Quad-Motor Control - Long Distance

[JavaDog]

Ok, once again I come to the smart people for electronics help. This isn't related to my CNC machine, rather it is for my Underwater ROV.

I received my motors and I am now working on a way to control them. I would love to use my 4-way analog arcade joysticks (they use cherry switches) for control - or even toggle switches. A software based control would be awesome, but I think that is out of my range right now. Just to make it more difficult, I am limited to 8 conductors on my tether. Three of those are used for the camera/video.

I found some interesting off-the-shelf kits that I think will work for some things. For instance, one motor will be used to vertical control - and for that I was thinking of using this kit. Looks like it will be perfect for the one vertical thruster.

Now, for the other four (or two if that is all I can manage) motors, I had looked at this kit, which seemed ideal (the two wire/10 output control would be excellent) but I don't think it has the power to drive the motors I am using? Correct me if I am wrong? Also, not sure if this kit can drive two (or more) outputs at the same time?

I also found these schematics that another ROV builder had come up with. They look great! They even look like they would work excellent with my motors too and they use cheap old PC joysticks. However, they use PIC chips - which I have no idea how to use? He has the ASM code for the PIC chips, and the chips themselves (actually the whole package) are very afforable - but how do you get the code from a pc to the PIC?? I think this might be the most promising route...

Any new ideas or thoughts would be much appreciated! Thanks guys, I know you will be able to come up with something!

[Evodyne]

Easier than the PICs are the BASIC stamps. Look at the Parallax site. These are programmed in (I'll bet you can't guess) BASIC. Your program on the PC and download to the chip via a serial cable. Actually the chip sits in a motherboard for this-you can pop it out, pop in another one, program it, etc.

The chip configurable I/O pins and can do an A/D converion of sorts. This is how the joystick would be interfaced.

The chips can talk to each other as well! They can communicate via a serial connection (3 wires-transmit, recieve, and ground). To go any distance though you might need a special driver circuit, i.e. line drivers or current loops, etc.

So, for your setup, one joystick/topside chip could send commands to a bottomside chip that would run the motors. Given the number of I/O, it could do more(pan/tilt/zoom/lights on-off).

I've got an older development kit (one motherboard and chip, cable, documentation, etc) I'll donate to your project. The software is free off of the parallax web site. You'd need one more chip and a handfull of other stuff we can figure out to make it talk over a distance. All I ask is that you pay shipping. How's that sound? Email me if you're interested.

Your ROV soulmate,

Lance/Evodyne

[JavaDog]

Lance,
I actually have a BASIC Stamp development kit floating around. I got it a while ago, and never played with it. It never even occured to me that I could use them for this project. Heck, I even know how to write BASIC code to boot.

So, is Parallax's website the best source of info for working with these guys?

Would I have to add something like their MotorMind boards, or can I control the DC motors directly like that schematic I posted did with the PIC chips?

[Evodyne]

Originally Posted by JavaDog Lance, I actually have a BASIC Stamp development kit floating around. I got it a while ago, and never played with it. It never even occured to me that I could use them for this project. Heck, I even know how to write BASIC code to boot.

Wow! Now you sound like me. Doy!

Originally Posted by JavaDog So, is Parallax's website the best source of info for working with these guys?

You'd have to browse it and see for yourself-I really haven't played with my kit in quite a while, so I'm not really sure. In general though there are lots of good resources.

Originally Posted by JavaDog Would I have to add something like their MotorMind boards, or can I control the DC motors directly like that schematic I posted did with the PIC chips?

Do you know what motor drivers those are? I'm guessing they are direction and PWM (pulse width modulation) types. Electrically, yes, you could use these. The problem is that the Stamps are S-L-O-W and probably couldn't handle the PWM signal generation. Motor Minds or similar might be the best bet, as they free the Stamp from needing to worry about any of this.

I did see somewhere where a guy had used stamps in an ROV and had a lot of success. I don't have a link-sorry, but you might google Stamp and ROV and see what pops up.

[JavaDog]

Hmm...so I would still need to buy one of the motormind boards to get the basic stamp to do what I want - in addition to a second basic stamp. Those motormind boards are like $40-$50...more than I can spare. I like the idea of the basic stamp (I am going to dig out my kit and play with it regardless)...but maybe not for this case.

It seems like the PIC route, although more difficult (programming wise), is the cheaper alternative? Plus, I have those schematics and code to work from.

I already answered my "how do you program a PIC" question. Seems you can make a serial programming cable for just-about free.

Any other thoughts/ideas?

[Evodyne]

J.D,

Vibrator motors? Ten amps? Hmmm. There are so many things I'd like to say, but I'd better not. Hmmm again. Ten amp vibrator motors-he he he.

O.K. Back to reality. Take a look at this site. Might be interesting for you.

I looked at your motor specs. When stalled you can pull 9-10 amps per motor. Think weeds in the props! The L298 chips (the motor drivers) are good for four amps total. :frown: At four amps they will get hot pretty quick. I've attached the .pdf with the specs for the chips. Plus these are just "dumb" H-bridges, you get nothing in the way of overheat shutdown protection, etc. There are better choices.

You might get a trolling motor blade and hook it to a shaft and hook that to your motor. Put an ammeter in series (on the ten amp range), stick the prop in a pool, and drive the puppy with a car or cycle battery. Get a feeling for your current draw-you might be suprised.

Remember that the motor current is going to have to travel up and down your umbilical. Actually the sum of the current for the four motors all together. What gage wire are you using-and how long? You'll want to avoid losses in the cable.

Evodyne

[JavaDog]

Originally Posted by Evodyne J.D, Vibrator motors? Ten amps? Hmmm. There are so many things I'd like to say, but I'd better not. Hmmm again. Ten amp vibrator motors-he he he.

Ha!

Originally Posted by Evodyne I looked at your motor specs. When stalled you can pull 9-10 amps per motor. Think weeds in the props! The L298 chips (the motor drivers) are good for four amps total. :frown: At four amps they will get hot pretty quick. I've attached the .pdf with the specs for the chips. Plus these are just "dumb" H-bridges, you get nothing in the way of overheat shutdown protection, etc. There are better choices.

Crap, didn't think of that. If I can make it so that the props shouldn't get fouled - that will help a bit. But still, I get what you are saying here.

Originally Posted by Evodyne You might get a trolling motor blade and hook it to a shaft and hook that to your motor. Put an ammeter in series (on the ten amp range), stick the prop in a pool, and drive the puppy with a car or cycle battery. Get a feeling for your current draw-you might be suprised.

I will do that and find out where we are...

Originally Posted by Evodyne Remember that the motor current is going to have to travel up and down your umbilical. Actually the sum of the current for the four motors all together. What gage wire are you using-and how long? You'll want to avoid losses in the cable. Evodyne

Um, RJ11 cable? I know, I know - I will need new cable. I need to keep the cable around 8mm-10mm dia, and flexible. Any thoughts on gauge?

[Evodyne]

J.D,

Look here for a wire gage vs. current chart. #12 to #14 is "house wire" gage and can handle about 40 Amps. If you bet on never running all four at 100% you might decide to go smaller yet. You can always use tie-wraps to bundle power and data cables together into one unit. I've seen somewhere where a guy placed little floaties so many feet down the length of the cable to keep it neutrally bouyant too. One more thing (and I don't know the answer): not all insulations are equal-some will "waterlog" (bad). Maybe the whole thing (data and power wiring) all needs to go in a protective sheath???

Lance

[JavaDog]

Originally Posted by Evodyne J.D, Look here for a wire gage vs. current chart. #12 to #14 is "house wire" gage and can handle about 40 Amps. If you bet on never running all four at 100% you might decide to go smaller yet. You can always use tie-wraps to bundle power and data cables together into one unit. I've seen somewhere where a guy placed little floaties so many feet down the length of the cable to keep it neutrally bouyant too. One more thing (and I don't know the answer): not all insulations are equal-some will "waterlog" (bad). Maybe the whole thing (data and power wiring) all needs to go in a protective sheath??? Lance

Well, at most there will be three motors running at once. That would be the one vertical thruster (which will always be on) and both rear motors. I think for simplicity I will start out with three thrusters.

Problem with a lot of those larger gauges is that they are not even close to flexible. I really wonde what companies like VideoRay and SeaBotix do for their tether. They run MUCH higher voltage/amperage than I am, and have a tiny 8mm tether - and I think it is only a 4 conductor. Sadly, can't just call and ask them - for some reason they don't like to give out info like that.

[Runner4404spd]

you want to buy wire thats called robotic cable. its very finely stranded and very flexible. we use that in industrial assembly machinery. its not super cheap but its the best stuff out there for freedom of motion.

[JavaDog]

Originally Posted by Runner4404spd you want to buy wire thats called robotic cable. its very finely stranded and very flexible. we use that in industrial assembly machinery. its not super cheap but its the best stuff out there for freedom of motion.

Thanks. Any idea on where to source it? I'll check google, but I thought you might have known someone with better prices...

I found this from Alpha - is this what you are talking about? I didn't even know stuff like this existed!

EDIT: Holy crap! It is over $3.50 a foot!!

[Al_The_Man]

Another thing to remember is wire current carrying capacity is based on conduit or raceway installations, if a conductor is water cooled or used in a completely different environment, amperage rating changes, the voltage drop will still exist, however.
The larger the amount of strands, the more flexibility but the cost goes up.
Another source is welding cable, but I don't know what gauge they make that down to.
Al.