Vertical Deployment Tomy Timer
VDTT - Most Advanced
Mechanical Deployment System
Developed by Robert Youens
The extended system is 14 cm long. In the cocked position 10 cm long. Weight is 14 grams. The system uses a Tomy Timer (TT) from a toy truck I purchased in a kids meal at Jack In The Box.

Basic function:  A plunger powered by rubberbands is restained in the cocked position by a rubberband wrapped around two posts located at the top of the plunger and extending down to the TT which is restrained by an inertial release until take off. The inertial release is held in the released position after takeoff by a small magnet which keeps negative G's from making the release move back into the lock position and catching the TT.

Deployment time can range greatly, 1.5 rotations allows 6.5 seconds, 2 allows 8.0 seconds and 2.5 allows 9.5 seconds.
This is the only photo that illustrates the VDTT in the cocked and restrained position. You can see the ejection rubberbands attempting to kick out the plunger and the restraining rubberband wrapped around the posts on the plunger and adjacent to the plunger sleeve then going down to the TT.

The TT is restrained by the Inertial Release.

This is also a nice view of a packed chute in my latest version of Insane Air. The chute is located under one of the nose cone I recently had custom made by Balsa Machining Service. It is now available on their website at:  The cost of the nose cone is $2.50 USD and the part # is BNCFLMS.
This is a back view of the a loaded system. The back of the VDTT was designed to hold an Adept ALT1R altimeter.

You also get a nice view of how I pack the shock cord. Some of the cord is packed below the chute to allow for initial plunger movement.

You need to be aware that the VDTT system can fool altimeters, since internal pressure is lowered as the system deploys. This creates a false altitude spike. To get an accurate reading with a non-recording altimeter, it will be necessary to have  deployment occur at least 75' below apogee.
This is a nice view of the deployed system. I use a 10" diameter parachute with a deployment dampening ring on the shrouds to control the pop of a high speed deployment. Shroud lines are made of nylon upholstery thread.

The nose cone comes unpainted with a flat base. I shaped the base for optimal
space utilization and stable fit, then treated it with CA to make it more resistant to wear. The top of the cone was sanded and painted. The cone comes from the
manufacturer with a very snug fit, you can adjust with light sanding.
Construction Tips:

Plunger shaft is Square 1/8 inch Bass Wood. The plunger sleeve is plastic square tubing I purchased a the local hobby shop. The top of plunger and inertial release arm are made from credit card material. A nylon hing is located at the base of the inertial release arm and was purchased a the hobby shop. The inertial release is restrained in the released position by a small rare earth magnet I purchased at Radio Shack. The head of the TT and the base of the plunger shaft have a wire shaft placed through them to hold the rubberbands.  The wire shaft is made from a large paper clip an secured with gap filling CA glue. The rubberbands were purchased a drug store and are used to secure pony tails. The top of the plunger and the plunger sleeve are glued with PL Premium. The post on the plunger shaft is a tooth pick and secured with thin CA. The top of the plunger is first secured to the plunger by a toothpick place in a hole drilled through the top and into the plunger shaft.
The TT is secured by thin wire. Best way for many reasons. The wire was obtained from the core of a twisty used to close a bread bag. The two pads located at either end are to support the ALT1R altimeter. Holes are tapped in each pad and hardened with CA glue to secure the altimeter. The large hole between the pads is to allow clearance for some of the integrated circuitry. The blocks on either side of the TT are for the screws that secure the VDTT inside the rocket. The frame of the unit is made from 1/8 thick plywood purchased from the hobby store.
The main purpose of the side views are to show the lengths of posts in the system. There are three:  the post located on the plunger shaft must be as long as possible to eliminate the chance of a rubberband hangup. The length of the post adjacent to the plunger sleeve just needs to be tall enough to support the restraining rubberband after wrapped. There is also a post on top of the TT head to prevent the rubberband from slipping over the head as it unwinds.