Servos for AL5D arm with wrist and elbow upgrades

Lynxmotion Robot Arms
1

a copy of this message was sent to [email protected]:

we have the AL5D arm put together now with both the wrist and elbow p-481-low-profile-axis upgrades.
Our base servo (352 oz-in) seems burdened. I want to upgrade the base to a significantly higher
400+ oz-in servo. What do you recommend? Is the HS-7950TH (486 oz. in.) 7.4V Digital Standard High Voltage Servo compatible with the arm? Is a 187 0z-in servo sufficient for the elbow with the wrist upgrade also? What would you recommend for a replacement (spare) elbow servo?
Any recommendations about using both the wrist and elbow on the AL5D?

From: RobotShop Inc. [[email protected]]
Sent: Friday, February 01, 2013 9:52 AM

Subject: AL5D Arm Hardware-Only Kit

Hi,

The elbow rotation can be done easily using the following:
lynxmotion.com/p-481-low-pro … ervos.aspx
You can install it between the two brackets - we’d suggest at least a 645MG servo, if not more powerful.
Digital vs. analog servos… we don’t quite use the programmable aspect of a digital servo, and its best to choose a servo based on the required torque.

Hope this helps,

Coleman
Technical Team - Équipe Technique
RobotShop inc.
Putting Robotics at Your Service!®
La Robotique à votre Service!®
Web: robotshop.com

2

The shoulder bracket included with the AL5D is specific to the 805BB / MG. Hitec does not many many servos which use this same case, and which also would fit the corresponding C-bracket. Changing the servos in the elbow and wrist are possible, but keep in mind that those too require a specific sized servo from Hitec. The more you add to the arm, the less it will be able to lift. For the 7950, the size is completely different from that of the 805, and we do not have any brackets for this series.

3

do you recommend the 805BB for both the shoulder (the servo rotating the arm vertically - placed on top of the round base) rotation and the elbow rotation (currently a 187 oz-in solar D227)?
are the HSR-5980SG (417 oz. in.) Digital Standard Servo
or HSR-5498SG HMI Digital Robot Servo or anything with greater oz-in than the 343 of the 805BB usable in the AL5D?

do you recommend a 7.4 V power supply for any?

What we currently have is 7 solar servos and the hi-tec servo that came with the wrist upgrade
as a spare. I am trying to get more power in the shoulder rotation and at the very least to have
a couple of spares. If I order before midnight tonight can I get the servos by Friday?

4

The 805BB is a very large and heavy servo, so if it is used in the elbow, it adds to the weight the shoulder servo needs to lift. The “weakest” point in the setup is the shoulder servo, followed by the servo in the elbow. Since the servo in the shoulder cannot be easily exchanged with one that is more powerful, using a larger servo in the elbow will not help. The 805BB does not fit in the elbow directly (even though it looks to be about the same size as the 755).

The HS-3xx, 4xx, 5xx, 6xx, 54xx, 56xx, and 59xx servos are verified to fit in the standard sized servo brackets. The AL5D however uses large brackets in both the shoulder and elbow, so you’d need to swap the brackets as well.

If you choose a 7.4V power supply, you would need to ensure that all servos in the arm operate at 7.4V. If you have a 6V servo and apply 7.4V, you could fry it.

You would need to really customize the brackets in order to get a different servo to fit in the base. It would be quite a different setup.

It depends on where you are located, the stock status and the shipping option you choose. If you are outside of North America, we suggest ordering via robotshop.com/eu

5

are 755MG and 755HB interchangeable?

I bought on 2day delivery
S755HB HS-755HB (183 oz. in.) Quarter Scale Servo-HS-755HB (183 oz. in.) Quarter Scale Servo 1

S805BB HS-805BB (343 oz. in.) Mega Servo-HS-805BB (343 oz. in.) Mega Servo 1
to make sure they arrive before the weekend.

we already altered the brackets for the solar servos. I am concerned about the balance of
the arm with the elbow added. We should have some replacements.

6

Yes - the only difference is that the MG uses metal gears. The electronics, motor and casing are all identical.

7

We are mounting the arm vertically (see attached photo). Even with the 805 in the shoulder, we only get about 30 degrees elevation. A small servo in the base - a Solar servo equivalent of the HS-485HB (83 oz. in.) Standard Servo - literally almost doesn’t rotate at all. We are considering a counter-balanced weight arrangement to get better shoulder elevation. What do you recommend for the base rotation? another 755 or 805? Any suggestions on the shoulder elevation? base rotation?
You gave a suggestion previously of new brackets with double 805 servos for the shoulder rotation - do you think that could give us 90 degrees elevation?
arm_photos.docx (316 KB)

8

If you can handle the reduced speed, these robotzone gearboxes at servocity would greatly increase torque
for base rotate.

servocity.com/html/robotzone_servos.html

Joel

9

Correct. You likely need a geared down servo. RobotShop / Lynxmotion will be carrying that range of products shortly:
However, it’s important to note that the hole patterns between the SES and ServoCity is not the same, so you will have some customization to do.
robotshop.com/pan-tilt-servo-gearboxes.html

10

805 does the job! we found the problem with the shoulder rotation - the 805 has to have 1.5 amps or more when used in our vertical arrangement with the elbow and wrist added - depending on which power supply we connected gave varying ranges of motion. Our base rotating servo isn’t hi-tec (solar) and is making bad grinding noises and gives little rotation. Can we get +/- 30 to 40 degrees in the vertical arrangement with a 485 or 5485? will anything bigger like 645 or 5685 fit the base fixture?

11

A 645MG is likely not enough to raise the arm, and likely cannot be used at the elbow either. You need something closer to the 755MG.

12

I mean the base rotating servo inside the black plastic circular piece that we have mounted at the top of our vertically mounted arm - will a 755 fit inside this? the original 5 dof arm recommends a 485. We have the 805 installed on top of the base and the 755 at the elbow. Is there are an advantage to the metal gear servos / all our gears are plastic. I meant +/- 30 to 40 degrees in sideways rotation.what servo inside base_4_18.docx (162 KB)

13

Not at all - the mounting is specifically for a Hitec standard sized servo. The 755 is a 1/4 scale servo.

Metal is a lot harder to strip than plastic and should help the servo last longer. However, it does not change the max torque.

For moving the arm forward and backward, you’ll need a fairly powerful servo such as the 805BB (drill new holes to mount it to the SES brackets and use an 805BB C-bracket and multipurpose bracket to support it:
lynxmotion.com/p-807-aluminu … -pack.aspx
lynxmotion.com/p-808-aluminu … -pack.aspx
lynxmotion.com/p-655-mechani … -pair.aspx

14

we need to replace the solar servo in the base. what is the max power (torque) hi-tec servo that will fit inside the black plastic base (side-to-side motion in the vertical hanging arrangement)? anything stronger than the 485?
or are you saying remove the black circular base and replace with the bracket arrangment above with an 805?

15

Ideally remove the black plastic based and replace it with an 805BB.

16

concluding post:
thank you for your responses and info,
the project was moderately successful considering we only worked on it for 4 weeks because of a 7 week delay in getting servo motors. Anyone interested in the project can view the course required documentation at
eecs.ucf.edu/seniordesign/fa2012sp2013/g10/