convert resistance to motion

hgmjr

Joined Jan 28, 2005
9,027
I read somewhere that the HXT900 is made in China. They manufacture two version of the servo. One is more robust than the other. I would beware of the ones that are priced low. They may be the ones that are not so robust. They both have the same part number unfortunately.

hgmjr
 

Thread Starter

dhanurbhagat

Joined Jul 2, 2010
23
Sir tell me one thing, what material are you going to use for the hexapod? Are you going to have plastic/metal parts fabricated according to your preference or are there such things readily available?
 

hgmjr

Joined Jan 28, 2005
9,027
Sir tell me one thing, what material are you going to use for the hexapod? Are you going to have plastic/metal parts fabricated according to your preference or are there such things readily available?
I am using sintra which is a plastic material that is lightweight and easy to cut and sand. I got this material from www.solarbotics.com.

My experimenting has informed me that the weight of the outermost section of the hexapod leg is best kept as light as possible to avoid mechanical oscillation when the segment is rapidly moved.

To improve on the stiffness of the sintra material which leaves a bit to be desired, I have sandwiched double sticky-back tape between two pieces of the sintra material.

hgmjr
 

GetDeviceInfo

Joined Jun 7, 2009
2,192
'linear actuator', refers to the axis rather than the control method. They can certainly be implemented in a closed loop servo arrangement.

Not to add complexity, but at some point your going to be visiting PID loop control.

I have no idea what your vision of the finished product would be like, but any fluidity in motion is going to require some real computing power.
 

Thread Starter

dhanurbhagat

Joined Jul 2, 2010
23
I've dropped the idea to use linear actuators, the arrangement will be too congested for me to handle, considering that this would be my first microcontroller based project.
The placement of the variable resistors/variable capacitors on my hand would occupy a lot of space, leaving not much space for motion as it is, so I'm trying not to include complex motion into it now.
Is this process going to require a lot of processing power that the motion wont be smooth?
Also, would it really be necessary to incorporate PID controlling in it? After all, the motion of the limbs is going to be restricted to my own degree of motion.
 

GetDeviceInfo

Joined Jun 7, 2009
2,192
I reread the thread and missed the part of you replicating your own hand movement.

this in it's basic form, does not require a micro, but rather straight up analog in a servo setting. Digital would be useful if you where transmitting the control over some media.

human motion has a number of attributes to consider. Velocity / speed, pressure, touch response, etc. Each has a unique requirement in transducing, over the range of mobility.

You might want to consider emulating a single digit, your pinky for instance, that has simple motion.
 

Thread Starter

dhanurbhagat

Joined Jul 2, 2010
23
I want to make the whole hand movement, though not very accurately, but one should get the idea. The Arduino Mega has 54 digital I/O pins and 16 analog input pins. I need one with at least 45 Digital I/O pins and 30 Analog input pins. I'am unable to zero down on the microcontroller.
I don't know any other way to make it except the microcontroller way, as it would be extremely difficult for me to synthesize my own circuit for it.
 

retched

Joined Dec 5, 2009
5,207
You should use more than 1 microcontroller. Remember they CAN talk to each other. (Get it 'CAN' ;) )

So you can use one for 3 fingers and the other for the last two fingers and the wrist.

Or you can use 1 micro for the input operations and the 1 for the output.

If you need 30 analog inputs, you can get that with two microcontrollers.
 

hgmjr

Joined Jan 28, 2005
9,027
I've dropped the idea to use linear actuators, the arrangement will be too congested for me to handle, considering that this would be my first microcontroller based project.
The placement of the variable resistors/variable capacitors on my hand would occupy a lot of space, leaving not much space for motion as it is, so I'm trying not to include complex motion into it now.
Is this process going to require a lot of processing power that the motion wont be smooth?
Also, would it really be necessary to incorporate PID controlling in it? After all, the motion of the limbs is going to be restricted to my own degree of motion.
dhanurbhagat,

If you are thinking that you need the analog inputs to support the servos, I can assure you that you will not. The servos are self-contained units that require only a single digital line to support them.

If I am correct, the main thing you will need to consider in your design is how you will multiplex the eight servo software objects to provide control lines for all 19 servos.

hgmjr
 
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hgmjr

Joined Jan 28, 2005
9,027
If you just need a board onto which you will place your own interface circuit then the arduino megashield would seem to be a good choice.

Have you succeeded in programming your arduino board yet? The first thing I did was use the blinking LED example sketch (program in arduino-speak).

hgmjr
 

Thread Starter

dhanurbhagat

Joined Jul 2, 2010
23
Yes, I am able to program the arduino board, though have tried with the LED blinking one only yet, and that too the on-board one. I have a bunch of LEDs lying around, so am trying to do something with them too.
The board's much smaller than I expected, fits inside my palm!
 

Thread Starter

dhanurbhagat

Joined Jul 2, 2010
23
I have just finished a course in the PIC microcontroller. We used MPLAB software to program it. Is there any similar software, that is more advanced and versatile than the Arduino software, with which I can see like which pin is behaving how and whats going on in each register?
 

hgmjr

Joined Jan 28, 2005
9,027
Absolutely, YES. Even better you will find that it is FREE and available for download right now. You will need to obtain a programmer which can be had for around $30 USD.

Go to www.atmel.com and download and install AVRSTUDIO4 then go to www.sourceforge.net and download WINAVR (C-langauge compiler). You will have a very powerful set of software development tools. You will need to spend around $30 for an off the shelf programming tool that is supported by avrstudio4. I am assuming that you are using a Windows PC.

The arduino mega has 2 by 3 row header on it. That is the In-system Programming Connector.

hgmjr
 

Thread Starter

dhanurbhagat

Joined Jul 2, 2010
23
I have written the program that's going to run the hand, and right now I'm able to successfully control 3 servos independently. More also I can do but I'm yet to buy more servos!
I've to figure out how to correspond the variable resistors to the motion of my digits.
 
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