower of Power":

Front and back:
Front - back.jpg
Bottom view with isolated suspension mount plate:
IMG_4235.JPG
Some testing with round belt - not screwed down, and in front of the 8D. This will be mounted in the back as soon as I make a longer bottom mounting plate:
IMG_4225.JPG
The aluminum extrusion is called V-Slot. I buy it in 5' lengths and cut to what ever size I need for a project. It's available from http://OpenBuilds.com. I also got the right angle brackets and the black corner pieces from them. The brackets where the motor plate mounts are ones I made for another project, then slotted them so the plate could adjust 10mm to tension the belt. That left 40mm of space between them. But the motor turned out to be 42mm wide. So I milled each bracket down a bit for the motor to fit and be able to slide forward and aft.

The MXL belt is a 680 tooth continuous one I found on e-bay. It's about 1300mm long. It's hard to find a continuous belt this long so it kind of dictated the pulley size. 40 tooth was a hair too big to fit but 36 tooth was fine. The 36 tooth pulley was transferring a bit more noise to the rim than I expected so I pulled it off after an hour and found this $6 Chinese pulley had some belt debris in the teeth. It looks like the teeth are not cut exactly correct. That should not be happening.
IMG_4231.JPG
I remembered that I had a few spare USA made 22 tooth pulleys left over from another project, and put one on. What a difference. Those took 6 weeks for them to make (I needed 5mm ID and they didn't stock them) and they cost over $25 each, but I guess you get what you pay for.

Bryan
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EpicenterBryan
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Re: Bryan's Presto "Tower of Power" servo / belt mod for 8D

Post: # 39337Unread post EpicenterBryan
Mon Dec 28, 2015 10:14 pm

A package arrived today. One pound of copper plated lead shot.
The idea was to fill the 9 large cavities in the V-Slot structure with a dense but small grain material to add mass and reduce the chances of the structure resonating at one of the speeds I plan to run the servo at. I looked at various types of sand, as well as lead. I decided on copper plated lead to reduce exposure risk and to get the highest density per volume . It turns out 1 pound is just about enough to fill one piece of V-slot so now I know how much more to order.
IMG_4236.JPG
I can say that after filling the cavities on this extra piece of (same length) V-slot - it's clear by tapping on the outside that I can't get it to ring no matter what. Yay!

There is an interesting discussion about using things other than lead in competitive shooting "sand bag" Benchrests since lead is not allowed. These substitutes include Zircon, Chromite, Riverbed sand, and playground sand. Two of these are way more expensive than lead. Since I can use what ever I want but still want to remain safe, I chose copper plated lead. Then I plan to pot the top of the cavities...

Check out the discussion:

http://www.accurateshooter.com/technical-articles/bag-sand-comparison-test/

Bryan
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EpicenterBryan
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Re: Bryan's Presto "Tower of Power" servo / belt mod for 8D

Post: # 46159Unread post EpicenterBryan
Mon Feb 20, 2017 10:37 pm

Got around to finishing this project last weekend.
Now mounted in the back of the 8D. It has one idler wheel and 3-4 pounds of copper plated lead in the channels of the extrusion. The lead filled channels have ninja flex plugs installed. Sorry for the dark photo but you get the idea.
IMG_5426.JPG
Originally, my plan was to use the 5 volt output from the servo for the speed control pot but I found it was not stable enough and drifted slightly with temperature change. I also decided to add an RC network to ramp the servo speed up on power up. Eventually I decided to make a little board with a precision 5VDC reference with really low drift. Here is what it looked like mounted in the back of the tower. 24 volts input, with a 3 pin connector for the speed pot, and connections to the servo. The parts were on a header so I could swamp out if I needed to change something.
Servo board.jpg
The range I wanted to cover was 33 and 45 rpm but I also wanted to adjust to 1/2 speed if so desired.
And here we are!
speeds.jpg
One more project off my list of stuff to do!

Bryan
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2bitcomputer
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Re: Bryan's Presto "Tower of Power" servo / belt mod for 8D

Post: # 46708Unread post 2bitcomputer
Thu Apr 20, 2017 2:14 am

Hello Bryan,

Nice project!

How about the cogging issue?
Is it not a problem because of the gear ratio?

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