RG 65 Mass Build? - Page 3 - RC Groups
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Dec 03, 2014, 11:47 AM
Flying without a licence
FWAL's Avatar
Quote:
Originally Posted by tim_uk
Hi FWAL

Glad your making progress, i'm still gathering stuff for my build. I have carbon fin, rudder and fin box from Dave creed sat on my bench so I have to build something now!
Hi Tim
I see you're going posh I'm soon going to be purchasing a DF fin, bulb and 'A' rig. But I might push the boat out and purchase some Cat sails.
Is there a real noticeable difference between these fittings and the more expensive makes?
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Dec 03, 2014, 12:15 PM
wolfgang
tuppesw's Avatar


So is it a 1:3 purchase,
1:2 on the right side plus 1:1 on the left side
(plus a little bit of friction)?
Dec 03, 2014, 01:49 PM
Registered User
Quote:
Originally Posted by FWAL
Hi Tim
I see you're going posh I'm soon going to be purchasing a DF fin, bulb and 'A' rig. But I might push the boat out and purchase some Cat sails.
Is there a real noticeable difference between these fittings and the more expensive makes?
Don't think there is anything wrong with the fittings but the dragon A rig is lower aspect and has smaller sail areas than a RG65 A rig and the bulb is light at 550grams. I'm aiming for 700/750g bulb depending on displacement tests in the bath but I could be way out!!
Dec 03, 2014, 01:56 PM
Registered User
Here are the goodies from Dave Creed, a lot posher than the fisher price wooden keel and eBay'd RC helicopter blade rudder I used for my first RG65
Dec 03, 2014, 02:00 PM
Thomas Armstrong
Quote:
Originally Posted by tim_uk
Don't think there is anything wrong with the fittings but the dragon A rig is lower aspect and has smaller sail areas than a RG65 A rig and the bulb is light at 550grams. I'm aiming for 700/750g bulb depending on displacement tests in the bath but I could be way out!!
Because the hull of the DF65 is heavy (by class standards, that is), its bulb/keel is lighter, so that total displacement is not too much. This means it cannot bear a full 1250 sqcm sail... that is why the mast is shorter, too. For heavier winds you can swap to a longer fin (available from Josway).

If you ask me, the overall design balance of the DF65 is great. It sails better than any other kit you can buy, and it is very well built.

Just FYI: if you look at winning boats in Brasil, currently they are using 1250 sqcm sail with 110cm long mast, 650gr bulb with 35cm long fin, and an overall displacement around 1100 gr.
Dec 03, 2014, 02:01 PM
FROM THE MIND OF A MADMAN
gpzy's Avatar
Brighton Boat works has some building goodies on there website.
http://stores.rcsailboatparts.com/erc/
Dec 03, 2014, 02:02 PM
Registered User
Dick L.'s Avatar
Gotcha!

thanks for clarification - still nice to know what can be done. Looks like a multi-turn drum winch remains my only option for a narrow hull and a lot of string.



Dick

Added: I am looking for a solution where I can sheet in a mainsail at boom end instead of mid/front half. This means I need enough sheet travel to attach to near end of boom, and at the same time have enough to allow the boom to swing out near 90 degrees. Doing this would also provide a bit of leech tension, allowing a loose vang off wind, but some tension when sheeted upwind.
Last edited by Dick L.; Dec 03, 2014 at 02:06 PM. Reason: added thought
Dec 03, 2014, 02:11 PM
Lucas
"there's no way you cannot affect the torque rating and increase sheet travel simultaneously mechanically."

Increase the angular distance through which the arm travels!

I agree with Tuppe, if the 5 cm arm rotates through 180 degrees, it will pull roughly 15 cm of line. A standard double purchase setup with a 5cm arm through 180 degrees, would pull roughly 20 cm of line.

Due to the varying angles, neither the line pull, nor the force in the line is constant over total distance. The point in the rotation where the line is 90 degrees to the arm creates the maximum travel / degree but also the least force in the sheet. This moment of minimum mechanical advantage occurs roughly half-way through the total line travel.

If the servo can produce 22.5 kg-cm of torque (not an RG65 sized servo), then at this worst point, the linear force available would be 22.5 / 2.5 = 9 kg but divided between 3 moving lines so the line tension or pull force at the end would be 3 kg minus the frictional loses of three pulleys.

In the double purchase, 5cm arm, the linear force at the end of the arm would be 22.5 / 5 = 4.5 kg, but split between 2 moving lines so line force is 2.25 kg minus frictional loses of a single pulley.

Does all that sound right?
Dec 03, 2014, 02:19 PM
Registered User
Quote:
Originally Posted by tarmstro
Just FYI: if you look at winning boats in Brasil, currently they are using 1250 sqcm sail with 110cm long mast, 650gr bulb with 35cm long fin, and an overall displacement around 1100 gr.
thanks for the info tarmstro, those are some scary numbers to try and build to with my heavy handed approach!! must build it lighter, must build it lighter, must build it lighter is my mantra!
Dec 03, 2014, 03:01 PM
Thomas Armstrong
Quote:
Originally Posted by tim_uk
thanks for the info tarmstro, those are some scary numbers to try and build to with my heavy handed approach!! must build it lighter, must build it lighter, must build it lighter is my mantra!
My mantra, too!!! I managed to get overall weight down to 975gr, without sacrificing sail area nor bulb weight!! (bulb+keel=662gr, hull+rudder+electronics=233gr, A-rig=80gr)

Build log here: https://www.rcgroups.com/forums/show....php?t=2098471

Regards,
Thomas
Dec 03, 2014, 03:32 PM
Lucas
Dick, by sheeting at the end of the boom, you increase your leverage to resist the force at the CE of the sail. You just need a system which can move the amount of line required. The problem with an arm type is the pulleys required multiply the distance moved. A drum winch with multiple revolutions seems like a great solution. I imagine there are some nice little blocks out there, but I'd rather put the money into a better winch motor.

If you really like arm winches, a double cascade in reverse could give you four times the sheet travel with only two pulleys. It would take a lot of room, but you have that in your long skinny hull.
Dec 03, 2014, 03:35 PM
Lucas
So back on topic ... do I still have time to join this mass build? The prices is right on those ERC parts!
Dec 03, 2014, 04:15 PM
Registered User
Dive in Ihurt, i'm going to be at this for months if past builds are anything to go by!
Dec 03, 2014, 05:16 PM
Useful Idiot
Quote:
Originally Posted by FWAL
I know I'm affecting the torque but would my method require less torque than the more normal extended arm? Also, I'm a bit dumb so can you please explain how increasing the sheet travel decreases torque? Surely you mean increasing the length of the servo arm decreases torque


....
For a set torque to haul in time X a sheeting of Y cms requires a certain servo power, which is basically torque times speed. If increasing the sheet travel to 2Y, using the same power and in the same time X, the effective torque exercised on the sheets is reduced by a factor of 2. The effect of increasing the arm length by 2 would have exactly the same result.
You could probably confirm it by attaching a spring balance to a sheet.
Dec 03, 2014, 05:23 PM
Useful Idiot
Quote:
Originally Posted by lhurt
"there's no way you cannot affect the torque rating and increase sheet travel simultaneously mechanically."

Increase the angular distance through which the arm travels!

I agree with Tuppe, if the 5 cm arm rotates through 180 degrees, it will pull roughly 15 cm of line. A standard double purchase setup with a 5cm arm through 180 degrees, would pull roughly 20 cm of line.

Due to the varying angles, neither the line pull, nor the force in the line is constant over total distance. The point in the rotation where the line is 90 degrees to the arm creates the maximum travel / degree but also the least force in the sheet. This moment of minimum mechanical advantage occurs roughly half-way through the total line travel.

If the servo can produce 22.5 kg-cm of torque (not an RG65 sized servo), then at this worst point, the linear force available would be 22.5 / 2.5 = 9 kg but divided between 3 moving lines so the line tension or pull force at the end would be 3 kg minus the frictional loses of three pulleys.

In the double purchase, 5cm arm, the linear force at the end of the arm would be 22.5 / 5 = 4.5 kg, but split between 2 moving lines so line force is 2.25 kg minus frictional loses of a single pulley.

Does all that sound right?
By increasing the angular movement of the servo, you are reducing the speed of the servo. If moving 90 takes x milliseconds, rotating it 180 will take 2x milliseconds. Double hauling keeps the speed constant (x milliseconds) but reduces the "pulling power" by a factor of 2 as well.


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