Stepper Motors...Help Please!

[Warhog]

I have been using the VID series of stepper motors for most of my gauges and they have been performing extremely well. The VSI and Speed Indicator and all of the engine gauges have them. They do have one shortfall however...they have hardly any torque. However, most gauges don't require much torque. They just need enough to smoothly push a super light little pointer around. Except...

 

 

My Standyby ADI:

 

 

The side stepper motor in the picture above adjusts for attitude with no issue whatsoever. The roll indicator is not so lucky. I guess its all the weight up front. I used extremely high quality bearings so it turns like silk but its the initial force required to get it moving.

 

With all the varied expertise on this board, is there someone who knows stepper motors, especially the smaller micro steppers and could recommend a stepper motor they know would work with this gauge. Obviously, it will need to be small. I will use an Arduino to integrate it with DCS.

 

There are so many stepper motors on eBay but I really don't want to be buying and experimenting over and over until I find a suitable motor. You can see the gear I have on the shaft that will drive the roll. That last bay is where I planned to install it or it can be on the very outside and I'll add a second smaller shaft with a gear to make the connection.

[bnepethomas]

No answers from me John, but hey thats beautiful work that'll you've done there!

 

Cheers

 

Peter

Edited April 20, 2015 by bnepethomas

[agrasyuk]

John, have to share Peter's sentiment - hard to recoment anything to you as I don't yet have any hands on experience with this. Perhaps motor from old floppy drive? But then the motor on your picture looks suspiciously like the one

[98abaile]

Why not use two stepper motors either side of a gear?

[Boltz]

Hi John,

I think standard Arduino steppers and ULN2003 drivers will work like this.

The torque is 28 times that of VID-29 so if it doesn't work then I don't know what will. Only thing is that some kind of zero sensor is required. Check out http://www.mikesflightdeck.com/instruments/stepping_motor_instruments.html and you could probably make some kind of optical interrupter setup with a trim pot somewhere for tweaking the zero position. For the size you should be fine since they look small enough.

I have not used these steppers but they should be up to the task and the resolution actually beats the VID-29 series.

 

And I have to repeat what has already been said, outstanding work John!

Edited April 20, 2015 by Boltz

[Mike Powell]

Hi John,

My knowledge of what stepping motor models are readily available is unfortunately dated. I saw your post and thought I could easily recommend a few options, but after visiting a few of my favored surplus providers and finding no stock, all I can do is offer general thoughts.

 

My preference is to not drive a motor directly from a microcontroller. The thought of switching an inductive load that way makes me cringe. I know that instrument movements like the VID series can work okay, but moving up to a motor with higher torque gets increasingly dicey. Using a driver protects the microcontroller as well as opening up the possibility of using motors with a variety of voltages.

 

A quick look at Ebay turned up a NEMA 14 hybrid stepping motor with a 400 step per rev rating. This can be easily half stepped to deliver 800 steps which will give you 0.45 degree steps if you mechanically direct drive the roll motion. You also get the advantage of using the motor bearing to support the gauge mechanism.

 

[Hybrid stepping motors are those robust motors used in small CNC machines. You can see the motor laminations on the sides. Hybrid motors come in a variety of sizes. A NEMA 14 is 1.4" inches square.]

 

If you don't use a hybrid motor, you're most likely left with selecting some type of "can stack" motor. These have two sections that look like steel cans spot welded together. They are generally smaller and cheaper than hybrid motors, and they offer much larger step sizes. A 15 degree step is common, some offer a 7.5 degree step. To get smooth motion of your instrument you'll need to use gearing. Half stepping a 7.5 degree motor and using a 5:1 gear reduction would delivery fair results in a small instrument.

 

I got fair results using Delrin gears. I was also lucky enough to find motors that already had a small pinion gear on the shaft.

 

I notice that there are a few offerings of stepping motors on Ebay with reduction gearing. These may work, but a potential problem is that the backlash is not specified. I believe I read somewhere that some of these geared motors were originally designed to operate valves. A few degrees of slop in turning a valve may not be an issue but would probably be objectionable on an A/C instrument.

 

Personally, I would lean toward a 400 S/R NEMA 14 hybrid motor. If you decide to go with a can stack motor and gearing, I think I have a couple of small ones with pinion gear in my junk box which I could send your direction.

 

And, BTW, that's a really nice looking project.

[Warhog]

Thank you all for the kind words and praise. This really is my first time building what I would consider a more precision type of instrument.

 

Here's a few more pics at different angles.

 

 

This shot is before I installed the gear, side motor and slip ring for wiring.

 

 

@Boltz...I had a couple of those same motors in my "soon to try" box. So I tried that motor last week and it definitely had the torque I needed. The problem was, I just couldn't get it moving fast enough. I set it to max rpm but in the end it just couldn't keep up. It was too bad because it wasn't expensive and it was a good fit.

 

@Mike...I had expected I'd require a driver for anything beyond these little VID and Switec motors and I actually bought a supply of darlington arrays just in case. Thats a good point about backlash. It was always a critical part of milling operations but I never considered it when applied to a/c instruments. In that light it would be more appropriate to consider direct drive motors with an optical zero setting device. I'm just a bit concerned with the size of these motors. Something in the order of 1" diameter would be preferable. But if I could find a small can motor with minimal backlash, that would work as well. Size and weight need to be minimized as much as possible. Too much weight and I may not get off the ground...:music_whistling:

 

BTW Mike, if you do have something in your junk box that's small, I would be interested in it if it would indeed provide sufficient rpm to meet the speed requirements for the ADI.

 

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On a different, although possibly similar note, I will be needing a variety of small, high torque stepper motors for a new project I am starting. The HSI has been one of those instruments I put out of my mind because I just couldn't conceive of building something that complex. In fact, it had been quite troubling considering the effort I have gone to for all of my other instruments/panels. In the end the HSI would probably end up being a glass instrument. Certainly not in keeping with what I will have built myself. Well not anymore (maybe). I bought one...a real HSI for $25.00.

 

Ian has been so gracious as to help me with this project as I expect the programming will be way beyond my very limited abilities. I will be maintaining a photo journal on its progress. I won't go into any detail on this yet but I though you might enjoy some pictures of it. I will start a thread on this project when it starts moving forward. All I can say is that its from a 737 so its not an exact replica. But it has many of the functions of the A10C HSI so we will try to integrate everything that's there into DCS and if its not there then we will see if we can add it ourselves.

 

 

 

 

 

 

 

 

 

Thats it for now. And Mike, let me know if you have anything that might fit, and if anyone else has possible solutions to my ADI problem please post them.

[towsim]

A couple of years ago I did the same with a F104 PHI. The problem was speed and precision.The solution I used was a worm gear. It gave 40 times more precision and torque. The remaining problems were speed and cooling. The precision you need for a bearing pointer or a horizon should be less than 0.2 degree. Over all, it worked successfully. To move the pointers with an acceptable speed, it needs a tricky software. The steppers I used, caused a lot of heat. Therefore the holders made as coolers.

[Warhog]

A couple of years ago I did the same with a F104 PHI. The problem was speed and precision.The solution I used was a worm gear. It gave 40 times more precision and torque. The remaining problems were speed and cooling. The precision you need for a bearing pointer or a horizon should be less than 0.2 degree. Over all, it worked successfully. To move the pointers with an acceptable speed, it needs a tricky software. The steppers I used, caused a lot of heat. Therefore the holders made as coolers.

[ATTACH]116752[/ATTACH]

 

 

I assume your making reference to the HSI. Thats an excellent way to handle the precision needed.

 

Once I get it somewhat dismantled I'll be able to assess how precise each pointer will need to be. With the export values coming out of DCS I will have between 0 and 65,350 which I'll map to whatever resolution will make the pointers behave as required and then match a stepper motor/gearing to it. The mechanical side of this venture will certainly be a challenge for me. The software side is already covered by a master programmer, Ian of DCS-BIOS fame. I have complete faith in his abilities to make the software work...its the mechanical part that worries me. But as I said, it's a challenge and I love a challenge.

 

In reference to the heat issue, I'm aware of the heat steppers produce. The design of steppers inherently causes a great deal of heat. The Nema 23 steppers on my CNC mill get so hot, especially at idle, that you cannot touch them. Apparently thats perfectly normal. I added fans to them none the less.

 

Towsim, if you have any further incite on converting "real to sim" please post them. I would appreciate all the input I can get especially from someone whose has already been through this process. I think I will start a thread on this later today so I keep the HSI project separate from this thread. I would like to share this conversion with the rest of the community. I'm sure a few people here will like to see how it can be done and then do the same for their cockpits.

[bnepethomas]

Hi John

 

If you are looking at using a stepper that does not have an integrated zero position sensor, look at using a disk with a small slot in it' that's what is inside the vid steppers and it works very well.

 

Cheers

 

Peter

[Warhog]

Hi John

 

If you are looking at using a stepper that does not have an integrated zero position sensor, look at using a disk with a small slot in it' that's what is inside the vid steppers and it works very well.

 

Cheers

 

Peter

 

Yes, thanks Peter. I have actually been looking at photo interrupters to set zero. How large is the disk they use in the Vid stepper? I am thinking I'll just build my own.

 

John

[bnepethomas]

Yes, thanks Peter. I have actually been looking at photo interrupters to set zero. How large is the disk they use in the Vid stepper? I am thinking I'll just build my own.

 

John

 

They are close to the full width of the motor assembly, but the real magic is the narrow slit, which gives a pretty repeatable zero point to within a degree. Given your skills it'll be easy as :)

 

I've got the IR receiver connected to an analog port on the Arduino so I can adjust the sensitivity.

 

cheers

 

Peter