Maker Pro
Maker Pro

Need help on servo motor output gear sizing

sanyibacsi

Sep 15, 2015
6
Joined
Sep 15, 2015
Messages
6
I bought a TowerPro MG996R motor. It is not precise, but at least it works so it will be handy for my hobby project.
The only question I could not figure out from the specification is the actual size of its arms/horns. It is said that the standard 1.5" / 38.1mm would fit. For those I need some standards, especially about the gear size what comes out of the engine and generates the torque. As far as I could measure, it is something 5.7mm diameter and has around 32 teeth in it; but of course that is rather vague.
Can you please guide me to a source where I can find standard specs what then I can model in CAD myself (I would like to use a different servo horn, not the supplied one?

Thanks a lot - I have been googling for sizes for 3 days now, no luck, maybe my keywords were not good enough.
 

Martaine2005

May 12, 2015
4,400
Joined
May 12, 2015
Messages
4,400
Hello,
Have you checked here.
The torque is normally down to the motor itself.
The servo horn size is dependent on the throw you need.
That is why servo horns come with holes at different positions.

Standard-Servo-Arms.jpg


Martin
 

Minder

Apr 24, 2015
3,335
Joined
Apr 24, 2015
Messages
3,335
The very simple down and dirty way to measure the output torque is to place a horn of a certain length and measure the distance from the hole you intend using to the centre of the horn.
Then use a sensitive spring scale attached to the hole in question and holding the spring scale perpendicular to the horn direction, increment the servo in steps until it stalls, the torque of the output is then is read off in newton-metres, ounce-inches, gram-centimetres etc.
M.
 

Old Steve

Jul 23, 2015
734
Joined
Jul 23, 2015
Messages
734
The very simple down and dirty way to measure the output torque is to place a horn of a certain length and measure the distance from the hole you intend using to the centre of the horn.
Then use a sensitive spring scale attached to the hole in question and holding the spring scale perpendicular to the horn direction, increment the servo in steps until it stalls, the torque of the output is then is read off in newton-metres, ounce-inches, gram-centimetres etc.
M.
I think that sanyibacsi is actually after output shaft specs, not torque.
ie Diameter, # of splines, depth and angle of splines. I did a bit of a search earlier, and found that the number, depth and angles of splines vary model to model and manufacturer to manufacturer. (And I always thought they were all the same.)
 

Old Steve

Jul 23, 2015
734
Joined
Jul 23, 2015
Messages
734
I realize when I re read the OP.
Here is a couple of links that may help.
25 SEGMENTS/ Ø5.96(FUTABA TYPE)
https://sites.google.com/site/3dprinterlist/home/tutorials/more-on-rc-servo-s
M.
They appear to range between about 15 and 25 splines. I found a lot of queries about exact numbers and angles of various types, and even did an in-depth search for more info on the (infamous) TowerPro MG996R and it's predeccessor, the MG995R, but found nothing definitive relating to this servo.
Most seem to have the same diameter shafts, at least.

I bought a pair of Dagu continuous-rotation servos with wheels last week, and while the wheels fit the output shaft well, the horns very obviously have either a different number of splines, or their depth or angle differs. (They don't @#$% fit. :mad: )
Until tonight, I thought it was bad moulding or something, (my eyesight is very bad, so I can't examine them closely), but now I think it's a case of the wrong horns, made for a different servo.
 

sanyibacsi

Sep 15, 2015
6
Joined
Sep 15, 2015
Messages
6
Thank you very much for all the answers. You helped to get to the right direction and that writing on measuring motor strength was really interesting.

It looks that towerpro uses the same 25 teeth output as futaba (at least shops offer the same for both). The futaba code is 25t f3 for this particular motor. They do not publish (or they put into a very hard to find place) angle size and teeth length for some reason so I will be experimenting on that a bit.
 
Top