Lynxmotion Tech Support

I have the universal bracket, and the C bracket with ball bearing.
I have assembled them as per the illustrations -- nut, back of universal bracket, locking washer, ball bearing, C bracket, screw, in that order.
I have two separate "standard size" servos. One is a SG-5010, and one is a EXI D226F (yeah, going for torque
I'm trying to use the plastic horns that come with these servos -- especially for the EXIs is needed, because they use JR style 23-tooth splines, which is hard to find other horns for.

Now, the problem is that the C bracket won't *quite* fit the servo/universal bracket, with the horn on it. The horn pushes the bracket up enough that it does no longer sit on the ball bearing, and it rubs against the back of the universal bracket, and there's a very slight bend needed to actually fit across the horn. This doesn't seem right to me -- at a minimum, it means the ball bearing is useless.

I believe both of these servos are "standard size" -- they have exactly the same height with horn mounted. So, what am I doing wrong?

Picture of the servo in the bracket without the horn, with C bracket properly aligned on ball bearing, and the top of the C bracket pretty much in plane with the spline:
https://www.dropbox.com/s/hblwrljhykquwlx/IMAG0629.jpg

Picture of the servo with the horn on it, jamming the C bracket:
https://www.dropbox.com/s/8ck8dh6pl894ye0/IMAG0630.jpg

Hi, Jwatte,

I am not certain about this, but a few thoughts:

It does appear by comparison with my T-Hex that you have everything assembled in the right order, so I don't see anything "wrong". Also it does not appear that spreading or springing the C bracket further outward would help at all because it would make the C bracket ends further out of parallel.

Is there any chance that you are using slightly extra thick nuts on the ball bearing screws? If you could replace these with thinner nuts, or grind or file these nuts thinner it might solve the problem. (Tedious I know.) You might have to shorten the bolts slightly also.

Conversely, although you say the servos with horns are exactly the same height, can you reduce the height of the EXI horn somehow? Perhaps you could use an end mill Dremel bit to bore the spline hole in the horn just a little deeper so it would fit lower on the spline. You would have to exercise great care not to damage the horn splines of course. A hand tapping devise like this http://www.micromark.com/microlux-tapping-fixture,8363.html is what I use for similar precise work.

Good luck,

Ted

_________________
Ted, RoboTed
Never quite finishing means never having to admit failure!

The servos you have there actually do have smaller case design. so yes they should fit right? ... No.
Im not quite sure they are the same from bottom of casing to top of horn.:

SG-5010:
47.2mm

HS645MG
44.3mm

Also I think there is a dramatic difference in the measurement from the Servo tabs mounting surface to the top of the horn.
The correct measurement should be 17.3mm.


These Simply don't fit the bracket! and your not the first to ask this. sorry.

_________________
Jonny Poole,
Freelance Concept Art & Animatronics, 3D Art and 3D Modelling, as well as Physical Modelling, Mechanical design, and illustration.
http://www.innerbreed.co.uk/
Create, Innovate, Inspire.

You could try mounting the horn for the servo on Top of the braket.
So it would give you some more space.

If i am not clear let me know i will give you some drawing.

_________________
Eric Nantel
Qc Canada

Always liked Robot... Now i am learning to make some...! Wonderfull...

yes Eric's got a good idea there. if you bore out the 8mm hole in the bracket 'so it can fit the horn in from the top, then you might be in for a fighting chance.

_________________
Jonny Poole,
Freelance Concept Art & Animatronics, 3D Art and 3D Modelling, as well as Physical Modelling, Mechanical design, and illustration.
http://www.innerbreed.co.uk/
Create, Innovate, Inspire.

I was afraid of that. So, "standard" isn't, reallly... I imagine a few more millimenters on the bracket sizes wouldn't break compatibility with the 645 servos, but would allow other servos like these to work, too?
The problem is not the nut at the bottom (although I can grind that if needed,) but instead the distance from bottom of mounting tabs to top of horn. I measure 19.5 mm. I think even with 17.3, there would be a slight problem, as the bottom of the bracket would not be sufficiently pushed into the flange of the ball bearing, though.
Finally, i did consider the "top mounting" of the horn. The bottom of the horn arm/plate is at the top of the spline (dumb design -- it adds additional lateral torque on the spline!) and the diameter of the horn mount is about 9mm. I'm considering either polishing it down a bit, or widening the bracket 8mm hole.

Or I could get me some Dynamixel AX-12s instead. They're more expensive, but they do come with brackets already (plastic, though) and you can program them serially instead of using pulses. I'm starting to see why those are seemingly so popular...

Attention, New Robot Shop Overlords: If you're looking for things to improve, try extending the size of the standard brackets and width of the C brackets a little bit to allow for a wider variety of hobby servos

I wonder if a custom "horn" made by pressing some shapelock/insta-morph into the spline would be strong enough?

Yes i agree there is a slight mis-understanding regarding what one would call a standard size. The standard brackets line can use most standard size normal or digital servos. The HS-3xx, 4xx, 5xx, 6xx, 54xx, 56xx, and 59xx servos are verified to fit.
But..
im not sure that extending or changing the current brackets will help anyone.
I honestly don't mean to sound rude or arrogant, but
To be honest the SG-5010 are a very poor, low quality servo...
Servo quality is all in the price. you will pay for what you get with servos.

Dont be fooled by the over-exaggerated numbers when it comes to torque per $.
HS645MG+ will serve you well for most projects.

..and they fit the brackets.

_________________
Jonny Poole,
Freelance Concept Art & Animatronics, 3D Art and 3D Modelling, as well as Physical Modelling, Mechanical design, and illustration.
http://www.innerbreed.co.uk/
Create, Innovate, Inspire.

The brackets were designed for Hitec standard servos, and it's never implied otherwise.

From the website...

Standard Servo Brackets
The standard brackets line can use most standard size normal or digital servos. The HS-3xx, 4xx, 5xx, 6xx, 54xx, 56xx, and 59xx servos are verified to fit. Note: we include a round servo horn with the servos we sell if it's not normally included, but other sources will not... ...Beware of Bluebird or GWS servos. They are drastically oversized and will not fit the brackets!


Further, there are other supporting bracket designs that will not fit a widened "C" brackets. -and how do you plan to retain the good fit with the servos they were designed for... It's not as easy as you might think to just make the bracket wider.

_________________
Jim Frye, the Robot Guy
http://www.lynxmotion.com
I've always tried to do my best...

Yeah, that was just a servo I had laying around, that I tried after the EXI D266F didn't work out. I had assumed that, because these servos work in RC cars where Hitec 422 servos also work, they are "standard."

What would actually be best, is to just document the actual measurements needed in the catalog on the site. Say "Designed for a bottom-of-tabs to top-of-horn distance of 17.3 mm" and "Designed for a bottom-of-tabs to bottom-of-servo distance of 26 mm" and perhaps even the tab hole pattern. There really isn't a "standard" that's precise enough to work for these kinds of applications. Document the requirements, and there's no room for confusion.

I think the point Jim is making is quite clear..
The brackets were designed for Hitec standard servos, and it's never implied otherwise.

Other servo ranges may (and this thread proves it) carry a different "standard size servo" to there specifications to what they call standard.

To be quite honest, there is already quite a bit of warning about these servos on the net.
Most of which is documented right here on LM.net
just a couple:
viewtopic.php?f=11&t=5486
viewtopic.php?f=31&t=7460

You cant really buy a cheap brand of servo, that's not specified for the use with another product 'and then blame the product because the servo you chose doesn't fit.

_________________
Jonny Poole,
Freelance Concept Art & Animatronics, 3D Art and 3D Modelling, as well as Physical Modelling, Mechanical design, and illustration.
http://www.innerbreed.co.uk/
Create, Innovate, Inspire.

Another thing to think when not using Hitec servo is that it will most probably not be at the angle it shoud at the normal command in most of the sample code.
I have some InoLab servo (High end China servo) and they dont work good on a SSC32.

_________________
Eric Nantel
Qc Canada

Always liked Robot... Now i am learning to make some...! Wonderfull...

The right place to document the compability is on the catalog page, not anywhere else. The catalog page does not say "Hitec servos only," it says "Fits standard size servos."

I don't understand why there is any resistance at all to making sure that the catalog page actually documents the full specifications of the parts? It reduces all confusion and better describes the product -- should be a win for everyone.

Also, the spacing of the hole pattern could also be documented right in the catalog, or at least in a document linked directly from the catalog. This is a best practice in online shopping in general; it leads to happier customers and overall better business. I'm making this as a constructive suggestion, not as a complaint, btw.



The brackets come with no software, so I don't understand what this means.

However, I do know that *all* hobby servos that use PWM commands center at 1500 microseconds, no matter what the brand. Some servos may be better than others at centering, but the EXIs are actually pretty darn spot on. For servos that don't center right, the best place to fix that is in the driver software IMO, but that of course depends on what particular driver/controller you're using.

Centering will not be the problem.. yes they all center at 1500.
But to move them to a point let's say 1800 for a Hitec will not be the same for another brand.

It's nothing against you ... I am making my MiniHEXapod on another post with some China servo myself.. :p

I don't know why there is not all that information on the LX website.
But one thing i know is they say it fit Hitec servo so you can look at Hitec dimensions.



A = .780” (19.82mm)
B = .530” (13.47mm)
C = 1.33” (33.79mm)
D = .400” (10.17mm)
E = .380” (9.66mm)
F = 1.19” (30.22mm)
G = .460” (11.68mm)
H = 1.05” (26.67mm)
J = 2.08” (52.84mm)
K = .368” (9.35mm)
L = .172” (4.38mm)
M = 1.57” (39.88mm)
X = .120” (3.05mm)

_________________
Eric Nantel
Qc Canada

Always liked Robot... Now i am learning to make some...! Wonderfull...

No, it does not. It says "Fits standard servos."

Separately, in other areas, it says "verified to work with types ...." which doesn't in itself say anything about what it doesn't work with.