RE: Electric Retracts - Modifying existing Air/Servo-operated Retracts
 

By the way, if your worried small thrust bearings wont be strong enough, think about the forces acting on heli blades spinning at thousands of rpm.

If your still worried - double up and use two bearings back to back :)

RE: Electric Retracts - Modifying existing Air/Servo-operated Retracts
 

It occurs to me that many, maybe even most, thrust bearings are designed to handle thrust in only one direction. In that case, you would need to use two back to back in order to handle the up/down forces. Check the specs when you order.

RE: Electric Retracts - Modifying existing Air/Servo-operated Retracts
 

Thanks for the tips, Larry, I'll incorporate them into the new design.

RE: Electric Retracts - Modifying existing Air/Servo-operated Retracts
 

I did some quick looking and I cant find the thrust bearings I had in mind in the sizes that would work easily. I know they exist because I have them in the tail of my 450 sized heli. All I can find are larger sizes that would probably work ok for large scale gear but not the smaller stuff.

You may have to use the type Tom used. Its more of a thrust washer type of set up.

Here is an example.

http://www.rcplanet.com/ProductDetai...30-068&click=3

You will need to change the way the bearing is fixed in place but thats simple to do. In fact, ths type of bearing may be easier to use over all.

RE: Electric Retracts - Modifying existing Air/Servo-operated Retracts
 

Guys,

Great thread...keep it coming! I'm building a 1/6 scale Lockheed Lodestar that is going to require screw jack operated flaps due the large amount of for/aft travel involved.
An ECU that could be used to operate these would be ideal.

I have to go back and re-read the whole thread before I start asking a lot of questions (in case they have already been answered), but it sure would be nice to have a plug and play module to do the sequencing!

Cheers, Nigel

RE: Electric Retracts - Modifying existing Air/Servo-operated Retracts
 

Nigel,

If you are using Futaba and have the required transmitter the channel
expander ECU is on sale at Tower for $9.99 from its original $99.99. It
should provide control for a screw jack.

Futaba MPDX-1 Multi-Proportional Decoder 8-Channel

RE: Electric Retracts - Modifying existing Air/Servo-operated Retracts
 

Nigel,

If I can locate it, I have a four channel ECU you can have for the cost of shipping.
It has never been used. A Chinese IC developer created it several years ago. Its
yours if you want it.

RE: Electric Retracts - Modifying existing Air/Servo-operated Retracts
 

How does this provide control of a screw jack? It has no current sensing and no motor control built in. It just adds additional channels to an existing rx.

If this can be made to work, then any rx could be made to work.

Can you expand on this Ed?

Here is a link to the specs.

http://www.futaba-rc.com/radioaccys/futm4158.html

RE: Electric Retracts - Modifying existing Air/Servo-operated Retracts
 

Larry,

I have never known of a flap system requiring anything more than
deployment at variable amounts in two directions. An ECU is not a
necessity for flaps unless speed per segment of travel % is needed
to be controlled.

You are apparently thinking the programmable Futaba unit is more
than a programmable device for servos. That being programmable
distance across time with possible incremental stepping and reversing.

An ECU designed for retracts has more attributes like current loads
during use in additional to programming distance across time. Stalls
are the issue with retracts. While a flap stall could benefit from the
current management, most flap stalls are mechanical in nature from
a component failure.

RE: Electric Retracts - Modifying existing Air/Servo-operated Retracts
 

I'm a self professed "electrical idiot", have a channel expander and I'm certain that it won't do the job.

There will be four screw jacks (2 per flap) and three positions: Up, Take Off, Landing. Flap deflection is accomplished by the tracks, so all the screw jacks have to do is move them fore and aft.

The only difference I can see from landing gear is that there is an intermediate position between the end points (take off flap position) What I would like is to have a unit that could accomplish this sequencing without the use of micro-switches.

What do you think you electronic wizards? Is this doable?

I'm not quite at the point of building the wings just yet....but soon!

Cheers, Nigel

RE: Electric Retracts - Modifying existing Air/Servo-operated Retracts
 

Nigel,

Do you want the ECU I offered?

RE: Electric Retracts - Modifying existing Air/Servo-operated Retracts
 

Thanks Ed,

But I'll pass until I fully understand what my requirements are.

Cheers, Nigel

RE: Electric Retracts - Modifying existing Air/Servo-operated Retracts
 

Unless Im misunderstanding things, a jack screw is exactly what we are building here to operate the retracts except that Nigel will be using one to drive the flap mechanism on his bird.

It doesnt sound to me like he has a servo operating the jack screw and no way to control the screw travel or drive the motor portion.

That Futaba ECU you talk about isnt an ECU at all. Its just a channel expander and adds no more functions than would be available on any hi end rx.

You cant just plug in any old motor to an rx chanel and expect it to work via your tx signal.

Thats the entire point of the Pololu boards and software that has been discussed to date.

I ask again - how do you expect it to operate a jack screw type mechanism without a motor controller and some sort of feedback to sense the end travel?

RE: Electric Retracts - Modifying existing Air/Servo-operated Retracts
 

It sounds to me like Boeing314's setup could do it all. The only part Im not sure of is the intermediate takeoff position. The motor would not be stalling and sending an amp spike that the controller could sense to determine that position accurately. Might have to set that point based on time alone.

Boeing314 would need to address that to be sure.

RE: Electric Retracts - Modifying existing Air/Servo-operated Retracts
 

This is getting real sideways for some reason. A screw jack driven by a servo, as has been described here
in detail, can be operated in any of two directions across time with variable end points (aka stops) set by
12Z or 14Z Futaba transmitter, plus any additional attributes set within the channel expander set up
sub-menues.

No one ever claimed there were any electrical monitoring attributes attributed to the Futaba channel
expansion unit in its application to a flap set up. You are creating issues which do not exist in flap
applications. Aside from failure of a servo, flap control issues are usually mechanical linkage or
geometry issues.

The ECU I offered Nigel would control servo motors be they with altered or unaltered stops. He could drive
a screw jack in-kind to a spline drive setup with servo laying on its side.

RE: Electric Retracts - Modifying existing Air/Servo-operated Retracts
 

Thanks Larry.

You hit the nail on the head. There are no servos to be used anywhere in the system! The plan is to use small gear motors to drive the jack screws. In fact, my concept is for the finished product to be unitized....motor and jack screw together as an actuator (x4).

What's needed is a system to allow for adjustable end point stops plus a mid-point stop. If this unit could also sync the units, that would be a tremendous bonus!

I'm sorry if anyone feels that I have altered the course of this discussion, but I felt that the flap jack screw was so similar to the retracts in function that it was worth discussing hand in hand with regard to the development of an ECU....

I hope Boeing 314 will chime in here with his thoughts!


Cheers, Nigel [sm=regular_smile.gif]

RE: Electric Retracts - Modifying existing Air/Servo-operated Retracts
 

It sounds to me like you've completely missed what we are talking about in this thread Ed.

Where did we discuss driving screw jacks with servos any where in this thread? If thats what you thought, then I now understand your earlier complaints about the control board discussion and programming.

Thats not at all whats being discussed in this thread.

If you did connect a servo up to a screw jack as you suggest, driven directly off the splined output shaft, you could only get, at most, about one half of a full turn on the screw. Hardly enough to drive a flap over any useful distance unless the gearing of the screw jack was extremely hi. Just the opposite of what we have been looking at mechanically.

Even if you switched to a servo the was capable of continuous 360 degree rotation, like a sail winch servo, you still couldn't control where it stopped (end points), beyond that initial 1/2 to 1 full rotation, via the Tx. When doing multiple rotations, its either on or off. There is no built in control over when it stops or how many rotations it does other than by flipping a switch on the tx after its turned as many times as you want. Kind of hard to judge when the flap is fully deployed or retracted or at 30 degrees when the plane is way off in the distance. You would end up jamming the servo or not getting full deployment at either end.

You would still need to build/program an additional controller board over and above that channel expander.

In other words - you still need a motor and gear drive to turn the jack screw and an ECU specifically designed to control that motors stopping points after its turned many many revolutions.

THAT is what we have been discussing in this thread from day one.

Hope this helps clear that up.

RE: Electric Retracts - Modifying existing Air/Servo-operated Retracts
 

Here are some ready made linear servos/actuators that might get you to where you want. Some of them have proportional control and some dont so you need to read the specs. You may need to buy a seperate RC control board for them to work with your rc gear. Again, RTFM :D

Most of them are way to big and heavy to fit in a typical wing or any existing retract but they do have a few smaller ones.

They are also a good bit more $$ than the motor/controller options we have been looking at so far.

http://www.robotshop.com/firgelli-actuators-2.html

RE: Electric Retracts - Modifying existing Air/Servo-operated Retracts
 

There is a huge dificit in understanding how servos work and what "stops" and stops them. As was more than adequately explained and illustrated by Tom earlier in the first 160 posts of this thread...one need only remove a servo's stop vehicle and it runs as a normal motor with its powerful gear train.

In today's world of powerful servos for very little money, this translates into a spline drive which is capable of lifting or moving large control surfaces without having to displace a lot of space in a wing or fuselage.

The motor will run continuously or at a reduced speed relative to the servo's reaction to input from a receiver receiving input from an intelligent transmitter. Depending on selections and settings in a transmitter there are built in controls for flaps if enough channels remain available to do so.

In the case of a transmitter not having multiple channels open for use an intelligent channel expander (otherwise known as an ECU) is integrated depending totally on the system OS and runtime rev. This is with some constraint exactly as if there were additional channels within the transmitter.

Channels gained through utilizing the device described above are adjustable and in best cases servo travel is programmable over time from the transmitter though they are attached by the ECU. As for a Futaba ECU/channel expansion unit it is dependent on the rev and OS to function with specific receivers and transmitters operaating in specific modes.

Multiple switch combinations can yield variable positions of multiple servos within the model to achieve a function. These functions are assigned to a switch or series of switch settings before they will operate to prevent their accidental activation. The most common function performed is motion over time so the scale feature can be performed.

The Futaba system does not integrate current management as would be the case in an optional ECU so the operation of the servo or motors attached to it will not stall and run the battery down. Circuits in a model permit placement of "y" harnesses within and through out the model where additional downstream batteries may be placed to offset an incident where a stall may occur.

A custom application ECU is most valuable asset to a system because it reduces overall system vulnerability to a failure onboard an airplane. It localizes the effect of the affect in addition to providing more precise and more easily managed motion over time functions.

That is what a servo is, how it works, and how it can be utilized/made to function. With modern compact, high torque servos you can accomplish unique mechanical function without having to jeopordize an entire model for sake of a mechanical feature.

I applaude those who work to create an ECU which can be used universally. As I mentioned earlier, from time to time over the last ten years many ECU's have appeared with too little appreciation for what they could do for modelers. Mechanical functions can be more easily accomplished with an ECU and actuators at a much lower cost to the modeler.

RE: Electric Retracts - Modifying existing Air/Servo-operated Retracts
 

Wow, thanks for the link Larry!

RE: Electric Retracts - Modifying existing Air/Servo-operated Retracts
 

Larry. Why do you need flaps on your helicopter? Ive seen you fly that thing. You need a parachute.



P.S. Electric flyers don,t wipe.



antiquefer

RE: Electric Retracts - Modifying existing Air/Servo-operated Retracts
 

LOL

I tried the parachute but the darn lines kept getting tangled up in the blades! :)

RE: Electric Retracts - Modifying existing Air/Servo-operated Retracts
 

Here is a way to use two of those thrust bearings I linked to above. This would easily handle any thrust loads in either direction.

RE: Electric Retracts - Modifying existing Air/Servo-operated Retracts
 

That looks like a good start Larry. 
Here are some stepper linear actuators If you want go that way.

RE: Electric Retracts - Modifying existing Air/Servo-operated Retracts
 

Thats a site I wasnt familiar with. At a quick glance I dont see any interfaces that would allow direct RC control from a standard Tx. Do you know off hand if they have any?

Thanks!