I have noticed that when sailing my Footy in strong winds and with a large sail area there will often be a squealing noise from the boat when I try to draw the sheet in.
I am using a Hitec HS81 servo with the Nylon/Carbonite gears powered by 4 x NiMh batteries.
Does this noise eminate from the servo motor or the gears ? If it is the gears then presumably they are actually deflecting enough to cause slipping and hence the noise.
Cheers,
firstfooty
First Footy
My expectation (raised mainly from Hitec’s advertising) is that these are the mutts proverbials, and will not slip, break or otherwise disgrace themselves.
So my tentative belief is that it won’t be the gears slipping, but might well be the motor bearings or gearshaft bearings screaming, in which case i would expect a “dry” sound. I can’t imagine that it can come from the low speed (output) end of the gears - it must be up at the high-speed end
It can’t happen without load, or you would have mentioned it.
Is it worrying? if so you could dive in and examine - and lubricate if it seems appropriate
Seeing your query sit there alone (for weeks) I found myself wondering if a servo squeals in the forest when there is no-one to hear it how would you know which tack you were on?
andrew
First Footy - It may be that your servo was overloading. The HS-81 is not my first choice for a sail winch. It is heavy at the rated weight of 19.6g while delivering only 32 oz. in. of torque. It is my belief that Footy winches should spec at around 50 oz. in. at a minimum to work well in all conditions. Newer, more powerful, light weight micros are cropping up all the time. I would prefer more headroom in the torque rating but right now any jump above 50-60 oz. in. comes with a steep gram increase.
However, there are micro sevos available now that would be an improvement over what you are using and that deliver more power and weigh less and are reasonably priced.
I use a Bluebird BMS-380MG rated at 16.4g/50 oz. in., and runs under $30.00 US. I also have a Hitec HS-225MG in my Bantam, rated at a hefty 32g/55 oz. in. (it also converts to 180 degrees of travel which is why I bought it).
There a few other choices out there:
Bluebird BMS-380MAX - 17.2g/57 oz. in @ 6v
And a servo I haven’t tried yet but I find interesting:
Raiden DMA-046H 15.8g/64.08 oz. in. (this rating is for 6v, 4.8v would probably drop the torque to something similar to the Bluebird)
I don’t think that any of these servos will squeal on you. 
First Footy - It may be that your servo was overloading. The HS-81 is not my first choice for a sail winch. It is heavy at the rated weight of 19.6g while delivering only 32 oz. in. of torque. It is my belief that Footy winches should spec at around 50 oz. in. at a minimum to work well in all conditions. Newer, more powerful, light weight micros are cropping up all the time. I would prefer more headroom in the torque rating but right now any jump above 50-60 oz. in. comes with a steep gram increase.
However, there are micro sevos available now that would be an improvement over what you are using and that deliver more power and weigh less and are reasonably priced.
I use a Bluebird BMS-380MG rated at 16.4g/50 oz. in., and runs under $30.00 US. I also have a Hitec HS-225MG in my Bantam, rated at a hefty 32g/55 oz. in. (it also converts to 180 degrees of travel which is why I bought it).
There a few other choices out there:
Bluebird BMS-380MAX - 17.2g/57 oz. in @ 6v
And a servo I haven’t tried yet but I find interesting:
Raiden DMA-046H 15.8g/64.08 oz. in. (this rating is for 6v, 4.8v would probably drop the torque to something similar to the Bluebird)
I don’t think that any of these servos will squeal on you.
Andrewh,
Sometimes I think I must hold the record for the posts with the fewest number of replies :rolleyes:
I doubt it can need lubricating as it is a brand new servo and it has being squealing under high load since new - starting at Burton when you were down at Chertsey. But read on . . . .
Niel,
At last, I must be doing something right, as my own calcs based on wind speed and sail areas also suggest that 50 oz.ins would be a good torque to try and achieve. Its the sail force being proportional to wind speed squared that causes all the problems. “A” rig conditions seem to be limited by the ability of the hull not to nose dive downwind whereas “B” rigs are limited by servo overloading and a reluctance to tack.
Not being a user of Ebay, my usual source of servos her in the U.K. is either Howes or The Servo Shop. The best either of these can offer - if it is in stock - is the Hitec HS85MG with BBs. This comes in at 42 oz.ins at 4.8V and 49 oz.ins at 6.0V and weighing 22 grms. I am now agonising over spending 9UKP on a set of metal gears for my HS81 - purely in the interest of testing you understand :lol: - or bite the bullet and spend 19 UKP on the HS85MG with BBs.
I have to make up my mind before a semi serious event at Angus’s club over Easter. I’ll let you know what happens.
Cheers,
firstfooty
Just google micro servos and see what comes up.
Also, check out robot sites, in particular “Ant” and smaller. Park Flyers and indoor planes and helis are a good source for small servos and components. R/C cars can sometimes be cannibalized for servos and motors. I’ve seen a small “Venom” servo that I believe came from a Venom heli.
I am sure there are more options for you than those you’ve mentioned.
The HS-81 is not known as a very high quality servo in the airplane/glider/sailplane world (where a good quality servo costs can reach $100 plus each)
Sounds like your gears are slipping - quite common on an over stressed small servo. I have heard mine make the same kind of noise before when overstressed and/or with damaged gears. The the pins that hold the intermediate gears in place distorts the plastic case under overload and the gears move out of alinement. Doesn’t take much movement to make the gears slip. That’s why BB’s are good.
Might be a waste of time changing to metal gears in the HS-81 as the 1st gear in the metal gear train is plastic anyway…
If you can, try sourcing one of the more powerful micro servos as others here wisely suggest. Try the SuperTec Micro 2 BB MG (known as GWS elsewhere in the world) It has metal gears, Balls (bearings that is), 5.4 Kg/cm of torque (more than ample for an overpowered A rig) and weighs 28 gms (a little more than the HS-85MG) Oh yeh - it costs £12.99
Available at http://www.servoshop.co.uk
http://www.servoshop.co.uk/index.php?pid=STECMCRBBMG&area=Servo
A SuperTech Micro 2BB MG has been ordered, delivered and fitted - a proper mail order service from http://www.servoshop.co.uk/ . Unfortunately the U.K is in the midst of some pretty severe weather at the moment. As I write my local airfield is quoting winds of 38 mph gusting to 60 mph - so I’m not prepared to risk my little 500 gram balsa boat at the moment.
What I did notice when I removed the original Hitec HS81 with plastic gears was that the sail arm felt quite notchy as if it was slipping over a few gear teeth. When I removed the servo casing I noticed that of the 4 meshes, the first 2 starting at the motor were about 120 dp and the other 2 were about 80 dp. The large gear on the second mesh looked as if it had lost some tooth tips in a few places which could have been the source of the problem.
The torque created in a gear train such as will increase with every meshing which is probably why the gears change dp part way through. Obviously the HS81 could have done with 80 dp in the last 3 meshes instead of just the last 2. In fairness to Hitec though, it had probably been trying to turn 60 oz ins in some recent high winds. Hence I have great hopes for the 75 oz ins SuperTech 2BB MG.
I never thought a Footy would need so much power :graduate:
Cheers,
firstfooty
Firstfooty
Glad you are sorted, and that the “Assembled Intellects Group Therapy Session” was spot-on.
Now I’m confused!
OK, so that’s not difficult or unusual, I hear you think.
<<At last, I must be doing something right, as my own calcs based on wind speed and sail areas also suggest that 50 oz.ins would be a good torque to try and achieve.>>
THIS is where my confusion accelerated. I rejoice at the calculation, (and have a high regard for FFs calculations and their relationship to reality).
We are using balanced rigs, and probably balanced rudders too, so we can chose exactly how much force to apply to the servo, and how much it has to overcome.
So my confusion is this. What have you calculated, FF?
Is is the total force of the given wind on the sail area?
Or the unbalanced force, given the geometry of the rig?
Since we can chose the amount of balance/unbalance/self-servo by the pivot point of the rig presumably we could make a completely balanced rig with almost zero force required from the servo. Why not?
Confused, but not unhappy
andrew
Andrewh,
As you know, I use the McCormack rig.
I calculate the total area of the sail and then assume that the wind force is proportional to (Area^2) x (Wind Speed)^2 x .0043 where sail area is in ft^2 and wind speed is in mph.
I then calculate the effective C of A of the sail and its position relative to the mast pivot.
Then, knowing the lever arm length of of my sheet pull position relative to the mast pivot point I can estimate the sheet force required to rotate the sail against any given wind.
Lastly I can then relate that sheet pull to a servo torque at the end of whatever servo lever arm I chose to use to get the sheet movement I need.
I found this to be one of the big advantages of the McC rig in that it requires only a relatively short arm. I am sure many people forget that whilst using the double pull system of sheet attachment may give you double the sheet movement it, at the same time, halves the torque available - you don’t get owt for nowt as they say up here.
Finally, yes, you could come up with a layout that needed a very low servo torque. This would only require the area in front of the mast pivot to be equal to that behind. However, the down side of that would be that the sail wouldn’t know which way to set - owt for nowt again. Brett didn’t suggest a 3:1 ratio for fun, it seems to work. Most of my sails seem to work out at about 2.8 to 3.1 :1
As a previous post suggested, these calcs point towards a servo torque of about 50 oz ins being required - so my shiny new SuperTech 2BB MG should do the business. I’m sure that if you are swanning around with 150 ins^ inches and 10 mph then there won’t be a problem with a standard servo torque, its only when you are trying to beat Gary Boyde or Roger Stollery with MORE POWER or get caught out with 25 to 30 mph gusts that the problems arise.
Are we going to meet at Colwyn Bay ???
Cheers,
firstfooty
Now you’ve got me worried. I was thinking (just for a change) of using that sort of servo output to control the approx 350 sq inches (2250 sq cm) of an RG65. The rig is semi-balanced, being a swing rig, but your reasoning makes this questionable at over force 3 or so.
firstfooty,
Thanks - thats what I hoped and expected you would say - I do know why we don’t go for 100% balance and 100% self servo:D. (I used to ride my bicycle with the front forks reversed)
I’m not myself an advocate of BB servos - other than it suggests good quality - because mine live out on the deck and I believe that BBs can get corroded whereas bushes survive and are sometimes water-lubricated!
I won’t make it to Colwyn bay at all, but some of the fruits of my labours might - I can’t say more, Angus is in charge of bags, cats and pigeons!
martin - sorry that you are now confused.
If it is any consolation I feel that Firstfooty is correct in his calculations, but I will continue to use what I have in stock for sail servos - including some 4gm parkflyer servos if required!
andrew
Martin,
You have a PM.
Cheers,
firstfooty