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Author Topic: Jet Drives, how to set up?  (Read 3994 times)

big-geoff

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Jet Drives, how to set up?
« on: September 28, 2010, 03:50:07 PM »

I am looking at building a fast boat for my grandson (Yes I will use the C word), for Christmas.

I hit upon the idea of using a Graupner Mini Jet Drive, but the issue of reversing has come up.

So here is the question.

How with a 2 channel system can I have a reversing funtion?

I have found a foward only ESC, which makes sense. I have looked at radio costs and do not want to have to shell out for a 3 or 4 channel set.
If I can get this working, I have another hull and will build a duplicate for his dad to have one as well.

All help will be gratefully received.

Cheers

Big-Geoff

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Martin [Admin]

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Re: Jet Drives, how to set up?
« Reply #1 on: September 28, 2010, 04:25:39 PM »

Can we ban people off mayhem for using the "C" word in September?!?!?!  ok2

I'll PM HS93, he's built a couple of Jet Drive boats.....
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malcolmfrary

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Re: Jet Drives, how to set up?
« Reply #2 on: September 29, 2010, 11:15:08 AM »

The price of the low end 2.4GHz sets is in the same area as a 2 channel 27 or 40 MHz outfit, with the advantages of no worries about crystals, and you dont have a long and fragile transmitter aerial.  This last could be a worthwhile consideration for use by a young 'un.
The extra channels would make operation of a reversing bucket much easier to arrange, as well.
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big-geoff

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Re: Jet Drives, how to set up?
« Reply #3 on: September 29, 2010, 11:20:11 AM »

Thanks

I shall have to trawl the internet for some cheap sets.

Last one I bought was 160+ mind it was 6 ch.

cheers
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Circlip

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Re: Jet Drives, how to set up?
« Reply #4 on: September 29, 2010, 02:56:53 PM »

Quote
I have found a foward only ESC, which makes sense.

 Hmm, yer might need to think about a speed limiter when using the reverse function.

  Regards Ian.
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big-geoff

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Re: Jet Drives, how to set up?
« Reply #5 on: September 29, 2010, 03:03:02 PM »

Speed in reverse is an issue.

I have E-mailed one of the manufacturers of ESC's posing the question, I await a reply.

although I could forgo reverse altogether, which might seem a good idea intil I am trying to get out of the weeds......

Geoff
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barriew

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Re: Jet Drives, how to set up?
« Reply #6 on: September 29, 2010, 03:58:14 PM »

One of the issues discussed about some of the cheap Chinese ESCs is that they only have a 50% reverse - seems like this is just the application for them ;D

Barrie
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HS93 (RIP)

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Re: Jet Drives, how to set up?
« Reply #7 on: September 29, 2010, 04:10:47 PM »

One of the issues discussed about some of the cheap Chinese ESCs is that they only have a 50% reverse - seems like this is just the application for them ;D

Barrie
Just for information
when you go in reverse with a jet boat the motor still runs forward and you lower a bucket behind the outlet that diverts the thrust, so the motor only ever runs one way.

peter
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big-geoff

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Re: Jet Drives, how to set up?
« Reply #8 on: September 29, 2010, 04:18:53 PM »

There lies the problem that I have.

If I have a forwards/reverse ESC I would have to either turn of the reverse function or devise a way that upon reverse the motor polarity is switched and at the same time the reversing bucket is lowered.

This could get tricky with all that electronic gizmo, but could be the solution.

Geoff
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Circlip

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Re: Jet Drives, how to set up?
« Reply #9 on: September 29, 2010, 04:26:28 PM »

My point being that if little hands drop the reversing bucket at full chat, the boat might also double as a submersible.

  Regards  Ian
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malcolmfrary

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Re: Jet Drives, how to set up?
« Reply #10 on: September 29, 2010, 05:54:22 PM »

If its a forward only ESC, off/dead slow will likely be the stick fully back.  If the reverse bucket was worked by a servo on another channel, it could also work a switch such that when not fully forward, it did not short out the nice chunky resistor that would calm the motor down.  Just thinking aloud and theorising.
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sailorboy61

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Re: Jet Drives, how to set up?
« Reply #11 on: September 29, 2010, 06:03:32 PM »

Thanks

I shall have to trawl the internet for some cheap sets.

Last one I bought was 160+ mind it was 6 ch.

cheers


www.giantcod.co.uk

www.howesmodels.co.uk


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big-geoff

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Re: Jet Drives, how to set up?
« Reply #12 on: September 30, 2010, 09:30:43 AM »

It look like the solution has been found.

An E-mail to Action RC has provided a very neat way of solving this problem.

A Condor 20A ESC programe to drive the motor in one direction no matter what direction the stick is planced with a neutral at halfway.

Plus a magic boc that on a Y lead recognises the reverse position of the stick which trows a servo operating the reverse bucket.

as for limiting the reverse function a physical barrier placed on the TX to limit the throw of the stick in reverse.

Sorted.

Now all I have got to do is work out the best way of installing the jet drive on a shallow Vee hull.
I will post photo's of the hull tomorrow.

Many thanks
Guys.

Geoff
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grasshopper

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Re: Jet Drives, how to set up?
« Reply #13 on: September 30, 2010, 09:53:02 AM »

Now you have a speed controller that works the motor throttle regardless of stick direction, use a 'Y' lead to connect ESC and 'bucket' servo,  create a mechanical linkage
to the reversing bucket  so it's deployed by the servo in the downward direction and sprung to lift it out of the way as soon as the throttle is pushed forward again.

As most buckets divert the jet outflow downwards and forwards the stern of the boat tends to lift rather than submerge like some prop driven boats - interesting handling though!
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Welsh_Druid

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Re: Jet Drives, how to set up?
« Reply #14 on: September 30, 2010, 05:37:13 PM »

Some of you may have seen my  Stena Sealink HSS ferry at Wicksteed.  This is powered with two Graupner jet drives. If I reverse the thrust by dropping the buckets, the model reverses - but slowly. If I leave the buckets up but reverse the motors the model goes into reverse much faster !!!

I suppose that theoretically this should not happen - but it does !

Don B.
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