Thanks for the comments and expert opinion. Regarding the hipot test, we connect the negative terminal of the insulation tester to the water through an exposed copper conductor. The thrusters are submerged and allowed to fill completely with water. The positive end of the insulation tester is connected to one of the motor leads (they are all connected together inside) and then the test is performed. The thruster is placed less than 6 inches from the copper lead to minimize the effect of water resistance.
Rusty … I would recommend switching your leads around. Remember “electrons” are negative in charge and will migrate to a more positive source. It will give you a better indication of your true insulation resistance value. Try it and you should notice a difference in your readings. Please remember plate geomerty will come into play also.
The water / copper conductor will be a super sized plate in relation to the windings so you should notice a lower reading energizing with a negative potential vice a positive one. I have EE’s call me crazy but just try it … physics and the laws of nature have a strange way of working.
Rusty, we passed your documentation onto MATE and they cleared the thrusters. Thanks again for helping out. Kids were wondering if you had more stickers they could get a hold of to use on the ROV and any brochures that they could pass-out to other teams intrested in Blue Robotics thrusters.
We got everything wired up and programmed, and we can control on the vert thruster is working great. Left and right, come on and run for a second. The ESCs flash red a few times and never goes green. Than the thrusters stop all together and won’t do anything. We have check wiring, switched joysticks, and put the vert signal on one of the other thrusters just to make sure they are working correct. Any suggestions?
I’m sorry you’re having trouble! I want to verify your setup.
You are using two Parallax gimbal joysticks and an Arduino, correct?
How long are the cables from the battery/power supply to the ESCs? From the ESC to the thrusters? If the cable is very long, you could be seeing a large voltage drop. With just one thruster, the voltage only drops a little but with two it drops lower and the ESCs reset, causing the error and flashing lights.
Are you running in water or in air? The thrusters will draw more power in water.
We have a second pair of 18 gauge power wires running to the ROV for aux power. Should we try wiring that into one of the thrusters to counter the voltage drop?
For that length of tether, 18 AWG is too small to handle the required current. You can use a voltage drop calculator to estimate the voltage drop. Here’s an example calculator.
According to the calculator, the voltage drop will be over 7 volts at 10 amps and the ESC will see 5 volts. Below 5 volts, the ESC will not longer function properly.
I would highly recommend getting a thicker cable for your power tether or using multiple conductors, like your aux power lines. With two sets of conductors you’ll be able to draw around 17 amps before the voltage drops too far. It would still be best to get something thicker (or use 3-4 conductors) because you will have significantly reduced thrust with a large voltage drop.
First, I would put all of the power that I require local on the ROV or you are going to have a tow cable and not a tether to push your power downstream. About the only thing that you can do to keep your wire gauge small is switch from DC and send AC down the wire and convert it local.
Lets assume you need 100 watts local to the ROV and you can only push 10 amps down the line, with a 60 foot tether at 18 AWG you are eating 38.3 watts just on the wire itself. That is a huge amount of power loss. That loss is being computed by Power = Current (Squared) x Resistance. 10 amps x 10 amps x 0.383 ohms. Power loss = 38.3 watts being turned into heat on the tether. Your wattage delivered is now on 61.7 out of what you need. Guess what … little light goes RED. You end up in a crappy circle where you jack up the input voltage to supply your load and burn more power and the saga continues.
If you were to run 120 VAC down the line and use a switch mode power supply like this:
This unit runs with an Efficiency of 77-80%. So with that in mind you will be pushing about 194 watts of power down to the supply to get the 150 watts out … but lets look at how much we are loosing because of current.
We are going to play ideal for a second … our input voltage at the top of the tether is 120 volts with 194 watts of power being delivered. That is 194 / 120 = 1.62 ampere. Now we still have the 0.383 ohms of resistance but now we are only burning ( 1.62 x 1.62 x 0.383 ) = 1.005 watts of power loss on the tether. HUGE difference. That is why Edison got his lunch served to him by Westinghouse and Tesla during the fight of AC versus DC for power transmission.
With the power supply I gave the link to, that would give you 12 volts out at 12.5 amps. If you need more, the same principle still applies. You can push more power down the tether using AC vice DC. I don’t know what you are using for cable, but I would ditch the hobby junk and use some real cable.
You could use SOOW 16/2 or 18/2 and have superior power cable that I KNOW works down to deeper than your ROV will ever see unless it is heading to the bottom of the ocean. This cable is also rated for 600 volt service.
Thanks for helping. I switch the ESCs this morning before going to school, off the vert thruster input and all the ESC worked. To check voltage drop, I unhooked the power wires from the ROV and went directly to the ESCs from the battery and powered each one. The horz. thrusters will still not go green. They flash red and start running immediately. They respond somewhat to the joystick, but they will not zero. After a few moments of try to find a zero location with the joystick, one thruster will drop out and the other continues to run and then eventually drops out. This is basically the same thing that happened before.
Okay. Could you please replace the vertical thruster ESC with one of the horizontal thruster ESCs to make sure that they work alright and are not damaged or faulty? If that works, then there must be some error in the code we provided or the connections to the Arduino.
It’s also possible that the joysticks are not providing the expected “center” command. The code actually prints the signal values it is sending to the ESCs. Can you open the serial terminal in Arduino at baud rate of 38,400 and check the outputs?
Sorry I guess I didn’t read your response well enough. It sounds like you have already switched the ESCs and they work fine. It must be something with the joysticks or the code then.
I think it’s most likely that the joysticks are not behaving as expected. Please open up the serial terminal while connected through USB and check the values. You don’t have to have the ESCs or thrusters connected. Keep in mind that 1500 is “stopped”, while 1900 is full forward and 1100 is full reverse. If the joysticks are being read incorrectly for some reason, it may be sending incorrect values.
Just wanted to up-date you on our progress. We took first place at the Great Lakes Regional and headed to Internationals for our 4th time. Thanks for your help.
