How to mount a rotating tray above a servo - Page 1
Forum section: electronics / projects

author: Youkai
author_rank: Regular Contributor
timestamp: February 15, 2020, 03:54:05 am
content: I'm working on a project where I want to have a servo rotate a tray. Originally I was going to use a larger servo so I was just going to mount the tray directly to the servo and let the servo bear the weight. But in my new attempt at the project I'm going to use a smaller servo (MG90S Servo 9G Micro Servo) and I don't think it will hold the weight that I want. It's not that its supporting much weight but the servo is going to be at the corner of a pie-ish shaped tray and all of the weight will be at the bell end. So even with just some random light junk in a 3d printed tray it will still have a fair amount of torque on the mounting point.What's the best way to mount the tray so that the servo can still rotate it? Ideally I'd like to directly couple the tray to the servo for rotational purposes (i.e. no gears or belts, but on extension axle from the servo head to the tray is fine). I guess what I need is some kind of bearing that has a bracket on it that I could screw the tray onto but that is hollow in the middle for my drive axle to go through. Does something like that already exist and if so what is the name?I'm hoping that something already exists and I won't have to design/print my own.

author: ataradov
author_rank: Super Contributor
timestamp: February 15, 2020, 04:30:37 am
content: From reasonably cheap options this encoder comes to mindhttps://www.ebay.com/itm/360RES-Rotary-Encoder-A-B-5-24V-D38mm/381383100145It has aluminum machined flange with bearings already in it. It is very smooth.

author: twospoons
author_rank: Frequent Contributor
timestamp: February 15, 2020, 04:35:17 am
content: I think you're looking for a "pillow block".e.g.https://www.amazon.com/UCF202-10-Quality-Pillow-bearing-square/dp/B00RKEXXAS

author: ataradov
author_rank: Super Contributor
timestamp: February 15, 2020, 04:38:37 am
content: Quote from: twospoons on February 15, 2020, 04:35:17 amIf I'm imagining the application correctly, traditional pillow blocks would be a bit heavy and big for this.

author: Youkai
author_rank: Regular Contributor
timestamp: February 15, 2020, 05:25:37 am
content: Ok so a pillow block is kind of what I'm thinking I guess. Though those are a bit bulky and expensive for my purpose. It's going to be used in a mechanical jewelry box. I guess I'll probably need to make something like that out of an RC car bearing or similar. I could probably print a housing for the bearing that would support the tray.I'm not sure how exactly the Rotary Encoder helps. Does that replace the servo?

author: ataradov
author_rank: Super Contributor
timestamp: February 15, 2020, 05:29:49 am
content: Quote from: Youkai on February 15, 2020, 05:25:37 amNo, you don't use the encoder part. Here is how it looks on the insidehttps://wemakethings.net/2014/05/26/rotary-encoder-teardown/If you remove all the electronics and the disk, you will end-up with machined aluminum base and a straight-though axle. It is seriously well made for the price.

author: beanflying
author_rank: Super Contributor
timestamp: February 15, 2020, 05:56:13 am
content: So I was bored and sketched an option upGo with a Thrust bearing to mount your platform to and carry the load. Link to a small thin evilbay exampleeBay auction: #273822333430Only use the servo IF you want positional control otherwise use a small gearmotor. Mount the servo/motor under the bearing and drive it through the hole in the bearing (not attached to it!). The bearing carries any load and gives your platform lateral support. The only load on your motor or servo is then radial. It will need some thinking about the actual platter design more than the sketch shows.

author: Amper
author_rank: Frequent Contributor
timestamp: February 15, 2020, 09:31:00 am
content: Mh, i think if ithats a difficult task already you should look for stuff to re purpose. Look for hard drive motors for example, they have exceptionally play free bearins, are smooth running, have srew holes an are available everywhere. They usually dont have a shaft access on the backside though, so you will need some non direct drive method for attaching.

author: Youkai
author_rank: Regular Contributor
timestamp: February 17, 2020, 10:05:02 pm
content: I was able to get it to work with a custom printed mount and a couple RC car bearings. Couple photos attached with my test piece. The drawer on my test is oblong and has the support post near one corner. Still rotates freely even with a reasonable amount of weight in the tray. I think this concept will suffice for my project.

author: Youkai
author_rank: Regular Contributor
timestamp: February 18, 2020, 05:52:09 am
content: I posted a quick video to Twitter showing the block in action for anyone that's interested:https://twitter.com/YArtificery/status/1229644008873283585

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: February 18, 2020, 10:50:56 am
content: What about a counter weight attached to the other side of the tray?

author: Youkai
author_rank: Regular Contributor
timestamp: February 18, 2020, 09:34:35 pm
content: Not really possible. The tray is going to be mounted inside a jewelry box and the servo will rotate it outside the box when the lid is opened. There is no room on the other side for a counter-weight because that would be outside the box.

author: beanflying
author_rank: Super Contributor
timestamp: February 19, 2020, 12:59:39 am
content: Looks like you have something that will workWith your tray consider making it without a bottom then fit either an Acrylic or 1/8" Ply one with a champher to locate it with a few spots of glue (epoxy preferably).It will speed up your print and save you either having to deal with supports or the bridging issues above.Just my rough idea below. In this case print it upside down with supports in the corner any marks or divots from that will be hidden by the floor.

author: Youkai
author_rank: Regular Contributor
timestamp: February 19, 2020, 02:28:49 am
content: Quote from: beanflying on February 19, 2020, 12:59:39 amInteresting idea. The one I printed for the video was printed without supports and I'm still figuring out my 3d printer so my bridges are terrible. didn't really matter though it was just a test piece. I'll probably print the final with support as one piece but that's an interesting thought. I'll definitely keep it in mind for future items.

author: beanflying
author_rank: Super Contributor
timestamp: February 19, 2020, 02:45:01 am
content: The basics of it are supports SUCK (mainly the removal process) and should be avoided at all costs whenever possible at the design stage bridges over 30-40mm I avoid where I can tooThe 45 Degree champher on my lash up will print fine inverted without supports so it is only the corner/pivot section that would need to be supported your slicer should handle that automatically. 3D printers for large flat slabs suck to a greater or lesser degree so adding in an external Flat bit of material saves time and will get you a nicer result.As it sounds like your printer is only new to you your prints are underextruded (gaps in the print). Check the diameter of your filament first, make sure your slicer is set to that value not the stock one. If your filament is under the nominal 1.75 then you will need to bump up your extrusion multiplier, start with 5% in your case, print inspect and tweak also make sure the filament is not slipping at the extruder (spring and lever is tight). Also depending on your CAD package see if you can export in a higher number of poly lines this will smooth the circles to look more circular.Watch a couple of these search resultshttps://www.youtube.com/results?search_query=extrusion+multiplier