Robotic Sushi - FAO Davy

[anonymous]

Hi Andy,

The "swimmer" PIC and

Hi Andy,

The "swimmer" PIC and board are on thier way to you.

It has ahead,left, right and stop controlled by switch input. Any switch would work - even controlled by servo. It could even be a single channel fish! PWM inputs will take a little longer.

Let me know how you get on with it and I'd appreciate some info on the mechanical linkage.

See you at Norwich Sub Day??

David

[Guest]

Dave,

That's great news!

Wow, really have

Dave,

That's great news!

Wow, really have to get my finger out now, and get this thing built.

I should hopefully be at Norwich.

So to control this fish, I'll need a switcher unit with four outputs, correct? These feed into the PIC input channels for stop, go, turn right and turn left.

Or have I got the wrong end of the stick here?

Andy



Edited By Sub culture on 1152039842

[anonymous]

Hi Andy,
A switcher may be

Hi Andy,
A switcher may be a bit over the top. You'll see what I mean when you have a go with the board. Earthing a pin puts the function on.

It would be possible to activate 3 micro switches or push buttons with a servo arm to get the functions. If this seems a little in-elegant, the PWM version should not be too many weeks away!

My first thoughts were to see if the fish swims forward, right left etc. (I still find it hard to believe!) and if a servo is powerul enough So maybe we should aim for an initial "lash-up" trial in the home test tank!

Let's get swimming!

David

[Guest]

Dave,

Servos are pretty torquey these

Dave,

Servos are pretty torquey these days.

Check this one out- 417 oz in. torque!! -

http://servocity.com/html/hsr-5995tg_ultra_torque.html

Now I don't think we'll need anything like that, but it's comforting to know that those kind of things are now available. Not cheap though.

Now regarding a switcher. This is a unit i had in mind-



It's our way, and the outputs act as grounds, so perfect. It's also tiny and quite cheap (about a tenner).

Works off a single channel. More info here (in German I'm afraid)

http://www.cti-aichtal.de/shop/anleitung-ps4a.pdf

Andy

[anonymous]

Hi Andy,

At least it's not

Hi Andy,

At least it's not in Chinese!

That could well do the job and for a tenner I could hardly get the parts.

Slight health warning though since my German will not get me more than a beer! Don't put more than 5v on the Swimmer PIC.

Get that fish tail flapping!



David

[Guest]

This is what I had

This is what I had in mind-

[himszy]

If the 4 ch switch

If the 4 ch switch is, left, right, forwards, backwards, then how to you go forwards and left?

Michael

[Guest]

No reverse.

Swim forward
Swim left
Swim right
Stop.

Four

No reverse.

Swim forward
Swim left
Swim right
Stop.

Four functions.

It's basic, but it does work well, because I've used that system in the little toy RC shark.

Unfortunately the RC shark is very small, has terrible batteries, and the range of the radio on mine was abysmal, although others have reported more success with theirs- perhaps I got a duff one.

With a scratch built fish, I can use a decent radio, better batteries, plus I can ballast the thing easily, and make it a decent size.

[himszy]

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Edited

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Edited By Himszy on 1152121662

[Wheelerdealer]

Sounds neat, I'll have to

Sounds neat, I'll have to see this fish when its done. 7.2 will shorten the life of the tail servo considerably, best stick with 6v.

[Guest]

Why do you say 7.2

Why do you say 7.2 volts will shorten the life of the servo considerably?

I'm referring to special Hitec robotic servos, which are designed for use with this voltage.

Andy

[Wheelerdealer]

Why do you say 7.2

Why do you say 7.2 volts will shorten the life of the servo considerably?

I'm referring to special Hitec robotic servos, which are designed for use with this voltage.

Andy

Missed that bit, thought you were usung a normal servo

[Guest]

As it so happens I

As it so happens I purchased a servo yesterday.

I plumbed for a Hitec HS-635HB. This is a high torque servo with 'karbonite' gears. These are exceptionaly rugged gears which wear much better than either nylon or metal.

On 5.0 volts the thing is virtually unstoppable.

It cost £20 from Als Hobbies (good price) and is fully ballraced with a lovely smooth action.

I considered a digital servo was complete overkill for this application.



Here is a little picture of what I have together so far.

On the top left is the afore mentioned servo, next to that is the little PIC board sent through from Dave Forrest.

Next to that is a very nice little BEC board I purchased with the servo. This little thing is a switch-mode device that can supply either 5 or 6 volts at 3 amps from a 5.5 to 23 volt power source.

You can select the output voltage using a small jumper which you can just see on the bottom of the board.

It's made by Dualsky and cost about £10.

The three small boards to the bottom right are some little switchers I'm making up. These trigger the various functions on the PIC board.

I did find an off-the-shelf switcher, which is tiny and cheap. However I considered the means of controlling the switching didn't quite work for the fish. So I looked around for an alternative.

These baords are designed by Ken Hewitt. The design can be downloaded here, and it is very simple and cheap (about £1 per switch) to put together. I'm waiting for some more components to arrive to finish the boards off, which should hopefully arrive in the next couple of days.

I'm using a much smaller logic level MOSFET for the switches, than specified in the design. The original was overkill for this application.

They are bulkier than a commercial design, but that isn't an issue as I have plenty of room inside the fish.

Andy

[himszy]

Andy,

What's changed on a servo

Andy,

What's changed on a servo to increase its torque? Can't just be a case of changing the gear ratio surely?

Michael

[Guest]

Hotter motor, slightly lower gear

Hotter motor, slightly lower gear ratio (high torque servos are usually marginally slower than high speed) and thicker gears.

Andy