bilge vs brushless

[perfo]

I can't believe this question hasn't been asked many many times but after doing a few searches I couldn't find it. So with risk of repeating stuff here's my question:-

What are the pros and cons of the converted bilge pump vs brushless motors.

I'm thinking of going with a hobby king boat ESC and brushless out runner motors and wondering if I'm doing the right thing as most folk seem to use converted bilge pumps.

The costs seem comparable as the bilge will need a h bridge and PWM controllers for full range forward / reverse
and a brush less will need an ESC. I guess the brushless is slightly more expensive but not much in it really.

Water proofing. The bilge looks great in the shallows but can run in to problems at depths (is this right ?) where as the brushless can run at almost any depth but needs a bit of TLC before storage if used in salt water (rinse and spray with WD40 ?)

So as my knowledge has just been all used up (and is theoretical at best) I wondered if you learned types could give us newbies a run down of the ins and outs between the two...
Thanks

[theinlinaung]

There are posts about bilge pumps and brushless motors if not comparison.
I initially planned to use bilge pumps in my ROV but changed to brushless motors because of compact size and water resistance.

Brushless motor is the one used by OpenROV http://goo.gl/3SYsCY
HobbyKing reversible ESC 30A http://goo.gl/NmkpLK

I have been using them for a while now with no problem so far. I have noticed some rust in the inner core of the motor but it does not effect the motor performance.

I haven't used or tested the bilge pumps so I can't compare the two.

[perfo]

Thanks for the post. They are slightly smaller motors and ESC than I've ordered so what size is your ROV and do you think these are big enough? Have you got two for forward reverse ?
at 7 GBP per motor replacing them every few years isn't a major downer. Where as the bilge pumps do need a bit of fiddling with to prepare them.
I guess a squirt with WD40 after a dive would probably help. How do you get on for cooling? Are the ESC inside the ROV ?

[ROVER3D]

Bilge-pumps are for an easy control-solution with relais and direct electrical connection. If you still plan to use it with h-bridge and pwm-controller you better fund your money for the brushless ESC-solution.
It might be more expensive but brushless motors are even much more powerful than bilge-pumps... no comparison

[perfo]

Ah ok. Yes I can see if you want an on/off type arrangement through a relay then bilge pumps could be a lot simpler.

[theinlinaung]

Thanks for the post. They are slightly smaller motors and ESC than I've ordered so what size is your ROV and do you think these are big enough? Have you got two for forward reverse ?
at 7 GBP per motor replacing them every few years isn't a major downer. Where as the bilge pumps do need a bit of fiddling with to prepare them.
I guess a squirt with WD40 after a dive would probably help. How do you get on for cooling? Are the ESC inside the ROV ?

The size of my ROV is around 1 feet squared and weight is around 3 kg.
We used four horizontal thrusters but the motors turn only half speed when moving forward. When moving 45 deg to forward, two diagonal motors turn at full speed.
The thruster assembly provides more than enough thrust for my ROV. The max speed is around 1 m/s!
The thrust won't be a problem unless you have a very big and heavy ROV.
If you can see in the photo, our ROV consists of two stainless steel plates which sandwich the control box. They are used as heat sinks.

The only glitch with the thruster assembly is the propellers produce less thrust in reverse than in forward.

I'll try to post about my ROV in the near future.

IMG_1674.jpg (63.63 KiB) Viewed 6614 times

[a_shorething]

Thanks for the post. They are slightly smaller motors and ESC than I've ordered so what size is your ROV and do you think these are big enough? Have you got two for forward reverse ?
at 7 GBP per motor replacing them every few years isn't a major downer. Where as the bilge pumps do need a bit of fiddling with to prepare them.
I guess a squirt with WD40 after a dive would probably help. How do you get on for cooling? Are the ESC inside the ROV ?

The size of my ROV is around 1 feet squared and weight is around 3 kg.
We used four horizontal thrusters but the motors turn only half speed when moving forward. When moving 45 deg to forward, two diagonal motors turn at full speed.
The thruster assembly provides more than enough thrust for my ROV. The max speed is around 1 m/s!
The thrust won't be a problem unless you have a very big and heavy ROV.
If you can see in the photo, our ROV consists of two stainless steel plates which sandwich the control box. They are used as heat sinks.

The only glitch with the thruster assembly is the propellers produce less thrust in reverse than in forward.

I'll try to post about my ROV in the near future.

IMG_1674.jpg

WOW, thanks for the post. I wish there was a 'yearbook' kind of thing for everyone's ROV with a brief write-up or link to more info. I've never seen one quite like this. I have been thinking about doing some kind of thru-hull thing and using it as a heat sink with a pass-through for the heat-generating items like lights, motors and whatnot.

This setup addresses that really well. COOL! (also thanks for the info on the amount of thrust required for a small class ROV). I had started another thread about the different power requirements for different sized (weighted) ROVs and it didn't really go anywhere. Good to see that a small unit like this is amply supplied by small motors.

[perfo]

I like the ideas...thanks...
Good to know the smaller (cheaper) motors do a fine job. 1m/s (2.3 Mph ish ?) is plenty enough for me..in fact its a bit scary fast for my plans.. I'm not sure I could be trusted with something that is verging on torpedo speeds

[theinlinaung]

I like the ideas...thanks...
Good to know the smaller (cheaper) motors do a fine job. 1m/s (2.3 Mph ish ?) is plenty enough for me..in fact its a bit scary fast for my plans.. I'm not sure I could be trusted with something that is verging on torpedo speeds

Haha that's why we don't drive it at full speed for long.

The problem with a small rov is the cable is large relative to the ROV and so the stiffness of the cable has considerable effect on the movement and the maneuverability of the vehicle. You should address that in your ROV.

You guys motivate me to produce my "yearbook" of the ROV. I'll post it ASAP.
Cheers.

[perfo]

I'm using a very flexible fiber optic at the moment with on board power ... hmmm I should say (for correctness) I plan to use fiber optic. I've got the fiber and it is pretty flexible and light weight compared to cat 5 or other tether..