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Author Topic: Novice is in need of some wireless servo assistance.  (Read 1815 times)

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Offline Ryan the Robot NoviceTopic starter

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Novice is in need of some wireless servo assistance.
« on: October 10, 2009, 11:58:11 PM »
Hello everyone.

I am trying to design a servo wireless control system for a personal passion project.

These are my criteria, and after, I'll tell you where I am in the process and how I'm stuck.

I am in need of a highly accurate and sensitive wireless servo control. The servo motor must be able to be programmed with travel 'stops' and preferably but not necessarily a 'middle' point. The operator will control the servo's motor via a highly sensitive potentiometer control. Ideally, I need a servo because it holds position accurately and can communicate position to the controller. However it will be driving a gear which needs to move a larger gear 180*-360*. I've learned about winch servo's and the possibility for 1400+ degrees of rotation should satisfy my needs. Ideally, the operator would set the travel stops (because they will change upon different applications) on the servo, but the Potentiometer would always turn the same distance, the difference being it may be moving the servo across a further or shorter distance only effecting speed. That is about it. The main thing to stress, is the operator has control over a potentiometer which moves the servo in 'real' time with accurate and relatively sensitive and repeatable fashion.

The following is where I stand in my design. You must know that electronics are not my strength, so I rely heavily on putting other designed pieces together for my application. I have come up with several designs using different robotic sites products, but this is the most recent:

The site I have set the basic hardware from ishttp://www.bpesolutions.com] [url]http://www.bpesolutions.com[/url]/ .

My main controller board is the Wizard 12. This offers the programmable function stops I have been looking for. http://www.bpesolutions.com/bpemanuals/Wizard.12Manual.pdf

The servo I want might be an issue, this is one factor I need help on. I need more then 90* movement... so I found a winch servo. Is this compatible? Will setting my stops work? The Wizard 12 can come in 180* movement... but that is not quite enough. I need to turn larger gears about 180*! If a servo is not what I am looking for then what kind of motor can have programmable stops, and rotate over 180*

I'll continue on with my idea, even though it might be dead already. Anyhow, I was planning to have a pot on the Wizard 12 for calibration of the travel stops w/o needing to use the wireless pot. Therefore needing both pots, I thought I would hook up the R/C single servo switch board (http://www.bpesolutions.com/rcequip.html#anchor3180253)... which will allow for a R/C unit and the controller board pot to work... I will only be operating one or the other, but two pots will be connected to the system.

The next big hangup is on wireless... how do I get a wireless transmitter on the remote pot and a wireless receiver on the controller board/ servo motor? It is important the wireless potentiometer be as light and portable as possible, hence the hardware boards being on the servo side of the wireless transmission. I can't quite figure out how to connect this. The wireless reciever/transmitter on that website is confusing and seems to have a digital connection, which I am an amateur, so I have no idea how to deal with this:http://www.bpesolutions.com/bpemanuals/RFJWBoards.pdf

There are other details I am leaving out because I think they are all underlock down, and I've figured it all out.


Thank you in advance for helping me with what is probably some obvious and simple things for you folks.

-Ryan the Robot Novice.

Offline Ryan the Robot NoviceTopic starter

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Re: Novice is in need of some wireless servo assistance.
« Reply #1 on: October 11, 2009, 01:33:24 AM »
I should add, that any motor, wireless remote control with a potentiometer setup is welcome for suggestion. Budget is around $500 or more. If I find that doing it optimally and doing it right costs more I'm down to do it right.


Offline Soeren

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Re: Novice is in need of some wireless servo assistance.
« Reply #2 on: October 11, 2009, 05:02:41 PM »
Hi,

Lets have some rigid quantifications:
- How many degrees of rotation do you need?
- What precision (in degrees) do you need?
- How repeatable (in degrees) do you need it?
- How powerfull do you need it to be (i.e. what is it going to move)?
- What power supply [V and A] are you going to use (for the stationary part)?
- Any other quantities you think might be even remotely usefull?

Loose specifications yields loose answer ;D
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline Ryan the Robot NoviceTopic starter

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Re: Novice is in need of some wireless servo assistance.
« Reply #3 on: October 13, 2009, 03:39:17 PM »
The need of rotation will vary upon application and circumstance. So ideally infinite... so much as I can program the motor to have travel stops.
Precision is a must, the most accurate, repeatable, and small increments is desirable. Repeatable action is also a must with accuracy... for what is accuracy if repeating the action is inaccurate?

The motor does not have to be strong. It is simply rotating the barrel of a lens (can you guess what I am building yet?).  Power supply can be as high as 24v. Lower is no problem as well. Lower is preferred.

I understand details are important, so forgive me for being ambiguous. I hope this helped!

Stepper motors are more precise then servo... right?

Offline Soeren

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Re: Novice is in need of some wireless servo assistance.
« Reply #4 on: October 13, 2009, 05:37:56 PM »
Hi,

The need of rotation will vary upon application and circumstance. So ideally infinite... so much as I can program the motor to have travel stops.
I thought it was for "a personal passion project", but now it sounds more like you want engineering done for a large commercial range?


Precision is a must, the most accurate, repeatable, and small increments is desirable.
What part of "rigid quantifications" didn't you get?
Terms like "the most accurate" and "small increments" are not metric quanta (unless we're talking Fuzzy Logic). In your case, degrees should be a useable nominator and I'd be surprised if you need something much more precise than what you can do by hand, but you are the one having to spec out what's needed and you have to do it in terms that means the same to you as to everyone else.

And... Never go for a precision which is far beyond your real needs, as it will at least make it more expensive and harder to do and Worst Case, it might result in no answers at all.


Repeatable action is also a must with accuracy... for what is accuracy if repeating the action is inaccurate?
What is accuracy if not quantified?
Accuracy could be eg. +/-2° with a repeatability of +/-1° and that would be engineerable, superlatives, on the other hand, doesn't really cut it until after the job's done ;D
When you go shopping, do you eg. say "I'd like several bottles of milk of a rather lean quality please" or do you say something like "5 bottles of skimmed milk (and a single bottle of Jack Daniels to cure the milk breath) please"?


The motor does not have to be strong. It is simply rotating the barrel of a lens (can you guess what I am building yet?).
So, does the barrel have any mass? Does the thread have friction? Does it have to do the job within a certain time frame? Or will even the weakest motor imaginable do?


I understand details are important,
Apparently not!
so forgive me for being ambiguous.
Don't confuse confusion with ambition.
I hope this helped!
It didn't, try pushing some numbers.


Stepper motors are more precise then servo... right?
Well, it depends... If you're going many revolutions they can be, but within eg. a single revolution, their precision depends on how precise the poles are mounted. If gear reduction is used, precision suffers.
In a servo system, the motor type doesn't matter for the precision, as it is all in the position feedback system.

If you're solely talking about R/C-servos (those used for remote controlled toy cars) and you want several revolutions, the position feedback system has to be removed, so it's not really a servo anymore, but rather a tiny geared down motor with a motor controller reacting to pulse width signals following the R/C protocol.

Since you're not really keen on quantifying your needs, they're impossible to provide an answer for, but did you consider how you're gonna use it, once it's working - perhaps that would help you define your needs and put them into numbers.


Until such time that numbers start entering the specification in a reasonable amount, please don't expect anybody to have a chance of helping you out here.

Engineers aren't oracles - we just seem to be since we make the world go 'round ;D)

Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline Ryan the Robot NoviceTopic starter

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Re: Novice is in need of some wireless servo assistance.
« Reply #5 on: October 13, 2009, 07:22:31 PM »
Ugh... Thanks? I'm not sure if you were being passive aggressive, helpful or both.  :-\

Thanks for the advice at the end of your post. It was actually helpful. As for the rest, I'm not sure what you wanted from me. All I wanted was some basic guidance. The most accurate is in fact a quantitative statement. Sure it's not a hard technical spec, but if I knew all that you demanded, I probably wouldn't be calling myself a novice and asking for help. Since the time of this thread, I have done much more research. I was hoping to take my findings and cross reference them with advice from here. I've seen what has been offered, and thank you for taking the time to help.

I think I have found some solutions and will continue to search further. I'll be on my way.

-Ryan

PS: No more confusion, just ambition. Ambiguous...adjective for lacking clearness or definiteness.


 


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