How to evaluate a servo spec

[Polaris]

hi all,

 may i ask how to evaluate the spec for servo, there are too many of them am not sure what i am looking for in a servo, as i just something simple and will like to modify for continuous motion. does a cheap of the range will do???

Hitec Hs 422
Torque at 4.8/6 V(kg/cm) - 3.3/4.1
Speed at 4.8v - 0.20sec
Bearing - Dual Oilite
Dimensions(HxWxL) - 41x20x38
weight - 45.5g

[dunk]

hi Polaris,
so servos are designed to be fairly similar to each other.
the idea being you can use different manufacturer's servos on different radio controll receivers.

if you do a quick search:
http://www.google.com/search?sourceid=navclient-ff&ie=UTF-8&rls=GGGL,GGGL:2006-34,GGGL:en&q=hacking+servo+Hitec++Hs+422
the 2nd link:
http://www.alsrobotics.co.uk/servohack.html

There are many types of servo but I believe (and I know!) the best for modification is the hitec HS-422 servos. These offer a substantial amount of torque....etc

so, yes, i'd say these would be a safe bet.

dunk.

[Polaris]

Thanks dunk!  , my concern is paying for high price for servo performance that i do not need right now for a simple robot. Another concern is hacking of the servos may differ from one servo to another. any recommendation for the type of servo for 1st time robotist?

[dunk]

so the only problem i have ever had with servos was using a few very cheep ones that had a maximum voltage rating of 4.8V.
i didn't realise until i'd allready damaged them with 5Volts.

but as far as the mechanical modifying of them goes, any i have opened (maybe 3 or 4 different types) have been of a very similar design.
there is usually a plastic tag that you have to cut off so the servo can rotate all the way round and you have to remove/cut/enlarge something so the potentiometer doesn't turn with the rest of the mechanism.
i'd say you are 90% likley to get one you can modify in this way if you buy the first one you see.

i'm afraid i can't remember the make/model of any i have modified. (the only ones i have near me just now are unbranded.)
there are a lot of articles on the net on servo hacking. try searching for what others have used.

or maybe someone on this forum can remember what servos they modified in the past...?

dunk.

[Admin]

Ive modified like every servo in existence . . . ok maybe like 8 different types, for a total of like 40 servos . . .

Anyway, they are all basically the same. All major brand servos today are designed to be modified, except for maybe the micro servos . . .

The hardest servos to modify are the ones with metal gears, because the metal pin is damn hard to remove without damaging the gear . . .

and just in case you havnt seen this:
http://www.societyofrobots.com/actuators_modifyservo.shtml
I tried to write that tutorial so that it is useful for any type of servo . . .

[Polaris]

Ive modified like every servo in existence . . . ok maybe like 8 different types, for a total of like 40 servos . . .

Anyway, they are all basically the same. All major brand servos today are designed to be modified, except for maybe the micro servos . . .

The hardest servos to modify are the ones with metal gears, because the metal pin is damn hard to remove without damaging the gear . . .

and just in case you havnt seen this:
http://www.societyofrobots.com/actuators_modifyservo.shtml
I tried to write that tutorial so that it is useful for any type of servo . . .

Thanks for the advice, the tutorial is definitely come into handy as i will be "surgically" opening up my newly bought HS-422 servo.    Btw, it is really true that we don't need any interfacing electronics such as motor controller/driver for servo? i infer that we can plug our servo's control signal line straight into our microcontroller's port?  Btw how do we connect the servo cable to our processor and power line? sorri for this dumb question, but i infer that we are supposed to get a male connector which have three pins and from there we connect each of the pin to the respective points?

i think i will use a seperate power source for the servo and microCtrler as the former draws more current and to isolate both circuit. Am thinking to put a power regulator for the servo to regulate the power supply to the servo.

[dunk]

so i always solder some 3 "header pins" onto my stripboard for each servo.
servo connectors have the same standard 2.54 millimeter pin spacing as most standard through hole electronic components so you can just push these pins into your plugblock (or whatever you are using for prototyping).

some pictures of header pins:
http://www.unicornelectronics.com/Connectors/cohp10.html
http://www.packetradio.com/cgi-bin/shopper.cgi?preadd=action&key=HEDR40
http://www.hebeiltd.com.cn/?p=pin.header.connector

using a separate power source is definitely a good thing to do if you plan on connecting a few servos.
just remember to connect all the negative terminals of any power supplies you use together.

hope this helps!

dunk.

[Admin]

Btw, it is really true that we don't need any interfacing electronics such as motor controller/driver for servo?

Yeap. Its why I use them so often, and highly recommend them to beginners 

i infer that we can plug our servo's control signal line straight into our microcontroller's port?

Yeap, use a digital output port.

[Dosbomber]

Interesting write-up on modifying a servo.  Sort of a mechanical jury-rig to override the pot's signal.

Another way, is to remove the pot entirely, and replace it with a pair of identical resistors, wired in similar fashion as a pot.  It might be a little more complicated the first time, but it accomplishes the same task and might be necessary if your servo is a different design (either way works with the Futaba S3004 shown in your write-up).  I'm not sure I'd trust some Krazy Glue on the pot shaft.