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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 ...
6
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 ...
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
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
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
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
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
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
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
You might find that the rPI boards are more durable than you expected. There isn't much mass to them, so a small amount of rubber or foam padding (to reduce rattling around) should be sufficient to protect them -- provided that your robots aren't bashing together with enough force to crack the plastic casing around them.
Offloading the processing onto a ...
2
Generally you won't need a servo. The more common way to throttle a flow is to use pneumatic solenoid valves (which are either open or closed) and control them with PWM.
See (for example) this link. This is also how the boost controller in many cars works.
2
Servos are by definition, in the position you told them to go (or in a fault condition). This is the difference between a servo and a stepper. You tell a stepper to move 1 step at a time and do not know if it did or not. A servo on the other hand will continue trying to get to the position you asked. For hobby Servos, you are setting a pulse width / duty ...
2
Multiple channels are time sliced onto "one-wire". The real wire count is usually three. Typically there is a positive voltage wire (may not be there depending on whether both ends have their own power or not) and always a shared ground wire.
Perhaps 40-100 times per second the transmitter broadcast the settings of all controls which map to servos on ...
2
You might be driving the servo beyond its limits. As noted in the pololu.com article “Servo control interface in detail”:
If you keep making the pulses wider or narrower, servos will keep moving farther and farther from neutral until they hit their mechanical limits and possibly destroy themselves. This usually isn’t an issue with RC applications since ...
answered Sep 22 '15 at 16:56
James Waldby - jwpat7
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2
It sounds like you are developing a robotic manipulator from scratch so I also assume you will be writing software for position control too. Both the design and control depend on not only the dynamics but also the kinematics of your robot.
Kinematics cover the relationships between the joint angles and link lengths (each "arm" is referred to as a link) so ...
2
Raspberry Pis can be used for a huge range of things! And I like your idea!
Although, you could use an Arduino Pro Micro board as that has everything you need and doesn't have unnecessary items like Ethernet cables etc... It comes a lot cheaper - £2 here in the UK from Amazon!
Bence Kaulics explains it very clearly and I suggest you use that idea.
My ...
2
You might be able to use the the opposite foot to begin the rotation of your chassis, but it will be dependent on your chassis and foot geometry.
Using your photos for reference, the left foot would push up beginning the chassis rotation, while the right foot would rotate simultaneously. At some point the center-of-gravity (CoG) would shift enough so that ...
2
The attachment of something that's screwed in is not so much the screw, as it is the friction between the material around the screw (the "faying surfaces.")
If you have good friction, and the load/torque isn't higher than the friction, this will work fine.
A drop of super glue can also help this along!
This works with both plastic and metal gears.
Another ...
2
While all sorts of things get used in experiments, screws really intended to tap into plastic have larger more aggressive threads than those intended to go into a pre-tapped hole in a harder material like metal.
Generally speaking, you want the screw's minor diameter (which is to say that of the body between the threads) to fit through the hole, with only ...
2
The problem with most papers about LQR controller is, that they are describing only the half of whole problem. The key aspect of understanding LQR is that an additional "Finite State Machine" (FSM) is used which controls the robot. A good paper which combines LQR with FSM for bipedal locomotion is Bayesian Gait Optimization for Bipedal Locomotion†.
...
2
IMHO it depends on two factors:
if there is gear on the servo (so to motor rotates fast, the result is slow precise motion with high force), then moving it manually even little means to rotate the motor fast, which accumulats resistance araound the all way, multiplied by the gear ratio
if there is some electronics, then it can switch to "braking" state when ...
2
I suspect that you will need a more powerful motor controller. This one is a 10 amp controller, and I suspect that the motors will have a higher stall amperage than that.
The RoboClaw 2x30 amp motor controller is the minimum I'd use, and can be bought from the same place (I use ServoCity as well). I might go up to the 45 amp version. I build robots that are ...
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