For my project, I need to rotate the base more than 180 degree.
(240 degree would be ideal. But I think 210 degree is ok.)
My questions:
The base of the assembled AL5D might be able to rotate more than the specified 180.
Can it reach 210 degree or more?
I think the motion range is limited by the servo (HS-485HB for the base).
In the HS-485HB data sheet: lynxmotion.com/images/data/hs485hb.pdf
It says: “Operating travel: 40 degree / one side pulse traveling 400 usec”
It sounds like the servo can rotate only 40 degree in one direction.
So the total movement of the servo (hence the base of AL5D) is only 80 degree?
From servocity.com: servocity.com/html/hs-485hb_servo.html
It says a regular HS-485HB ($16.99) rotates only 90 degree.
But you can pay extra $10 to buy a version with 180 degree rotation.
I want to make sure the servos that come with AL5D are the 180 degree version.
(since the lynxmotion specification sheet says the motion range of AL5D is 180 degree.)
Is it possible to use another servo so that the base can rotate 240 degree?
If so, which one?
If that doesn’t work, any suggestion to modify AL5D, so that the base can rotate more?
I think 180 deg is the rotation for the with the supplied servo as stated. No real easy fix to change the rotation range of a standard 180 deg servo.
The should be. The lynxmotion sheet saying 40 deg rotation is for the 400 us timing change listed below the 40 deg spec. Per the servocity site “This servo can operate 180° when given a pulse signal ranging from 600usec to 2400usec. Since most R/C controllers cannot generate this wide of signal range, you will need to purchase our servo stretcher for 180° operation” . You would need the servo stretcher if you used an R/C Tx/Rx for control, and not the usual servo controller.
You might look at digital servos or sail winch servos with 270 deg capability, but more $$$ an extensive rework might be required.
Servo city has gears/chains for use with servos that might change 180 deg servo rotation into 270 deg rotation of a platform, but it would be a DIY project. lots of possibilitys, but also more involved than the easy 180 deg standard setup.
Thanks for the help.
I plan to use a BobBoarduino, using potentiometers to control servos,
without using R/C. Assuming I program it correctly, will this give me the specified 180 degree rotation without using any additioanl part (such as “servo strecher” from Servo City)?
Actually I am a bit confused here. From example codes at //arduino.cc; for a analog servo,
1500 msec is the center position, 1000 msec is the ccw most position, and 2000 is the cw
most position. Per the servocity site data sheet: “This servo can operate 180° when given
a pulse signal ranging from 600usec to 2400usec.”
It looks like that, for HS-485HB, the center is 1500, ccw most is 600 and cw most is 2400.
So to move HS-485 to cw most from center (90 degree), I should simply write:
BaseServo.writeMicroseconds(2400);
Is this correct?
If I write:
BaseServo.writeMicroseconds(2600);
Will that rotates servo more than 90 degree? Or (I guess) it will simply damage the servo?
My second question is about digital servo. (If I can solve my problem by simply using
a digital servo, it will be great.)
If I use a digital servo, can I just plug it into Bobbaorduino (just like an agalog servo)?
Is the code for controling digital servos the same as the one controling analog servos?
I looked at the avaible servos at lynxmotion site. All digital servos have range (at most) 180 degree.
The only servos with 360 degree range are “Continuous Rotation Servo”.
I guess these are totally different servos, and I cannot use them for robot arm, correct?
Do you have a link to the arduino page stating the limited range? That range is usually associated with R/C equipmemnt, and not the servos and microcontrollers. The arduino servo library has some internal limits (default min is 544, max is 2400), but you could probably change those if needed. The typical hobby servo is usually mechanically limited to ~190 deg of rotation.
Also, about the question about digital servos:
Can they be connected and programmed the same way as analog servos?
(Where do I find info for sthese stuff).
Also on the arduino page you reference. You need to go with the specs of your specific servo and not generalizations. There is a “servo” section on this forum with servo info that might be of use to you. As to digital servos, they generally accept standard servo control signals. They often have other features that you would need to research for the particular servo. To change the programming in a digital servo may require extra hardware and software. A lot depends on how much time, effort, and $$$ you want to put into the arm to have greater than 180 deg rotation.
“Note that some manufactures do not follow this standard very closely so that servos often respond to values between 700 and 2300. Feel free to increase these endpoints until the servo no longer continues to increase its range. Note however that attempting to drive a servo past its endpoints (often indicated by a growling sound) is a high-current state, and should be avoided.”
After searching around, I found another possible solution: use a HS-785 HB Winch Servo
(see: servocity.com/html/hs-785hb_ … tions.html)
It can rotate full 3.5 turns!
But this leads two questions.
The base servo for AL5D is HS-485HB with size 39.9mm x 19.8mm x 37.8mm. It is put into the base directly.
However, HS 785HB is larger (59 x 29 x 50). Can It be placed into the base? If not, what bracket should I use?
HS-785HB is not conventional. Does any one have experience with it?
(For example, since it can rotate more, may be it is less accurate?
Also, what usec value should I use to make it rotate 90 degree from the center?)
So, there is no easy way to make a servo rotate more than 180. That already makes me sad!
I am thinking of a way to modify the servo. You guys are experts, tell me if this idea is totally out of line.
From what I read, it seems that the resistance of the pot in servo is the only thing that affects the servo position
(of course assuming the input signal is fixed.) The servo output shaft and the pot are directly connected.
So it seems that the only real physical limitation on the rotation range is the pot itself. However, regular
pots rotate at least 270 degrees! Let me make up some numbers.
Suppose the pot in servo is 30K, and rotates 270. But only 0 - 180 rotation is used to limit the servo position.
This corresponds to 0 - 20K resistance range. Suppose I add a resistor of 60K parallel to the two ends of the pot. Then, when the pot rotates 0 - 270 degrees, the resistance range would be 0 -20K.
Would this modification fool the on-board servo control circuit to rotate the servo 270 degree?
Is this worth a try? or it is completely wrong?
(The modified pot is no longer a liner potentiometer. But I think my application can tolerate this).
One more thing: I heard that some GWS servos rotate 360 degrees, (they are NOT “continuous rotation servo”.
They are regular servo, but rotate up to 360 degrees.)
Does any one know anything about this? (It is hard to find servo rotate range information.
Maybe because they are assumed to be 180 degrees).
If you are a DIY type you could probably make a variation of the below. You can move the servo pot to the outside of the servo, and replace it with another linear pot with similar resistance (~5k or 10k) that has a larger turn range to be connected to a rotating arm base. Make a new turntable base (home improvement stores have the turntables) with the pot under the turntable and rotate on the outside with the servo (with travel stop removed).
Thanks. Just one more question about AL5D arm:
I need to extend the length of the arm by 4 inches. I plan to do this:
Replace the supplied tube between the elbow and the wrist (AT-03, 4.5 inch long)
by a 6.5 in tube.
Add a 2 inch tube between the two C-Brackets (ASB203 and ASB-205 between the
shoulder and the elbow).
Is there any problems with this?
(The maximum lift weigh of my robot arm is < 6 oz. In the AL5D specification sheet,
the max lift weight is 13 oz when the arm is extended. So I guess the servo torque
is not a problem). But are there other thing I need to worry about?
The servos torque is rotational, so the longer you make the segments the weaker the servos are. For example if a servo has 50oz. inch of torque it means it can support 50 oz. at 1" from the center of the output shaft. But at 2" it can only support 25 oz.
