# Tag Info

8

Raspberry Pi has only one hardware PWM channel and Linux distribution it runs is not a real time system, so software PWM may be very unstable. You are not guaranteed, that your program will be executed at exact frequency you want, so you will have trouble getting precise timing required to drive servos. If you already have Arduino Mega and SSC-32, I would ...

6

In short, what you are trying to do is well beyond the capabilities of top robotics research labs. That said, here is a short list of general areas you need to look into: Robotic arm dynamics (to swing the racket) Vision processing to track the shuttle Shuttle dynamics to predict shuttle path (this is not well studying so you would most likely have to ...

6

Let's try and clear things up a little bit... "RC Servo" motors These can be found in radio controlled cars and airplanes to e.g. turn the wheel or actuate various controls in the airplane. They are pretty cheap brushed DC motors, with gears and some sort of crude feedback mechanism. They typically convert an input voltage into a position within a given ...

6

Brushed motors are easier for servo systems, but are not better. Many high end servo systems are brushless/AC. It is possible to control the motors at low speeds with only 3 hall sensors. You really don't want trapezoidal commutation, especially at low speeds so could add an encoder or estimate the rotor position if necessary. It is possible to estimate ...

4

The servo.write(angle) function is designed to accept angles from 0 to 180. (The value 180 is significantly larger than 100). Could you tell me where in the Servo documentation you read "100 (motor at full power)", so we can fix that typo? Please change the line int maxspeed=100; /* wrong */ to int maxspeed=180; Also, please run servo.refresh() ...

4

Your code uses the typical servo.attach(pin) where you can use the overload of servo.attach(pin, min, max) to set the min and max microseconds of the pulse width to match the desired ranges for you ESC. Additionally to make it a bit more clear where myservo.write(90); is used to set the angle, you can use myservo.writeMicroseconds(1500); to set the duration ...

4

In industry, there is a strong preference for low maintenance brush-less motors over relatively high maintenance brushed motors. While the former may me more expensive in terms of the motor itself and the drive electronics, the reduction in the term long cost of maintenance usually out weighs the extra capital cost. As user65 suggests, you may need ...

4

You need a controller like this that can address them individually over I2C. These can be chained together to control more than you'll likely ever need: Adafruit 16-Channel 12-bit PWM/Servo Driver - I2C interface - PCA9685 https://www.adafruit.com/products/815 How to use them with a Raspberry Pi: https://learn.adafruit.com/adafruit-16-channel-servo-driver-...

4

This is going to depend on the style of motor in the servo and the style of gearbox. If the servo can't be back-driven when unpowered, then it's likely some form of a worm gear assembly that will prevent static force transmission back to the motor. This means that you won't be able to tell weight by current draw for holding position because the holding ...

4

The Boston Dynamics’ Atlas robot doesn't actually use servo motors. It uses electrically-powered hydraulic actuation. I saw a presentation by Boston Dynamics' Marc Raibert where (if I remember correctly) he said they used to use Moog actuators designed for the aerospace industry, but that they were now using a motor that they build in-house that is ...

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

If your computed torques are out of the range for your robot, then you are no longer modelling your robot but a different one. You can ignore the torque limits as good as the joint angle limits of your robot (i.e. not at all). If the required torque is to high, your robot will either be much slower (if you are lucky) or won't be able to reach its goal ...

3

Search aliexpress for '6V switching power supply'. You should find 5Amp or 10Amp ones for $10-$20. Silver boxes with holes in them. You can find them on ebay as well (usually the same chinese vendors as aliexpress). You will need to add your own AC plug. Keep in mind that you will probably not be using 12Amps because not all motors will be at full torque ...

3

Going forward, a Klann linkage has a near-vertical leg drop action. (See the legs at left in the wikipedia animated GIF.) It has a near-vertical leg lift action if running in reverse. (See the legs at right in the illustration.) Note, this linkage and some other leg mechanism linkages use a rotary crank; ie, rather than using a 180° back-and-forth motor, ...

3

What you're asking for cannot be accomplished with a PID controller. As I understand your question, you want to be able to choose PID gains that would always produce a "good" trajectory, without tuning. You said it's alright if the motor output is unrealistic, i.e. the motors are "very strong" therefore can produce unlimited torque. However, you cannot ...

3

I have been working on upgrading an autonomous robot as part of a university project for the past year. As part of my work I have been switching the old skid steering system to a new active steering one, so have some experience with both methods. Steering accuracy Skid steering: Fairly good, need to use a PID loop to keep an accurate heading using a compass....

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 ...

2

Not servos explicitly, but I've obtained low end nema 17 stepper motors on occasion from electronic typewriters at goodwill. The typewriters I've seen there usually have 1 such motor in them (in addition to some other neat pin mount components) and fetch for $1 each. In my case the only other source for parts is radio shack and online outlets, so for me it's ... 2 A servo is not a basic motor - it's a motor plus some means to control its position. If you want DC motors. A small servo costs around £1.75/$2 new for 1-10 quantities. Servos have three wires going to them - ground, power, and a pulse width modulation signal to control them, which is fairly easy to generate with a microcontroller. Plain DC motors are ...

2

While some people scavenge even for cheap parts, I do not do that, simply because it will cost you more than just ordering the exact thing you need and knowing it is working. Don't forget that you probably have some specific requirements, i.e. the servo must be of some size, have some torque and so on... Majority of toys (if not all of them) you will find ...

2

First a little warning: This answer is one big AFAIK. I have some limited experience with RC electronics and don't know anything about industrial servos, and other simillar stuff :-) BLDC motors (just motors) don't have any kind of RPM feedback, they are just three sets of coils and a bunch of magnets. The electronics that drives them can do some magic, ...

2

It's python but easy to install: https://learn.adafruit.com/setting-up-io-python-library-on-beaglebone-black/pwm. Otherwise you can fopen files in the device tree and write to them, or you can open /dev/mem and directly access the registers for the PWM drivers. I strongly recommend using the first method it is far easier than the third and basically the ...

2

Since you didn't state your accuracy requirements in terms of degrees, I assume you want it to be accurate enough to the eye. Pretty much any RC servo motor will do the job. These can easily support a few grams weight. All you need to do is provide it with the control signal to tell it which angles to go to, and the simplest way to do that is with ...

2

A series elastic actuator is really just a motor/gearbox with passive compliance built in (hence the spring). A google search finds http://ihmc.us/groups/sea/ (with links to some specs and information) and an older thesis, http://groups.csail.mit.edu/lbr/hrg/1995/mattw_ms_thesis.pdf So the motors & gearboxes you use will still have to be pretty high in ...

2

A machinedesign.com article, “Exclusive interview: Gill Pratt on how compliant actuators revolutionized robotics”, includes a close-up picture of an SEA (series elastic actuator) mechanism developed by a robotics research group at Vrije in Brussels, and a picture of a Baxter arm, captioned “In the larger red circle is one of Baxter's many compliant ...

2

The linkages suggested by jwpat7 are great, and I would probably prefer to use something like that. But, if you want something really simple, then you might be able to get away with a four-bar linkage like this type of thing. Although it does depend on continuous rotation, so maybe not appropriate for your application. With a servo-motor that rotates back-...

2

Automotive style steering can actually be simple. The conventional car has just one motor that powers two rear non-steering wheels through a differential. The differential solves the problem of how to compute a speed for each wheel. The front wheels are not powered so we don't have to compute their speed. Ackerman Steering moves the front wheels so that ...

2

This type of question "how much torque does my robot arm need" has been answered many times on this site: Simple equation to calculate needed motor torque Design and construction of universal robotic arm (5kg, 1m) Getting started with robotic arm design Choice of a motor for robotic arm The equation for torque is pretty simple. It is just force times ...

2

I assume that all the servos are identical, so it is enough to measure only one, and multiply the result by 9. The best would be if you could use a lab bench variable power supply, like this. With one of these you do not even need a multimeter as these power supplies are able to measure the current they are sourcing. You simply just need to connect the "+" ...

2

No. If there is no {installation, electrical, maintenance, etc} manual/description etc. (and maybe add also quality certificate also here) it is not fair to assume anything. Buying something without knowing its characteristics and placing it under current is a fire hazard, therefore it is not safe to assume characteristics! Guessing characteristics form ...

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