Obviously you are way better at this 3D thing than I am.
Very nice idea.
Scott, I'm not sure about that, but you could be right.
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Obviously you are way better at this 3D thing than I am.
Very nice idea.
Scott, I'm not sure about that, but you could be right.
That may well be the case mate, but we'll need a smarter head than mine to figure out how to build that! I was right with you up until the word "differential" :DQuote:
Originally Posted by cscotthendry
I've been thinking about the gearing. It'll come, it just needs some cooking time.
Hi Scott,Quote:
Originally Posted by cscotthendry
My friends Joe and Nerina have bought a property on Russell Island and they own "Russell Island scoota cars". They are Perth based but will be living there after Christmas.
Gwyn
Gwyn
I don't know them personally, but I know of them. Some friends of mine who own the island restaraunt know them. Six degrees of separation eh?
Rgr that, Nerina has been singing at the restaurant, she is currently my partner in music! I will no doubt be visiting Russell Island at some stage in the future.Quote:
Originally Posted by cscotthendry
I see you are a machinist capable of producing gears, I am also a machinist but only have a lathe. I have been trying to locate stock plastic gears to suit my Airbus TQs without success, would you be interested in a job producing a few for me? I want to use gears to drive the pots instead of the current drive system I am using. I'm also thinking of changing the trim indicator drive chain. Cash or trade services, no probs! I'll PM my phone # for a yak if that's ok.
Looking forward to your reply,
Regards,
Gwyn
I've bought gears from Serv-o-link in the US as recommended by Mike Powell's book. It's obviously not the cheapest way to get gears, but they come in a good range of sizes if plastic will work for your application.
Do any aussies know what tooth pitch/PA the Jaycar gears are?
A little more design work this evening:
http://mycockpit.org/forums/images/HSI/hsi02.jpg
Might do some more after dinner. That is based on the dimensions of a servo I had to hand, which is unbranded, though it is roughly the same size as the Futaba S3107 micro. The CDI needle sticks out about 6mm to give full travel; to reduce parallax you could mount the servo farther back from the CDI plate. It's too late for the maths right now :)
When the model's a bit more advanced, I'll publish an animation showing how it all works.
Thats nice. The problem is the servo must be further back so the From/To indicator can fit in there. It could be a couple of LEDs with a servo switch somewhere else in the housing. You will need your first set of brushes for this. To help you visualize this, add the wires to each servo, (or LED).
Also, the servo you are showing has to be attached or at least move with the inner CDI plate that will have the arrowhead on it. That whole assembly needs to be able to spin 360. This is where your second set of brushes is going to come in.
And since you are so good with the 3D modelling, how about if I forget about making mine and just comment on yours? (It's not as easy as it looks ya know... :roll: )
Why 4 outside gears for each ring?
Yup that's not hard to do, the design is in my head. Or you could move the TO/FROM indicator slightly outwards from their usual position - I will cut holes in the CDI plate later to show you what I mean.Quote:
Originally Posted by AndyT
Great idea, I was thinking a solenoid, but LEDs are much simpler.Quote:
Originally Posted by AndyT
Spot on - my thought is to actually have microcontroller-driven circuit mounted on the back of the servo/CDI assembly, so only 5 wires are needed through a brush contact arm, and it can drive the servo, TO/FROM indicator and off flag all from one device.Quote:
Originally Posted by AndyT
Just supports for the main gear assemblies. Probably overkill, but with the close tolerances on the HDG BUG and RMI flags, you wouldn't want too much wobble. They should be able to rotate independently of the two other support gears on the same axis.Quote:
Originally Posted by AndyT
Sounds good.
The TO/FROM can both be on one side of the CDI needle slot. The problem here is that as you turn the plane and the CDI plate turns, so do the TO/FROM arrows. So either we create some logic that flips them on the turns or we need a different way to mount them so they don't spin.
Put a small tab between the LEDs to prevent light bleed-thru.
The flags are hidden under the outer ring which is where you have the 4 supports at. A simple shaft to a flipper/solenoid down in the housing could handle them.
Also two of the support gears can be used to connect the front panel knobs to. Or would we want them to go to a pot somewhere to feedback the position info? If we build position sensors into the rings, then we can connect them directly.
Ah - now I see the problem. You're picturing a King-style TO/FROM e.g.http://www.esmofly.net/HSI-esm.jpg whereas I'm picturing the F-16 style e.g. http://home.priorityonesystems.com/hsi/HSI_layout.jpg :)
Should be straightforward enough to mod the design for either.
The approach Mike Powell used in his book is to have the knobs as rotary encoders, which drive the steppers to position to ring, rather than have the knobs geared directly to the ring. I'm gunna go with what I know for now! :)Quote:
Originally Posted by AndyT
Ok, I see what you mean. Yes, should be pretty easy to handle either.
This is beginning to sound like a combo of the two you have pictured above.
The encoders are perfect for the knobs.
Can anybody figure out the gear trains? The big gears have 120 teeth, and it would be nice to gear them to commonly available 24- or 48-steps/rev stepping motors so that we can move the rings in 1/2 degree or maybe 1/4 degree steps?
We need a position sensor on each main gear so that when it powers up, it can calibrate itself. All we have to do is have either a small tab that breaks an optical sensor or trips a micro switch when it hits the 360 mark. Then the software can do the math on its own. Once its done that, it can set itself to the whiskey compass.
Ooohh...Bit of a stretch calling me a machinist ;) I have the machines, but the talent is pretty raw. Nonetheless, I think we could probably work something out in trade services. Don't want to do cash as that implies I'm open for biz. I'll phone tomorrow. Today's full on with the boat.
Ruprecht:
Love your drawings mate. Here's some practical considerations. The CDI needle needs to be elastically attached to the servo. Servos can rotate through about 180 degrees and from experience, when the sim is first powered up, there's always the chance that a servo will run feral. If the pointer is rigidly mounted to the servo, you'll get some damage at worst or some mis-alignment at best.
I like the idea of using LEDs for the to/from flag. Simple and elegant.
Gear trains are straightforward. At 48TPI, just divide the number of teeth by 48 and that is the working diameter of the gear. Halve that and you have the working radius. Add the working radius of the two gears that must mesh and you have the centre distances. Your gears look great in the 3DS, but you don't need to be that fancy. Just draw circles at the appropriate working radius.
The three gears you have in the drawing are going to be difficult to "home". As you've discussed, we'll need some kind of sensors on the gears. If we use opto-interrupters, there will need to be a LOT more space between the gears. Another option is to place small magnets on the gears and position reed switches around the periphery of the gears.
Also, the gears/compass plate/CDI card/Heading bug carrier need to be supported somehow.
I know all this sounds like criticism and it is, but constructive criticism. We'll get there with this.
BTW, I have a copy of the actual facia of one of the BK gauges and it's a bit frightening how small this unit is and how much stuff has to go inside.
Good thought, noted.Quote:
Originally Posted by cscotthendry
I've got it sorted in terms of fitting the gears together, I meant more the gear ratios. For instance, it would be nice to be able to move the CDI assembly in half-degree steps. If I have a 12-tooth gear on the pinion of a 48 steps/rev stepper, and mate that directly to a 48-tooth gear on the CDI assembly shaft, 48 steps will give me 90 degrees of shaft rotation, or 1.875 deg/step. So what different and/or intermediate gears are needed for 0.5 deg/step?Quote:
Originally Posted by cscotthendry
I've got something in my head about where to put optointerrupters, will get that into the design tonight.Quote:
Originally Posted by cscotthendry
Also in my head ;)Quote:
Originally Posted by cscotthendry
No worries at all with constructive criticism, this is a collaborative process.
We need to know the RPM and the smallest step the servo is capable of to determine the correct gear ratios.
Given that all 4 major axes (compass card, heading bug, RMI needle, CDI assembly) need to rotate continuously, I don't think servos are viable. Servos have only a limited range of movement, we really need to be looking at stepping motors. Servos are ideal for the CDI needle and the glideslope indicator, with only limited (~ 90 degree) range of movement required.
Even the highest performance aircraft can only turn at about 20 deg/sec. I'm not sure how fast you can get common 48 steps/rev steppers to turn, but at 1/4 degree steps, 20 deg/sec equates to 80 steps/sec or 80Hz. Is that possible? Given that Mike Powell's book (henceforth BSAI for simplicity!) talks about accelerating through 250Hz to 1KHz (pp 192), 80Hz seems like it should work easily.
Most servos have a small tab that keeps them from 360 movement. Break it off and there you go. But I agree that steppers are likely a better choice.
And as small as this unit is likely to be, I think 1 deg steps will be more than enough resolution.
Whether we use modified servos or steppers we still need to have a home sensor. However, steppers allow you to predict where the driven gear is at any given time. Modified servos work on the priciple that 1.5ms PWM signal centers or stops the servo rotation, A narrower pulse causes the servo to turn one way and a wider pulse the other way. The problem is that you don't know how far the servo has turned unless you couple an additional feedback mechanism such as a rotary encoder or some other type of encoder. Now you're getting really complicated and then steppers look a lot simpler.
If you have a 48 steps/rev stepper and you want .5 degree res, then you need to get 720 positions on the driven element. You just need a combination of gears that gives you 720/48. It works out that a ratio of 15:1 will give you that. This can be accomplished a few ways. You could have a large gear with 180 teeth and a pinion on the stepper that has 12. Or you could have a divide by three followed by a divide by five. This could be done with a compound gear.
The problem with a 180 tooth gear and a 12 tooth gear is the overall case size and the size of the stepper motor. If you position even a small stepper at the radius that a 180 tooth gear will demand, You will find it probably won't fit within the required profile of the instrument. However, we can use multiple gear shafts to offset the stepper. This makes the construction more complex, but only a little.
While you're sketching, have a scope around at steppers on the net. We'll need a source of cheap steppers all the same size. I bought a batch from a company called Futurlec, but they're not terribly prompt suppliers to do a project from. But they are CHEAP. I've seen some criticism of them in some forums, but my experience has been generally that they are slow, but basically honest. BTW, my steppers are 40 steps/rev. and they're an excess stock.
Also, if at all possible, look for units that already have a 48TPI pinion mounted (around 12-14 teeth).
Hope this helps. You guys are doing a great job tossing this around. I'm confident that we can come up with a workable design.
Jaycar carry this one: YM-2751 48 steps/rev though I'm sure our american cousins can get steppers cheaper than AUD $19 each!Quote:
Originally Posted by cscotthendry
PS I am about to do an order to Serv-o-Link for some gears for the Altimeter project in Mike Powell's book - if any aussies want some gears and want to split the shipping, let me know before thurs night.
Just been sketching the gear trains in my "pit book" :) I think I have it sorted:
For the main ring gears (x 3):
- components: 48 steps/rev stepper, 1 x 12 tooth gear, 1 x 36 tooth gear, 1 x 24 tooth gear, 1 x 120 tooth gear, idler shaft.
- assembly: the idler shaft has a 24 at one end and a 36 at the other. The 12 is mounted on the stepper. the 12 mates to the 36 for a 1:3 ratio, and the 24 (at the other end of the idler shaft) mates to the 120 ring for 1:5 ratio.
- result: 48 steps gives 1/15th rotation, or 1/2 deg/step.
for the CDI:
- components: 48 steps/rev stepper, 1 x 60 tooth gear, 2 x 12 tooth gear, 1 x 36 tooth gear, CDI shaft, idler shaft.
- assembly: a 12 on the stepper, a 60 on the end of the CDI shaft (with the CDI assembly at the other end), idler shaft has a 36 and a 12. Mate the 12 on the stepper to the idler 36 for 1:3, and the idler 12 to the CDI shaft 60 for 1:5.
- result: 48 steps gives 1/15th rotation, or 1/2 deg/step.
Thanks for the help on the gearing, now to see if the gears will fit inside. I feel like I'm on an episode of MythBusters - "Hobbyist HSI - it can't be done!". Hoping to bust that myth!
I just had a great reason for making layered gear rings and I got interupted and now I lost it. It had something to do with embedding position sensor triggers.
So before I forget, we can use flexible drive shafts for some of the elements. Ever see a Dremel with the Flex cable hooked up? Same principle.
After spending two days on this, I have a much better understanding why BK charges $15,000 for an HSI. I don't even want to think about what Simkits would charge.
And by the way,
By posting the development process in the forum, we are making the designs that result public property and not avialable for any person to patent or copyright.
Collins are even higher. But they have a couple more functions as well.
quick update:
Have added H21A1 optointerrupters for the main ring gears. Had to be careful that the flag had a full range of movement, and still not convinced the flag on the compass card won't cause some problems with the 7-segment displays and off flag mechanisms.
Also added cutouts for the glideslope indicators, and mounted servos in positions that might work. Am using 0.5" and 1.5" spacers as used in BSAI.
http://mycockpit.org/forums/images/HSI/hsi03.jpg
Ok, Lets move the optical sensors to the opposite corner because the rotary encoders need to go where you have them now. (or just rotate the picture..)
Since this is a combo unit that fits many planes, I guess we can lose the outer facia ring that the BK unit has.
Now if you please, add the encoders and the 7 seg displays in the corners. That way we will know if the proper clearance exists or if we need to modify the ring flags with a greater bend.
Can we get a detail shot of how you have the inner servo connected at this point?
This is looking good. I imagine there are a few out there ready to build as we design. :D
Hmmm... If we add just a squidge of space between the rings, do you think we could fit the opto-interrupters between them? That way they do not interfere with the encoders or the 7 seg displays.
My largest Simkits instrument is about 5" deep, so we have plenty of room yet.
Ruprecht:
Love ya work mate! Here's a suggestion for the optos. If we drill a hole in each ring gear the optos can be moved up to straddle the gears and save some space.
Another practical consideration as far as the materials for the gears. Consider the standard thicknesses of metals. I'm not sure what the thicknesses are for brass (expensive in the sizes needed) but aluminum (aluminium for the Aussies watching) cover a pretty wide spectrum. 3mm is a nice thickness to work with but I've made gears successfully from thinner stuff.
The problem with thinner stuff will be the attachment of the bug and course pointers. As it appears in your diagrams, it looks like you've attached them to the inside edge of the gears. We might be able to make a tab on them and fold them and attach them to the face of the gear, but that adds thickness to the gear which needs to be accounted for, as far as the optos are concerned.
One more practical consideration, we'll be home building these, so try not to make the tolerances/clearances too tight. That makes them really hard to build.
Lastly (for now) for rotating bearings or concentric shafts, it's hard to go past the little brass tubes that you get in the hobby stores. I'm not really familiar with the sizes of the metric ones, but the imperial ones go from 1/16" upwards at 1/32" intervals and the slide inside one another very nicely and freely with minimal play or wobble. The wall thicknesses are just under 1/64".
Keep going mate your drawings are looking fantastic. I myself would prefer the BK style, but hopefully we'll be able to mod your mechanicals to suit the different style.
Guys:
I just had an idea for mounting the ring gears. Imagine the ring gears meshed with 4 small gears of the same thickness as the ring gear. Imagine these small gears positioned at 90 degree intervals (even three at 120 degree intervals would do). Now imagine that each of these gears rotates freely on a fixed shaft mounted to it's plate, but most importantly...Each small gear has a washer on both sides of it that overlaps the ring gear thus retaining the ring gear while the little gear acts as a bearing.
HA! Thanks Scott! I had that idea for drilling the hole the other day but as usual, my grandaughter chose that moment to ambush me. Apparently I have 'Climb on and beat on me' tattooed somewhere on me. So, thanks to her, I had forgotten that one. And the layered gear idea I had was a rather complex method of always knowing the exact position of the gear.
EDIT: I like the three at 120 better. Just as sturdy and less to build. So the washer is basicly a bushing to keep the spacing correct.
Roger that and less gears to cut. ;)
The washer is a spacer and retainer.
Is this what you meant by the support gears? The washers are standard steel off the shelf, and the shafts are 1/8" and 3/32" brass tubing. The gear is a 12-tooth.
http://mycockpit.org/forums/images/H...tingGear02.jpg
Guys, keep up the great work. You are making history as you progress here.
Thanks Trevor.
Guys, while I focus on the modelling (around my day job and other pitbuilding activities!) it would be very helpful if you could collect standard dimensions for the components we will be using. Things I'm thinking of are:
- rotary encoders
- 7 seg displays
- sheet metal
- LEDs
etc, anything you can think of. I am working in mm to 3 decimal places. Remember, use commonly available stuff, not random stuff from your "bits box".
cheers lads