manual control of a victor?

[neilcooper]

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?

[sciguy125]

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.

[Billfred]

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.

[mechanicalbrain]

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.

[neilcooper]

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

Originally Posted by mechanicalbrain

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.

[Rickertsen2]

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.

[DonRotolo]

Originally Posted by Rickertsen2

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.

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

[sciguy125]

Originally Posted by Don Rotolo

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.

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.

[KenWittlief]

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.

[Rickertsen2]

Originally Posted by KenWittlief

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.

I like your professor

[Matt Leese]

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

[Joe Johnson]

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.

[TimCraig]

Originally Posted by KenWittlief

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.

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?

[KenWittlief]

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 :^)

[Joe Johnson]

Originally Posted by KenWittlief

...
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.
...

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.