[i]“I remember another problem with arm servo, some times, under continuous pull effort they may burn out, this happen to me with the HS-815BB on the AC33 project, probably was my mistake to let my boat in the hands of somebody else !!!”
[/i]
A small, light and very cheap Resettable Fuse known as a PPTC, Polyswitch, etc. will protect the servo.
of course but you may loose the boat !!
CD
You forget to consider all the aspects I have already mentioned in various occasions, like price, weight, power consumption and speed.
Price : too expensive for the majority of RC modelers including myself if a cheaper solution is available.
Weight : too heavy for my project. The gain in weight will go in the ballast !
Power : powerful but not free of charge, you need also battery that may be heavy too.
Speed : I do not like high speed servo for two reasons : a) not necessary and b) dangerous for the boat construction.
To satisfy my project requirements I still have the double option : a) the arm servo for witch I do not need to make special testing so far I get the kg.cm I need , b) the drum servo that shall be specifically developed since not available on the market except the MRG.
The MRG will be considered anyhow, in spite of what already told, if and only if, I will manage to get the necessary weight margin during the construction. For the time being I’m not so sure !
I wonder why you are using a MRG on the IOM if the arm servo solution is cheaper and lighter to handle 0.6m² of sail ?
ClaudioD
to be honest Claudio I haven’t done near as much research as you do for the esterel but I really like that winch, plus I find Rob Guyat the designer/builder a sound guy who’s ready to help others like me when I started. After talking to other IOM skippers the hitec, futaba are either expensive relative to what they provide, or too slow and not good enough for stole torque and lack flexibility in programming. The eurgle is simply not reliable enough and I know others use off-set puleys setup or arm I find too complex and difficult to repair if needed during a race whereas I can repair my sheeting system very quickly between races if needed having it all above deck.
its weight is not an issue for me as I race in a class where the weights are regulated so no question to lower the CG but in your case absolutely it makes sense to increase righting moment and increase power by lower CG.
for the power I initially power the electrics of the boat through a single pack of AA size 7.2v 6 cells 2200mah LSD at c180g,but then I used AAA size 7.2v 6cells 800mah at 80g and recently I’ve been using a lipo pack 2s 7.4v 1000mah (59g) & one at 1600mah (70g) and I race for an afternoon no problem. Earlier in the year I completed 8 races in a blow (force 5, and 6 in the blows with C rig) with one lipo pack of 1000mah.
I really like the speed of RMG because we tend to sail windward - leeward course as great tactically and I can sheet out quickly at the weather mark which is handy to reduce nose diving in a blow or when I sail overpowered in my rig choice. But also great at the leeward gate as it sheets in quickly allowing me a tight rounding of the mark going back up on a beat.
As for the Mini40 the RMG280 is also good with 0.9m2 sail area and here I sail with the AA size 7.2v 2200mah pack no problem for an afternoon.
At the end for me it is what suits my needs the most and the RMG fits the bill but that a personal opinion.
Have you contacted Rob with your needs to see if he’d do something for you ?
Gilbert
Hi Gilbert,
so, you have good reasons for your purposes like me I have mine.
Rob, I’m in contact with him since months because I asked him if was possible to design a single servo to maneuver a Genoa.
Actually, he promised and described to me his new concept and, after many mails exchanges, I think is still working on to finalize the design to be applicable to small RC models too.
Cheers
ClaudioD
Claudio, the PPTC is self resetting. On removable of the excess load, the Pollyswitch resets immediately and power is on again.
Fine, but how can be removed the excess of load if the power is momentarily cut Off by the PPTC ?
Cheers
Claudio
The Pulley made by Alan arrived this morning.
She look very nice, my thanks to Alan of course.
The pulley is then equipped with the gear bought some years ago with Servocity.
Here below the picture of today work.
A small film is also made, but I wait the camera battery recharge to make another one with the TX joystick.
I shall now organize a pull test, of course with my old HS725BB.
ClaudioD
Its always a plaesure to see the nice work of two famous builders combined.Gilles B.
Thank you Gilles, Very pleased to (see) you back in this forum !
How is it in Quebec ?
The beautiful Blue Nose is ready for launch ?
Certainly was very nice to met Alan here in Nice. Hope will be other occasions next summer, who knows !!!.
Meanwhile I just playing with my ideas, not all the times are successful, but 1.2.3. is very good basis to improve a lot.
All the best
ClaudioD
Looking good Claudio & really great to see you here again Gillies 
Update on you Blue Nose would really interesting for me too !
Hi Claudio and Alan,I will maybe work on my Bluenose this winter if i have the time.The family comes first and i have still a lot of work to do for my daughter.I am so eager to complete that boat.I will surely post some pics of my work. Cheers Gilles B.
Bad new !
The pull test started with 1.65kg weight attached to the string coming from the new pulley. Made some maneuvers up/down where the current absorption varied around 0.65Amp under 6Volts. No problems for about 3 minutes playing with the joystick.
I decided to add 0.85kg, aiming to reach, step by step, 3kg.
The HS-725BB ceased to turn after about 1 minute under 2.5kg load.
Current absorption increased up to 1.6Amp under 6Volts. The calculated torque was 8.12kg, (2.5kgx3.25cm) out of 14.5kg.cm specified at no load.
The servo temperature was not very warm and I would say rather low. My suspect is that the final power stage is off due to current overload.
End of Story !
ClaudioD
PS: this was the set-up
Just curious, did you also do this test with the eurgle setup that you sailed with but wasn’t strong enough? It would be an interesting comparison.
8.12kg-cm is only about 55% of the torque (14.4 or 13.8) that you said was on the data sheet. I wonder what the percentage is of the other servos people use are? It would be great if we could test the different servos and put the data in a central location so everyone can have more accurate data than what the manufacturers provide. It could save people a lot of frustration in the long run.
Hi noob,
no I did not tested the Eurgle.
With 5.36kg load no problems - 2.5 times lower the 13.8kg.cm
Servocity suggested “as rule of thumb” to use only 1/2 of specified torque ‘under no load’ , in reality is the speed and current absorption that are specified at “no load”.
I asked therefore Hitec to tell me which is the maximum “load current” that can be considered before burning out a servo.
Waiting for an answer.
There is an interesting fact because Servocity is just providing this data only for one servo :
http://www.servocity.com/html/hs-7950th_servo.html
thus 300mA during running - no load and 4.8Amp at lock/stall, equal to 16 times the running current at no load , but without telling for how long can this load kept before burning.
My experience with the variation from 0.85Amp to 1.6Amp was sufficient of course to ruin the servo.
Previously with 0.64Amp and 1.65kg load, the servo was operating well and this was only 2.5 times the running current.
Cheers
ClaudioD
My expert contacts suggest that given a specified servo torque, divide it by 2 and use that torque as a max limitation.
So, my understanding is that a declared 24kg.cm shall not be used for more then 12kg.cm . This produce a very dramatic reduction of usable power.
As an example, let take a servo of 24kg.cm, mount an arm of 8cm long. The torque available without load will be :
24/8 = 3kg.cm and from that, to avoid damages under load, will be better not to use it for more then 1.5kg force.
I have to revise my calculations about the servo arm option and add a mini blower to cool down the servo radiator body !!!
ClaudioD
Today as yesterday, the temperature outside is above 20°C and is full compatible with the lamination for the female mold. RH also OK at 60%.
Gelcoat resting for about 1 hour.
Some pictures while I’m waiting to start glass tissue lamination.
In sequence :
2 layers og 105g/m²
2 layers of 165g/m²
3 or layers of 280g/m² - not excluded another layer
Total tissue weight 1218g
total epoxy resin 1218g
ClaudioD
ESTEREL female mold lamination completed ! Was a good October way, what we call here : ‘Indian summer’ .
ClaudioD
A few years ago I did a torque test on a Hitec HS-815BB. I don’t remember the numbers but I think it was about 50% of the advertized torque. I just assumed I was doing it wrong or that I had a duff servo. I guess not. Maybe we shouldn’t be using those numbers. Unless of course all the manufacturers consistantly lie. At least then we could trust their dishonesty. If that makes any sense. I do know that an 815 will just handle an IOM.
Don