Cody's Crane

[samcam]

Hi Cody,

First of all... I hope the whole girlfriend thing is working out for you.

I am about to start building a crane with a remote pan/tilt head to suit cams up to the size of the Canon XL1. In fact I think my design is almost identical to yours. So I was hoping you could save me some time/money and let me know if you discovered any tricks along the way.

Particularly, specs on the servo system you ended up with. I am worried I am going to put money down for the wrong type of controller/amplifier/motor combo.

Cheers,

Sam

[Cody Deegan]

Oh boy, here's a can of worms.

A while back I was informed of the aircraft frequency rules pertaining to r/c devices.  These FCC regulations were explained to me AFTER I had built my remote head, which just so happened to utilize that nifty 72 Mhz radio band.  

So what's the big deal?

Let's say I am within three miles of someone who is flying an r/c aircraft and we happen to be using the same channel on our transmitters (1 in 40 chance I believe).  I turn mine on and this poor person suddenly loses control of the plane which hurtles uncontrollably into who-knows-where.  

It's a safety hazard.

With all that said, I can now offer you the plans for my old remote head so that you may gleen some ideas and hopefully build a better one.

Send me an email to plans@codydeegan.com so I can email them to you.

Cody

[SirElliott]

Cody,

Have you thought about using a "ground" freq.?  It seems that the R/C community has been dealing with this lately.  Most of the "Battle Bots" robots use R/C aircraft setups that have been retuned to use "ground freq."

If I have my facts straight in the U.S. R/C air uses 72 MHZ while R/C surface (ground) uses 75 MHZ.  I have read that 72's can be "retuned" to 75.  This should be done by a qualified technician.

Because of the robot market the manufactures have added models that use joysticks vs. "triggers" and are on surface frequencies.

Futaba has several in their catalog http://futabarc.com/sellsheets/futz2002-2003-catalog.pdf

look for Surface Systems.

[Cody Deegan]

You're right.  At the time when I built my head, the surface transmitters were not where I could find them.  ServoCity has since announced that they are going to start supplying them soon.  I used to think one could simply change the crystals from 72 to 75, but I do not know enough about r/c to understand whether this is correct or not.  I suppose I could just email ServoCity and find out.  



If not, I think I will take your advice and find a qualified tech to change mine over.  Appreciate it.



Cody

[SirElliott]

I have a book somewhere (I'm looking for it) called Build Your Own Combat Robot. There is a chapter on R/C.  The author talked about going and having it done by a tech.  I think most of the newer R/C control units generate the frequencies as opposed to crystals.



I got the book to learn about motor control so that I can build a pan/tilt head and it does a good basic job.  A better basic book I just got is  .  While I haven’t got veryBuilding Robot Drive Trains far it looks like it will be a great reference.



The author suggests getting used printers and copy machines because they are full of great stuff like gears and motors.  On Saturday my city had a police auction where they sell old equipment and stuff that has been recovered from crimes and never claimed.  I walked away with two copy machines (they work, it seems a shame to tear them apart when they work) two printers, 5 working bicycles, a couple of spring arms for a lamp and a monitor, and two PCs.  The total, $42.50 US

[Cody Deegan]

ServoCity wrote me back and confirmed your statements.  They said I would be better off purchasing a new transmitter.  I'm curious if the speed controls I'm using will still function on a new ground setup.

[sacherjj]

While I'm a little late in this thread, I am more knowledgable in RC than camera equipment, currently.  What typically is happening in RC systems is the crystal suppied is not actually the frequency.  It is used along with the internal factory tuning to arrive at the frequency.  So the base frequency in the radio must be retuned.

[Cody Deegan]

Cool, finally some RC info.  So for me to switch over to the 75 Mhz frequency, I would need to get a new transmitter and receiver, right?  Or like you said, have them retuned - but I probably won't do that.



And also I would not need my speed controls, would I?  It seems to me (if I remember right) I bought them to fix the problem I was having with the servos reversing and returning to their initial position whenever I would let go of the joystick.  I assume that this is a characteristic of a flight transmitter and not a ground.  Am I correct?

[SirElliott]

First of all the disclaimer, this is not my field of expertise.  The R/C industry certainly has some options, but I wonder what the frequency gods have to say about controlling cranes with R/C frequencies?  If it is legal to use ground R/C controls, I think you need to think about interference.  While I suggested switching to the ground frequencies from the R/C aircraft frequencies, I just started to worry about the reverse problem.  Before, the concern before was about the possibility of sending a R/C aircraft out of control, now I wonder about a crane going out of control and smacking someone.  With just a pan/tilt head it probably isn’t a big deal but I plan to control the jib arm up and down as well a jib pan, possibly even the dolly.  Clearly, a panning jib arm out of control could be a big problem.  There are solutions to encroachment (encryption) available in R/C equipment, they are more expensive. http://www.uoguelph.ca/~antoon/hobby/rip.htm

Maybe there are other solutions using other frequencies?

http://www.abacom-tech.com/downloads.htm

http://www.rfdigital.com/index.htm

[sacherjj]

I'll admit that I haven't looked at how you are hooking up the servos on your remote head.  I'm satisfied with my Cobra Crane for now.  I did look at the video and like the results.

Servos are operated with a pulse chain.  The four wires are + power, - power, signal, and ground.  The signal is a a 1.0 to 2.0 ms (millisecond) pulse that is repeated 50-100 times a second (I don't remember exactly how fast the chain is, I'm sure this is available on the web.)  What happens is the signal ate 1.5 ms is "centered".  This means that the potentiometer (center tapped variable resistor) is at the setting where the servo is in balance.  When the pulse drops to 1.0 ms, the servo turns until the potentiometer gets to where the circuit is in balance again.   The further "off" the signal is from the current resistance setting, the faster the servo moves.

This is useful in robots or setups like yours.  What you do is take out the potentiometer and replace it with two resistors soldered together.  This will be the same as the potentiometer always in the center position.  Next, you need to break off the tab that keeps the servo from going past its "stops".  Once you put everything back together, you get a servo that will turn continuously in either directon with a speed that is proportional to the distance your stick is pushed (or the difference you pusle is from 1.5 ms).  When you let go of the stick, the servo will stop.  You might have to adjust the fine tune on the transmitter to make this happen.

Now, you can wire a fairly simple circuit using a 555 chip that will generate this pulse chain.  Then use a potentiometer mounted on a level to vary the signal.  With two of these, you have pan and tilt control without a radio.  Most joysticks use a system with two potentiometers, so they may be able to get modified for this purpose.  Or use a very cheap, one stick transmitter for the parts.

[cosmin rotaru]

"Now, you can wire a fairly simple circuit using a 555 chip that will generate this pulse chain. Then use a potentiometer mounted on a level to vary the signal. With two of these, you have pan and tilt control without a radio. "



Could you elaborate this, please! I whant to do something simple, without radio, like you described. Do you have some schematics for this?

Thank you!

Cosmin Rotaru

[sacherjj]

I thought I still had something around for that, but I don't.  If you look at the technical documentation you can find online, you should be able to put something together.  You will probably need to use a 556 chip for each servo.  This is a chip that has two 555 timers.  

The datasheet for both can be found here:

http://www.national.com/pf/LM/LM555.html#Datasheet

http://www.national.com/pf/LM/LM556.html#Datasheet

Looking at the datasheets again for the first time in years, you might be able to do this with the Pulse Width Modulation circuit they show on the LM555 data sheet.  What you would do is connect a potentiometer to Vcc (highest voltage you are using) and ground, then connect the center to pin 5.  As you move the potentiometer, you changes the width of the pulse.  You want a pulse width of 1.0 to 2.0 ms If you go out of those ranges without modifying the servo as I started in my previous post, you will break something.  It is probably not a good idea to do that even after you have modified the servo to just be a reversible motor.   You frequency of pulses should be about 50 Hz.  

I have not tried this, and it is very possible that the voltage changes as a battery discharges would really change this circuit.  It is probably advisable to use a 12V battery and a LM7809 or similar regulator, to have a fixed voltage supply (9V in the case of the 780 ) as the battery discharges.

Another possibility, which would add more complexity but more flexibility, is to use something like a BasicSTAMP processor.  These are pretty easy to program, and would allow you to control the pulse widths more exactly, rather than tuning analog components.

Lots of ways to do this.

[Cody Deegan]

I know this is all very informative but the explanations you are giving are hard for me to understand because I am not familiar with much of the terminology.  I think Cosmin would just like to see a simple diagram showing battery, motors, joystick, and anything else needed to make a complete functional circuit.  

[sacherjj]

I understand what you are saying, I just don't have the time currently to do that.  I can't give someone a circuit, without actually breadboarding it to make sure it works.  If I ever do make a remote head system, I will probably do it with a BasicSTAMP processor and make circuits available.  However, that is going to be after I build batteries for my Magiqcam, build a new dolly, Finish filming three shorts and one feature film, etc.  I'm just trying to give pointers on where you can go to learn the stuff needed to do this.

[cosmin rotaru]

"I think Cosmin would just like to see a simple diagram showing battery, motors, joystick, and anything else needed to make a complete functional circuit. "

Thanks Cody, that's what I needed...



Anyway, I understand this would be time consuming, Sam. I just thought maybe you have the diagram already and could share it with us. I'm not asking you to leave all you're doing and start designing stuff for me!  The 555 circuit seems the simplest solution and quite good for my needs. It is somwere between using a DC motor (maybe without any speed control) and a microcontroled stteper.

Maybe you have some links for DIY or something like that...

Cosmin Rotaru