Lynxmotion Tech Support

Dear forum members,

I intend to buy the lynxmotion AL5D robotic arm and require your expert suggestion in choosing the right combination of servos for a reasonable lift capability. At the present I am looking at either HSR-5980SG or HS-5685MH. Any suggestions?

Thanks

The AL5D arm already has a list of suggested servos: The arm uses 1 x HS-475HB in the base, 1 x HS-805BB in the shoulder, 1 x HS-755HB in the elbow, 1 x HS-645MG in the wrist, and 1 x HS-422 in the gripper. This provides a 13oz lift capacity. If you purchase the complete kit, you get all the servos included. The large bracket used in the shoulder and elbow can fit the HS-755HB/MG, 5745MG and 805BB/MG. The 56xx and 59xx servos can only be used with standard brackets, and the only standard brackets are in the base and the wrist, which don't contribute much to the lifting capacity.

_________________
Coleman Benson
Lynxmotion
Imagine it. Build it. Control it.™
http://www.Lynxmotion.com

Thanks for the reply.
Actually, my requirement is to assemble a robotic arm equivalent to "crustcrawler AX-18A smart robotic arm - http://www.crustcrawler.com/products/AX ... tic%20Arm/" in terms of precision (repeatability 2.5mm) and weight lifting capability (2-3 pounds, 0.91kg). I seek a solution from lynxmotion because I want to use r/c servos and a SSC32.
In the view of the above, I seek expert advice regarding the selection of servos. Which hitec r/c servos should be used to obtain equivalent: torque (AX-18A 18kgf/cm), speed (97 rpm) and weight lifting capability (2-3 pounds, 0.91kg) ? AX-18A dynamixels come with position-torque feedback but I am just concerned with the precision and torque requirements. Therefore please guide me in selecting the most appropriate hitec r/c servos for controlling a 5-axis robotic arm using SSC32.

Your guidance is highly requested and appreciated.

Thanks.

Your assembly requirement may be difficult. The AX servos appear to be mechanically more robust and may have better position precision than standard RC servos. The precision (repeatability 2.5mm) and weight lifting capability (2-3 pounds, 0.91kg) specifications are very vague as the conditions/positions under which these specifications were determined are not given.

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Yes, true about AX servos. But I have to assemble an arm with r/c servos. Let's say, an arm capable of lifting 3 pounds of weight. which hitec servos should I choose for such a requirement?

I would imagine that Hitec HS-7980TH might work. They are rated for 611 ozin at 7.4V. With two 6" links in the arm (so, total 12") this gives you 50 ounces of force at the tip, which is just above 4 pounds, altough you have to include the weight of the other servos and arm itself, so that seems about right.

Note that the elbow doesn't need to be as large -- a 7950 would be plenty strong enough, and even something weaker would work.
Same thing for the gripper -- the length of the lever there is very small.

If you need to build a significantly longer arm, then you probably can't lift three pounds with a hobby servo at the base.

So, if I go with this hardware kit (5-axis Smart Robotic Arm) (http://www.crustcrawler.com/products/AX ... tic%20Arm/), any suggestions about the following servos shopping list?

Servos:
1 - (1) HS-7980TH for the base.
2 - (2) HS-7980TH for the shoulder.
3 - (2) HS-7980TH/HS-7950TH for the elbow.
4 - (2) HS-7950TH/HSR-5980SG for the 5th-axis.
5 - (2) HS-7950TH/HSR-5980SG for the dual gripper.

Any suggestions for the servos in "5th-axis, gripper)? Since the torque requirement at these areas is not high therefore lighter servos can be substituted. I am sure there would be no difficulty in using the mentioned servos with the "Smart Arm" brackets. Any suggestions please?

Your kind assistance and guidance is highly requested please.
Thanks

You should also verify that those servos fit in the appropriate brackets of that kit.

Ok, with a little research I have found that the r/c servos are not compatible with "Smart Robotic Arm brackets" by crust crawler. So, now my choice is to build a 6-axis arm using SES brackets and I want to use a combination of HSR-5980SG and HS-7980TH servos for a reasonable torque. I have not used SES brackets before so I require expert guidance from the forum.

Anyone please write me the complete list of the exact SES parts required to build a 6-axis arm using HSR-5980SG servos.
I am really in a hurry to place an order from my school and therefore require expert advice in this regard.
Thanks.

I think you will fail in this assignment as it currently is. If you only have limited time you should just get one of the lynxmotion arm kits and go with that. Your arm performance requirements indicate a DIY arm that will be more expensive and complex than you realize.

_________________
Why I like my 2005 rio yellow Honda S2000 with the top down, and more!
http://youtube.com/watch?v=pWjMvrkUqX0
http://youtube.com/watch?v=qfyRA-g1nhI
http://web.comporium.net/~shb/S2000video.htm

Hi, Pyrrhicpk,

I think Zoomkat may be right in his answer. Perhaps you could give us a few more specifics about the requirements of your project:
- You speak of needing a "6-axis arm." Lynxmotion calls their AL5D a 4DOF arm. With optional wrist rotate, that would become 5DOF. But that may be in your ballpark if you are considering the gripper open/close servo as one of you axes. I am no expert, I remember reading that with robotic arms, the "end-effector" (gripper) is NOT considered a DOF. So, 5DOF plus gripper would give you six axes.
- Less happily, you speak of needing to lift 2-3 pounds using HiTec standard size servos. Lynxmotion says the AL5D is capable of lifting 13 ounces. That is with HiTec mega sized servos (and SES brackets) at the shoulder and elbow positions.

I just built the BotBoarduino version of the AL5D with heavy duty wrist rotate two months ago. It was a very satisfying project which will be even better when I screw on some homemade grip expanders. There is no way it will lift even two pounds.

Other builders more expert than I about a wider range of HiTec servos and SES parts may be able to give you better help.

My suggestion since your time is limited would be to download and study the free AL5D assembly guides to see what is possible. Then, if you still can, readjust your project parameters with your school. Afterall, it is probably more important to demonstrate the theory of robotic arms than to lift 2-3 pounds.

Good luck to you, Ted

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

Dear Ted,

Thank you for the detailed information. I have found a 6DOF configuration in the following thread:
viewtopic.php?p=1870#p1870

This configuration with springs instead of counterbalancing weights should suffice all my DOF requirements. All I am now concerned about is the best possible servos which may fit with those SES brackets. i think the brackets used are standard brackets. Can I use HSR5980SG servos with these? Can anyone write me the complete hardware list for building this configuration including a heavy-duty wrist rotate.

Thanks.

The arm you want to create did not exist before, so without actually building it, its difficult (time consuming actually) to see if the list below is complete or not. Please keep that in mind if you decide to proceed with the purchase. Take a look at the Robot Arm Torque Calculator to see if the servos will do what you want.
http://www.robotshop.com/robot-arm.html

Base
BR-NS: http://www.lynxmotion.com/p-578-base-ro ... ervos.aspx
BEC-KT: http://www.lynxmotion.com/p-793-base-el ... r-kit.aspx
SSC-32: http://www.lynxmotion.com/p-395-ssc-32- ... oller.aspx
USB2S-01: http://www.lynxmotion.com/p-699-usb-to- ... cable.aspx
WP-03: http://www.lynxmotion.com/p-753-regulat ... 30amp.aspx

Shoulder & Elbow
ASB-13: http://www.lynxmotion.com/p-583-aluminu ... ingle.aspx
ASB-10: http://www.lynxmotion.com/p-401-aluminu ... -pack.aspx
ASB-04: http://www.lynxmotion.com/p-286-aluminu ... -pack.aspx
ASB-06: http://www.lynxmotion.com/p-328-aluminu ... -pack.aspx

Elbow to Wrist
LPA-01: http://www.lynxmotion.com/p-481-low-pro ... ervos.aspx
HUB-08: http://www.lynxmotion.com/p-403-aluminu ... -pair.aspx
AT-02: http://www.lynxmotion.com/p-405-aluminum-tubing-30.aspx (other lengths possible)

Wrist
WRU-HD: http://www.lynxmotion.com/p-664-wrist-r ... -duty.aspx
LG-NS: http://www.lynxmotion.com/p-161-little- ... ervos.aspx

Servos
SCD-06: http://www.lynxmotion.com/p-811-6x-hsr- ... horns.aspx

Extras
PHTS-01: http://www.lynxmotion.com/p-298-phillip ... 2-100.aspx
PHS-02: http://www.lynxmotion.com/p-325-steel-p ... 56-25.aspx
PHS-09: http://www.lynxmotion.com/p-483-steel-p ... 56-25.aspx
SPR-01: http://www.lynxmotion.com/p-439-load-ba ... 158lb.aspx
SEA-03: http://www.lynxmotion.com/p-227-servo-e ... le-24.aspx (several in various lengths)

_________________
Coleman Benson
Lynxmotion
Imagine it. Build it. Control it.™
http://www.Lynxmotion.com

Many thanks for the list. I really appreciate that. Just a quick question, both the HSR-5980SG and HS-7980TH may fit in the SES standard brackets? I am thinking of using 2 HS-7980TH at the shoulder joint and 2 HSR-5980SG at the elbow joint. In total, I'd be requiring 7 servos for the 6DOF design, so 2 HSR-7980TH and 5 HSR-5980SG. Anything left?

Thanks again.

Hello again,

Are you sure about that count of 7 servos? I get 8:
- 1st DOF 1 servo Base Rotate
- 2nd DOF 2 servos Shoulder
- 3rd DOF 2 servos Elbow
- 4th DOF 1 servo Wrist Up/Down
- 5th DOF 1 servo Wrist Rotate
- 6th Axis 1 servo End-Effector (Gripper Open/Close)

Lynxmotion makes two kinds of dual servo standard brackets:
- http://www.lynxmotion.com/p-583-aluminum-dual-servo-bracket-single.aspx
- http://www.lynxmotion.com/p-477-aluminum-dual-inline-multi-purpose-servo-bracket-single-pack.aspx
- http://www.lynxmotion.com/p-758-aluminum-dual-inline-multi-purpose-servo-bracket-single-pack-v2.aspx
These are designed for situations where you need extra torque such as in arm shoulders and elbows. Remember that adding servos increases the numbers of ball bearings and horn connecting C-Brackets that you need.

I have never used any of these dual brackets and don't quite see how they work in practise. You will have to look them up and decide whether either the side-by-side or inline model will work in your situation. Whichever you might choose, you could rest assured that both servos would be held in proper alignment. That might be hard to ensure if you tried to design your own dual mountings.

Another thought, you have told us time is pressing, but you haven't really given us your deadlines or budget, or how these fit into your larger school schedule or funding. Without us prying too deeply, it might help us make suggestions if we knew whether you can reasonably trade money for time or whether budget constraints mean you will have to craft some of your own parts.

Again, best of luck to you. And please post some pictures and videos of your progress. Some narratives especially of design decisions and compromises would interesting and instructive also.

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