Attaching things to servo arms - Page 1
Forum section: electronics / beginners

author: Youkai
author_rank: Regular Contributor
timestamp: February 18, 2020, 08:44:32 pm
content: I have a super noob question here. I'm using an MG90S micro servo. I printed out a disc about 20mm in diameter and I want to mount it to the stock arm that came with the servo. The question is how? The screw holes in the stock arm are TINY.Am I supposed to find a nut/bolt or screw that's actually that small? If so where? If not how could I connect it? Should I just get some sewing thread and tie it on?

author: ataradov
author_rank: Super Contributor
timestamp: February 18, 2020, 09:17:42 pm
content: Those holes are not designed for machine screws with nuts. They are for small regular screws that can just self tap into the plastic of the arm. Or for wire rods to be passed though them.

author: Youkai
author_rank: Regular Contributor
timestamp: February 18, 2020, 09:36:31 pm
content: OK so I could just get a screw that is slightly bigger than the hole and screw it in. Still though where do you find screws that small. I don't think Home Depot is going to carry them. I would need like tiny computer screws or something?

author: ataradov
author_rank: Super Contributor
timestamp: February 18, 2020, 09:38:36 pm
content: Home Depot will not have this. eBay and usual sources should have them. I get my screws and stuff like that fromhttps://www.olander.com/and I can highly recommend them. Not sure if they have stuff this small though.Yeah, it looks like Olander does not carry stuff this small. But there are plenty of kits like thishttps://www.ebay.com/itm/1000pcs-M1-M1-4-M1-7-Miniature-Self-Tapping-Track-Screws-Black-Screws-Mini-Tiny/333134323633on eBay.

author: Jwillis
author_rank: Super Contributor
timestamp: February 18, 2020, 10:48:57 pm
content: Have you tried a RC hobby store. They will have all kinds of hardware for servos . Nylon and metal Kwik links , Micro screws and universal servo horns.

author: aeberbach
author_rank: Regular Contributor
timestamp: February 18, 2020, 11:21:54 pm
content: You have a servo there with a metal shaft, so you will want to find the exact screw and NOT use a self-tapper.Hobby store for sure, and make sure you take your servo when you shop unless you can match your manufacturer and shaft size directly. There are basically two sizes of common servo fittings but IIRC there are two variants of spline depending on manufacturer. In a hobby store you can probably find a servo accessory pack containing arms ("servo horns") and screws. Here's one online stores servo scores:https://www.servocity.com/servos/servo-accessories/servo-mounts/oem-mounting-hardware/screwsMy googling says M2.5 machine screw, and you probably want 6mm long. You could get one of those and carefully try to use it but don't force!

author: Youkai
author_rank: Regular Contributor
timestamp: February 19, 2020, 12:06:17 am
content: Quote from: aeberbach on February 18, 2020, 11:21:54 pmI think you are misunderstanding. The servo came with a screw to attach the arm to itself. I want to attach a 3d printed object to the plastic arm. The plastic arm has a number of small holes in it for you to stick a wire or whatever through. So a screw that would tap into that would work.

author: Jwillis
author_rank: Super Contributor
timestamp: February 19, 2020, 12:34:21 am
content: How small are you talking about. Model train screws are very tiny. Or eyeglass or watch making screws.

author: Youkai
author_rank: Regular Contributor
timestamp: February 19, 2020, 02:25:00 am
content: Quote from: Jwillis on February 19, 2020, 12:34:21 amOk yeah that will probably work. I'll try the hobby shop.

author: aeberbach
author_rank: Regular Contributor
timestamp: February 19, 2020, 03:40:48 am
content: You're right I'm misunderstanding. I would print the 3D item so that the servo horn slides in there and one or more holes match with the holes in the servo horn. Once the holes align a piece of wire or any tiny screw would do.

author: beanflying
author_rank: Super Contributor
timestamp: February 19, 2020, 06:03:00 am
content: The screw into the metal gear of the Servo will almost certainly be a standard metric pitch. So buy a longer one or a bit of threaded rod to suit. Possibly M2.5 or M3 but I don't have one I can check for you.Then mod your tray project to suit. Cut off the excess arm that protrudes past the boss. You could try ditching the arm all together but the resolution and hence the grip on the metal splines won't be very good with a 3D printed part entirely so using part of the arm makes sense. So just use the longer metal thread without additional screws to hold it together.Yes I want to see the result so hurry up already

author: brucehoult
author_rank: Super Contributor
timestamp: February 19, 2020, 10:26:18 am
content: Quote from: Youkai on February 18, 2020, 08:44:32 pmLooks like you're in the USA but in case someone in New Zealand comes across this later, I usehttps://www.coastalfasteners.co.nz/who have things down to M2 at prices a fraction of hobby shops (at least if you want a decent quantity).

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 19, 2020, 11:05:22 am
content: if you have supply over there, and if this is one off... find a suitable $1 china cheap toy, they usually have small self tapping screws connecting parts, and you probably will get some extra such as cheap dc motor, mini gearbox etc. super or hot glue should probably works too.

author: mikerj
author_rank: Super Contributor
timestamp: February 19, 2020, 01:59:25 pm
content: OP: packs of tiny self tappers are available on eBay or evenAmazon.

author: rrinker
author_rank: Super Contributor
timestamp: February 19, 2020, 07:49:59 pm
content: A hobby shop will have small machine screws, nuts, and washers. You don't have to use self tappers for this. Either way should work though. I think a 1-72 will fit typical SG90 horns. Maybe it's a 00-80 but I don't think it's quite that small. I'm terrible with sizes just by looking. I have tons of SG80 servos I use with my model railroad.

author: Youkai
author_rank: Regular Contributor
timestamp: March 01, 2020, 09:16:27 pm
content: I ended up printing something a lot like what beanflying showed in his render. I have a cavity the servo arm can just fit in and some holes to the outside of the servo arm. I'll just use some sewing thread to literally tie it in place. Will work well enough for my use.