Homebuilt ROVs Forum

Hi marcane. Yes. After a lot of checking of power supply, changing ESC settings again and again, etc etc, I found that the ESCs would not start up reliably at low speed when using 50Hz PWM for control. Changed to 400Hz and worked brilliantly. Hope that helps.

Ross

Thank you for the answer, will test this when I get home from work in a couple of days.

I have nearly the same setup as kenl yet my thrust numbers seem to be off by a factor of 10 on the low side. I have an equal length lever arm so I am at a loss to what I am doing wrong. I checked the scale and it is accurate at least in the vertical position. It is the same small digital luggage scale some others have here. I have it on its side so the only thing I can think of is that maybe it has to be on its back. Any ideas?

IT could be the Propeller? I know with different props I got very different results.

Try this link http://www.ebay.com.au/itm/3-blade-52mm ... 3f28c83e94

Cheers

Ken

I used 5 different props with the closest being the Graupner 55mm 3 blade. I should be in the ball park I would think but I may order those to see if that is it. I can't believe there would be 10x difference. I checked the scale in other positions and it seems the same. The only other thing is that I am using probably 20ga test clips to connect things which could be providing too much resitance even thought the lengths are 1 foot or so.

TigerShark wrote:I used 5 different props with the closest being the Graupner 55mm 3 blade. I should be in the ball park I would think but I may order those to see if that is it. I can't believe there would be 10x difference. I checked the scale in other positions and it seems the same. The only other thing is that I am using probably 20ga test clips to connect things which could be providing too much resitance even thought the lengths are 1 foot or so.

Can you test it by hanging something on the test clips and comparing that to the weight of it just hanging and see how far off it is (how much added resistance is introduced)?

That does seem like a lot to be off.

Are your power draws comparable (same amount of amps?)

I just finished my first thruster test.

Thruster cylinder :aluminium 6082 t6,magnetic coupling shaft
Motor: Robbe Roxxy 35-29 500 kv navy
ESC: Robbe Roxxy 930-6 (with reverse)
Propeller:Graupner D65 3 blade propeller (2308.65)
Battery:lipo 4s
Test tank:Ikea 60L (too small)

I test forward and reverse at 100% and 50% power.
FORWARD
100% power
THRUST:2.3 kg/5,07 lb
AMBER :8,7a
Watt:139,3
50% power
THRUST: 1 kg/2,20 lb
AMBER :2.5a
Watt:40

REVERSE
100%
THRUST:1.1 kg/2,42 lb
AMBER :7.07a
Watt:117
50% power
THRUST:0.300 kg/0,66 lb
AMBER :1,5a
Watt:21,45

a_shorething wrote:

TigerShark wrote:I used 5 different props with the closest being the Graupner 55mm 3 blade. I should be in the ball park I would think but I may order those to see if that is it. I can't believe there would be 10x difference. I checked the scale in other positions and it seems the same. The only other thing is that I am using probably 20ga test clips to connect things which could be providing too much resitance even thought the lengths are 1 foot or so.

Can you test it by hanging something on the test clips and comparing that to the weight of it just hanging and see how far off it is (how much added resistance is introduced)?

That does seem like a lot to be off.

Are your power draws comparable (same amount of amps?)

The connections are electrical test clips/ wires. I think they are limiting the efficiency. I am getting the about the same current draws. I have seen it run up to 40A briefly which is way over what my 10A multimeter should handle. I get ESC cutouts much over 75% throttle or my battery isn't able to discharge that fast. I have a 3s 25C 2300mA and a 12v 7AH gel cell I am testing with.

I am going to upgrade my wiring to the 16ga power cable I will use to feed the motors on the ROV and see if that makes the difference.

Sweet setup Bubbles, can you tell us more about your housing and shaft seal? Looks like a professional thruster!

Thank you Tigershark.The thruster housing is a combination of aluminium 6082 t6 and acetal.
Housing diameter is 60mm and the wall thickness is 7mm.Total lenght is 23 cm and the total weight of each thruster is 850gr.The shaft has two bearings and I made the magnetic couplings with 6 neodymium magnets on each side .The thickness of separation plate between magnetic couplings is 5mm.I use two orings between aluminium and acetal.