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Author Topic: Caldercraft Northlight Puffer with working Derrick Crane  (Read 86758 times)

Corposant

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Caldercraft Northlight Puffer with working Derrick Crane
« on: October 09, 2008, 07:44:12 PM »

Is there any way of increasing the dead-band of a servo (Hitec HS-322 HD) that has been modified to produce continuous rotation? It has a tendency to creep and I am concerned that the slightest lateral movement of the tx stick is going to start an unplanned function.

I imagine the continuously rotating Hitec HSR-1425 CR still has the standard 8usec dead-band since it appears to be used in computer controlled robots.

I should point out that I am building my first model boat and am new to the forum. Any advice gratefully received.

Mike
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Sandy Calder

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Re: Modified servo
« Reply #1 on: October 09, 2008, 08:25:53 PM »

I can only suggest looking up the IC datasheet of the servo amplifier.
If the servo had an old NE544 or ZN409http://www.meditronik.com.pl/doc/plus/zn409.pdf it would be a piece of cake.
Regards
Sandy Calder
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Weeds

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Re: Modified servo
« Reply #2 on: October 09, 2008, 08:33:15 PM »

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Sandy Calder

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Corposant

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Re: Modified servo
« Reply #4 on: October 09, 2008, 09:36:31 PM »


Sandy, Thanks for your initial reply. I peeled the sticker off the chip but can't find any data about it (Hitec's own). The surface mounted components would make any changes a bit tricky!

Weeds, Thanks for the link to the Runryder thread - very interesting.

Sandy, You're obviously more observant than me! The Servocity website was where I found the HSR-1425 CR but hadn't noticed the comment about the increased dead-band! It looks as if that would be the answer - if it can be obtained in the UK. Thank you so much for your help.

Mike
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Sandy Calder

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Re: Modified servo
« Reply #5 on: October 09, 2008, 10:04:58 PM »

Sandy, You're obviously more observant than me! The Servocity website was where I found the HSR-1425 CR but hadn't noticed the comment about the increased dead-band! It looks as if that would be the answer - if it can be obtained in the UK. Thank you so much for your help.
Cut it out!
Googled HSR-1425 CR and that link was hit #1

I thought that is what you had as I wasn't paying attention.
Post in Black Arts and you might get a response.
Stick the Hitec HS-322 HD board on a document scanner and take a topside photo and upload to photobucket as it might help those who have used them in the mini subs and warship rc conversions.
or wait the 4 days from US or find a UK source.
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FullLeatherJacket

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Re: Modified servo
« Reply #6 on: October 10, 2008, 08:37:01 AM »

Mike
Can I ask what application you are planning for this beast? There are several ways of controlling the speed and direction of a small geared motor. The CR servo mentioned only rotates at about 40 RPM anyway, which seems too fast to traverse a gun turret or crane and too slow for a main propeller or paddle-wheel drive.
FLJ
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Corposant

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Re: Modified servo
« Reply #7 on: October 10, 2008, 10:56:14 AM »


FLJ,
I'm building a Caldercraft "Northlight" and the aim is to make the derrick functional. I have re-made bits of the winch in brass and mounted a motor under it. The idea is to pass the thread for the main hoist and that for raising and lowering the boom once round the main winding drum and one of the warping drums respectively before passing through the deck to servo driven drums below - hence the need for continuously rotating servos. These would appear to have the advantage of a combined ESC and built in motor thus (hopefully) making them a cheaper option.

Mike
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Martin [Admin]

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Re: Modified servo
« Reply #8 on: October 10, 2008, 11:21:45 AM »


Hi Mike,
 I WAS going to attempt that for Jan's Puffer but found the the boom and hook weren't heavy enough to
 lower themselves back down, how do you plan to overcome this?

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Corposant

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Re: Modified servo
« Reply #9 on: October 10, 2008, 12:22:44 PM »


Martin,

I am anticipating problems! My thoughts so far are to make the pivot points very free moving, using thin thread (therefore more flexible) and possibly inserting a piece of lead in the end of the boom. The project is probably a bit ambitious for a first build. I will post a progress report in due time (but I am very slow!).

May I say how much I enjoyed your series on building Jan's puffer; it was really useful.

Having only just purchased the radio control set, my attention is currently focussed on the steering gear. Yes, I have remade the pulleys and bought a bit of silver chain!

Mike
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malcolmfrary

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Re: Modified servo
« Reply #10 on: October 10, 2008, 12:52:42 PM »

For this particular job, the deadband can be increased by changing components as detailed in the links previously given, or
1/  Intercept the wiring to the motor.  Connect a pair of sub-min relays and diodes so that the relays are operated by the electronics board output, one for forward, the other for back, the contacts working the motor.
2/  Remove the servo electronics altogether and replace with one of Action's micro controllers.
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FullLeatherJacket

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Re: Modified servo
« Reply #11 on: October 10, 2008, 01:26:24 PM »

Mike
Do you really need to control the actual speed of rotation by radio as well as the direction? If not, you could adopt a simpler set-up with a small geared motor (of which there are numerous on the market for pennies) which is run via a bi-directional switch. See this link:

http://www.action-electronics.co.uk/pdfs/Limit%20Switches.pdf - the top diagram refers. No dead-band problems here - and that's guaranteed.

You simply hold the stick over until the desired position is reached then let go and the motor stops. The limit switches prevent over-running at the end points.
If you need to adjust the speed of the motor then our buddy PMK published a simple PWM device on the Forum a while back which works a treat. You just tweak the pot to adjust the speed. I've built a couple for customers who report it does the bizz, and I have a couple of spares kicking around for anyone who wants to try one.

Suit yourself.

FLJ
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Sandy Calder

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Re: Modified servo
« Reply #12 on: October 10, 2008, 02:47:03 PM »


http://www.action-electronics.co.uk/pdfs/Limit%20Switches.pdf - the top diagram refers. No dead-band problems here - and that's guaranteed.
FLJ. Who did that lovelerly diagram of the P44 and limit switches?
Did you promise a free P45 for it?

Regards
Sandy
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Corposant

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Re: Modified servo
« Reply #13 on: October 10, 2008, 03:01:45 PM »


Malcolm,
Many thanks for your very practical suggestions. The second looks the easier to achieve (see my reply to FLJ!).

FLJ,
No, there will be no need for speed control. Your P44 looks just the job! It would also make it easier to run the winch motor in parallel. As I am heading into un-charted waters (I have no pond-side experience!), there remains in my mind the problem of starting a function inadvertently. Does the P44 have a "reasonable" dead-band?

Mike
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Sandy Calder

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Re: Modified servo
« Reply #14 on: October 10, 2008, 03:45:54 PM »

This diagram might be a better guide if you use that switcher.

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FullLeatherJacket

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Re: Modified servo
« Reply #15 on: October 10, 2008, 04:33:31 PM »

FLJ. Who did that lovelerly diagram of the P44 and limit switches?
Did you promise a free P45 for it?

Regards
Sandy

That'd be me. Got my P45 from HMRC two years ago and only then found out what "hard work" really means! Thanks for the addendum relating to two motors, BTW.

Mike
Ref P44 deadband - the switch triggers the relays at about 40% full deflection each side of neutral i.e. about 1.3ms and 1.7ms.You WILL need a proper proportional channel; one of the auxiliary ones which has a simple two-way (ON/OFF) toggle switch won't do the job. Ring me if you need any further info - phone number is on the website.
FLJ
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Sandy Calder

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Re: Modified servo
« Reply #16 on: October 10, 2008, 04:49:28 PM »

In case of confusion, M1 and M2 in my diagram just refers to the brushes of the single motor.

The diagram in the present pdf link will work but the 1N4003 conduct the motor current.


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Corposant

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Re: Modified servo
« Reply #17 on: October 10, 2008, 05:30:56 PM »


Sandy,
Thanks for the extra diagram.

FLJ,
"Perfick". The radio set has 5 proportional channels. We're off to Cornwall for a few days on Monday. I will give you a ring when we get back.
Regards,
            Mike
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Corposant

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Working Puffer Derrick crane anyone?!?!?
« Reply #18 on: October 06, 2009, 07:33:51 PM »

Last October (last October!!!!!!!!!!!!), when I said I planned to make the derrick functional on the Caldercraft puffer I'm building, Martin said he had hoped to do the same for Jan's "Highlander". He asked me how I planned to do it.

Herewith a progress report (if it can be called progress after all this time!).

There have been many periods of doing other things and several of giving up!

Step one was to make a mock-up to check feasibility - prior to purchasing FLJ's P44 devices to overcome the servo dead-band problem. I then spent an inordinant amount of time making the pulley blocks:






I naively thought that maintaining gentle tension on the lines for lateral boom movement would be simple! The current, elasticated, solution seems extemely crude - but how do you maintain even tension over a relatively long range of thread movement?



The final problem is finding suitable thread. So far, I have tried five. The ones that look best are not flexible enough to run freely through the blocks. The thin ones are too hairy.



There is great danger of a tangle occurring, out of sight, below deck. The winch will be a bit fiddly to remove.



The weight hanging on the boom is 4.5g so a slug of lead, weighing about 10g, inserted in the end, should ensure reliable operation.



I have completely given up trying to maintain tension on the secondary single line - it will just have to flap around in the breeze! (How was this used in real life?)

The project looks feasible - but only just!

Martin made the right decision!

Mike
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Dave Buckingham

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Re: Working Puffer Derrick crane anyone?!?!?
« Reply #19 on: October 06, 2009, 09:36:44 PM »

Hi Mike
I expect the Topping Lift was used to raize the Derrick then the single line was fixed to a cleat as a back up or depending on the method also used while fixing the topping lift.

Dave
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Corposant

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Re: Working Puffer Derrick crane anyone?!?!?
« Reply #20 on: October 06, 2009, 09:59:03 PM »

Thanks Dave - that would seem logical. The difference in ratio makes it a bit of a problem for modelmakers though!

Mike
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Martin [Admin]

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Re: Working Puffer Derrick crane anyone?!?!?
« Reply #21 on: October 06, 2009, 11:05:53 PM »


  At one stage I contemplated using a solid steel boom to keep a tension on the lines.....

    LOVE your winch! http://s949.photobucket.com/albums/ad338/photomultiplier/?action=view&current=08_06_14_01014.flv

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tigertiger

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Re: Working Puffer Derrick crane anyone?!?!?
« Reply #22 on: October 07, 2009, 02:25:13 AM »

If the bottom line is mostly cosmetic, you could consider using some of that hatters elastic thread. It could still run, if following not pulling, and maintian a tiny bit of tension without causing a lot of friction.

I don't know if it would work, but it is an idea.
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Roger in France

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Re: Working Puffer Derrick crane anyone?!?!?
« Reply #23 on: October 07, 2009, 07:20:58 AM »

One solution to "hairy string" is to run it backwards and forwards several times over a block of beeswax.

Roger in France
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Re: Working Puffer Derrick crane anyone?!?!?
« Reply #24 on: October 07, 2009, 08:30:06 AM »


  At one stage I contemplated using a solid steel boom to keep a tension on the lines.....

    LOVE your winch! http://s949.photobucket.com/albums/ad338/photomultiplier/?action=view&current=08_06_14_01014.flv



Oh why did you post that Martin. ill have to pull my winch apart to see if I can do anything to make mine look half as good. that's magic very nice

peter
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