RC Radios, Transmitters, Receivers, Servos, gyros Discussion all about rc radios, transmitters, receivers, servos, etc.

low friction servos

Reply

Old 10-12-2004, 02:51 AM
  #1  
freestyle
Junior Member
Thread Starter
 
Join Date: Sep 2002
Location: Redmond, WA
Posts: 17
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default low friction servos

I've noticed that the Futaba 9252 servos move much more freely than most of the other servos I have, and the Futaba tail rotor servos practically move if you blow on them. I'm about to start a robotics project where this 'low friction' aspect could be really helpful. Does anyone out there have first-hand experience with Futaba's lower-end digital servos, like the 3050 and 3151, who can let me know if they have the same low friction aspect as the 9252s? Or can anyone recommend a relatively inexpensive servo that moves equally freely?

Thanks!
freestyle is offline  
Reply With Quote
Old 10-13-2004, 10:34 AM
  #2  
PlaneKrazee
My Feedback: (14)
 
PlaneKrazee's Avatar
 
Join Date: May 2002
Location: Gales Ferry, CT
Posts: 4,878
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: low friction servos

Coreless plastic gear servos move more freely in general. 9202's are good depending on the load.
PlaneKrazee is offline  
Reply With Quote
Old 10-14-2004, 01:59 AM
  #3  
freestyle
Junior Member
Thread Starter
 
Join Date: Sep 2002
Location: Redmond, WA
Posts: 17
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: low friction servos

I just spent a few minutes wiggling 9202 and 9252 servos (nothing attached other than X-style horns) and the 9252s definitely move more freely than the 9202s. I think the torque of the 3050 or 3151 would be enough though, and I'm going to buy four so the price difference adds up... So I'm hoping those move at least as freely as the 9252. Does anyone have some side-by-side that they can compare and let me know?

Thanks...
freestyle is offline  
Reply With Quote
Old 10-20-2004, 08:29 PM
  #4  
Ernie Misner
 
Ernie Misner's Avatar
 
Join Date: Jul 2002
Location: Tacoma, WA
Posts: 5,037
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: low friction servos

Hi Freestyle,

Moving freely (by hand).... I do not think this has any direct bearing on servo operation or friction while operating in flight. It is nice to be able to move them freely when setting up linkages though. At least that has been my experience.

Was it a lack of friction while operating that you liked about the fee moving?

Ernie
Ernie Misner is offline  
Reply With Quote
Old 10-21-2004, 01:05 AM
  #5  
freestyle
Junior Member
Thread Starter
 
Join Date: Sep 2002
Location: Redmond, WA
Posts: 17
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: low friction servos

I agree that this isn't significant for flight. But like I said above, I'm embarking on a robotics project... I'm going to rip out the servo's electronics and hook my own circuit up to read the pot and drive motor (using my own feedback loop) because in this case, unlike with my cars and helis, I want the servo to deflect under small loads. That's the key thing. It will be acting as a sensor as well as an actuator... it's kind of a long story.

But in order for this to work I need a servo that moves easily when not powered. I could use 9252s, but since I need four servos I'm hoping that the 3050 will work as well - they're about $30 cheaper so the total cost is about $120 less... if they actually do most as freely as the 9252. I just cant get my hands on one, and I don't want to blow $50+ for one servo only to find out it actually has tons of resistance, so I'm hoping to hear from someone who has first-hand experience with them.
freestyle is offline  
Reply With Quote
Old 10-22-2004, 02:13 AM
  #6  
Ernie Misner
 
Ernie Misner's Avatar
 
Join Date: Jul 2002
Location: Tacoma, WA
Posts: 5,037
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: low friction servos

Ahhh, makes sense. Have you asked the people at HiTec or posted in the manufacturer's forum?

Ernie
Ernie Misner is offline  
Reply With Quote
Old 10-22-2004, 02:58 AM
  #7  
freestyle
Junior Member
Thread Starter
 
Join Date: Sep 2002
Location: Redmond, WA
Posts: 17
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: low friction servos

I bought a few Hitec servos to experiment with (two each of HS645 & HS5645) and they have a LOT of resistance so I haven't really given them much thought. I was hoping that all digital servos would move as freely as my Futaba digitals, but the Hitec 5645 blew away that theory. I will use those servos for other stuff so it's no big dea - the money wasn't wasted - but I'm hoping to learn about Futaba's S3050 without opening my wallet. :-) I never thought of this kind of thing as significant until now, but of all the servos I have in my cars and helis, the Futaba digitals really stand out in how freely they move. I only have 9252, 9250, and 9251 though so I'm not sure if the 3050 will be similar or not.

I just got the attention of the Futaba rep in that forum so I'm hoping for a response from him soon.
freestyle is offline  
Reply With Quote
Old 10-22-2004, 05:20 AM
  #8  
Geistware
Senior Member
My Feedback: (16)
 
Join Date: Apr 2002
Location: Locust Grove, GA
Posts: 12,942
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: low friction servos

Freestyle, what you may want to do is use a current sensing circuit so as loads are applied, the servo will have to supply current to offset this load, so then by sensing the force applied, you can determine if the amps response (your amp) is linear or not.
Geistware is offline  
Reply With Quote
Old 10-22-2004, 05:58 AM
  #9  
ZAGNUT
Senior Member
My Feedback: (1)
 
ZAGNUT's Avatar
 
Join Date: Feb 2003
Location: tel-aviv, ISRAEL
Posts: 2,635
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: low friction servos

seems to me that a coreless high speed servo would offer the least resistance when moved by hand.

a high torque servo gets a lot of it's power from a very high gear ratio and would be harder to move.

and why use a digital servo if you're going to toss the electronics?


dave
ZAGNUT is offline  
Reply With Quote
Old 10-22-2004, 09:52 AM
  #10  
jimjel
Junior Member
 
Join Date: Mar 2004
Location: Sarasota, FL
Posts: 27
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: low friction servos

Take a look at the Futaba 9101. Very free running, coreless, non-digital servo.

Jim
jimjel is offline  
Reply With Quote
Old 10-22-2004, 10:56 PM
  #11  
freestyle
Junior Member
Thread Starter
 
Join Date: Sep 2002
Location: Redmond, WA
Posts: 17
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: low friction servos

Geistware: sensing current will tell me how hard the servo is working, but not which direction it's pulling. That's only half the information I need.

Zagnut: you're right about faster servos moving more easily the strong servos. Futaba's heli tail rotor servos are all speed and no torque, and as I mentioned above, they move VERY freely. They cost a lot though. I am curious about the S3050 specifically because it's relatively inexpensive.

And to answer your second question, I would in fact be equally happy starting with an analog servo because I'm going to rip the circuit out and give it a digital feedback loop of my own anyhow. I'm not picky about the servo being digital, it's just that, of the many servos I have experience with, the servos that move the most freely are Futaba's digital servos. So, again I'd like to know how the S3050 compares to the 9202, 9252, 9250, and 9251 in this regard (in order of desirability).

Jimjel: thanks for the recommendation. When you say it's free running, what servos are you comparing it to? Do you know if it compares favorably to a 9202, or 9252, for example?

(Random observation: the 3050 is cheaper, stronger, faster, and digital so I wonder how long the 9101 will be in production.)
freestyle is offline  
Reply With Quote
Old 10-23-2004, 07:08 PM
  #12  
dirtybird
My Feedback: (5)
 
Join Date: Jan 2002
Location: San Tan Valley, AZ
Posts: 5,768
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: low friction servos

I think the 3050 servo is cheaper because it is a three pole motor servo. If so it will not move as freely as a coreless motor servo. There should be no difference between a digital or non digital coreless servo. There may be some resistance loading the servo motor when there is no applied voltage. If so when you try to turn the servo motor manually the motor acts as a generator that is loaded by the resistance. You have to remove the electronics to be sure.
BTW most Futaba servos mount the motor directly on the electronic circuit board. It makes it hard to remove the electronics and still have a mount for the motor.
dirtybird is offline  
Reply With Quote
Old 10-24-2004, 12:10 AM
  #13  
Ernie Misner
 
Ernie Misner's Avatar
 
Join Date: Jul 2002
Location: Tacoma, WA
Posts: 5,037
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: low friction servos

Similar servos with different speeds are going to turn differently, by hand, because of the different gear ratios. The slower servo with more torque is bound to turn harder by hand.

Ernie
Ernie Misner is offline  
Reply With Quote
Old 10-24-2004, 02:27 PM
  #14  
freestyle
Junior Member
Thread Starter
 
Join Date: Sep 2002
Location: Redmond, WA
Posts: 17
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: low friction servos

Ernie: but how do you know which servos have the same motors inside? It seems to me there's too many other variables at work for that rule of thumb (which I agree is based on a sound principle) to actually be useful.

Dirtybird: You're right that the 3050 uses a cored motor - so maybe it's not going to be suitable. But that's why I'm asking. I'm hoping for an anwer based on experience rather than theory (no offense - I do appreciate your trying to help). The problem with theories is that they don't always take into account all of the variables at work. For example you say that there SHOULD be no difference between digital and non-digital coreless servos in this regard, but as I mentioned earlier, my 9252s move considerably more freely than my 9202s, and both are coreless. The 9252 is both faster AND stronger than the 9202, so both the gearing and the motor are probably different, as well as other design variables that affect damping. So while theories are interesting they don't give me the confidence I need to my wallet and plunk down a couple hundred bucks for some servos.

Does anyone actually have a 3050 they can experiment with?
freestyle is offline  
Reply With Quote
Old 10-25-2004, 02:01 AM
  #15  
Ernie Misner
 
Ernie Misner's Avatar
 
Join Date: Jul 2002
Location: Tacoma, WA
Posts: 5,037
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: low friction servos

Good point.... hard to tell if the motors are exactly the same. Sometimes we get good clues that they are though, when the servos have similar numbers, weight, price, etc., but one servo will have slightly more torque but less speed than the other. The replacement gear set will be a little different. You guys sure are right about radical differences in some though!

Ernie
Ernie Misner is offline  
Reply With Quote
Old 10-25-2004, 12:56 PM
  #16  
dirtybird
My Feedback: (5)
 
Join Date: Jan 2002
Location: San Tan Valley, AZ
Posts: 5,768
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: low friction servos

If you don't believe in theory I am afraid you will have to plunk down your money and try it yourself.
dirtybird is offline  
Reply With Quote
Old 10-26-2004, 12:52 AM
  #17  
freestyle
Junior Member
Thread Starter
 
Join Date: Sep 2002
Location: Redmond, WA
Posts: 17
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: low friction servos

Dang dirtybird... it's not that I "don't believe in theory..." Except the theory about there being no difference between digital vs non digital coreless servos. I have the counterexamples to that theory sitting in front of me. Theories are helpful, but when they don't agree with experience they can't be taken very seriously.

I came here hoping that someone's first-hand experience could save me some buyer's remorse. And I'm still hoping! But I guess the 3050 is too new and/or too unpopular for many people to know about them.

How about Hitec 925s? Anyone here have those? How do they compare to other servos? They're fast and coreless, which is encouraging...

Thanks all....
freestyle is offline  
Reply With Quote
Old 11-26-2004, 01:02 AM
  #18  
freestyle
Junior Member
Thread Starter
 
Join Date: Sep 2002
Location: Redmond, WA
Posts: 17
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: low friction servos

FWIW, I bought some 925s to experiment with. They're Hitec's fast coreless analog servo. They move more freely than the 645s (torquey and cored) but nowhere near as freely as the 9252s.
freestyle is offline  
Reply With Quote
Old 11-27-2004, 02:06 PM
  #19  
Ernie Misner
 
Ernie Misner's Avatar
 
Join Date: Jul 2002
Location: Tacoma, WA
Posts: 5,037
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: low friction servos

Does moving "freely" by hand (backwards compared to the motion coming from the motor end) mean anything besides it has a different motor and gear ratio, in other words, less losses due to friction when in operation?

Just curious,

Ernie
Ernie Misner is offline  
Reply With Quote

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service