Thanks for the “memories” Bob - I had seen one also - but never paid much attention at the time. Was very early in my r/c hobby experiences.
Dick
My tanks also to Bob and Dick .
Obviously the diameter of the wheels will be proportional to the power and speed of the servo.
Small diameter = better torque = more turns
probably I should study how to modify the servo by removing the inner potentiometer and adding the external one of 10rev.+ a gears box as I deed on the past in various occasions .
Cheers
ClaudioD
I have not yet abbandoned the idea to use a ball-chain as depicted in post 113 . The chain I have is extremely flexible and this may be a problem !
The one was in my hand was taken from a nail cutter and tested in traction by adding some lead weights up to 4.85kg. I suppose that may resist to much more !
a couples of pics
ClaudioD
PS:
Just received the ball-chain 2mt long. Asked the manufacturer about the ultimate mechanical strengt
Slowly I will reach the end soon !!
ClaudioD
Hi Claudio
There is a type of ball chain used for drapery(vertical blinds). It consists of a piece of cord with plastic balls molded to it. It is not as limp as the steel ball chain. It might serve your purpose. I think that there is a small wheel inside the valence that is made to fit the chain.
Don
Hi Don,
This was my first idea, but later I found out that the chain get curled -up when pushed out from the gears. There is obviously the need to use some sort of guides.
In this picture is visible the phenomenon induced by the large flexibility of the chain. The gears are not the ones should be used of course.
According to my calculations, the exit speed should be around 100mm /sec. using a servo of 0.17sec/60°.
The RMG should technically solve the problem but it is to heavy and expensive for the 43-900 model.
The fastest servo found with 0.07sec/60°, is the HS 7940TH for 140$ , not very cheap either but very light, need to be modified to get more turns : http://www.servocity.com/html/hs-7940th_servo.html
Cheers
Claudio
This is !
ClaudioD
I spent these hours in calculating the mechanics of the “rope-eater” servo using the HS 7940 TH from Hitec.
The external potentiometer should be a 10 turns - 5kohm type AL910 from Megatron with life up 2x10^6 operations. The gears are availables from ServoCity
A compromise between speed and max revolutions for the potentiometer limited to 10.
The wheel box is an external element coaxially linked to the drive gear. principle depicted at post 116 (pdf)
According to what has been reported in various places, the wheels in the box are substituded with gears, the red marked are coaxial with the servo and potentiometer and the blue one is free running gear :
ClaudioD
Almost finish !
ClaidioD
PS : Now the hull is finish, time for sanding !!!
Epoxy filler outside and epoxy resin inside
ClaudioD
Enjoy the sanding!!
It’s looking really good, not long before you’ll be laminating the plug and then pulling hulls. What sort of layup are you thinking about for the finished hull?
Regards,
Row
Latex ? 
Hi Row,
I will laminate the plug with a couple of glass/epoxy layers of 80g/m²
Instead the finished hull should have a lamination between 6.0 and 6.5g/dm², therefore I have the choice between 3 layers of 105g/m² or 4 layers of 80g/m²
The surface of the hull is about 26.5dm² therefore the hull weight will be sitting around 160g to 170g
Cheers
ClaudioD
Hi Alan,
No latex since I do not have it !
Cheers
ClaudioD
Claudio,
How do you choose the resistance value for the AL910 potentiometer to ensure you do get 10 turns on your rope eater? I used a 10K ohm pot on a winch and got a maximum of 2 3/4 turns. This is shown on page 53 of the US One Meter Construction Guide. I believe a lower resistance value than 10K will give you more turns, or resistance added to the pot in the transmitter will (also) add turns. I wonder if arriving at 10 actual turns has to be done by triial and error or it is possible to calculate it. I wonder if it is even possible to get 10 turns from a 10 turn pot.
Hi Scott,
1 - generally the potentiometer resistance on the servos I used is of 4.7 Kohm while the external potentiometer is of 5k
2 - the number of turns of the pontentiometer is given for 10 or 3600° : http://www.megatron.fr/composants/position/angulaire/pot/sf_potmulti_f.php
http://www.megatron.fr/composants/pdf/pdfpot/sf_al903-905-910_0302_f01.pdf
3 - to protect the potentiometer is better to avoid to use more then 8.5 revolutions out of 10 - care shall be taken to avoid end of course including trimming.
4 - with a gears ratio of 1 : 1 the torque remains unchanged
5 - the number of turns can be taken either from the servo axis as well from the potentiometer axis :
in the attached drawing the axis of the servo will produce 10turns while the axis of the potentiometer will produce 8.4 turns - Much depend from the lenght of the pulse provided by the transmitter. Digital servo may be programmed , but I do not know if this is still the case when the internal potentiometer is substituted with an external one.
6 - changing the gears ratio, it is possible to change of course the number of turns but the torque will decrease proportionally.
7 - according to the drawing and to my understanding the torque from the potentiometer axis will slightly increase while reduced on the servo axis.
So this is the way I go since my first modification, but every time I have to check again the theory and the practice !
Cheers
ClaudioD
Further thinkings about the rope-eater prototype, now the most difficult for me is to make the " deck gears box" since I’m really bad in mechanical work !
I have to re-order my mind before placing and order somewhere !
Any comments ?
ClaudioD
i have nothing i could use one in, but i want it and you havent even made it yet xD.
just throwing out the idea though, why not make one of the deck adjustabe so you can move it closer and farther to allow use of larger/smaller lines?
and a question, what program are you useing to make all of these designs?
Hi ,
the basic idea is to have two indipendents elements.
The servo/potentiometer bloc integrated inside the hull and the external gear box mounted on the deck.
The two elements are linked by a simple coaxial mechanical coupling once mounted .
The first element is rather easy to make since already done it several times with the limiting use of a classic drum.
The triple gears box is more complicated and requires high precision manufacturing capability .
For all my drawings I use, since almost 20 years, a very old version of Corel Draw . the actual one is the version 5, but any other can be used altough more complicate.
Cheers
ClaudioD
1st round !!! heart pulse at 110/120 for one hour, time to stop otherwise my stent will start complaining !
ClaudioD