Hi Torque Servos

Have been asked to redesign a wiper unit. The current unit has heaps of issues design wise.

It currently uses a Hi Torque RC Servo to move a tooth brush over some light logger to prevent algae building up on them as they are used underwater.

Can I connect direct to the PICAXE and run the servo off a 6V supply as the PICAXE is only providing the move signal?

The nice people that created the original units have removed the label on the current controller so all I know its a 20pin device and they have a driver for the servo. Non of the documentation indicates a need a driver to use a servo.

The short answer is YES.

Servos have their own "driver" inherent in the design. Your immediate concern will be that the PICAXE power of 5 volts is different than the servo power of 6 volts. Easily handled, though.

The long answer might question whether there is a need for additional sensors involved to determine WHEN to wipe the "light logger."

Ok thanks for that. Haven't worked with servos before so just wanted to be sure.

They are marine biologist so they have requested every 15mins as the current system is every 30mins and doesn't work in every location. If they are wrong then it will be a simple timing change.

The hard part is they want the seal on the servo changed as a couple have failed at 30m depths. But is they get 90% of the request fixes I'm sure they will be happy.

Perhaps you could experiment with filling the servo with some high quality mineral oil or similar?

Servo & 30 metres depth - you'll be lucky !.

Waterproof Servos are only splash proof.

Maybe the current servo is a special variety and not a £2 hobby servo Neil.
Is that the case cybernet?

The problem here is that the term 'servo' is often interpreted as a hobby toy servo.
(It may be a modified hobby one but it would be nice to nail that bit)
Can you enlighten the readers about the make and type of servo?

If seals are failing you'll have an engineering issue as well as the drive - or is someone else doing that bit?

The servo is mount in a water proof plastic housing with battery and control PCB. There is a seal on the shaft the protrudes the housing that still needs to be looked at. The housing has a screw tread and o rings standard method used by most underwater probe manufactures.

The description 'High Torque RC Servo' is pretty meaningless without knowing more about the actual hardware you have. As you say 'O' rings are used for seals on subsea equipment but that's like saying resistors are used in electronic equipment.

Running the servo (model type) off a different supply is pretty simple, its also preferable.

You say there are heaps of problems, it does not sound like the Picaxe is one of them!

Ian

Ok the servo that is used is towardpro MG996R.

I have no idea what chip was used other than it has 20 pins.

The listed 5 key issues with the design of the unit and 10 key things they want changed.
As far as the servo is concerned they have had the seals fail twice (which they think may be a depth issue), has no defined ark (so trial and error setting the unit up) and needs to operate more.
The rest of the issues are things like battery is loose in the housing as well as the PCB. The spacers for the tubes that hold their loggers are not attached to the housing making it hard for them to assemble it as it uses to large hose clamps to hold it all in place.

Its almost like they lost interest in the project as the housing is well machined but the rest is just substandard botch job.

Not that I have used a PICAXE before, but it looks like it will do the job. I haven't done any programming in donkeys years. Only chip I programed was a PIC about 11 years ago and it only controlled the brightness of an LED. So if I can master controlling the servo I will be happy. Need a new hobby.

Any Picaxe will 'drive' that servo (and can set the operating arc) and the programming aspect should be easy if you have already done some programming before.
If the 20 pin chip is what was used for control (I assume its not the chip in the servo), has no ID and you have no data, then I would ditch it and just use a Picaxe. Its best to regard the servo as a 'black box' and not get involved with its internal circuitry or mechanics, just make sure that the servo load and its working conditions are within its specification. Bear in mind that model servos are meant for models and not rated for industrial use.

The seal problem is not a 'depth' issue is more to do with design, as are the other faults you mention.

Ian

See waterproof servos at http://www.bigsquidrc.com/hitec-waterproof-servos/

7 = Immersion up to 1M for the HitTec models - OP needs 30M

I pictured (in my mind) a "box" similar to an underwater camera housing where the servo shaft is EXTENDED to pass through an O-ring sealed opening in the housing.

Unless the "box" is open to water pressure, I don't see that the servo needs to be waterproof.

There may be a mechanical failure mechanism involved with the servo output.

http://rs859.pbsrc.com/albums/ab155/cybernet/LR15_zpsf399be5f.jpg~c100
http://rs859.pbsrc.com/albums/ab155/cybernet/P1030094_zpsd4128247.jpg~c100

Not sure if the links works didn't like any of them posting normally. If they work will give you a better idea of what this project is.

elanman99 said:

Any Picaxe will 'drive' that servo (and can set the operating arc) and the programming aspect should be easy if you have already done some programming before.
If the 20 pin chip is what was used for control (I assume its not the chip in the servo), has no ID and you have no data, then I would ditch it and just use a Picaxe. Its best to regard the servo as a 'black box' and not get involved with its internal circuitry or mechanics, just make sure that the servo load and its working conditions are within its specification. Bear in mind that model servos are meant for models and not rated for industrial use.

The seal problem is not a 'depth' issue is more to do with design, as are the other faults you mention.

Ian

Click to expand...

No its external and I figure with all the chip makers even taking into account the pins use after a month would be still looking for a needle in a hay stack.

As for PIXACE being able to do the job I'm a tad disappointed, was way too simple only issue I had was forgetting to move the programing cable. Still have to work out the required angles and go to real time. May need to complicated it. May be a magnetic start and stop. That would make it easier to deploy.

Just a thought, but would a fairly high jet of water be an alternative to the brush. With the pump within the watertight enclosure, just the water pump intake and exit would need to penetrate. No problem with sealing a rotating shaft. Small pumps can be found at model boat stores. The type used to squirt water through a fire monitor or as used for bow thrusters may be possibilities. A car windshield washer pump may be an alternative, but would need close to 12V.

Why limit cleaning to just an arc? You can program a scrubbing motion over those sensors.

Magnetic coupling too your output from inside a 100% sealed box?