JayGull

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Anybody out there familiar with or know of a link to make an electric jackscrew? I am wanting to make one out of a low voltage screwdriver (3.6 - 6.0 volt). I am not an electronics expert, so I need details on how to set up, and wire using microswitches, etc.

Thanks

Jay

JimTrainor

Do you want simple on/off control. Or proportional, like a servo?

JayGull

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I think simple on off control. In other words when the jacksrew reaches its end point I want it to shut off. Perhaps set up on a toggle switch on my transmitter, that way I can have it move in two directions. Make sense??

Jay

JNorton

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If no one else replies, I'll scan an image of how to wire it when I get home. No scanners at work. You will need a DPDT switch set up to reverse the DC motor. Center contacts are wired to each side of the motor. End contacts are crossed. In other words the top left contact of the switch is wired to the bottom right contact. Then the Top right contact is wired to the bottom left. Then each side is wired to your battery, one side for plus the other for minus. Do not have theses leads shorting! . I'd use a roller micro and a wheel on the servo used to control this. Make a cutout on the wheel so that it ramps the switch on or off depending on the servo direction in the center of it's travel. Then at each end limit position of the jackscrew wire a lever arm micro normally closed, so that the switch opens when the jack screw is at it's maximum travel. Zap you have it using 3 switches and a servo.
John

Man I wish I could spell!

tommy s

My Feedback: (55)

I don't know where you would ever find one unless you looked on a
site for antique radio equipment but Babcock R/C used to make one.
My father had a Live-Wire Cruiser with a jackscrew servo on the elevator.
It was not proportional it just moved as long as you held the control until
it reached the end of its travel. It wasn't very fast so you just used it to
initially trim the elevator after takeoff and flew the airplane with rudder only
basically.

tommy s

Flypaper 2

Jay:
I made a pair of retracts for a FW 190 from 3.6volt electric screwdrivers wired up as J Norton describes. Theres a not very good picture in the test forum a ways back a friend put in for me. I'll see if I can get it upfront.

DustOffUH1

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OK. I know other people are wondering too. What is a Jackscrew? At first I thought this was a "prop wash thread".

Joe

JayGull

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Hey guys, thanks for all of the replies. Using three microswitches is what I had in mind. One for each endpointand then one for the servo to control. 3.6 or 6v motors I beleive will do the trick. What I am trying to do, still in the test phase, is set up for a Corsair with folding wings. This bird will be large enough to accomodate the weight, 123" wingspan, and my goal is to set it up similar to the original. I was thinking of using air, but I am not sure that will be enough power even if I double up on the cylinders. Plus if I can get these size motors to work, it will be much cheaper. Any drawings that will layout the wiring would be greatly appreciated. Like I said earlier, I am not an electronics guru, so I have no idea how to wire such an animal.

Thanks again.

Jay

JNorton

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I deleted the ciruit that wouldn't work

JNorton

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Well it looks like you can read it! Yes! The CW and CCW limit switch are wired normally closed before the stop. Then at the stop the switch opens.

JNorton

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This will teach me to post while I'm eating! The circuit won't work! As it is traveling both switches will be out and short the battery. Give me a half hour.!
John

JNorton

My Feedback: (2)

I should know better than to think anything is simple. I do this for a living!

You need one 3PDT lever arm microswitch and 2 SPDT lever arm microswitches.

This will work. Fuse the battery!
John

Note the direction the switches operate. If the motor turns backward it wont shut off!
Reverse the leads to the motor.

Flypaper 2

John :
Mine is set up the way you mentioned in your first message with a DP DT toggle switch operated by a servo, and a microswitch on either end of the screwjack as stop switches. They are self contained out in the wings with their own two cell packs charging jacks included. The planetary gearbox is 1 1/2 in. dia. driving a 3/16 24 threaded rod at a nice scale speed. Hope this helps.

JL1

My Feedback: (93)

There is a guy in Texas (I think) who makes and sells one. He advertises in one of the magazines and I think the brand name is Janaco or something like that. I know that is a lot of potentially incorrect info but it might get you started on the right track

JNorton

My Feedback: (2)

Flypaper,
If you use just a DPDT switch, with 2 NC end travel limits. When it reaches the end it won't be able to turn back on again! I've looked and 3PDT switches are available as toggles or you can gang using bolts 3 SPDT switches from Radio Shack #275-017 for $2.69 each SPDT Switch with 3/4" Roller Lever

John

JNorton

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See!

SST

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Check with the R/C sailboat guys. Someone used to make a jackscrew servo for raising and lowering sails, and they may still be available. You'd be able to just plug it into your Rx.

Flypaper 2

Dave, Now, that's the way mine is wired up. When the switch goes to one end and opens to shut off, The other end is closed but the toggle switch won't energize it till the toggle is switched the other way. I'm getting a headache. Think I need a beer!! The micro switches are like the roller switch without the rollers. I'll see if I can get a buddy to put up a picture for me as I havn't figured out how to do it yet.

JNorton

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Flypaper2

Dave????


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John

JayGull

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John, thanks so much for the info. This is exactly the kind of info I was needing to get started.

Now another question, how do you determine how powerful the motor needs to be? I like the idea of 3.6 or 6volt motors becuase of size and weight. But what can I expect out of a 3.6v motor?

Jay

JNorton

My Feedback: (2)

Jay,
Can't get much info from either a 6V or a 3.6 V motor. Torque available to the load is motor torque multipled by the gear ratio less friction. If you don't have torque specs, I'd use the 3.6V motor because if I needed more power it would be readily available using 4.8 or 6 volt packs. Also another consideration is how often is this going to be cycling? If often, battery life might be paramount, then lower current draw would be a priority. Lower draw would result from higher gear ratios on the jackscrew at the expense of slow actuation times. Everything is a compromise.
Have fun,
john

Mike James

Here's the article on modifying servos for jackscrew operation, from Kronus Robortics:
http://www.kronosrobotics.com/an116/GAN116_3003.htm

DustOffUH1

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Thanks! That helps answer my question. [8D]

JNorton

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I like the idea of using a lobotomized servo motor! Gives you control over speed and direction. It a lot simpler. If you need only partial travel of the jackscrew - while observing the reaction in flight a lobotomized servo is the way to go.

However there is a big drawback, there is no easy way to use end travel limits. If you use a NC switch to cut the power, it won't start up again. An advantage in using the DC motor and switches is a self completing cycle. This would be the way to go if you need a specific distance for the jack screw to travel each and every time.

In some aspect our transmitters are extremely primitive. You should be able to tell a servo how many turns to make. Then you wouldn't need to use limit switches!

John

JimTrainor

I've considered modifying a regular servo to drive a lead screw (screw jack). I want to make an in-flight CG adjustment device.

It should be possible to simply disconnect the internal potentiomenter (mechanically and electrically), and use an external linear potentiometer for feedback.

I haven't found a supplier of an inexpensive, light, and long linear pots. That may have to be a home brewed affair.

The modifications described by kronosrobotics are applicable. Except they only disconnect the pot mechanically. If it is also disconnected electrically, and an external pot used to feedback the position. Then it can drive a lead screw proportionally.

Sorry... I haven't gone beyond thinking about it.