manual control of a victor?
 

I was wondering if it would be possible to make a circuit that would control a victor with a pot from full reverse to full forward? If possible using a 555 timer?

Re: manual control of a victor?
 

Googling "servo 555" turns up a few pages.

http://wolfstone.halloweenhost.com/T..._RCServos.html

About half way down, that one has a circuit that uses a pot to adjust it. I haven't tried that circuit myself, but I did use a 555 to control a servo a few years back. I was looking for specific positions, so I used resistors then a small pot to fine tune it. However, I don't see any reason that you couldn't get the full range.

Oh, and the victors use the same signal as servos.

Re: manual control of a victor?
 

I didn't think was possible (until sciguy's post), but I have seen on some combat robot site somewhere in the past a device that can create a PWM signal. If you can find it (for some reason, USC's network can't connect to Google right now), it may be a starting point.

Re: manual control of a victor?
 

http://www.chiefdelphi.com/forums/sh...t=voltage+loss
Here you go. I'm currently making one.
http://www.geocities.com/BourbonStre...rvobasics.html
That's the link with assembly directions.

Re: manual control of a victor?
 

Thanks I will build the second one. I was just looking for a schematic ran a search and all it was was discussions about the topic no schematics

Re: manual control of a victor?
 

absolutely. The control signal is very simple. All you need to do is supply it with the necessary voltage on the power lines and a 1-2 ms pulse periodically on the signal line. 1ms corresponds to full rev while 1.5ms is neutral and 2 is full forward.

Re: manual control of a victor?
 

555 timers are like using 'GOTO' statements in C

in fact, I had one professor in college who would give you an automatic F if you used a 555 timer (or any other one shot timer) in any type of project or assignment.

a better solution would be one of the 8 pin PIC Microchip uCs. You could hook a pot to one of the ADC inputs, and use the PWM output to generate the control to the victor.

Re: manual control of a victor?
 

I like your professor

Re: manual control of a victor?
 

For my senior project this past quarter, we controlled Victors with a Motorola 68HC12. It worked quite well overall. Just remember you only need to connect the signal and ground wires (not +5V).

Matt

Re: manual control of a victor?
 

The 555 is one of the most important pieces of standard hardware on the planet (KenWittlief's prof's opinion not withstanding). Bias against it may well be justified, but it does not take away from the fact that the world as we know it would simply (and literally) grind to a halt if the anti-555 snobs waved a wand and made all the 555's in the world disappear.

I take the more practical approach of Steve Ciarcia, who said, "Solder is my favorite programming language."

Driving a Victor with 2 555's is a piece of cake (use a 556 - it has 2 555's in one package). Go HERE for some easy examples of how to make useful 555 circuits. The basic idea is to have one 555 set to make a 50Hz signal and have that repeatedly trigger a "one shot" that will give you the pulse for the Victor (roughly .5ms - 2.5ms pulse).

Joe J.

Re: manual control of a victor?
 

Did he say 555 timers and their ilk had no place in the world or did he simply think they were a slam dunk to use and wanted the students to have to put some more thought and effort into the projects? :rolleyes:

Re: manual control of a victor?
 

I thought the automatic F made his intentions pretty clear. It was the same deal with 'goto' statements in any high level programming class, instant F.

The problem with one shot timers is, they are temperature dependant, voltage dependant, and rely on the RC time constant, which also can create a wide range of tolerance issues.

The real problem with one-shot timers is they act sort of like digital circuits, in that they have two states: on and off. BUT real digital logic is controlled and regulated by a clock. Every state should be registered relative to a well defined clock

a one shot timer by contrast is more like lighting a fuse. Asychronous logic is one of the fundemental causes of system instability, design bugs, and system failures. Its better in the long run to design a good, deterministic digital solution (with a clock) than to mess around with asychronous logic. You end up spending more time and money designing and debugging asynch circuits than just doing it right the first time.

hence, the automatic F :^)

Re: manual control of a victor?
 

Guilty as charged, but even so it is silly to argue that they don't have a place in the world.

Point 1: Last week, I needed to exercise a curcuit as I debugged some design issues. I literally built a 555 circuit, had my scope hooked up and was solving the problem in about the same time it would typically take to boot up a PC and open an IDE like MPLab, yet alone designed and debugged a PIC circuit, written code for it, and downloaded and debugged that code.

Point 2: Many applications can live with temperature & voltage dependency as well as wide tolerancing issues.

Point 3: The claim that "real" digital circuits require a clock is a blanket generization that just doesn't hold up to serious evaluation. 1000's of chips, useful ones that even the purest of the pure Digital Gurus could not argue is not a "Digital," have no such clock but depend on internal, well planned logic races to function as designed.

Point 4: The 555 is dirt cheap. The reason that Programming Purists have been able to hold the line on the "GOTO's ARE EVIL" mantra is that (1) you can (almost) always make cleaner, easier to maintain code without them and (2) these work arounds do not cost more. I can tell you right now, the 1000's of engineers that put the 555 in the millions of commercial products that ship each year are not ALL stupid. They are being driven by cost. Professors can argue all they want about inelegant solutions. Jonh Q. Public doesn't pay for elegance, he pays for features. If 555's provide the feature at a lower cost, 555's win the day. If not, they don't.


Point 5: Sometimes Programming, Electronic Engineering and Computer Engineering Purist really get my blood boiling ;-) Perhaps it is just a reflection of the relative youth of these fields, but I can't think of similar analogs in the fields of Civil Engineering, Mechanical Engineering or Industrial Engineering. Have you ever heard a Civil Engineering guru argue that only the only way to cross a valley is with a suspension bridge - all other methods are beneath consideration? Or a Mechanical Engineer ever insist that the only REAL heat engines are based on the Stirling Cycle? I see this kind of borderline religious zealotry all the time in the electronics & computer engineeing worlds and it drives me nuts.

I have already said more than I should have. I will end by just saying that there is no such thing as an ideal solution. All solutions involve tradeoffs. I urge folks to understand advantage and disadvantage not to memorize a set of rules ("don't use gotos," "never use 555s," etc.). In the former you can choose a solution that optimizes your Performance Index. In the latter, you may be able to keep a Prof from giving you an automatic F, but I don't think life is likely to give you an A.

Joe J.

Re: manual control of a victor?
 

the thing is, a 555 timer may be cheaper than an 8 pin PIC chip, and if you need to rig something up quickly then who cares about anything else?

But if you are designing a product, that will be produced by the thousands or millions, then you must consider the entire engineering and life product cycle.

One shot timers are the simplist form of asynchronous logic - but if you open the door to these, then you allow asychronous logic into the designers toolbox, and then where do you draw the line?

Looking at SW again, if a subroutine has one entry point, and one exit point, its easy to understand the flow of your code - but if you have goto statements allowing your code to jump all over the place, you quickly end up with spagetti algorithms

same with digital HW. With one system clock the only parameters you have to worry about are setup time and hold time - what happens between the rising edges of the system clock become irrelavant, as long as everything settles down to meet setup and hold.

But if you allow one shots, or async clears, or you gate your clocks, then your timing becomes complex, and simple things like changing a chip from TLL to CMOS, or even from one supplier to another will make your system stop working, or worse yet, will make it unstable, so it fails under certain temp or application conditions.

There are golden rules to designing digital logic:
No asynchronous logic (including one shots - everything must be registered by a clock)
no circuits that can glitch
no gating of clocks (one master clock for the system)
asynchronous inputs must be double registered (to prevent metastability)

if you take a short cut and break one of the golden rules you will pay for it sooner or later: when you try to make a simple modification to the system, when a part goes end of life and must be replaced, when the system is used outside its normal environment, when you need to upgrade, when you need to interface to something new or different, or when someone else has to work on something you designed.

that 60 year old Professor really knew his stuff. From my experience over the years, the golden rules remain untarnished.

Re: manual control of a victor?
 

Couldn't agree more with this. I think an important aspect of being an engineer is being able to evaluate lots of different solutions to a problem and pick the one that best meets all the requirements (including things like cost, time to implement, robustness, how easy it is to understand for future engineers who may need to modify it, etc.). And hopefully you don't feel that all computer engineering people are zealots ;) .
Shouldn't it be the burden of the engineer designing the solution to know where to draw the line? He/she should understand the risks/rewards of such a solution and should be able to understand where to draw the line given the needs of the project/product (which are not constant from one project to another - as Joe pointed out, sometimes the tradeoffs are acceptable given the project requirements).
Hard and fast rules such as "absolutely no gotos" can sometimes do as much damage as using gotos all over the place. While rare, there ARE times when the use of a well-placed goto (or break, or continue, or early return, etc.) can greatly simplify code and therefore increase readability and maintainability, or be necessitated for performance reasons in small embedded systems, etc. Enforcing the "no gotos" rule in college might make sense such that the students don't develop a bad habit of using them, but in my opinion it should be explained like this: "Sometimes, using a goto may be necessary or appropriate. This will be your job as an engineer to make that determination. However, the assignments for this class are not sufficiently complex to justify the use of a goto statement. Hence, use of goto is not acceptable in your solutions."

Re: manual control of a victor?
 

A goto statement in a subroutine is kinda like the hyperspace button on a video game - you have coded yourself into a deadend, and there is no other way out

thats not good. The golden rules that each discipline of engineering have come up with over the years are the result of many painfull and expensive blunders and mistakes.

When you find yourself tempted to break one, its a red flag that you didnt think things through before you started writing code, or drawing schematics, or designing your logic.

On military projects they have many of the same rules. If you dont follow them your project will be rejected at your next design review, and they dont grant exceptions either :^)

Re: manual control of a victor?
 

We prefer to call them waivers. ;)

Re: manual control of a victor?
 

You can't possibly understand all the different situations that come up so I don't understand how you can make blanket statements such as "it's a red flag that you didn't think things through". I would agree that any time you think you need to use a goto it should be a red flag to reevaluate the problem to make sure there isn't a better way of doing things, but I can't claim that there is never a situation where it would be appropriate. And besides, if the person writing the software hasn't thought through the program before starting, "golden rules" such as no gotos won't save him - it'll be a spaghetti-code mess either way.

I personally have never encountered a good reason to use a goto in my own work. I have, however, seen enough cases where even the best, most well-thought out designs will run into certain practical limitations that sometimes cause us to have to do things in a way that is less than ideal. This can often be the case, for example, when writing code that interacts directly with hardware. Tight timing constraints or poorly-done hardware interfaces (on external chips) can put you in a corner where a nice elegant software design just won't work. This tells me that there most likely are cases that I have not seen yet where the use of a goto might be justified.

(Sorry to original poster for continuing to take this tread off topic... :o )

Re: manual control of a victor?
 

thats what drives the need for golden rules, and thats why they are instituted very carefully (and thats why they are golden). When the situation comes up, there it is!

It has amazed me that engineers from all over the world somehow know the golden rules that apply to their profession, and they are not afraid to point out to you (during a design review) that 'this is a problem, you should never do this'. Seriously, I though Dr Eric Schmidt at Suny Buffalo came up with "Dr Schmidts Golden rules of digital design", because he shared them with us as if they were his own children, in a hushed tone, almost as if they were sacred.

but somehow, everyone seems to know them :^)

Re: manual control of a victor?
 

Ken,

You are just plain wrong. According the the Wikipedia's entry on the 555,

"Still today, Samsung in Korea manufactures over 1 billion units per year (2003)."

Ken that is BILLION with a B.

You don't get to a Billion units with yahoos and hobbyists.

Can you mis-use the 555? Yes, of course.

Would it be unacceptable to use a 555 in a billion dollar satellite project? Yes, of course.

Can they be put to great use by hobbyist, toy manufacturers, and others who are willing to live with their inherent limitations? Yes, of course.

Is a blanket condemnation of using 555s anywhere under any circumstances just plain silly? Yes, of course.

This is not to say that "golden rules" are not useful. But if I have the choice between understanding the reasons for rules and blind adherance, I am going to advocate understanding the rules.

I am going to go even further. In answer the the question that started this this thread, it is hard to argue that the best solution for the problem as presented is anything other than heading down to the local Radio Shack with $10*, buying a 555 and a few extra goodies and building a circuit that works as desired within 15 minutes of arriving home.

I am getting my undies all in a bunch because I believe with every fiber of my being that Engineering is an Art. It is a beautiful, wonderful, delightful art.

There are laws of physics, useful rules of thumb, and cold hard economics that come into play to be sure but at its core Engineering is Art. For these artists, there is no substute for sound engineering judgement.

Joe J.

*For an additional few buck he could have put in all in a nice pretty box to boot!

Re: manual control of a victor?
 

However, I have used them to test billion dollar satellite projects...

In particular, I needed a PWM stream with two specific pulse widths, and used two 555's as one shots, fired by logic that picked which one based on if I needed a "1" or a "0". The logic was driven by clocked logic that followed all the "golden rules", but the 555 was far and away the easiest way to get the two pulse widths. Took 10 minutes to put it all together, which was far less time than I spent listening to various design engineers tell me I needed a PIC, or a FPGA, or ..... (all of which, in addition to having the added time of writing the software, in the spaceflight test world have the added burden of having to place all of the code used into configuration management, so the <$1 PIC now costs considerably more to use once in a test fixture).

There is almost always more than one solution to any engineering problem. One part of elegant design is picking the one that makes the most sense for a particular design problem, even if that means "breaking" some normally established "rules".

Re: manual control of a victor?
 

your examples of being able to put together a one shot circuit quickly and easily assumes you already have experience with 555 timers, or similar devices, and you dont have to consult a data sheet to look up the equations, figure out whether to use ceramic or electolytic or tantilum caps, variable resistors, carbon, wire, precision resisitors, to get the performace you need under all conditions

I could equally argue that with my 10 years of experience using PIC chips I can pull a PWM or timer subroutine out of my existing libraries, compile the SW in a minute or two, and all I need is power and gnd to the 8 pin PIC chip, and it will be producing a very accurate, very precise waveform in a matter of minutes

and with the in-circuit programablilty of PIC chips, I can change any of the parameters faster than you can unsolder and solder caps and resistors.

I dont know where those 1 billion one shot chips are going each year. I can honestly say that in my 20 years of electrical and computer design experience, on both military and commercial products, I have never used one, and I have never seen any product at any of the companies Ive worked for use one either.

Re: manual control of a victor?
 

And there in lies the rub!


I can say in my 20+ years working for one major medical imaging company, among the dozens of other thing GE is into, that I have seen multiple systems and circuits, from various vendors and corporations, that do use 555's.

I guess my point is: Until you have seen everything, every situation, every design, every possibility, making blanket statements and setting hard and fast rules, with no room to bend, is just not a good idea.

BTW, I did a quick Google search and found a great little 555 circuit that will suffice perfectly to generate a 1 to 2 ms pulse at a period of 17ms. One 555, one cap, one pot and a resistor. It even had charts on the site for the mathematically impaired to help decide what component values to use.

Don't get me wrong, I understand the Prof.'s reasoning for doing things his way. He has every right and privilege as a Prof. to do so in his class room. But unless he meets the "Until you have seen everything, every situation, every design, every possibility...." rule, his ways outside the class room aren't always the best ways.

Re: manual control of a victor?
 

taking a step back from this discussion, Dr Schmidt taught the senior level Digital Design class

the focus of my career has been digital design and programming

and the 555 timer and other one-shot chips are analog devices

so this is really a discussion of the merits of digital systems vs analog systems - and the merits of hybrid digital/analog systems

so from Dr Schmidts persepective, he was correct. Analog timers have no place in a digital design class, and they have no place in a digital system (ie, you would never plop down a 555 timer to generate the CAS and RAS signals to an SDRAM bank on a pentium motherboard, you would use digital counters and state machines

I concede that if you are designing an analog system, then things like one shot timers are acceptable

and Im certain that analog designers have their own set of golden rules

but back to the original question of this thread, I think the debate that has been raging here is really a question of which approach is better, a digital or an analog solution?

BTW, part of the problem is that the PWM control of the victors is a carry over of the PWM of radio control model servos. Originally all RC systems were analog, but now here we are with these digital FIRST controllers interfaced to Victor speed controllers, with a legacy-analog PWM signal format. :^)

Re: manual control of a victor?
 

Ken and Joe,
Let us not forget that no matter what the individual benefits or pitfalls, I can go down to the local Radio Shack and pick up a 555 usually with a schematic on the back and have something useful, albeit inaccurate, within an hour or so. I would love to use a PIC, but don't have any at a local store or my junkbox or even at work. And the fishing timer I built for my wife's aunt, works great and no one cares if it times out at 15 minutes or even at sixteen minutes. As long as it times out and reminds us to move on to a new spot, everyone is happy.
BTW, I used a dual 555 to make a really annoying alarm output for my Heathkit digital clock. It has lot's of distortion, dual frequencies and darn near knocks me out of bed at 4:44 AM each morning. (for an audio guy, the distortion does the trick) My wife likes that better than having 220 volts hooked up to the bedsprings.

Re: manual control of a victor?
 

15 minute fishing timer? thats an interesting idea. How does it let the fish know its time to move to a new spot? :^)

Re: manual control of a victor?
 

I don't know but it works really well. I haven't caught a fish on their lake yet. As a matter of fact I was presented with a plaque two years ago with the words "Fish laugh at the mention of your name".

Re: manual control of a victor?
 

You may want to change your fishing tactics. May I suggest Dynamite! :D
Worst case, the fish won't laugh any longer. They'll be deaf and never hear your name mentioned again. :p

Does it affect anything that the motor is an analog device and needs an analog signal (PWM)?? It's pulse position modulation for the incoming signal not pulse width modulation. Pulse width modulation is the signal that controsl the motor.

Re: manual control of a victor?
 

After all of the interesting discussion of 555s I'm not exactly sure if you are more interested in building a PWM controller from a 555 or if you are more interested in a PWM controller just to test your Victors.

If it is the latter and you just want to buy something off the shelf, may I suggest the FMA Direct Servo Lab. You can get it from Tower Hobbies (http://www2.towerhobbies.com/cgi-bin...?&I=LXJVD9&P=0) or other hobby places for less than $35. It is really useful for testing Victors and test driving motors connected to a Victor (and power) without having to have the whole IFI control system hooked up. It also will "read" the PWM signal from the IFI Robot Controller which can be very useful to see how the joystick and code are responding. You can even hook it up in line between the RC and the Victor. Works great, I highly recommend one. If you get one you will need to get a cheap RC battery as well if you don't have one.

Another COTS option that is a little less expensive (~$20) is the Astro Flight Servo Tester (http://www2.towerhobbies.com/cgi-bin...&I=LXVK79&P=0). I don't personally have one of these but it should do what you want (manually control the Victor) but it will not "read" the PWM signal from the RC like the FMA Direct Servo Lab.

Now everyone can get back to discussing the pros and cons of a 555...

Re: manual control of a victor?
 

Adam,
That's kind of the beautiful things about this control. It is a digital signal, running from +12 to ground, that is converted to an average mechanical power with no real active circuitry. The motor does all the conversion with a little help from physics (conservation of momentum) and a little from electrical (inductance) etc.
The control signal and the output of the controller are both PWM. Pulse position signal uses the same size pulse but varies it's position in relation to a reference. In PWM the pulse width varies over the time of a single cycle but the cycle length doesn't vary. That makes it sort of self clocking in that for the most part there is a start and end to the pulse cycle. (about 2 kHz) The output PWM is not an amplified version of the input. The input pulse width varies over 255 steps where the value (width) of 127 represents no motor current at all. A "0" will make the output turn on to full 12 volts (no PWM) and a 255 will do the same but reverse the leads (+12 becomes common and common becomes +12 to the motor) which reverses the direction of the motor.

Re: manual control of a victor?
 

That is correct for an R/C servo, but incorrect for a Victor or similar PWM motor control.

For a PWM motor control, the duty cycle of the signal varies from 0% to 100%, corresponding to full reverse and full forward, respectively, with 50% being neutral.

[EDIT:] I stand corrected, the Victor uses standard R/C type PWM control, which operates as described in the quote above. The circuit I have won't work here, but there was a circuit in SERVO (or maybe Nuts & Volts?) earlier this year that had such a circuit using a 556. When I find that I will post a reference to it. [/EDIT:]

I have a circuit somewhere that does exactly what he wants, uses a single 555 and a few passive components, and varies from about 3% ro 97% duty cycle. I'll post it when I find it.

Don

Re: manual control of a victor?
 

You're thinking of the output of said motor controller. The original poster was looking for a device to connect to the Victor input. This uses the same signal as R/C servos.

However, I recently finished a PIC based motor controller (for true motor control PWM). If anyone wants it, I'll send them the code. As for hardware, you just need a 12F683 (or similar) and the appropriate "glue" components to connect it to an h-bridge. I've got code to read a pot and the R/C PWM signal.

Re: manual control of a victor?
 

As promised, here is the circuit that produces variable width pulses (1 to 2 uSec) at about 60 Hz. This is fairly simple to build, components are not very critical, Radio Shack sells all of the parts. All of the resistors are 1/4 watt 10% or 5% tolerance, the capacitors 1 uF and above are electrolytic or tantalum, the small caps are ceramic monolithic (ar whatever is on hand).

I have included a way of converting some higher voltage (e.g. 12 volts) down to 5 volts using a 7805 regulator, along with the pinout of the Victor PWM signal inputs. Remember, black is ground and white (or yellow) is the PWM signal.

This will drive a Victor or any R/C servo from nearly full reverse to full forward, depending on the setting of the 1 k Ohm potentiometer. Note that there are some PWM motor controllers that do NOT use R/C type PWM inputs; this will not work with those.

Have fun

Don