33
They aren't. The word servo refers solely to a device that uses negative feedback for control.
Gearboxes or cheap brushed motors can be noisy. You can get very quiet systems if you are willing to pay for it.
Cheap hobby grade servos can sometimes chatter if they do not settle in a stable state. This is normal and is caused by poor tuning, a lack of a ...
18
In theory, you're correct. But in practice, slight differences between the two motors will make them fight each other instead of working in perfect harmony:
Even the smallest mismatch in wire tolerances, lengths etc. will create
different back emf characteristics due to different impedances.
So both will work separately, but the actual ...
13
What you're asking isn't going to be very easy with a standard RC servo.
What you're asking for is a back-drivable servo. I.E. one which you can freely rotate by applying an external torque. It is certainly possible to create these, and they are used on many robots, but most RC servos require considerable torque to back drive them. I would call them semi-...
11
What Ians answer says about the two motors fighting is true however, I wouldn't go as far to say that you can never put two motors together for more power. In general if the two motors are identical and you are hooking them up and controlling them identically then you can probably get away with it but I would expect some wasted energy and thus extra heat ...
11
In a nutshell, servo motors and stepper motors are not technically the same things. The link you posted is only for servos and not stepper motors. A servo motor assembly does not rotate freely like a DC motor. The rotation angles are usually limited, and every servo has a "lock" position where it stays by default. A positive pulse makes it move clockwise, ...
7
Take a look at a kids "spincast" fishing reel and rod.
We built one in 2008 (still works, rain, snow and all!) using a automobile door lock solenoid to operate the "thumb release" and an automobile power window motor (PWM & MOSFET) via rubber hose driveline to operate the retract. Choice of MCU is yours, but we've since added spooky lights, MP3 with ...
7
Interesting question.
The first option I'd investigate would be cutting the power as you suggested (perhaps control a MOSFET in software to switch the power).
Another more complicated approach might be to monitor the current consumption of the servo to detect when it is under a heavy load. When you want to go into "free running" mode, have your software ...
5
Usually, these types of hobby servos are not made for continuous rotation, and will often include a mechanical stop. Beware, what I outline below is a surefire way to never get actual closed-loop operation, but will instead make the servo continuous-only.
Most of the time, you can do a quick search online for "Continuous modification for x servo", but I ...
5
Whether a motor can spin continuously depends how is is constrained by other parts of the system.
An rc servo like the MG995 will typically have a motor, a gearbox and a limited travel potentiometer to provide position feedback. It is this final component which prevents the rc-servo from rotating continuously. In the case of the MG995, it can apparently be ...
5
There are 2 (or 3, depending on how the planned lifetime of the robot is) thing thats you have to consider.
Static load:
The motors stall (zero revolution) torques have to be able to hold the weight in the robots most unfavorable pose (usually the arm stretched out). You can determine this by static modelling, that involves only an equilibrium of forces for ...
4
I have worked with quite a few servos (Industrial and RC) and from my experience they don't come with a limit switch that actually takes the current off the motor when they hit a limit. They are however limited in rotation by the PWM signal you send them and are as such limited to a rotation safe area.
It does become a bit more complicated when you link ...
4
Put some value on your time and on system reliability. You're increasing design time & failure points with this approach. Good small gear motors are pretty cheap to start with, it's a lot more valuable to have a working robot that's reliable than a broken or unfinished robot on the shelf.
3
If you want to detect how tall your target is and tailor the drop height to suit, then you are going to need more precise sensors and control than the other (excellent) answers here.
One option might be to use a Sonar Range Finder as suggested in this answer to What is the cheapest / easiest way of detecting a person? (Thanks Ian)
Basic idea
While the SRF ...
3
Holding torque, by the stepper motor definition, is not a valid way to quantify servo performance. Stepper motor torque drops off with speed whereas in a servo it remains relatively constant. (Operating torque is never half of holding torque and is RPM dependent, your guide lied to you).
A real servo will always have a torque (continuous/operating) rating ...
3
I'm guessing you're using the arduino libraries (haven't used the Teensy), in which case, if you read through the documentation (http://arduino.cc/en/Reference/Servo), you'll see that the Arduino servo library
Supports up to 12 motors on most Arduino boards and 48 on the Arduino Mega
You can manually bitbang the pwm signals for your servo if you don't ...
3
According to the Arduino reference for Servo.attach( ), you should be using pins 9 and 10, not 0 and 1.
Note that in Arduino 0016 and earlier, the Servo library supports only servos on only two pins: 9 and 10.
Verify that you are setting the proper pin number in code. Specifically, look at these lines in your originally-posted code:
void setup()
{
...
3
I rewrote your program a bit. Not tested since I have no servos.
#include <Servo.h>
Servo ULF; // Upper left front servo
Servo LLF; // Lower left front servo
byte index = 0;
int commandnum=1;
int steps = 0; // position of LLF servo
int partnum = 0; // unused for now
String command = ""; // the command we're building
char in; // ...
3
It is possible to do it. Take a look at this link.
Of course you will not have the encoder possibility with that servo. But you dont have it currently either. You have to solder middle pin from rotary encoder (resistor) and read the value of resistance to determine current position of shaft.
If you need positioning i would suggest DC motor with encoder or ...
3
Digital servos accept the same pulse width and pulse repetition rate as regular analog servos.
a
b
With many RC servos -- both digital and analog -- as long as the "frame rate" (how many times per second the pulse is sent over the control wires to the servo, aka the pulse repetition rate) is in a range of 40 Hz to 200 Hz,
the exact value of the frame rate ...
3
Many (perhaps most) radio control transmitters multiplex all the "RC PWM" channels into a single physical wire, using a system called "RC PPM" (radio-control pulse position modulation).
(a) (b) (c) (d) (e) (f) (g)
Often this "PPM" signal is transferred from the a student's RC transmitter through the buddy box wire to the teacher's RC transmitter.
The "...
3
Unfortunately, with just an IMU there's virtually no way for your quad to know that it's drifting so it can't stop it.
For outdoor flight you can add a GPS to detect the drift. For indoor flight, many people use vision systems to detect the drift. Depending on how close you are to walls, you could also look at ultrasonic range sensors to detect drift.
3
IMUs have accumulating error and can not be a reliable sensors by themselves if you want to measure velocity or even worse, position.
I believe your safest bet would be doing a sensor fusion between an IMU and a vision sensor using feature extraction and Kalman filter. Using only a camera can introduce unpredictable errors specially in featureless ...
3
Though, there is not much information about your servos let's assume that they consume at least 1A each. This value will probably be higher given that you want to move doors and that requires torque.
Now let's see the RPi's capabilities. An answer from Stack Exchange Raspberry Pi, tells you the necessary information and sources about the RPi's power rails ...
3
Servo mechanisms are not the "popular" RC-Servos (not-only). Servo is a closed-loop control, not only for motors. Even Steppers could or not be servo-motors. RC-servos are in major cases a DC brushed motor, with reduction gear and a potentiometer for position feedback, and electronic control.
This is a common RC Servo. The fact that it has no ball bearings ...
3
You got the second picture by physically manipulating the robot to get the center of mass above the rotated foot. What you need to do is to get the robot to shift its own center of mass in a similar fashion.
You should do some research into support polygons. The center of mass of the robot is not above the polygon made by the contact area between the foot ...
3
While originally creating this question I ended up finding an RC servo that can do this.
HiTECH makes an RC servo (HS-785HB) that uses a muti-turn potentiometer rather than a standard rotary potentiometer is its position senor. This allow the servo to rotate 3.5 turns (1260 degrees!!!) while still maintaining positional control. It is pretty slow (almost ...
2
With all you're going to invest in your robot, it's a better idea to start off with a more solid drive train than a servo. Take a look at a DC motor with an integrated gearbox and start from there. Your servo approach won't be as energy efficient, performant, and it won't last as long.
A great reference to start with is Building Robot Drive Trains.
2
Forgive me I seem to get caught up in people looking for answers to a question they didn't ask a few times already. So given this question;
"How do I determine how many amps will be needed from the power supply?"
You can roughly guess it, in your case you say 4 servos drawing an amp each, 4 amps total.
Pick any BEC that will supply greater than 4 amps, ...
2
There's two possible current requirements to consider here.
Ideally, you need to be able to supply enough current to account for the rated stall current (that is, the current drawn by the servo at its maximum rated torque) of all of your servos simultaneously. Imagine a bunch of your mechanical components getting jammed on each other in some gruesome ...
2
Don't, instead get yourself some decent motors and drive them via an h-bridge like you'll find on this motor shield.
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