Magnetic switches

[Adrian A]

I'm starting to run low on stock on my av-bays and the magnetic switches, so I'm getting ready to place orders for new production runs of the av-bays and magnetic switch.

Unfortunately, the part that I have been using for the most recent revision of the Featherweight magnetic switches and av-bays has been discontinued for some reason. I'm looking at replacement parts for these next production runs, and there are some tradeoffs to consider. The choices are:

1. Operate the same way that the current magnetic switches do, in which you turn the switch on with the magnet in one direction, and turn it off with the magnet in the other direction. The LED lights when the switch is on. Unfortunately, the only available replacement sensor that works this way is half as sensitive as the current part, which means that either the range is cut down by about 20%, or the magnet volume and cost need to go up 2x for the same range. Currently the magnets cost about $3 for a range of one inch or $15 for a range of 2 inches. And the large magnet is kind of a pain to work with, so I'm not very inclined to double it. The maximum range would be about 1.6".
   .
2. Operate such that when the magnet is near, it toggles the state of the switch. Move it close, and farther away, and the switch turns on. Do the exact same thing, and the switch turns off. This is similar to the way the first rev of the 38mm av-bay worked, except that now the toggle would take place with either orientation of the magnet. I would have the LED turn on when the magnet was close and off when it was further away, regardless of the state of the switch, though I could just as easily design it to have the LED stay on when the switch is on. The sensitivity for this sensor is as good or better than the most recent version of the products, but the parts count goes up a bit and the size and cost of the board would go up slightly. The cost increase would be much less than the cost increase of the magnet required with option 1 to get the same range.

I think that sensitivity and range is more important for user happiness with the product, and magnets have doubled in price in the last year, to become a significant part of the overall cost, so I'm leaning toward #2. If you are currently a user of Featherweight magnetic switches or av-bays, which option would you prefer? If you are voting without having used one of the existing products, please let me know what you voted for in the comments.

Thanks.

 

[Rocketjunkie]

You need to have a way of verifying the status of the switch. Blinking LED when on?

 

[gdiscenza]

I haven't used one of the mag switches yet, but an "armed" light would be tremendously reassuring.

I would also like to not need Adrian's mad solder skills to install the thing. I have *no* solder skills.

G.D.

 

[gtm3323]

I like the current version. I marked my magnet so I knew what side would turn the switch on and off. The switch was inside the rocket where I could not see the led light.

 

[troj]

Definitely #2, Adrian.

As I've been playing with various designs, I find that range does matter. I also agree that larger magents would be a bit scary -- I have a pair of the big ones, which my son was messing with, and he made the mistake of getting his finger in between then....

I know it would add size, but for those that didn't design such that they can see the LED, how about a small speaker that lets out a short chirp when it turns on?

-Kevin

 

[Adrian A]

Definitely #2, Adrian.

As I've been playing with various designs, I find that range does matter. I also agree that larger magents would be a bit scary -- I have a pair of the big ones, which my son was messing with, and he made the mistake of getting his finger in between then....

I know it would add size, but for those that didn't design such that they can see the LED, how about a small speaker that lets out a short chirp when it turns on?

-Kevin

Generally, the things you're turning on have a way of telling you that they're on, so I'm a little surprised that the LED is coming up as a care-about. I can keep the LED on when the switch is on for either option. With option 1, there isn't a way to power the LED just when the magnet is in range like there is with option 2.

 

[Adrian A]

Thanks for the responses, guys.

Generally, the things you're turning on have a way of telling you that they're on, so I'm a little surprised that the LED is coming up as a care-about. I can keep the LED on when the switch is on for either option. With option 1, there isn't a way to power the LED just when the magnet is in range like there is with option 2.

You need to have a way of verifying the status of the switch. Blinking LED when on?

I haven't used one of the mag switches yet, but an "armed" light would be tremendously reassuring.

I would also like to not need Adrian's mad solder skills to install the thing. I have *no* solder skills.
G.D.

With the current and future magnetic switches, you can wire wrap the wires around/under mounting screws so you don't have to solder. The holes are sized for 4/40 screws.

I like the current version. I marked my magnet so I knew what side would turn the switch on and off. The switch was inside the rocket where I could not see the led light.

Definitely #2, Adrian.

As I've been playing with various designs, I find that range does matter. I also agree that larger magents would be a bit scary -- I have a pair of the big ones, which my son was messing with, and he made the mistake of getting his finger in between then....

I know it would add size, but for those that didn't design such that they can see the LED, how about a small speaker that lets out a short chirp when it turns on?

-Kevin

 

[Burner]

It's kind of a toss up for me, but I went with option 2.

In case nobody has tried it, you can stack magnets end to end and the range substantially increases. Stacking magnets improves the measured flux up to a certain ratio between diameter and thickness. At a certain point it will not produce any additional benefit.

 

[Wingarcher]

My $.02 is range matters. Increasing the size of the magnet sounds like it's getting into "big magnet" range which with rare-earth magnets brings a host of potential trouble. Increase the sensitivity of the device.

Lights are wasted on me. The beeps of the altimeter are most important. The Raven I fly has lights, and I don't have the faintest idea what they do. As long as I get the high high low low beeps, I know I'm good. Can't see the lights in the rocket, anyway!

User of Raven and a featherweight screw switch.

N

 

[Handeman]

I have not used a magnetic switch and right now, I'm not sure I will.

If I did, I guess I would go with option 1. As you say, the altimeter has a way of letting you know it's on. The only altimeters I have are a couple of Perfectflite. They beep through their power up sequence when turned on and continue a beep pattern if it senses ematches on the pyro channels. LED not needed.

With that said, I mount the switches to the av-bay, not the sled. The switch wires get connected to the sled along with the pyro connections to the end caps when the sled is installed. This allows me to use a sled that fits a 2" ID rocket in my 3" and 4" rockets. If I used a magnetic switch, I would want it mounted on the inside of the av-bay instead of the altimeter or sled. Range would only have to be the thickness of the av-bay wall (coupler and BT) thickness, about 0.10" unless you're using a stiffy too, then about 0.225".

The only other advantage is can see with a screw switch over a magnetic switch is that if you lose your activating tool, it's much more likely you can find someone to borrow you a small screwdriver then a magnet that will work. I'm not sure that's much of a concern if I were to get a magnet with each switch I bought. I would want each magnet to work all the switches I might have. That would mean you need to pick one method and type of switch and stick with it. Backwards compatibility! I hated it when my SAE tools couldn't be use on all the cars that suddenly became metric and I had to buy more tools.

My :2: on the subject. I have an opinion, like everyone else, take it for what it's worth and good luck.

 

[Adrian A]

Thanks for the inputs.

I have redesigned the switch based on option 2, and with a little creativity I was able to keep the board outline and mounting hole locations the same. The magnetic sensor is supposed to be a little more sensitive than the last version, and oriented to sense field lines that are in the plane of the board, rather than perpendicular to the board. I'll develop a prototype and do some testing before I go into production, so it's going to be a while before the new ones are ready. In the meantime I still have a dozen or so in stock from the last production run.

 

[cjl]

Definitely #2 for me as well.

 

[Missileman]

Have a couple of these switches in 1.5" and 3" bays which work quite well, Option 2 sounds good so long as the size increase is not too big, but please make the LED stay on whilst the unit is powered up as some altimeters do not make any sound when pyro charges are not being used, and it keeps it the same as the previous switches for less confusion.

Mike.

 

[Adrian A]

Thanks for those photos. I didn't know there were altimeters that don't beep when they're turned on without charges. Interesting. I think you'll like the next version, as I've kept the LED-when-on feature in the design, and the range should be better. One difference that's probably an improvement is that the magnetic field direction that the switch is sensitive to is in the plane of the board, so you'll be able to mount it on the edge of an av-bay sled in a large rocket and be able to point the end of magnet at it.

 

[Missileman]

Excellent, looking forward to trying them out.

 

[Adrian A]

I assembled a prototype of the new magnetic switch last night, and it works. It has the exact same size and screw hole locations as the existing ones, and the only differences are:

• The magnetic field it's sensitive to points into the edge of the board, rather than perpendicular to it
• The activation range is longer, about 1.2" with the small magnet, instead of instead of about 0.9"
• Either end of the magnet works the same, instead of having specific on/off ends
• The switch changes state when the magnet is pulled away, rather than when it approaches

All but the last one are improvements, in my opinion. That last difference is just an inherent result of keeping a simple design with the parts that are available. I looked to see if the parts that affect this are available as a drop-in replacement that wouldn't add size or cost, but that's not the case.

The way the prototype works now, when you bring the magnet in close, nothing happens. It's only when you take the magnet away that it turns on. To me, this gives the subjective impression of having less control over it, even though it's just as repeatable, and more sensitive, than before. I think when it's installed in a rocket there will be less difference than when you're playing with it and watching the LED come on, because when its buried in your rocket and you're out at the pad, it takes a few seconds to get beeped feedback that it turned on in either case. Also, if you swipe the magnet along your rocket to turn it on, the behavior would pretty much seem identical. So I'm leaning toward running with this design as it is, to keep it simpler, smaller, cheaper, and fewer parts to break. But I thought it wouldn't hurt to get some feedback before committing the design to production. This is also the same magnetic activation design that will go into all the Featherweight av-bays and the new RavenPlus that I'm working on.

 

[frankgh]

How do the magnets that come out of old hard drives compare with the magnets you use?

 

[Adrian A]

The magnetic switches are back in stock. (and yeah, a lot of them!) Testing has been 100% successful so far.

 

[Zeus-cat]

I would like the one that is five down and seven over from the right.

Seriously, I'll let the wife know as she tried to order some for my birthday. Now they will be Christmas presents.