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Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Does anyone know if the micro servos move the standard rotation of about 180 degrees? Im looking at the Hobby King webpages, especially this one ->
Ive tried this site too ->
The spec i need is called "rotational range".
Ive done some research, but havent found anything on the web that seems reliable. I see the 0.07 sec per 60 degrees, but nothing on the total rotation possible.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
Most servoes will only do limited rotation. As they are expected to work with a crank arm, it's pointless to have more than 90 degrees total.
However, you can get servoes specified for more rotation, if you look hard enough.
You can get servoes with infinite rotation - available for model yatchs for winding in the sails - the command sets the speed rather than the position.
And you can buy standard servoes and hack the feedback potentiometer. Once you have removed the mechanical stops (if any) you can "pot down" the pot so that more rotation is required to match the command input. Most use standard pots which actually have 270 degrees of rotation, but only use 60 to 90 degrees of that range.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Dr. Slack wrote ...
Most servoes will only do limited rotation. As they are expected to work with a crank arm, it's pointless to have more than 90 degrees total.
However, you can get servoes specified for more rotation, if you look hard enough.
You can get servoes with infinite rotation - available for model yatchs for winding in the sails - the command sets the speed rather than the position.
And you can buy standard servoes and hack the feedback potentiometer. Once you have removed the mechanical stops (if any) you can "pot down" the pot so that more rotation is required to match the command input. Most use standard pots which actually have 270 degrees of rotation, but only use 60 to 90 degrees of that range.
I only really did the RC super-fast car stuff in the mid 90's, and only some RC flight stuff back then. I thought that 160 or 170 degrees was a standard but maybe not, i definately like the HXT500 ill be using that for sure, many users say it has lower deadband and no slop then the other cheaper ones.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
I am working on a way to use those small mini fans used on many laptops as a bidirectional servo.
It seems that if you reverse the signals to the Hall sensor the fan spins in reverse, BUT you need to pulse one input to +V to get the fan to start.
Putting a PIC 12x between the fan drives and Hall outputs would allow this to work well, and any compatible fan can be hacked to do this.
The software ought to be easy, just High Z the outputs to stop the motor and drop current to low levels, and periodically pulse it to maintain relative position.
Use a simple toothed gear set from a dead analogue clock (cheap from charity shops) and voila.
Even count number of pulses seen in each direction so you can not only do +/- 180 degrees but speed control and continuous rotation with the same servo.
Control servo using MCLR with the relative pulse width determining the position. If you have it set up so pulses outside the normal range are interpreted as 0-full speed and 0+full speed then the same line can be used for wakeup AND position control.
Use a pulse counter to set the speed to a linear factor of pulse width on MCLR, possibly also have a built-in limit switch derived from a laser mechanism magnet glued to the smaller wheel so it has auto-home functionality.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
I guess ill have to buy one and see.
HS-55 HiTec sub micro servo, Got it! I'd like to get the HXT-500 too, but going too cheap seems scary. So ill stay away from the $3 ones.
pics
Looks like 190 or 200 degrees to me!
Showing the rotation of the red tip. does anyone have this type? does anyone disagree?
EDIT:Yep, a little more than 180 degrees of rotation, ive got it running right now off a function generator and o-scope, 2.5ms full right, 1.5 is about centered, .8-1.0ms seems to be full left.
Registered Member #618
Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628
Sounts about right since 90-99% of hobby receiver parts be it a servo, a ESC or what ever runs from1-2 or in your case 1.5-2.5mS on time with 2mS being rougly center for your servo's, but see I told you that almost all servos rotate 180 degrees or so. :p
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Micro RC servos for robotic device.
