Hi all,
I have a bit of an odd problem and was wondering if anyone had any tips as to what I can do to fix it. We have a rc boat with an orange cube that drives in circles at low speeds and straight as an arrow at full speed. To give some background to better understand:
We had a short circuit a couple weeks ago and I have since rebuilt things, replaced esc’s, new cables, etc. I had some trouble getting the propellers to spin but am back on track with some oddities. We have two thrusters on our boat.
I have callibrated the ESC’s throttle range, callibrated the transmitter, etc and for some reason when I have 0-75% throttle the boat stears sharply right but when I have 100% throttle the boat goes straight ahead as usual. If I use trim to get the boat to go straight at lower speeds it then doesnt when at full gas. It is almost as if the left thruster has a linear throttle curve and the right thruster has an exponential curve.
@SoundSearcher First thing I would do is try and find where the issue is? i.e. is it the thrusters or mechaical issue or maybe in the configuration and parameters. Can you swap the thrusters themselves and check if the issue persists. If the same thruster misbehaves then I would look at investigating connection to the thruster and thruster itself. Otherwise do a full param reset and start from scratch, that way if you had a bad config that goes away.
If you can drive the boat fully manually, ie without the influence of the stabilization of the controller, you can work on eliminating the boat generated issues.
Are the prop rotations correct? Both props the same size. Both turning correctly relative to the blade pitch, and on the correct shaft. Is there any binding in either shaft? Are the motors the same KV and size? Again do the motors turn correctly to the blade pitch? Are the ESC’s the same? Are the connections from the batteries to the ESC’s then onto the motors, all resistance free? Do both ESC’s get the same power?
If all that checks out, then you are sure the boat is good, and you can work on the controls and behaviour of the esc’s. Good luck!
We have used the boat despite the throttle problems until one of the ESC’s finally gave out. A clear indication that it was part of the problem. I have since changed the ESC but still had some odd behavior with the thruster. Then replaced the thruster and after quite a few callibrations was able to get both thrusters to spin at what sounds like the same rpm’s when driving forwards. The odd thing now is that when reversing the left thruster gives equal until around 25% reverse when it then gives 100%. The other thruster gives a normal linear curve.
Ideas?
To answer some questions, the prop rotations are correct, motors are the exact same with the same propellers (Blue Robotics M200), ESC’s are the same (QuikRun 8BL150), all wiring has been replaced and should be therefore of equal resistance/resistance free, the ESC’s are connected to the same battery pack.
The system did work OK before the problems started, so that is a good indicator that the bits were correct.
To make performance easier on model boats, often props are chosen 1 with clockwise pitch and the other with anticlockwise. Then when looking from the rear, both turn outwards at the top of the blades. This makes turning tighter. If they both turn the same way then the boat can bias turns one way better than the other.
Don’t reverse the ESC for the prop turning the wrong way, but just swap only 2 of the leads from the esc to the brushless motor. In this way the motor will turn the other way, correct to drive the boat forward, and the esc will still have the 1500-2000microS signal driving forward, and below 1500 for reverse. Sometimes speed controllers have a lower output for reverse, than forward. (The QuicRun are like that.)
Because you are running 2 esc’s, both have a BEC at 6V, make sure the receiver or flight controller can accept 6V, some like 5V, and take out 1 of the red power wires from the 3 wire connector to the receiver or flight controller, on 1 esc, to stop the fight over which esc can give more power down the red wire than the other! BEC obviously is battery eliminator circuit.
The ESC’s are much higher powered than the motors, so it seems odd that the esc failed? Do you know why it failed?
Good luck, it will all come right in the end!
Hi again and happy new years!
We’ve been off for the past couple weeks and I just sat down with our thruster problems again now.
We have different propellers (SB/BB) and have our thrusters set to turn opposite directions but it seems my colleague remembered incorrectly as we had both thrusters turning inwards, not outwards as you suggested. I will swap cables to remedy this. I tested the thrusters again this morning and the forward throttle curve seems to be linear for both sides, so that problem is still fixed. The reverse problem with one thruster giving full and the other linear is unfortunately still there.
If I am understanding your suggestion correctly we would have to clip one of the red power wires from the esc. I unfortunately cant do this as in our case, there is none. We have only a signal cable going from the Pixhawk to the ESC. There is a common ground as well but that doesnt go to the Pixhawk.
I know that this makes things even harder to help from a far but any suggestions are warmly welcomed.