Does anyone have any tips or links to sites that detail building a DT timer from scratch?

There are a couple of options.

First is the classic DT using the fuse that burns through a sacrificial one time use rubber band to release the tail.

Another is a home made timer using Silly Putty as a viscous drag source to control the unwinding of a line to the tail up to release. The issue with this style is that it's highly temperature sensitive. So you need to compensate for the temperature a few times per day by winding the DT line fewer or greater turns around the shaft.

Then there's the clockwork timers that are typically made from the actions found in the clockwork style toys. The classic source used to be made by Tomy Toys.

For the clockwork toys the clue that you have the right style is where you can wind up the toy and there's a high pitch buzzing and legs or arms or whatever moves with a deliberate and constant speed.

The little pull back and let go cars or other rolling toys do not have the escapement pawl you need for making a timer.

So which style are you after?

In the meantime try a google for "building dethermalizer timer". I just did and got a lot of highly useable hits. Too many to list here.

a couple of notes about Silly Putty timers here:
http://www.freeflight.org/DigestOnline/library.htm#T
I wonder if anyone has tried a more tightly fitting timer that uses damping grease? Perhaps it's less vulnerably to temperature? I don't remember who makes it, but I had a sample kit and it was interesting stuff. Damping grease might be best used between consecutive sizes of brass tubing, i.e. clearance of several thousandths of an inch or less. Many values of damping (I don't think it's viscosity?? are available.

There's another way to do a Silly Putty timer which is to set up a pivoting arm that drags a wire through a trough of Silly Putty. The wire is perpendicular to the path through the Silly Putty. You have to smooth over the groove that the wire leaves before launching again. This kind is vulnerable to dust, etc. so it's probably best to replace the putty now and then.

The homemade mechanical timers are usually called Tomy TImers. The main thing is to attach a small weight to the arm that goes back and forth to slow it down. Tomy timer seems to bring up a lot of links on Google. Tomy timers are usually heavier and bulkier than Silly Putty timers, or at least mine was. One of these days I'm going to have to put it in something.

Thanks guys! I'm more interested in the mechanical/clockwork type timers. As a kid, I dabbled in the smoldering fuse type gliders, but now that I'm getting back into free flight, I'd like something a little cleaner. I'll search the web as described above and also see if I can scrounge up one of the wind up toys from my sons old toy box and tinker with it.

Thanks again!

I've done the Silly Putty tube in tube timer and had problems with adjusting the time. Here in New Mexico we fly in 35-95 degree weather. It would never go off at less that 50 degrees and would just spin at over 90.

You might have more luck with your more consistent temps in FL.

bill

texastimers.com has some mechanical DT bits and pieces you may be interested in.

on the main webpage, in left column, go all the way to the bottom button that says "Plastic clocks"

Also if you want to assemble your own sillyputty timer in about 10 minutes StevensAero.com has a 9$ complete DIY timer kit with mounting screws that is 100% rock-solid for a FF sillyputty dt timer.

I like the Tomy Toys Timers--they wind up with an escapement that is pretty fool proof. Been using one for 24 years on my Pacific Ace.

Hi, this is my first DT homemade, not used yet, just finished today, but here two pics. hope it helps.

Has anyone ever made a dt timer based on magnetic damping? Temperature might not affect it very much.

Well, there's magnets and there's damping. But other than in connection with magnetism related to inductors in resonant circuits I don't know of any use of magnetism and damping together related to timing.

two articles from Model Aviation

For my part I found that I couldn't seem to get the timers slow enough to run with the internal coil spring. I tried but the run was not stable enough and some always seems to stop.

So I went with removing the spring and using a tensioning rubber band in the DT hold down line instead. This way I was able to get a more even run out of the timers and I would not have any issue with flyoffs where I needed to go for the 4 or 5 minute times.

JRS

Thanks for posting that article--I lost my copy some time long ago. I have been using Tomy Timers for almost 30 years now. Great stuff!

Recall dad showing me an old escapement .. Think it was air-powered with a piston mounted in the nose. You pulled out the piston before the flight. Any info what do we call these? I am hoping I still have one of those things.. I'm thinking it was from the early 40's.

Rebel, those are pneumatic timers. They worked a little like a bicycle pump where you control how fast the air leaks out or back in. They were available for a lot of years both before and after WWII. The ones used for spark engines had a switch that would cut off the spark. The later ones for glow engines had a fuel valve.

I've got one here that came in a batch of old model stuff. It's a fuel cutoff style so I'm guessing it is from the early to mid 50's. It was the princely sum of $2.25 at the time when an .049 engine was only around $6. So they were not a cheap item.

It's got some sort of needle valve to set the run time but it's not very easy to use. I think the cup gasket is also pretty hard and perished since it doesn't let air into the timing chamber all that easily either. It works but it's not easy to set.

All in all I'm pretty sure that when the early camera self timers first started to be adapted over to mechanical shutoff timers that most flyers of the time smiled and were happy to put the pneumatic timers on the shelves.