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help :robotic arm

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tshAL

New Member
h! guyz
i need your help,plz

i have a robotic arm and i need to modify it

wanna control the robotic arm by using the movement of the human in such a way that it follows the same pattern of human hand
and get red of using the wire to power the servo-motors
so i have to use the wirless
how can i do all that
thankx!
 
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Triode

Active Member
So you have the kit with the servos and controller right? Do you want to controll it through use of a PC or with an integrated system?
 
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Triode

Active Member
Are those normal hobby servos? Cause if so I would geuss that the easiest way would be to get an 8 channel radio control set, modify the controller so that you can plug a ribbon cable into the side and have it connect to where all the potentiometers from the controlls connect. Then I'd make something that attaches to your arm using potentiometers with similar ranges. A good base to build this on might be an old orthopedic arm brace, the kind with a metal plate. Then use wires and springs to turn or slide the pots with the apropriate arm and hand motions. This method will cost some money, but it will work, I've modified the guts from one rc remote to work with different pots in another. My actual expertise is in mechanical systems, so if you actually want to do that I could give you some ideas about how to make the arm control. If you want more sophisticated electronics than just a modified store bought controller, someone else here would need to help with that, but the good thing about direct solutions is that they get done.
 

tshAL

New Member
thankx a lot "Triode"
i need the elctronics part ....
am interest about your ideas about how to make the arm control
 

Triode

Active Member
are you sure you want to make the electronics from scratch? It may cost less to buy a old 8 channel set from ebay than to start from scratch. You would still learn a lot by doing that modification. Unless your skill level is already fairly advanced it may be the way to go. If you build it yourself would you want to use a premade transmitter module at all or do you want to make that from scratch as well?
 

Triode

Active Member
These are kind of general tips, but as someone who's only been into electronics for half a year or so myself, they'll help you with this:

-Use connectors and headers rather than soldering wires onto the board, or onto the wires in the controller. This will save you trouble later if you have to correct something, or if you want to use the transmitter or your control device with another part or another project.
-Consider adding a switch to toggle between the origonal pots and yours rather than cutting the old pots out of the system, this way when you debug you can use the origonal joysticks and dials to help narrow down what the problem could be if the controlls aren't working right, and you can use the set for other things later on.
 

tshAL

New Member
i will consider these things... from your view
"Triode" thanks a lot
what is your comment on the servo motors? coz you know that we have to take in the effect of the gravity?
 

Triode

Active Member
by that do you mean that the servos might have a hard time holding up the robotic arm? I would guess that it has been designed to work with the servos provided. It should have some counterweighting. Most robotic arms have counterweigting at the base of the boom, or shoulder, in terms of a human arm. And the larger ones sometimes have it at the "elbow" as well. Do you have the arm working with its normal controller?
 

tshAL

New Member
by that do you mean that the servos might have a hard time holding up the robotic arm? I would guess that it has been designed to work with the servos provided. It should have some counterweighting. Most robotic arms have counterweigting at the base of the boom, or shoulder, in terms of a human arm. And the larger ones sometimes have it at the "elbow" as well. Do you have the arm working with its normal controller?
i don't know about the counterweighting ...
i thought that we have to work on
 

Triode

Active Member
So you want to use an accelerometer? I admit that would be sleeker looking and easier to put on to your arm, but it's going to be a lot harder to get it to track well than by using potentiometers rigged to move with the joints of the arm. For one thing accelerometers only track acceleration in straight lines. You would have to use several of them and some extreemly clever coding to make this work. Say you get the sensor working and it gives your program a sizeable accelleration in the x direction from a sensor on the persons hand. Did the person rotate their wrist rapidly, turn their hand up and move it up, or did they swing their arm out? Theres no way to tell for sure. Using multiple sensors you can interpret motion better, if theres one on each side of the hand, and they accelerate in opposite directions, the hand turned, if they accelerate in the same direction, it moved. But the software to interperet that kind of motion well is extreemly sophisticated, even if you can write it, there are few chips that could handle it and you would need several sensors. Try just making a program which points an arrow in the direction you move the accelerometer as you move it around, and you'll see what I mean.
 

tshAL

New Member
thanks again Triode for your help ....
so i have to work with several senors :\
 

Triode

Active Member
That depends on what kind of detail you want. Have you ever used a wii remote? It can kind of tell what you're doing, like most of the time it moves in basically the same direction you do, and it can usually recognize "gestures" (these are not hand gestures but broad movements like swinging an arm in an arc), but not within a precise range. That's what you can do with 1 accelerometer.
 

tshAL

New Member
That depends on what kind of detail you want. Have you ever used a wii remote? It can kind of tell what you're doing, like most of the time it moves in basically the same direction you do, and it can usually recognize "gestures" (these are not hand gestures but broad movements like swinging an arm in an arc), but not within a precise range. That's what you can do with 1 accelerometer.
no i didnt use this remote ...how can i get it and if there is any other choice
 

Triode

Active Member
Oh, I wasn't reccomending using a wii remote, its a game controller, I just thought that would be a good example of a one excellerometer system if you had seen one. Though it actually uses a bit more than just the excellerometer, it has an IR sensor array that references a pair of IR LEDs which are about a foot apart, by comparing the distance it sees between them, their location, and their angle relative to eachother. It can detect its relative location to them, and its roll. But you probably dont want to work with stuff that advanced.
Anyway, what you do want to use still depends on the amound of precision you need, and how simple and cheap it has to be. For high precision I would still recomend mechanical sensors (potentiometers) rigged to a thing that is worn on the person's arm. Besides precision, this offeres the advantage that its output will be compatible with a radio control set without any conversion, though you might need to add something simple for calibration.
But if you want something mechanically simple and high tech looking, although it will only roughly follow the motions of the person controlling it, the accelerometer may work. But for that you will need to program a microcontroller to interperet the accelerometer, and setup some kind of wireless transmission method, as well as a reciever that could interperet the signals and put out the apropriate PWM signal for the servos. This could be simplified using microcontrollers with built in RF units, but it would still be a tall order. You would need to understand pic programming well enough to do multitasked pwm to run the servos, some fairly intuitive AI to interperet the accelerometer, A/D conversion (depending on the output of your sensor, but this is an easy part), and set up the encoding, transmission, reception and decoding of the data.
Personally I'd take the first approach, mechanically more complicated but electronically simple, but then I'm a Mechanical Engineering Student, not a Software or Electrical Engineer.
 
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