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Control loading with heavy servo

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Hi,Do you probably remember my attempts to get a force feedback feel on my column using an heavy 12 VCC screenwiper motor.I took a very long time to get from Australia the electronics ( surface post, means by sea) able to transform the motor into an heavy servo. Finally I could test it using the servocontroller of my IOCARD.It is interesting but from far the "good" solution. Major weak point is the overheating of all component and finally the weak Torque which does not simulate the heavy forces induced by a flight.After that experiment I am convinced that the "good" solution consist of using an AC brushless high torque motor able to stay stalled for a longer time without overheating and furthermore able to deliver up to 100 - 150 NM on the column.The column should in that case be directly connected to the main axis, and not linked mechanically as I did.I would like to go that way with such motors since they are not that expensive but I do not now how to connect them to the PC.Any idea are welcome.GreetingsRoger

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Just to get a catch on this:your intent is to make the centering force stronger with speed, or some other variable?If so, maybe you can use a simple stepper, driven by the speed variable (or whatever you are using).I try to explain:your centering spring is attached to a moving slidethis slide is moved on a rail by a stepper motor (or servo, i explain this further down the page).The more your variable increases, the more the stepper "pulls" the spring thus hightening the tension on the control.How to use a servo in place of a stepper:just place the servo reference in another place.Usually servos have the position feedback on the rotating axle.Just use a sliding potentiometer (of the same value), attached to the slide, and you have a nice servo pulling down the slide.Hope it is clear enough.

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Claudio,I have no centering spring. That's exactly what I wanted to avoid. My servo was connected to the column as shown on the picture. The values came from the setting of the trim. Trim centered = yoke column centered. Trim in the UP position = yoke column backTrim in the DOWN position = yoke column forward The result I was looking for is a strong resistance of the column as long as I have not trim the plane correctly ( as it is in the reality without any spring)And the result is like that, nevertheless, the torque is not strong enough and one can easely counteract the motor.And so I believe that a strong AC servo would make the business but dont know how to drive it with the PCRegardsRogerhttp://forums.avsim.net/user_files/97627.jpg

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Well, in that case you actually have a centering force.I think that if you apply my idea, but turn it horizontal instead of vertical, it can work.In practice it means using an infinite turn screw (how is it called in english? i only know the TPN screws...), moving a carriage sideways.Your column is attached to this carriage with a centering spring (centering in respect to the carriage).In practice i am suggesting change the dampning mechanism:right now you are using the reverse torque of your motor, in my case you use a spring.In this case you won't have that need for a high torque motor (difficult ot operate anyway), but achieve the same (i think) effect.

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Yes and No. Claudio, I do know if you are a real world pilot, but if so you know that there is none centering force. The column or axis comes back to the position corresponding to your trim setting. I understand what you mean by infinite turn. But I am a bit afraid about the mechanic involved, carriage, spring, oh dear, I like simple designs. I am searching the best and smoothest movement possible. With carriages I guess that the feeling on the yoke wont be smooth or then I would have to get it manufactured by professionnal guys using ball bearings and expensive precise CNC machined partsI am not sure that your design may get the result I am looking for, but could you nevertheless make a picture or sketch of it ??Thansk ClaudioCiaoRoger

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>Yes and No. Claudio, I do know if you are a real world pilot,>but if so you know that there is none centering force. >The column or axis comes back to the position corresponding to>your trim setting. There sure is a centering force, but I think I know what you mean - it is very weak in the trimmed position - you can control the plane with very small forces once it is in trim.But turn the trim to the opposite end and try to fly the plane - it takes two hands to hold attitude even in a Cessna 152 if the trim is way off. There sure is a force there.>I understand what you mean by infinite turn. But I am a bit>afraid about the mechanic involved, carriage, spring, oh dear,>I like simple designs. I am searching the best and smoothest>movement possible. I have the same problem - basically I am building the yoke now. I sorta finished the pedals from plywood and hinges, they work fine with springs.What I worry with the yoke is the canceling effect of two opposite springs and the creaking feeling (though, that can be very realistic :)) But I very well see what you are after. I'll let you know if I come up with something.How strong is the motor? Is it having any torque? One thing you could do is move the motor to the bottomside of your panel instead of having it on the floor near the pivot point. By moving the motor and the pushrod up closer to the yoke steering wheel, it gives your setup more lever length, thus increasing the torque force. It is way down there currently, so you need a lot more force to move the wheel up there in the tip of the longer shaft. Make them more equal in height and put the pushrod under the panel like Philip-the-Fokker-50-guy did with his yoke mechanism..? Would that help enough? The pushrod will be behind the yoke column anyway so it wouldnt be on the way at all.//Tuomas

Current:	____________	 | panel	 | W|  |__________  |  :  |  :  |---+__|__:|(motor)suggestion:	____________	 | panel	 | W|  |_|(motor)__	  |----+  |  :  |  :__|__:________

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I thought of something else, simpler.Once you have trimmed the plane, the yoke will hold the position.But if you want to move it, you'll feel the pressure of the airflow pushing on the stabilizer trying to keep it at the old attitude.So in respect to the trimmed position you have a centering force.Not that strong but it is there nontheless.Now try to follow me.You want your column to have a certain degree of progressively harder movement, simulating a real one.This range of movement must follow the trim setting.So in the end you would have a spring (generating the shallow centering force) and something that moves the spring back and forth to move the movement range.Now this something can be many things.I am just in the process of building my own homemade cnc, so i am experimenting with carriages, and i admit it may be costly.But it sure would be easy: lay down the rail, screw it, place the carriage and there you go.But i thought of a simpler solution:use your motor as a pulley, to move a rope.This rope is not directly attached to the column, rather it ends on two shallow springs.This way when the column is centered there is a shallow force, when you move the column out of trim the force increases.In this way you could maybe still use your motor in "counter-torque mode", i don't know.Here is a hand sketch (don't choke on it please :D)http://forums.avsim.net/user_files/97640.gif

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The problem is, those springs will mostly cancel each other out.//Tuomas

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>The problem is, those springs will mostly cancel each other>out.How?If you move the column one direction, one spring will highten its force, while the other will lighten it.In what sense they will cancel each other?By the way, you could try using only one spring:one end attached to the rope/chain/whateverthe other end to the column.

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Hi Guys,Nice design but I did test such design already and as Tuomas says, those springs do cancel the strenght since as you say Claudio, one spring will highten its force qhile the other will lighten it.Tuomas, what I mean when I am talking about centering is "coming back to the center at mid way" what do every joystick or yoke sold for our hobby.There is fact always a "point" where the column comes back, the point corresponding to the setting of the trim and it feels, of course like a centering point, with high pressure on both sides. I guess that you mean that by centering and that's right.Your idea Tuomas, would not help either, because the motor (now) is too weak for such purpose. The motor by itself when you get directly 12 volt and try to counteract on the column, gives you an heavy feel and that's way I was so entusiastic during the early stages of the tests. Put I had to transform that motor into a servo and used a special designed pcb allowing more torque that the usual called heavy torque RC servo. Those circuit, simply takes back a lot of power and whatever your design will be, the forces are gone, and the resistance is too weak.It would open a big door, what a simple RC heavy duty servo would not do, drive an robot arm, but will never get enough power to counteract the power of a normal human being arm forces. I think that the right feeling should be somewhere around 200 Nm ( I have made test, one way, with gas spring loaded at 200 NM and that feel was ok) and my system gives may be 10 or 20 currently. And, Claudio, your design with the spings would not give more and in any case not he 150 -200 required. I would also know how much can be given by a strong electro-magnet. I read somewhere that an american company is working on car dampers using that technology, no hydraulic, just electro-magnets.Electro-magnet are cheap and if driven via a small servo which would open and close a potentiometer getting more or less power to the magnet, such system could probably also make the job. But I still have some difficulties to imagine a simple design just using one or two magnets, and have not find yet very strong electro-magnets on the market, like the ones closing the doors of sophisticated safes.Any idea out there about that ??Many thanks in any case to allRoger

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>Hi Guys,>>Nice design but I did test such design already and as Tuomas>says, those springs do cancel the strenght since as you say>Claudio, one spring will highten its force qhile the other>will lighten it.>>Tuomas, what I mean when I am talking about centering is>"coming back to the center at mid way" what do every joystick>or yoke sold for our hobby.Yeah. But Claudio does have a point here. And I think we might be able to solve this with springs.Lets say if you have strong bungee cord (rubber rope), and you fix its middle part to the yoke bottom part and pull both ends (say, 30cm both sides) just tight enough, then it should work: When you pull back, one bungee stretches (causing a centering force) and the other just hangs loose. When you push, the other band does the same. But the problem is it returns to the same point always.Now, imagine you dont bolt the bungees to the base of your yoke.Instead, you get a piece of wood, about 65 cm in length and fix the bungees to *that* instead. So that the bungees are tightened okay and if you hold the wood piece in place under the yoke, it works just like before. Centers, but always on the same place.Then get those kitchen drawer slides. Put one of those between the piece of wood and your yoke baseplate (or the simulator floor). Now when you move the wood back and forth, it will move the centering point, right? Move it back, and hold there. The yoke will still move around, and the centering force will just center it on a different place.Now figure out a way to connect the trim wheel so that it just moves the wooden block back and forth. Maybe with a threaded rod that rotates and two nuts welded in two L-pieces of metal?

  ~~~E|~~~~~~~~~~~~~~~~~~|E~~~~~~~   ___|				  |___---------------------------------------

Then fix the wooden block in the middle of the rod somehow.This is along the lines I have been thinking - since I am about to finally build my yoke as well. I just need to figure out if this will work. What do you think?//Tuomas

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Tuomas,It's a nice idea but my mind is probably too complicated and that's why I do not like system involving ropes, wooden, and so on. I have seen so much design on the web and since I am in front of a computer and a simulator, somewhere in the early 80th in front of my Commodore 64, my obsession as regards the simulation is the perfect reproduction of the feeling a pilot has in its plane.That's why I used now for several years all sorts of hydraulic dampers which is probably the one of the best solution. I put dampers in times where all commercial product still were stuck with metal springs. Now, since I dismantled all my system I am looking for a cost effective and long term solution, what could not be compatible.So I am in a kind of "terra incognita" somewhere hesitating betweensuch system:http://www.frasca.com/web_pages/brochures/ECLbro.htmor such:http://www.wittenstein.aero/e/_application...lar_loaders.htmThis one seems too complicated beside the fact the work done is terrific:http://www.bob-ma.org/modules.php?name=For...viewtopic&t=506His one is my favourite, but as I said I do not have yet a design in my head adapted to a column:http://www.ft.bs.dlr.de/flugsystemtechnik/.../1/inhalt_e.htmMike Powell did akso suggest one time a design involving a torsion spring on the column with my heavy servo connected to the base of that torsion spring. This did not work out too due to the weakness of the motor. There must be a very strong one able to counteract a torsion spring giving bout 150 to 200 NM.Greetings and thanks for all suggestions.Roger

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Sorry for bumping an old thread...What did you use to convert the motor for servo duty? I have been looking for a schematic/kit/whatever than can do just this but haven't had much luck (at least not within my price-range).As for the low-torque problem you are having: have you considered a different linkage scheme? The one you have now is using a considerable amount of leverage against the motor. Perhaps a bell crank would do a better job of putting torque further up the control column?

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I hope I don't sound rude, but are you sure that is the kit you used?

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Thank you for the link. I may order one or two of these for testing.I'm sorry for bothering you about this...If you could, I'd like to know:Which motor you used (bosch or other).The motor voltage you used.Which motor input you used (low speed, high speed, or mid-speed).Approx loss of torque when the servo circuit was added.And anything else you might think noteworthy for someone who is about to spend $100 on parts :)

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Hi BaldieJr,I used the Bosch windscreen wiper motor. It is 12 VCC motor with brushes.See here details of the motor: http://www.cpg1.freeserve.co.uk/servos/servos.htmI used the low speed input for my purpose.I cant say excatly but guess that I lost for about 50% to 75%. But may be did my power supply not be the best. Anyway, the holes into the circuit where you connect the power, and were you connect the cables to the motor are very thin and not capable receiving high amp cables. There is probably the most issue. There are four power Mosfet. They are conna hot very quickly and need mega cooler not included. The servo was controlled using IOCARD and the servo expansion card. GreetingsRoger

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Thanks Roger, this is what I needed to know :)After the holidays I'll order the parts and start hacking :)

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And what will be your application?? Also controal loading??regardsRoger

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Yes. I'm also working on a robot project, so the motors will come in handy no matter the outcome of my experiments.I'm thinking I can recover some of the lost torque by using a direct-drive system to a control sticks' gimbal and by using the high-speed input on the motor at 18 or 24vdc. As long as the h-bridge can source the current, everything should work.

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What about doing something like this? Basically you have a "block" with two springs on it that the control column passes through. There's a space firmly attached to the column that separates the two springs. The whole block slides back and forth on simple rails. The block is moved back and forth (changing control pressures) by basically a pully driven by a worm gear and a motor.I saw something similiar to this a number of years ago by a guy who was proposing a design for a force feedback yoke. This is basically the same idea, but his design required some very complicated manufacturing pieces. I think my design could be built with relatively few parts... The only hard thing would be getting a good worm gear.Now for a jetliner-style control column that comes up from the floor, this could still be utilized below the floor and a simple push-rod linkage.

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