Got it
This was our first year to utilize a turret, but we went in a different direction. Rather than use a “bearing stack”, we opted for V-groove bearings (REV has them, as does amazon) and a bevelled carrier plate (to match the groove in the bearings). The fixed (base) plate was then drilled with 8 equi-distant mounting holes and we used a combination of concentric and eccentric bearing spacers (also at REV) to mount the bearings. The carrier plate - with sprocket - then slips inside the grooves of the bearings. The eccentric spacers allow us to fine-tune the plate for minimal “slop”, and side loading isn’t a concern. The sprocket is offset on the underside of the carrier plate, driven with #25 chain. Powered by an old andymark 9015 (550 equivalent, IIRC) mated to a versaplanetary with internal encoder, we control it with a talon srx (using limits, it’s quick) and it runs as smooth as glass. All plates are 1/8" aluminum, sprocket and carrier plate were the only machined parts, everything else was COTS. Part of our reasoning here is to keep the pass-thru hole “clean”, so nothing interferes with the ball as it’s passed to our shooter. Wish I had some good pics for illustrative purposes 
Edit: Base plate is 1/4" - we made one out of 1/8" but made weight so we didn’t use it. Also, the black plastic conduit in the pic is part of our lift system and is only beside the turret when we’re climbing.
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Just putting this out there:
There is NO reason bushing(s) can’t be used for a turret application.
Keep in mind there is nothing that says that both of the surfaces of the bushing need to be round (i.e. a round plate and guide blocks)
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5460 used this bearing from amazon for 2020. Since we didn’t complete, I can’t tell you how long it would last, but from our experience they seem pretty well built/good quality. It has survived turret collisions with the control panel in practice. I know individual ball bearings/custom setups are cool and are very customizable, but for most teams, if there is something off the shelf that you can buy, then do it. Individual ball bearings for custom designs are relatively cheap and wouldn’t have to be included on the BOM, but they are still going to cost the team a lot more money to actually buy all of the bearings required (8 stacks of 3 bearings =24 bearings at $2.99 a piece=over $70 dollars), then to just buy the $20 lazy susan bearing.
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4130 used this exact same bearing this season. It went through 18 matches on a tall robot going over the bump and a few hours of drive practice. Absolutely no issues.
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The loads on a turret are quite low and the RPM is also low so crude ball bearings will suffice. Big clearances like 0.002 to 0.003 inches between the balls and the races are also acceptable when the race diameter is big enough to clear a 7" diameter ball. Angular tolerance is 0.003/7 = 4.3x10-4 radians or .025 degrees. Spartronics 4915 used a MarkForged Onix printer to make ball bearings with bolt-together segmented races to fit on the printer platen. Commercial balls with 3/16" diameter were purchased on the internet from the source with the lowest price. One segment of one race was left out to the very last so the balls could be inserted. Both inner and outer races had unique features for mounting to the robot frame and to the shooter.
One of Spartronics’ mentors made a series of proof of concept, paradox planetary gears that used 3-D printed bearing races and balls inserted through a tapped hole in the outer race that was later plugged. The outer race was one piece with the output ring gear and the inner race was one piece with the fixed ring gear. These bearings successfully carried much higher loads than the shooter turret bearing.
330 used this bearing of the same style to support most of the weight of a robot
They get…very sloppy in that size range
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Thats a cool approach for supporting the carrier plate. How did you bevel that carrier plate to fit exactly in the V-groove of the bearings?
We did this in 2019 as well. All we did was use our router with a chamfer bit to create plates with half the V and bolted 2 of those plates together.
You can find a few pics of the setup here.
Out of the few turrets we have built over the years, this has by far been our most favorite setup. We have run into massive quality control issues with lazy susan bearings from Amazon in the past and like the robustness and ease of use of the v bearing setup.
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+1 on this design. You guys did a great job with that turret.
There is some really nice explanation in this post and in the thread that follows. I particularly liked the bit about how you determined the involute for the “gear teeth” that would interface with the pegs in you driving wheel.
I really loved that design and I even bought some of the V-groove bearings for my team hoping that they would do something similar for our turret. They went with the bearing stack design for 2020, but I still have the V-groove bearings so maybe this will be something we re-design for 2021 (I doubt it, but I can hope…).
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I can’t honestly answer that, I’ll have to ask our machinist mentor. He did the sprocket and carrier plate at the same time, borrowed the use of a CNC from a friend of his, and spent several hours there one saturday. Turned out great tho!
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Agreed. 3476 did an awesome job, I really like the way it’s driven, that’s pretty cool. We toyed with stacked bearings in the shop, but because we’ve got experience with the REV lift kit, we decided to try the v-groove/chamfered plate route, and it came out better than anticipated. Not only do we have a simple way to fine-tune the turret, it’s also super smooth. Programmed to center the forward mounted Limelight on the target, the turret performed flawlessly in the 17 matches we were lucky enough to have played. ~sigh~ I’m gonna miss those competitions this year 
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Do you know how much friction this has (McMaster-Carr)? Does it free spin or does it have a lot of stiction?
It’s been a while since I’ve touched one, but I remember it being pretty good when not experiencing high moment loads.
It’s so easy to throw a lot of power compared to what’s needed for a turret, so I’m not sure friction is a big deal for most teams. You’re also generally going to have wild torque overhead once you gear for a reasonable speed.
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What about on an FTC scale? (If you have familiarity with the power of motors)
I suspect it would be totally fine, since whatever is on the turret is unlikely to be that heavy and won’t cause huge moment loads.
They’re pretty cheap, buy one and play with it 
Bolt a stick on it with a weight at some distance and then see how the bearing feels.
We used one this year and while you cannot spin it up (give it a push and watch it spin), it spins without getting stuck. We used a 775 pro through a 300:1 gearbox/belt (60 RPM) and it worked well. The biggest issue is the lack of precision on the 5/16-18 and 1/4-20 holes. They are visibly off center and off angle. We had to measure where they were when machining.
Here is a smaller (140mm) slew bearing that may be useful on an FTC scale. It may also have some application within FRC, although it is most likely way too small for an FRC turret.
I am using one of these for a small turret I am building for a personal project.
Likewise. We used this bearing on 2 robots this year. Used it on the turret, and also had it on the prototype spindexers. Same bearing we used for 2012, and that robot is still happy. Plus, the 2012 bot took some nasty nose dives and landed on the turret when other robots got a little happy on the 2012 ramps.
