Wow, $15. They are $3.49 at Harbor Freight (http://www.harborfreight.com/7-function-multimeter-98025.html).

I thought you had at least one. Sorry.

John

I'm in Vancouver, Canada and some items locally bought are a tad expensive. The 555 timer at The Source ( Canada's Radio Shack) sells for $5.00 EACH, I can't image them selling them for that price.


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Canada's Radio Shack sucks monkey balls. Best to find a local electronics shop or order online. Anything is better than Radio Shack in Canada. Any time I walk in there they try to cram cell phones up my nose. Have to keep the sales reps at bay by asking about something relatively technical, like how to tie your shoes.

 

Twenty years ago, the ads for RS had this tagline ... You got questions; we got answers. The very next time I visited a RS and they used that line I asked ... "What's the square root of 2?" The look on the representatives face was priceless. I thought for a moment, reminded him of the tagline, and then told him the answer.

 

Multimeter (I know, I don't know why I don't already have one) is in the mail. I want to test the motor with this brushed ESC: http://hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=6468

Is there any way to test it using only the speed controller, or will I need the Tx/Rx system too?

 

Search on "555 servo controller." There are many out there. Pick one you are comfortable with. Our own Bill Marsden may have one in his blog here. [Edit: Actually, it seems Bill's entry is to a list I prepared a long time ago. Here's the link: http://forum.allaboutcircuits.com/showpost.php?p=104945&postcount=4 ] Eventually, a servo controller may be helpful in setting up the sub, but it is not essential.

My advice, however, is that if you have or can get access to a Tx and Rx, you should use them. They are known to work. Why introduce another variable and a long learning curve at this stage?

John

 

Helluva blizzard we just got in the Northeast. My Christmas vacation was "extended" when I was stranded at my uncle's house. I can order the radio system whenever, although we're still not getting USPS service so it won't hurt if I hold off for a few days.

Can you explain how a 555 servo controller will assist in testing? 555 servo controller: 555 IC generates a pulse every so often, and commands a servo (based off a potentiometer)

Got my hands on a multimeter. Results look good, right?

Ohmmeter Test: Touched leads to each end of motor wire.
Black Lead <-> Brown Wire 3.2 ohms
Black Lead <-> Black Wire 3.4 ohms

Voltmeter Test: Touched wires to 9 batteries in series, then touched leads to end of wire without touching batteries. Didn't have alligator clips, so this required some dexterity.
Black Wire <-> Positive (CW spin) 7.8V
Black Wire <-> Negative (CCW spin) 7.5V

Here is what I will order, once I have your "blessings".
30A Brushed ESC: http://hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=6468
Futaba 4GWD 4-Channel 27MHz controller w/ receiver: http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXSNP1**

Happy holidays everyone!

 

Got my hands on a multimeter. Results look good, right?

Ohmmeter Test: Touched leads to each end of motor wire.
Black Lead <-> Brown Wire 3.2 ohms
Black Lead <-> Black Wire 3.4 ohms

Voltmeter Test: Touched wires to 9 batteries in series, then touched leads to end of wire without touching batteries. Didn't have alligator clips, so this required some dexterity.
Black Wire <-> Positive (CW spin) 7.8V
Black Wire <-> Negative (CCW spin) 7.5V

See how many amps are drawn. The leads in the multimeter have to be re-arranged and you use the multimeter leads as an extension of the wire to the motor - one lead to the battery, the other lead to the wire that was connected to the battery. The motor will draw more amps as the load increases.

Checking amps can be pain with the cheaper multimeter's because you have the extra steps in getting the meter ready - and it's easy to fry your meter if you do it wrong. It might even be a good idea to have two of the cheaper multimeters, with one setup for checking amps only.

 

Can you explain how a 555 servo controller will assist in testing? 555 servo controller: 555 IC generates a pulse every so often, and commands a servo (based off a potentiometer)

Re-read post #104 (quoted below) and my response to it. That should answer your question above.

I want to test the motor with this brushed ESC: http://hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=6468

Is there any way to test it using only the speed controller, or will I need the Tx/Rx system too?

As for your radio selection, that is a very limited radio. I have not shopped radios in awhile, but for about twice that price early last year (2009), I got a JR 9303 with twice the channels, ten times the capability, and it included batteries. It appears your selection does not include batteries; although, the Tower listing is a bit ambiguous on that point.

As for whether it will do the job, what jobs will it need to do? That is, I believe it is time for you to draw up a summary of exactly what controls will be needed, how the thrusters will be arranged, and how each channel will be utilized. The operator's manual for radio linked to on the Tower site shows a "shift" plate. The picture does not. I don't think you want a shift plate. The biggest deficiency I see is the inability do "mix" channels (as explained before in this thread). However, whether you will need to do that will depend on your final design and summary that I hope you provide.

As for ESC, I am guessing you will need an ESC for each thruster. My suggestion was and still is that you get one to try before ordering the whole lot.

Did you visit any clubs over the holidays?

John

 

I think I measured amps, with one lead touching the battery and the other touching the wire connected to the battery. It ranged from 3-11mA when spun in either direction, but didn't settle on a current.

It's very hard to find any radio systems that still operate in the 27MHz or 75MHz band. The radio I have chosen is the only radio system I found in the 27MHz band with 4 (or more) channels. The JR9303 is 2.4GHz, right?

Remember how I mentioned an end-of-semester report? I've pared down the 150 page document to roughly 50 pages. You can see in their own words what the mechanical team has decided and their reasoning. I've tried to remove non-important sections to reduce how much is in this document. Ignore the page numbers and figure numbers, they're wrong since I removed some pages. .pdfs have a filesize limit of 5MB, while .doc only has a limit of 2MB, so I made it a pdf.

I've made a table of contents so you can quickly find what you want to read:
3 Three body designs, each improving on the last.
16 Center of gravity, stability
18 Buoyancy
22 Sealant
24 Propulsion (bilge pump motors)
32 My section in its entirety
-49 Propulsion logic table (to go forward: spin left, right motors, etc.)

In my section, I detail the parts I need, rough placement of them, logical wiring diagrams, attenuation calculations, and other stuff. Please take a look.

Do you have any advice on how to find local chapters of hobbyist clubs?

 

Couple typos and grammar errors so far:

Run Grammar Check in MS Word, couple errors in the first 20 pages is all.

This part doesn't make sense, related to the motors:

As the motor spins, brushes make contact with electromagnetic coils, energizing them and creating a magnetic field that works against permanent magnets. This causes a spindle. As brushes continue to lose and
make contact with other coils the motion continues to create energy.

The spindle part, I think you mean rotor, but it is an incomplete sentence so I can't be sure.

Nothing can create energy, motors convert electrical energy/power to rotational energy/torque, which is transferred to the propeller which converts the torque into thrust.

They seem to have left the hardest and most in-depth/complicated part out of their initial designs. There are NO concerns for thermal management from the motor drivers mentioned in the enclosure design section. Since no air is moving inside an ROV this size, heat will be a huge problem. There was a thread just last week where motor drivers were burning out in an ROV because the user couldn't sink heat to the enclosure/water.

Optimal placement would be on the "ceiling" of the submarine's interior.

Actually, the enclosure may be ground if it is metal, acting as a faraday cage, so the best route for the antenna would be to drill a small hole in the top of the sub, and allow the wire to trail along behind the sub. Seal the exit hole for the antenna the same as for the motors. For better results, the transmitting antenna should also be held parallel to the receiving antenna (horizontally). I don't believe submersing the antenna in the water would help greatly, as the loss due to the polarization difference (vertical vs horizontal) is around 20dB, far more than the refraction loss.

The propulsion logic you have shown can all be done with a programmable radio that allows for channel mixing, no extra logic would need to be onboard the sub. The radio linked above doesn't have that ability, nor do any other ground frequency radios. The only simpler solution is to make each motor an axis on one stick. e.g. left side, front motor = left stick X axis, left rear = left stick Y axis, etc.

 

Re: Center of gravity, stability, buoyancy and hydrodynamic.

I think you guys are over analizing center of gravity, stability, buoyancy and hydrodynamic. With the ROV speed of only 1.5”/sec you don't have to worry about streamlining the ROV, if that is a typo and should be 1.5 feet a second then the speed might be too fast depending on what you are doing.

Center of gravity, stability and buoyancy can be taken care of very easily and there is no need to calculate displacement or precisely position equipment for center gravity. Take a look at the attachment.

• 1: 3 inch PVC pipe with end caps, water tight and empty. Provides lots of buoyancy.
• 2: 1 inch PVC pipe. Insert required length of 3/4 inch round steel for neutral buoyancy, to be determined after ROV is completed and placed in tub of fresh water.
• 3: Steel washers are placed over bolts for fine tuning balance (if needed) and to maintain neutral buoyancy in fresh or salt water.

The buoyancy provided by the 3 inch PVC pipe and the weight of 3/4 steel ballast provides lots of stability and center of gravity is a mute point with this set up.


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Thanks for having a look.

thatoneguy
The sections before mine may be draft versions (I'm hoping), I only know for sure that my section is 100% up-to-date. Hopefully the mechanicals caught their errors before submission. I don't think I've even considered heat management before today, and assume the mechanicals haven't if they didn't write about it. Did that other ROV builder come up with a solution to this issue for his?

The enclosure will be PVC piping. Is the best antenna placement still outside of the submarine?

I haven't been able to find any other 4(+) channel radios in 27MHz. Is this one worth a shot? A "Laser 6" 6-channel 75MHz transmitter. http://www.robotshop.com/hitec-laser-6-1.html It's the one that pops up more often when I Google "75MHz radio system channel mixing". Doing the same calculations, the maximum attenuation will be 22.8dB, compared to 27MHz's 13.7dB but if it's necessary for proper (and simple) control, I'm all for it.


Len Whistler
I can't even fathom 1.5 feet a second haha. 1.5 in/sec it is. Thanks for being reassuring on CG, stability, etc. and letting me know that it's something we can't screw up too badly . Of course, as budding engineers, we have to analyze and document every factor in the project. I think we plan to utilize some sort of weight calibration system like yours with movable metal washers.

 

Walking speed of 3 mi/hr is 4.4 ft/sec.

 

Does anyone have any concerns with me purchasing the following:
6-channel 75MHz radio (capable of mixing) http://www.robotshop.com/hitec-laser-6-1.html
and
this brushed ESC? http://hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=6468

I want to test them with my reversible 2-wire DC motor, but if you can spot a major issue, please, point it out.