358/360º Servo

Have you ever had a time where 100º isn’t enough? Ever wished you could have a complete turn servo?

I sure wish I could have one. There are plenty of times when i want full turn capability, but using a motor won’t work- I want it to stop at a certain place. I have no room to add limit switches either.

So, do you like the idea?

yeah, i don’t see why not! one thing that would be cool though is a servo that has a dial (like on an engine carborator) that you can change the limit of rotation.

that would be sweet!
or maybe a virtual programmable dial.

This may be possible if you modify the gears inside to only start turning the potentiometer at 260 degrees in so it will stop 100 degrees later at 360 degrees.

I made a mod video to make it fully rotational on youtube, just look up vex motor mod. There is a part inside that catches the potentiometer that needs to be modified.

i watched your video(if you are Halo2maniaccc) and i don’t think you are getting the point. bloodesheddragon means a servo that will spin 360 degrees and stop, like a servo. yours only keeps spinning, so you basically made a continuous rotation motor.

yah, I know its possible to turns servos into motors, but i want a servo that stops at 180º both ways. For example, lets say you were mounting a camera to turn all the way around the robot. For some reason you need it autonomous.

Sure, you could use a motor, but you wouldn’t be able to get to stop at a specific spot.

You could gear a servo to have 3.6% more degree variations, but that wouldn’t be accurate.

What a close to 360º servo would do would be to make you able to go in a full circle but stop at a specified point.

I know what he wants but I didn’t explain it clearly enough I guess. I meant that the white piece in the motor the attaches the big black gear and the potentiometer could be modded to spin 180 degrees in each direction not a continuous rotation. The white piece would be detached from the black gear until it rotated 120 degrees at which point a nub would catch the white piece and start to rotate it, essentially you a deceiving the servo. It thinks that its only rotated 60 degrees when in fact its rotated 180 degrees. Thats basically how my continuous rotation mod works.

Although I think it would just be a lot easier if vex offered differnt rotations, say 90, 180, 270, and 360 degrees. It can’t be to hard I mean its not like they would have to go with a whole new motor they could just change the potentiometer for one that can be rotated 360 degrees and the software on the speed controller to accept a 360 degree rotation instead of 120 degrees.

Oh, I understand what you mean.
Your idea would work but not with much accuracy, but its temporarily good.

It would work if the channel in the gear was cut perfectly but unless a machine did it there will be imperfections such as bumps and the white parts may turn at random intervals so it would not have much accuracy.

Once again, it would be so much easier if vex made the servos that way you know that they will work good.

I really want to be able to control the motion say it was a 120 degree servo I want to be able to spin 40 degrees and stop but the vex servo is just to fast for that.

I also want to be able to retrieve the resistance from the potentiometer in the servo that way you could tell its position just like the vex potentiometer kit.

that WOULD be sweet,
again the topic of built in motor sensors comes about.

I could probably mod a servo to do that. Remember the potentiometer is built in so all you have to do is strip a pwm cable and soleder the three wires to the circuit inside.

I don’t really have a need to do this but it would be awesome to try but then again you could destroy your motor

What you need is a Stepper Motor. A wider Servo would be nice too.

stepper motors are magnetized, dunno if it would throw something off like lets say the magbots

Stepper motors usually require lots of I/O and lots of current. It would be cool if IFI implemented a stepper motor controller that interfaces over SPI or PWM so you don’t have to write all the detail code to make the stepper motor turn.

This Allegro stepper motor chip would be an easy PWM method (it only goes to 600mA),

Allegro has many other options as well,

There’s a name for a vex 360 degree servo. It’s motor module. a regular motor and servo from vex are the same thing other than the fact that the servo has a plastic stop

you aren’t getting the point. vex motors are continous rotation. servos are programmed to stop at certain degrees on the servo. a vex motor doesn’t stop at a certain point, it continously rotates at different speeds.

The Vex Servos “maps” a given PWM output from the Vex Controller to a Position in the rotation of the Servo. This is based on a feedback device in the Servo. I would have to guess that the reason the Servo is not able to rotate more that 120 Degrees, is because of that feedback mechanism. It could also be based on the PWM value and the Rotational Movement of the Servo Motor.

A “stepper motor” is not Better or Worse, just different. Each Pulse to the Stepper Motor moves it a given number of Degrees ( Radians ) of Rotation. This is something that CAN NOT be done with a regular Motor, without the help of a VEX Optical Shaft Encoder or if 360 Degree rotation is not needed, a VEX Potentiometer.

My point is that it may be possible to convert a normal servo yourself

Why not just buy a 360degree servo and adapt it to your Vex robot?

Allegro has many other options as well,

The Allegro UDN2954W and Freescale L293, L297, L298N stepper motor chips work great! I have used them for my robotics applications. Another IC that works very well and is easy to use is the UNC 5804B translator.

For those of you just starting out using Stepper Motors, I recommend the 5804B or the equivalent EDE 1200 for uni-polar stepper motors or the EDE1204 for bi-polar stepper motors. These ICs generate the drive formats, wave-drive (one-phase), two-phase, and half-step, full-step waveforms for clockwise (CW) and counter clockwise (CCW) directions and some of the more advanced ICs can generate micro-stepping waveforms.

The simplest stepper being the full-step but when used with a high resolution stepper motor, it can provide 0-360 degree coverage needed for most Vex and Vexplorer applications.

Allegro and Freescale also manufacture high power DC Motor Drivers H-Bridges used in electric drills and other power tools. My favorite PWM DC Motor Controller Driver is the National Semiconductor LMD18200T

Acroname, Jameco and Digikey, Pololu and Parallax also sells low cost Stepper Motor IC drivers and driver boards that are easy to use.