some Fin Box constructional trials.
The retained solution will be a mix of carbon fiber sheet and wood support.
The monolithic with carbon sheet is the lightest ~ 12g, but most difficult to be made and not based on the actual Fin form.
Finally the expected final weight, once assembled, is about 15g where the wood version would be around 20/21g.
ClaudioD
New Carbon fiber flat lamination started with 200g/m² .
The single Fin Box side surface is 0.57dm²
The expected Fin Box weight will be :
2g/dm² carbon sheet x 2layers x 2 resin x 0.57x 2sides + 4 = 13.12g
I will be happy if less then 15g.
ClaudioD
Carbon plate ready to be re-dimensioned.
The weight is as calculated.
ClaudioD
Fin Box almost ready and actually weighting less then 12g ! A glass layer will be wrapped around and paint inside the box !
Finally I choose the samba plain wood for the spacers instead of plywood.
Similar construction will used for the Mast step Tube.
ClaudioD
Verification of support positions !
mainly for Fin Box and Mast Trunk or Step.
Mast can be raked by +/- 1.5° which allow to shift the CE by +/- 15mm. Same condition as on real boats.
…
ClaudioD
Carbon patches and Fin Box slot arrangement.
ClaudioD
In Nice the Carnival is finished, but the rainy season started and impossible for me to work outside while the temperature is raising slowly.
Next work, between two showers, is to cut the sloped transom and add the rudder trunk.
ClaudioD
Jumping from one work to another one !
After some considerations about new MRG clones made in Italy, I decided to stay with the Servo Arm solution.
What afraid me is the swing speed of the servo arm as well of the clones, I need to learn how to control my fingers with the joystick !!!
One of the representative of MRG Clone told me that to reduce the speed of the winch, the motor can be substituted with a slower one.
Here the last “worst case” servo arm calculations .
ClaudioD
claudio,
i know the hitec digital servos, you can program servo speed. but from time to time having a fast transit time is good to be able to “flip the boom” over on a jibe
Hello Claudio,
The winch clones you mention are not “MRG” as you have mentioned in previous posts, but they are clones of the RMG, Rob and Michele Guyatt.
John.
You are right John was a typo, but “clones” remains !
ClaudioD
Hi Marc,
a servo like the Hitec HS7954, a possible candidate for my application, exhibit a speed of 0.15"/60° at 6volts.
Practically, the Main Boom will swing to a maximum of 85° and this will be done in 0.15/60° x 120° = 0.3seconds. Of course under load this speed will be less. The Servo arm will swing for 120° to obtain the Boom swing of 85°
Would you please check with a chronometer how is fast 0.3" and imagine the Mail boom full swing within that time lapse ?
I’m afraid that many parts composing the main Sail setup will not last long under such a slap acceleration !
Cheers
ClaudioD
Claudio,
Unless my little ‘grey cells’ have completely shut down, your calculation for boom speed from close hauled to run is worse than 0.3 seconds (no load conditions). As you need to effectively double the arm length using a block to gain the required travel that speed will actually be closer to the 0.15 seconds which I’d imagine to be virtually uncontrollable - obviously when put under load (ie: a real world scenario) this will almost certainly increase the time taken significantly. I don’t know what degree of servo speed control/setting is achievable with the programmable Hitec servos but I do think you’d need to go down the route of the programmable digital servos rather than the much cheaper un-programmable type to give controllable speed…
Cheers,
Row
Edit: Just looked at your torque requirement calculation again and as I mentioned previously, as a block is being used to effectively double the arm length, won’t that also double the torque required? If so, then instead of an approximately 20Kg/cm servo, the requirement would be 40Kg/cm, maintaining the same safety factor etc. The alternative would be a reduction in the windspeed in which the boat could be used or look again at the drum winch servos. I hate throwing the proverbial spanner in the works, but infinitely better that the mistakes are made on paper rather than having a detrimental effect on your bank balance!!
the digital servos can be programmed to go slower as well, they also have overload protection which can be programmed, as well as 180* rotation can be programed. plus many digital, at least the hitecs, are high voltage and can handle larger loads and higher voltages from newer Lithium packs and weigh less than their analog counterparts. I love the cheap Chinese servo’s but having to replace them each year gets old. Cheap and reliable and quality are three things that will not coexist in the electronics world.
as my analogs wear out/break, ect I am replacing them with new digital units… and I am standardizing them which means on my smaller boats I am probably putting in a larger servo than what I need, but it also means one less different type of servo I need to maintain in my inventory…
[QUOTE=Twister;67004]Claudio,
Unless my little ‘grey cells’ have completely shut down, your calculation for boom speed from close hauled to run is worse than 0.3 seconds (no load conditions). As you need to effectively double the arm length using a block to gain the required travel that speed will actually be closer to the 0.15 seconds which I’d imagine to be virtually uncontrollable - obviously when put under load (ie: a real world scenario) this will almost certainly increase the time taken significantly. I don’t know what degree of servo speed control/setting is achievable with the programmable Hitec servos but I do think you’d need to go down the route of the programmable digital servos rather than the much cheaper un-programmable type to give controllable speed…
Cheers,
Row
(UNQUOTE)
Hi Row,
here the schematic of the Servo Arm setup that define also the power needed as function of various parameters :
…
As you can see the servo arm is swinging for 120° and this is what it count in term of speed evaluation.
The existence of the bloc is simply due to the fact that sheet length required is double of what the servo arm can offer.
The important thing is that the servo need to rotate by 120° and therefore determining the time required to operate the Main Boom.
So is correct what I have written above.
With a longer arm may rotate less and vice-versa while the useful torque will be in accordance.
About programming I do not know if the speed can be programmed as Marc suggested, I shall investigate.
Cheers
ClaudioD
Big slap on my forehead!! I can only assume that I was getting confused between time & distance - those severely diminishing grey cells have let me down!
Regards,
Row
Edit: Still a bit lost on the torque requirement - if you were to set up a system with the block fixed you’d effectively give yourself a power advantage of 2:1. Unless I’ve missed something obvious (which in all probability is very likely), the system you’ve drawn is basically a power reduction (1:2), which must surely require an increase in servo torque? Bit lost on this one & the pills aren’t helping my thinking abilities!
Row
Hi Row,
it is correct that the servo Arm with the use of the bloc requires half of the power, but I have also neglected other factors as frictions and power reserve for Safety factor.
I have already blow out two servo HS-815BB and an old HS -725BB because overloaded.
Cheers
ClaudioD
Raining “season” is substantially slowing down external work and the assembly process.
Fin Box epoxy bonding underway with previous 3 axis centering check.
ClaudioD
Return to ESTEREL - 123
Another thinking around the Roof …! Probably I will give a try (before the summer !!!) to that configuration :
…
The pictures below are the references
ClaudioD
Hi Claudio,
As I am new to the forums, comments are a bit on the late side. Apologies. Your finish work here is absolutely that of a master. The fact that you discussed your trials and experiments with pictures is a great gift for the rest of us, at least for me. At one point you seemed upset that your sheer line strakes for the deck and rigging support increased the overall weight of your hull. (14-15gr!) Its been a decade since Ive built any hull from scratch, but I can tell you that at one point I was interested in the weight diff between two closely weighed hulls after the strakes were set. I began weighing the material pieces I had on hand and discovered as much as 4-5 grams difference between them. The next trip to the hobby store had me sorting thru what I perceived to be the lightest of the required pieces. I purchased a dozen when all that was required were four. Cheap anyway. When weighed at home, the lightest went into the boats and the rest were used for stir sticks. De l’esprit de l’homme
Ciao,
David