Radioshack standard servo: splined tooth count?

Hey gang…

I have a Radioshack standard servo. (#2730766)

  • Voltage:4.8~6.0V
  • Torque:3.5kg.cm@4.8V, 4.8kg.cm@6.0V
  • Speed:0.17/60ТА @4.8V;0.14/60ТА @6.0V
  • Size:38.6x18.8x34.9mm
  • Wight: 37 g
  • Use Angle:<=160ТА

I was/am looking to buy some 3rd party arms/horns…

But I have NO CLUE how many teeth the ‘splined’ (gear? nub?) has?
23T - JR
24T - HiTec
25T - Futaba

Not sure if this Radioshack standard servo (2730766) falls into ANY of these categories?

Anyone know? Or help point to a reference? Googling hasnt turned any definitive answers for me

That being said… this does have a plastic splined ‘nub/gear’ (what is the appropriate name for that?)

And I -do- need to get another one (2 in total)… so maybe it would be best to abandon this one? And get 2 news one that are metal? -AND- a known tooth count for the splined gear thingy?

I’m not opposed to getting new one… but also dont want to ‘break the bank’ on these either.

I would PREFER the same size: Size:38.6x18.8x34.9mm

so it will fit nicely in the area already sourced/machine out for it…

Not really experienced in this area… so if there are other arms/horns to checkout? or a some ‘go-to’ servos…please share!

These are the arms I am currently looking at:

Alternate question:
How would go about trying fix/secure/mount some CUSTOM arms to a servo?

Say I wanted to laser cut my own out of some acrylic or wood or something? I need to (somehow) get the shape of the 23/24/25 tooth outline… so I can laser cut it, into the parts itself?

Or is there a pre-made part that you attach that allows for custom arms (shape/length) to be used?

Thanks for all feedback!

Use a felt tipped pen to ut a dot on one tooth, then start with that tooth as "1" and count around until you come to the dot.

I suspect the most important dimension is the outside diameter of your shaft.

Paul

Thanks for the reply...

Geez.. I didnt even think of that. :S

Most of the horns/arms are just specified by tooth count... (never saw anything about the OD!)...

but makes sense as the micro servos have a small OD 'shaft'.. (dammit!) HAHA..

I tried to count them last night... I -thought- I came up with 23... but just wasnt confident. (and then started searching, which came up blank).. I find it hard to believe this isnt documented somewhere?

Tooth count is a function of shaft diameter, right? Bigger diameter, more teeth!

Paul

xl97:
I find it hard to believe this isnt documented somewhere?

So post the info for reference in this thread when you find it.

I usually follow up on posts so there are answers for the community.

I wonder if the Radioshack branded servo goes by another name or model?

I didnt see anything with same RS# but.. found this:

https://www.servocity.com/servo-spline-info

You likely stand a better chance of getting an answer over in the RC Groups forums, I guess almost 99% of the users of that forum will use servos, only a small % of Arduino users will be regular servo users.

probably right...

but this is my first 'line of defense'.. and is the closest (only?) social outlet of people interested in 'electronics/arduino'..

I guess I can go randomly find a forum, join and ask.... but figured I would ask the collective brain trust here first. :slight_smile:

I’ve got servos with I think 24 and 25 spline shafts. It is tedious, but I just counted the splines. I did note that the the white servo horns had one count, and the black servo horns seemed to have the other count.

xl97:
Hey gang...

I have a Radioshack standard servo. (#2730766)
Standard Servo – RadioShack

The cost of those is rather high given they are more than likely a re-branded product.

Advice would be get some MG996 servos for around $7.00 a piece.
This includes metal gears in the servo and a stack of extra servo output arms.

They work fine in most applications, even have them in rc aircraft and boats.

You'll probably find even if you do track down the right spare arms to suit your radio shack that they will cost more than the MG996 complete.

1-20Pcs MG996R Torque Gear Digital Servo For RC Truck Car Boat Helicopter ST | eBay

Thank you for the alternate option..

I like the price and the metal splined gear..

However.... I guess I am in the same situation with those as well?

  • what is the spline tooth count?

I see this:

Compliant with most standard receiver connector: Futaba, Hitec, Sanwa, GWS etc.

Which is it? My understanding (which may be inaccurate) is that Futaba and Hitec have different tooth count on the spline.

And while they do some with some plastic arms/horns.. none of those will work my project.. needs t be longer.

  • also look to be a bit bigger physically...than the RS standard servo size.. (which I machine out a little packet in my aluminum plate for it to sit in..... I guess I could make another pass to widen it up?.. so not a deal breaker)

I looked in my stuff and found a Hobbico standard CS-61 servo, which is probably identical to your RS servo. i put some dots on opposite teeth and started counting. Then I got my LG cell phone and found that it can zoom in some, so holding the servo and phone I took the below picture. Having the servo on something solid would probably steady the focusing. It looks like this has a 24 tooth spline. If you have a cell phone, you might try something similar to count the teeth.

spline.jpg

spline.jpg

xl97:
Which is it? My understanding (which may be inaccurate) is that Futaba and Hitec have different tooth count on the spline.

The receiver connector is the 3 wire electrical connection from servo to receiver. Nothing to do with teeth or a spline.

Steve

Confirmed:

Radioshack Stand Servo: 23T - JR tooth count (spline)

I went to my local 'Hobby Town' store...

They have a bag of servo arms/horns for Futaba and a bag of arms/horns for JR..

The JR ones were the only ones that fit the SPLINE on the Radioshack Standard Servo.

Their website has ALOT of different stuff... (most of which seems to NOT be carried in the stores unfortunately)..

Also.. servos were behind the 'counter' not easy to see/view/research thats for sure...

And even when I found one that MIGHT Have been a solution (they only had 1).. NOT CHEAP!

Not one servo under $15.00 USD!..


Slightly changing the topic a bit here.. to MICRO servos..

Anyone know about their tooth count? I see conflicting info that they are 20 toothed parts... and some are 21..

  • possibly the same scenario as the standard sized ones? each 'brand' has its own size/tooth count for the MICRO servos too..

I was wondering about how I could use a normal sized arm/horn (23T/24T/25T..etc) on a MICRO servo?

Adaptor 'splines'?
Some sort of part that allows for mounting custom arms? (reaching here)

I going to continue along with testing out using the RS standard servo.. and some purchased 'arms'....

but wanted to start thinking/planning for a 'plan b' :slight_smile:

Update:

Well all of that 'work' was for nothing.. LOL

In the end, those Standard Radioshack servos just do NOT have enough torque to move/push what I need it to. :frowning:

But I guess at least there is FACTUAL information on what spline tooth count it has. (and now I have 3 arms with 23T count..that I doubt I'll be able to use in the future!) LOL

Now, I"m on the 'hunt' to find some similarly sized servos... but that have much more torque.

Q1: Does just having metals gears mean more torque? (by default, I'm sure more than plastic gears)

Q2: Is there anything else to look for to ensure hi-torque ability? (just the stall torque?)

You have not told us how far the thing connected to the arm must move. You can always multiply the torque by shortening the distance from the drive shaft to the connecting point on the arm.

Paul

vertically, I believe it (roughly) 1inches in height it needs to be pushed/lifted…

horizontally, the spline center is (roughly) 2inches away from the ‘stem’ of the optic measures to release the liquid

Here is what I created so far:

  • machined a bracket/platform
  • servos mounted
  • test code in place

Video in action:

I am looking at these servos for a swap out:
MG996R digital servos:

Not sure how much ‘torque’ a gram amounts to? but seems to be a little over double (running it @ +5v) than the current servos in the set-up

xl97:
Thank you for the alternate option..

I like the price and the metal splined gear..

However.... I guess I am in the same situation with those as well?

  • what is the spline tooth count?

I see this:

Which is it? My understanding (which may be inaccurate) is that Futaba and Hitec have different tooth count on the spline.

And while they do some with some plastic arms/horns.. none of those will work my project.. needs t be longer.

  • also look to be a bit bigger physically...than the RS standard servo size.. (which I machine out a little packet in my aluminum plate for it to sit in..... I guess I could make another pass to widen it up?.. so not a deal breaker)

Obviously you missed the point of the change to the MG servo.

Idea was to trash the radio shack gear and use a common brand which already has 4 sets of arms provided.
So 3 spare sets per servo once you use one on your project.

Servo arms , no matter which brand, will not be any longer than provided as shown.

As far as I am aware, spline count is the same as Futaba (25).

For torque requirement you will need to know what amount of weight is placed on the round bar @ the 2" mark. I suspect the poster of the video had problems also as the obvious use of 2 servos.
Not really a good setup to have output arms fixed together given no 2 servos are exactly the same in travel or speed.

A gram is not torque, it is weight and Google is a good reference in case you haven't heard of it.