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T200 loosing thrust while current increases

Hi there,

I made my first test with a T200 and Basic ESC using a servo tester. The motor is submerged by about 20 cm and I have built a pivot to measure the thrust.

The following behaviour can be reproduced:

When I set PWM to 1700 I get 1.7 kg thrust at 16V/4.5A
Thus lasts for some time between 10 seconds and a minute
Then, the current increases to 5.4A and the thrust decreases to 1.2Kg. The sound of the motor is also changing.
This switch from higher to lower thrust happens instantly.
The only way to get back to the 1.7kg/4.5A is stopping the motor (PWM 1500)

Any idea what could cause this behaviour?

Best regards

Thomas

Hi @TDP,

Based on how shallow you are running the thruster, it’s likely sucking air from the surface,

-Adam

Dear @adam,

Thanks for the feedback.

at this low current, it does rarely suck air and only for moments - but in any case, I think, this behaviour that the motor gets in a state with higher current combined with less thrust should not happen. It seems as if the ESC gets kind of out of sync …

As I use the basic ESC that came with the thruster: should this work out of the box or does it need to be programmed?

Best regards

Hi @TDP,

The Basic ESC is ready to go out of the box, no programming is necessary unless you want to change any parameters.

Any other time I have heard of or experienced a similar issue, it was either due to air or some other solid debris getting sucked into or otherwise affecting the thruster.

If you can try another ESC and still see the same behavior, the issue is likely elsewhere in your setup.

-Adam

Hi @adam

good to hear that the basic ESC should work out if the box.

I checked again today - the problem is repeatable, also at 14V input voltage. There is no debris is the water (it is a water bassin made from stone which gets water from a spring). It also does not suck air at all at 14V (rarely at 16V).

Additionally, I also observed that the thrust goes down to zero once in a while for a split second letting the whole setup shake. No way to use this with a SUP :slight_smile:

Today, I looked with an oscilloscope at the voltages - one can see the ripple caused by the ESC but this is normal - the ripple does not change when the motor switches from the high thrust / low current mode to the low thrust / high current mode.And again, the low thrust / high current mode comes with a different, slightly rattling sound.

Also the PWM for controlling looks fine. And yes, all contacts are well soldered, no loose contacts or shorts!

The ESC is mounted on a large cooling block and does not heat up remarkable.

I left the cable from the T200 in the original length because I plan to mount the betters and ESC on top of the SUB and would need the full cable length.

The whole setup is just the T200, the basic ESC, the servotester (generating the PWM) and 1500W regulated power supply. No any capacitors, coils, ferrite, … for any type of noise cancellation)

I have no other ESC with which I could try the setup.

Can you please confirm that my setup sounds good for running the T200 with basic ESC or if I should add any components?

Any other idea what I could do?

Best regards

Thomas

What is happening with your engine RPM when you lose thrust? Increasing or decreasing?

If RPM gets higher when you lose thrust, it really sounds like air is getting into your system. It’s possible that your static thruster mount is allowing cavitation at high thrust levels. This behavior might go away if the thruster was moving forward through the water. Mounting it deeper (higher water pressure) might also help.

If your RPM get lower and current goes up when you lose thrust, that sounds more like an electronic issue to me. I’d start by ruling out your power supply. Do you have a car battery you could power it with during testing?

Hi @StrikeLines,

thank you for your feedback - it helped me to get it running!

I had no air in there and the RPM was going down while the current was going up!

But what helped was exchanging the power supply against a LiPo battery and the servo tester against an Arduino Nano. The first solved the problem with the lost in thrust / current rise and the latter the intermittent complete lost in thrust for a split second.

Wille the lab power supply is perfectly fine delivering 1500 watt and I was using only a small fraction of this, it obviously did not like the chopped current - I assume that this did cause too much of a ripple and thus letting the controller in the ESP getting out of phase.

The servo tester was a very cheap one - seems not too good.

As I planned to build the SUP controller around an arduino Nano, it’s good that this is working now!

Next step is building a test stand with force gauge for the T200 to make the remaing development wor convenient and number driven. If of interest, I can post the steps here,

Best regards and thanks again,

Thomas

Awesome! Glad I was able to help!