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Old Dec 27, 2009, 06:27 PM
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larrykin's Avatar
Sydney, Australia
Joined May 2008
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Hew 565,
thanks you very much for that. Should have asked you for info before I finished my first IOM. Now too late as have no access to bow to fit block up front. Still have to wonder at using 5 blocks. With a drum winch looks like only need 2.

Purists will scream at this but... what I have done with a Hitec HS-815BB sail arm servo pulling 24.7 kg/cm torque is - drilled 2 holes in arm closer to center. Closest is jib sheet. Tied main sheet to dead end on bulkhead and passed thru outer hole on arm. Jib sheet tied directly to arm. Both lines then pass thru same fairlead in bulkhead. Main line goes straight to mast post. Jib sheet goes to block at stern then straight up to deck via offset fairleads. So I have only one block. This is the simplest method possible and on test sailing response is instant. When line not under tension seems to be no problem as lines are so short nothing to tangle with. I had tried with 3 blocks, then 2. Kept getting tangles. Now smooth and direct. This is the same set up as I have on my old MRP Voyager which has sailed for nearly 2 years and works perfect. I went to KISS after frustration with needless complexity of other sheeting layouts. Any friction in my sheeting is compensated by power of servo and shortness of sheeting.
Proof will be when I race next week against all the boats with normal RMG winches.

Mike -- thanx heaps for pic. Any chance of photo inside showing drum winch? For my new IOM build.

Larry L.

PS
Today I start sanding my new IOM. The hull and deck have just cured after over 24 hours on their molds. Have ordered all fittings which should arrive this week. Might have boat finished in fortnight.
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Old Dec 27, 2009, 07:23 PM
Slope,thermal and Scale flying
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Deception Bay
Joined Jun 2008
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Quote:
Originally Posted by hew565 View Post
Larry, let me know if you need other photos.

The elastic runs like it does so that it never really pulls on the servo arm, but loosens as the arm moves. It could be a solid line if everything was positioned perfectly!
So that pink looking cord is actually elestic band??? Where can i get some???
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Old Dec 27, 2009, 08:43 PM
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USA, LA, Mandeville
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http://radiosailingshop.com.au/index...roducts_id=103

I assume they are closer to you that where I got mine, in the US!!
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Old Dec 27, 2009, 11:27 PM
Slope,thermal and Scale flying
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Deception Bay
Joined Jun 2008
637 Posts
Thanks for the Hew. I might be repositioning my winch servo to up the front of the boat looking at your setup you have there. Dont know yet, still thinking about it
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Old Dec 28, 2009, 12:06 AM
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larrykin's Avatar
Sydney, Australia
Joined May 2008
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Chris,
I'll repost this drawing by Claudio. It shows a sail arm with elastic and only 2 pulley blocks. With no deck on your boat yet maybe worth considering for your Emo.
I bought elastic in the sewing section of Kmart. Looks same as Hew's link. 5m for $1.95.

Larry L.
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Old Dec 28, 2009, 05:17 AM
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Quote:
Originally Posted by larrykin View Post
Hard to test distance with no boat.

Larry.
For any sail arm any servo try this;

distance from centre of the arm to the attached line (r) fixed

Degrees of servo rotation (ds) adjustable using ATV or equivalent function on the radio


R X DS X 0.0175 = sheet travel.

for a 3" arm and assuming the normal 120 degree servo throw at 100% atv

3 x 120 x 0.0175 = 6.28"



0.01775 is 2 pi/360
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Old Dec 28, 2009, 03:11 PM
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larrykin's Avatar
Sydney, Australia
Joined May 2008
424 Posts
Mr May ---

thanks for info on sheet travel for a servo arm.
Question = I'm no maths wizard but... a 3" arm with 90 rotation will produce 3" of line travel. At 180 will travel 6". How can it travel 6.28" with 120 rotation?
I was talking about my new Hitec drum winch and sheet travel with a Spektrum DX5e radio which has no travel limit adjustments. Winch specs say it turns 3 times BUT may turn between 4 and 6 times with some brand receivers.

Winch travel = drum diameter (D) x Pi (3.1428) x number of drum rotations.

Hence - Hitec drum winch = 40mm D x Pi x 3.5 = 440mm or 17.3" of sheet travel

That seems like a large amount of travel........

Mike -- does the above sound right re sheet travel?

Larry L.
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Last edited by larrykin; Dec 28, 2009 at 03:26 PM. Reason: more info
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Old Dec 28, 2009, 06:26 PM
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USA, LA, Mandeville
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You can get a bit more than 3" with 90* rotation.

http://en.wikipedia.org/wiki/Pythagorean_theorem

A 3" arm at 90* rotation gives you the square root of 18, or 4.24 inches of travel if you have your leads set at the correct angle to the arm. Since most people use a one:two reverse purchase, that can be as much as 8.5" of sheet travel.

I have thought about using a cam type of servo arm to get more travel with an arm type servo. Done right, you can get more travel in some parts of the rotation, and less in others, for fine adjustments.

Remember, you can also adjust where you attach your sheets to the booms to make up for more, or less sheet movement. The servo is going to do a certain amount of work (it's torque rating) and it does not care if it pulls in 20" of line or 2" of line over it's rotation. You will lose some of the torque every time you change direction of the sheet, through pulleys. Some have said as much as 5% every time you reverse the direction!

That being said, you could use a 1.5" arm and no purchase system, but your sheet would have to attach to the booms about two inches from the pivot point/gooseneck! it would be hard to make small adjustments to trim at that close distance.
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Old Dec 29, 2009, 04:37 AM
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Quote:
Originally Posted by larrykin View Post
Mr May ---

thanks for info on sheet travel for a servo arm.
Question = I'm no maths wizard but... a 3" arm with 90 rotation will produce 3" of line travel. At 180 will travel 6". How can it travel 6.28" with 120 rotation?
I was talking about my new Hitec drum winch and sheet travel with a Spektrum DX5e radio which has no travel limit adjustments. Winch specs say it turns 3 times BUT may turn between 4 and 6 times with some brand receivers.

Winch travel = drum diameter (D) x Pi (3.1428) x number of drum rotations.

Hence - Hitec drum winch = 40mm D x Pi x 3.5 = 440mm or 17.3" of sheet travel

That seems like a large amount of travel........

Mike -- does the above sound right re sheet travel?

Larry L.
17.3" is righ even if it is excessive for your boat.

Apologies about the mix up on the servo, I confused your post with the later post which is an arm servo. The diameter is 6" and if allowed to the sheet would/ could travel only 6" but you also get non linear sheeting, which then has to be dialed out using Exponential function on your transmitter. If the sheet is tracked around the circumferance of the circle you end up with 9" of linear or proportional travel.

The cheapest solution is to make a smaller drum for the 3.5 turn winch.
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Old Dec 29, 2009, 05:21 AM
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Blackpool, Lancs
Joined Feb 2006
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Or double the line back on itself at the boom end to halve the travel and double the torque.
With a sail arm, doing the same thing at the arm end of the line will double the travel at the expense of reducing the torque.
The non-linear travel of the arm can be used to advantage. If the arm is arranged so that when the sails are fully pulled in, the arm is facing directly away from the line's feed point, you get the biggest arm travel for a smaller boom travel just when you need the most torque.
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Old Dec 29, 2009, 07:26 AM
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Perth Western Australia
Joined Jul 2009
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Larry.

Attached is the photos that you wanted and i measured the distance from the centre of the winch to the centre of the back block which is 510mm. With a Hobby King 2.4g radio i have set it up that full movement on the TX gets me full travel on the winch with the elastic stopping just short of the bulkhead, when i had a sanwa radio the elastic would go though the bulkhead.
Hope this helps

Mike
AUS669
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Old Dec 29, 2009, 02:38 PM
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larrykin's Avatar
Sydney, Australia
Joined May 2008
424 Posts
Mike,

your blood is worth bottling. Thanks - I owe you one

This now looks like the Hitec drum winch, as is, will not function in my IOM. Reason being I have a Spektrum DX5e radio which does not have limiting.
Choices are - contact supplier to buy a smaller diameter drum. Smaller diameter means less travel and increased speed. In fact I saw the winch is rated at 7.2Volts. Does that mean I can run a 6 cell battery pack thru this winch?

I was emailed last nite and told an IOM has 23cm of sheet travel. That means drum diameter should be:
No. of turns x Pi x Diameter = Travel
hence; 3.5 x 3.14 x X = 23 so max. diameter = 21mm. that is small.

My other options are to buy a programmable radio or a new sail winch. Did both last night. Was recommended this new winch. same torque as the Hitec and faster than an RMG. Price $US20.30

http://www.r2hobbies.com/proddetail....=rcps91116_10y

Also bought a TurBORIX 2.4 GHz 6 Ch digital programmable radio mode 2. Price $US40.40

http://www.r2hobbies.com/proddetail....cps61206_61411

Now I just need to build even more boats to fit all this gear into .

Larry.
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Old Dec 29, 2009, 04:13 PM
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Dick L.'s Avatar
Minnesota, USA
Joined Aug 2002
1,820 Posts
ServoCity will sell you a servo limiting device that fits between servo and receiver. You can set separate end points via screwdriver on both sides of neutral.

U.S. $ = $19.00 as I recall.
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Old Dec 30, 2009, 01:05 AM
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larrykin's Avatar
Sydney, Australia
Joined May 2008
424 Posts
Quote:
Originally Posted by Dick L. View Post
ServoCity will sell you a servo limiting device that fits between servo and receiver. You can set separate end points via screwdriver on both sides of neutral.

U.S. $ = $19.00 as I recall.
Dick,
sounds like a good alternative. Any clues what it's called for a Google search in Australia? Never seen this offered as an accessory.

EDIT - finally found the item at ServoCity. A ServoStretcher. Modifies Hitec servo with 90 rotation to 180. Specs say "not to be used with any other type of servo". Only servos with 90 rotation. The price was right .
http://www.servocity.com/html/180o_servo_stretcher.html

My news -- finally got around to testing the Hitec HS-785HB Drum Winch Servo with my Spektrum DX5e receiver. The drum turns 3 times. Specs say 1 turn = 120mm. That means I'll get 39cm of sheet travel. I have ~ 47cm from the bulkhead to the stern block. At least that means I wont have the elastic connection going thru the bulkhead . Also lucky as Hitec don't make a smaller drum for this servo .
Maximuss MkII update - the designer emailed me and suggested rather than building my own plug, he has a buddy with a good mold who can pull a hull and deck for me. He sails at the same club I'm planning on joining and lives close by. Also makes excellent keel fins and rudders for racing from his designs. At not exhorbitant prices. The club is SMMC at Norwest Lake.
Trakka - do you get hassled during the Winter Olympics? Winter sport involving hot kettles.

One sleep to go till 2010

Larry
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Last edited by larrykin; Dec 30, 2009 at 01:33 AM. Reason: New Information
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Old Dec 30, 2009, 04:44 AM
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Perth Western Australia
Joined Jul 2009
1,079 Posts
Larry,

Will measure the diametre and travel that I get from my hitec, just caharging batteries as I am off to Perth Radio Sailing club for some fun racing tomorrow, time to mis it with some of the best in Westren Australia, hoping it blows tomorrow looking like 15-20 knots he he A rig for the the TS-2 Clone :-)

Mike
AUS669
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