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Firestorm65
02-03-2009, 11:15 AM
Which servos are best-in-class?

My main question is what is the most powerful servo that works with standard-sized lynxmotion kits, but the tread is open for discussion of any high-end servos.

Adrenalynn
02-03-2009, 01:26 PM
The big mamma-jamma, to my knowledge, in the standard servo department is the HSR-5995TG Ultra Torque, coreless digital. About 417oz-in.

http://servocity.com/html/hsr-5995tg_ultra_torque.html

It's discontinued, so you have to shop around.

Its sorta-replacement is the 7955TG at 333oz-in. However, the 7950TG is "coming soon" most places, and is around 486oz-in.

The HSR5990TG is still available though, and tops out at 417oz-in as well as being quick at 0.12sec to 60deg.
http://www.trossenrobotics.com/Hitec-Servo-HSR-5990TG.aspx

DresnerRobotics
02-03-2009, 01:43 PM
The HSR-5990TG is actually the replacement for the HSR-5995TG, as those had some heating issues.

Firestorm65
02-03-2009, 01:51 PM
What voltage is that torque at? Can they take more without damage?

(These guys still seem to have the 95... http://www.e-clec-tech.com/hstiroh.html)

Sienna
02-03-2009, 02:27 PM
You don't want the 5995. If you want to use the LM SES system, stick with the HSR-5990TGs (unless / until their 7 series equivalent comes out). The 5990s are supposed to have built in thermal shutdown circuits, which the 5995s did not.

By all accounts the 5990s are good servos. They can be used for many things (due to the standard case size), and can be run off a 2S Lipo (no higher) according to Hitec. (And I have 12 of them, so I'm not likely to badmouth them for the hell of it.)

That being said, I wish I had waited on my servo purchases. The Bioloid servos, while more costly, represent a leap in servo technology. The control interface is better featured, more flexible, better documented, and well, works, compared to the flimsy 2 way control (HMI) on the Hitecs. Not to mention servos like the RX-64 are rumored to work up to 24V, which provides ungodly amounts of torque to play with.

The really sad part is that Hitec could do the same with the control interface on its 5990s as well. There is a Atmel in each 5990, and if someone could figure out how to flash it, it might be a much better servo then it is.

DresnerRobotics
02-03-2009, 02:37 PM
Well said all around Sienna. :)

5990TGs are the way to go with any high end 'hobby' servo, but if you look at all of the top competition bipeds in RoboOne, almost all of them are running RX series Dynamixels from Robotis.

I also have production ready 3D renders of brackets I've designed for the RX-64 series servo, which I'll be posting in the very near future for all to use.

Promagic
02-03-2009, 02:50 PM
If you guys are dishing out $100 bucks a pop for a single servo, then this is not a competition for the "average Joe".

Good thing I'm not an average Joe *evil laugh*

DresnerRobotics
02-03-2009, 02:53 PM
Well, he was asking for best in class.

We have people modding Robosapiens which are pretty cheap. Likewise you could build a Quad for probably $400-500 total and be competitive. Really depends on how crazy you want to go with it. But no, this competition isn't for the average joe. The simple fact that you have to design and build a robot capable of doing all that we have spec'd sort of raises the bar considerably.


If you guys are dishing out $100 bucks a pop for a single servo, then this is not a competition for the "average Joe".

Good thing I'm not an average Joe *evil laugh*

HakBot
02-03-2009, 03:17 PM
Firestorm,

This is just my opinion but Im guessing you dont want to spend thousands on whatever it is you are doing so if this is the case I would recommend the 645MG from Hitec. I think you can get these for about $35 each and its a great servo for the price.

Adrenalynn
02-03-2009, 03:19 PM
Actually - thousands is what he's looking to spend, per the other thread. ;)
The 645's are pretty wimpy for a humanoid... The AX-12's are a much better buy in that torque range.

Firestorm65
02-03-2009, 03:38 PM
Are there kits for the RX series? Are they "large" sized motors or non-standardized? Never shopped for servos before, so assuming 6DoF legs and around 2' tall, what is the correct size to be looking at?

DresnerRobotics
02-03-2009, 03:58 PM
I'm not entirely sure that my Lynxmotion scout with 5645s is going to be able to carry the extra payload required by Mech Warfare, so I would highly doubt the 645s at less torque would cut it. 645s are great for the price, but when you get into walkers its another story entirely.


Firestorm,

This is just my opinion but Im guessing you dont want to spend thousands on whatever it is you are doing so if this is the case I would recommend the 645MG from Hitec. I think you can get these for about $35 each and its a great servo for the price.

DresnerRobotics
02-03-2009, 04:06 PM
They are totally different from standard hobby servos. These are servos built specifically for the purpose of robotics, and are what any serious competition humanoid uses. No kits, as most people building on this level are designing their own.

Like I said though, I've already designed a complete set of brackets to build your own with, and they are production ready. I'd be more than happy to share them with you (and plan on publishing them anyway once I get around to it). Check out my image gallery for pictures of them.


Are there kits for the RX series? Are they "large" sized motors or non-standardized? Never shopped for servos before, so assuming 6DoF legs and around 2' tall, what is the correct size to be looking at?

robologist
02-03-2009, 04:45 PM
I've been thinking through using some cheaper servos that are on hand. I have a couple old Cirrus CS-80BBMG, rated at 114/129 oz-in, near the HS-645, and a couple Blue Bird BMS-630MG, 181/195 oz-in. That is if I can find them. I'll need some more cheapies, but have heard to stay away from the Tower 995s, might go for a couple more Blue Birds or maybe GWS. Just to see what a lower cost robot could do. (Since that might be how I could enter anyway!) :)

Sienna
02-03-2009, 06:48 PM
Like I said though, I've already designed a complete set of brackets to build your own with, and they are production ready. I'd be more than happy to share them with you (and plan on publishing them anyway once I get around to it). Check out my image gallery for pictures of them.
Publishing the brackets is laudable Tyb, really.

However, more laudable would be convincing Matt to finance a production order of them so that the rest of us with no machining equipment and not wanting to spend hundreds on a single bracket because we can't order enough of them to bring down the unit cost can get some... :P
(Its probably not practical monetarily, as I don't know how many people buy RX series servos, but hey, figured I would ask :P)

DresnerRobotics
02-03-2009, 06:52 PM
Publishing the brackets is laudable Tyb, really.

However, more laudable would be convincing Matt to finance a production order of them so that the rest of us with no machining equipment and not wanting to spend hundreds on a single bracket because we can't order enough of them to bring down the unit cost can get some... :P
(Its probably not practical monetarily, as I don't know how many people buy RX series servos, but hey, figured I would ask :P)


Funny you mention that.........

:)

Sienna
02-03-2009, 07:08 PM
Funny you mention that.........

:)

Oh no! You can't say that and then withhold on us!! Thats so evil!!!

Firestorm65
02-03-2009, 09:04 PM
Will this: http://www.trossenrobotics.com/dynamixel-rx-64-robot-actuator.aspx work with your brackets?

Adrenalynn
02-03-2009, 09:10 PM
That's the servo he's designing against, yes.

DresnerRobotics
02-03-2009, 09:12 PM
http://forums.trossenrobotics.com/gallery/files/1/4/9/2/dscn1704.jpg

You tell me. :D

Firestorm65
02-03-2009, 09:39 PM
Is that "the" servo to go with? Is anything else even comparable?

DresnerRobotics
02-03-2009, 09:41 PM
You could go a step higher for the EX-106, which will cap out at above 2000oz-in of torque. RX-64s are rumored to handle up to 24v at about 1200oz-in.... but I'm not planning on pushing them that far.

The EX-106 is also $500 a servo, $200 more than the RX-64, so based on that I think the RX-64 is a great choice.

Honestly the EX-106 is probably overkill for this, my friends at Farrell Robotics have two 30" tall, 5kg bipeds built out of EX-106s for the leg servos and they don't even push them very high on the voltage... they run them at about 70% their rated voltage and they're still more than enough.

Firestorm65
02-03-2009, 09:45 PM
What about the next step down? Or is the 64 the best fit for 5 kg?

DresnerRobotics
02-03-2009, 10:22 PM
Definitely 64s for anything past 3kg.

RX-28s would work for a high end lightweight.

Firestorm65
02-03-2009, 11:12 PM
Are speeds noticeably slower when the servos bear a load?

DresnerRobotics
02-03-2009, 11:26 PM
Not from what I've seen. These are very capable servos.

DresnerRobotics
02-04-2009, 01:31 PM
Here's a post on my custom RX-64 brackets, with links to download the Inventor and .DXF files for them:

http://forums.trossenrobotics.com/showthread.php?t=2877

Firestorm65
02-12-2009, 04:02 PM
I have access to some spare dc motors but I don't know if they'll work. Can stepper motors of motors with gearboxes work for the legs? It seems to me like that would be to big/heavy to get the necessary speed and torque.

Adrenalynn
02-12-2009, 04:24 PM
Gearmotors would have to be turned into servos - at additional expense and engineering.

Position dependence is critical.

Steppers would work, but their torque-to-weight tends to be lower than servos.

Firestorm65
02-12-2009, 09:19 PM
Would it make any sense at all to use large motors and use steppers to create a high torque rating? I am concerned about weight, complexity, and size. How would I get six assemblies in a leg for a robot 2-3' tall max?

Adrenalynn
02-12-2009, 10:09 PM
You're thinking about driving the steppers from the motors to create a positional feedback? Interesting idea - I'd never considered using a stepper as an encoder in-and-of itself.