Wind vane self steering design

Hi Fannie,

Cutting my own gears is my fall-back plan . . . but the design and cutting of gears of all sorts is not at all a trivial issue! If you do it right, that is. There are some mighty fancy machines for doing it right, and I'd much rather salvage what I need from something common, if I can.

The maximum force I need to design to is from a pooping wave hitting the vane directly from the side with a few tons of sea water. Lucky me, I've actually had this happen. At the time I had the vane tied in an upright position and it wasn't harmed. The idiot on the tiller (me) got himself ground into the cockpit sole after an altercation with the engine controls though, which hurt for the next ten years or so.

So you play with controllers? Are you using one with built-in A/D converters? If so, I'd ditch the pot and go with a bi-cell photodiode with a LED shining on the intersection. Mount the LED off axis just enough so that the light from it exactly bisects the split in the bi-cell when the vane is vertical, but biases the photodiode cells one way or the other as the vane rotates. The two outputs from the bi-cell will thus react inversely to one another, that is as the resistance of one increases, the other will decrease. The magnitude of the difference between cells is then an analog to the vane rotation magnitude, and whichever one is going up gives the direction. The advantage to this approach is that everything can be behind glass and protected. And no additional moving parts are required. No moving parts means infinite lifetime, too.

BillyDoc

 

You don't need a fancy machine, just the right cutter for the pitch. Attached a small HDPE rack I've cut for another machine I'm designing. I've cut the rack for the steering also but has a courser pitch. Have the cutters for the sprockets also. For the small rack I've made an attachment for the small milling machine. Guess what it was For the gears you need a vertical deviding head.

Cutting these gears are no black art, I have a nice pdf if you're interested I'll e-mail it to you. send a mail to fanie at faze .co .za I'll attach the file and post back.

The processors we use have a 10 bit resolution, that is 1024 steps full range.
I assume you refer to a motor doing the movement ? I'm not sure what this bi-axial led is that you refer to, but I know what you have in mind, but a pot is really easy to use. As I mentioned, you get some very nice stuff nowadays.

The way mine will work is you'd set the direction to wind for ie optimal speed using a manual steer control pot. Once you're pointing where you are happy with it, you flip a toggle switch and the controller keeps the direction wrt where the wind vein is set to. You get compass chips, if I can source some of them then you can have the steering unit warn you when you veer off course say be 10 degrees. This will prevent you from sailing in circles or go off course when the wind changes.

I seem to have read somewhere about someone who sailed all night to end up where he started the previous day... and something about the sun come up in the west ?

R i i i i i g h t Anyway, the compass unit would prevent that the sun come up in the wrong place providing you don't pass through any of the poles.

 

Cogswell Cogs is about to be in business
or will it be Spacely Sprockets

 

Hi Fanie,

I read that too. What an idiot! He should have had a fluxgate compass and an alarm set. If he had a brain, that is.

Nice pictures! I just sent you an email for the .pdf and I'm looking forward to seeing it. I've actually cut plain gears like you show before, and drive belt sprockets (cogged belt) as well, but I fear that the angled pinion gears for a differential will be quite a bit more challenging as the teeth expand as the radius gets larger on the taper. My mill is actually a four-axis model with the fourth axis being a rotary table, so it's conceivable that I could get the programming codes together to do the cutting . . . but it sounds like a real nasty problem to me this morning! Maybe after I get my coffee inside it will look easier.

I think you are going to have a very nice self-steering machine there when you get finished. The bi-cell photodiode I was referring to is basically two photodiodes manufactured on the same chip with a very fine divide between them. You can also get them as "quad" photodiodes (four sensitive areas). They are used to measure miss-alignments and usually to drive a servo feedback loop of some sort. I've attached a data sheet for one below.

BillyDoc

 

I'll have a look at those diodes.

Your file has been sent, let me know if you received it ok.

I bought a 2nd hand Hermle 810 machine I'm renovating currently (f heavy ), it is mostly extremely dirty, the oil is like mud. It has a verical and horizontal spindle, this machine will cut the gears, the smaller CNC machine will do the racks.

The gear cutting is going to be easy. You can calculate all the info (see pdf), devide the radius by the teeth, then when you cut, undercut and see when the gears fit. Once you have the final settings it's a matter of repetition. As far as I can remember the gear slot depth is given. I use the metrics only (Mod 1, Mod 2....) which is much easier than the inches thing you guys do.

 

I built a machine shop for a friend of mine from Ball Aerospace
everything is cc
he has a machine specifically for cutting gears that I would think would interest you guys if your going to be making a living slicing out bits and pieces

I could ask him what it is and who makes it if you like

things pretty slick
he spends a few programming locates the block on the table and clicks a button
stands back with a grin

guy was the head machinist down there for years
Im sure he would be willing to discuss what tool would work best for production work of the components your considering

best
B

 

Hey Fanie,

I got the file and it is a wealth of information. Thanks!

Then I went to the section on bevel gears (page T61) and started reading . . . and it's way worse than I thought! I'm going to order one of those units from Surplus Center right now. I REALLY don't want to go through all of that to make my own gears. I guess it's why, as Boston points out above, there are special machines to do it.

BillyDoc

 

Hi Boston,

Sometimes I have to leave my CNC machine on for days at a time working on some part. Like you say, I position the material on the bed, press "Cycle Start" and the thing starts downloading instructions from a computer in another building and executing them. It's just working away, I'm grinning and watching, and when it comes time to leave I go to the door and start to turn out the light . . . and pause and remind myself that I'm not really turning the lights out on a poor guy slaving away over a hot milling machine . . . but it sure seems like that sometimes. It's weird!

I love this machine! It makes so many things possible that I couldn't begin to do by hand.

BillyDoc

 

sometimes seeing various robots work I have to wonder if its not all true
that sentience in the machine world is inevitable

ok
back on topic

Fanny if you can cut gears and not even blink my hats off to you
I know it takes a fare bit of talent to get that accomplished and there are more than a few machinists who never learn how to do it
course there are carpenters who cant build a set of stares either
but cheers to you
its a knack

best
B

 

I'm sure you guys are missing something ! I'm not even a mechanical (kind of) guy

If I remember I'll make a short video so you can see when a gear is cut. You're going to kick yourself

 

no its the eliptical gears that are the hard part ( worm gears )
even bevel gears are kinda a pain with two sets for each group of passes if I remember it
there is a set up on the table that the gear spins on as you cut it
although I think Denis showed me that all you do it set once turn through each cut on an beveled gear then change the angle and cut the taper on the teeth
I think
its been a long time but there is a table attachment used for sprockets and bevel gears
Denis ( guy with the machine shop ) got sick of setting it up and tearing it down all the time so he got a dedicated gear cutter

I just help out in the shop every once in a while and no very little about the machines
although I can bludgeon something out on the three axis mill if I take my time
cutting gears is a pain cause of all the set up
seems like of all the guys in the shop Denis is the only one who knows how to program a gear
so I think it still takes talent to be proficient at those more difficult gears
and my hats still off to you

Im sure given enough time any fool with the right cutting head could cut a bar gear or simple cog
but all the cone gears in that wind vein thing look like they would be best salvaged cheep rather than spend all that time
specially for a one off

I take it you guys didnt like my idea of a optical sensing vein with more of a fly by wire system rigged to it

 

When you cut a gear, all you have to do is figure the first slot to cut out. Once you have that done you advance the deviding head the required degrees and repeat the same slot to cut, advance the deviding head and so on.

 

You're absolutely right Fanie, no problem. And in the case of Bevel Gears you can keep it simple by going with the straight cuts, forgetting about helical or offset approaches. I've extracted and posted the table of formulas for the setup from the excellent document you sent me below for those interested.

BillyDoc

 

Those formulas makes my eyes water Forget about that.

Just get the right cutter for the pitch of the gear you want to cut. In the US they are cheap to buy. One cut and one gear tooth emerge. The cutter's profile is made so that the gear shape comes out right.

The cutter cuts a streight slot through the material. Then you advance the required degrees and cut the next slot. Once you've cut all the slots you have a gear. Drill the hole the shaft fits into using a parallel drill and you're in business.

 

It's do-able Fanie, but still not within my definition of "easy." The problem is that the teeth do not have parallel faces, but taper from one end to the other.

Here's a step-by-step explanation here: http://www.sherline.com/tip27.htm

And reading this, I'd still prefer to salvage them! But if I can't, well, I guess I'll just have to get to work.

BillyDoc