Speedmotion Rockets Projects

Speedrunner 75 eBay

Here is the basic configuration of the altimeter ebay that I use in dual-deployment rocket configurations where the drogue deploys reward, and the main deploys forward. These pictures are of the 3 inch diameter by 8 inch long ebay from SpeedRunner 75.

I like to make the ebay completely removable for easy access. The ebay is made from coupler diameter tubing that is held in place by bolts that go thourgh the rocket body and into t-nuts or pem-nuts that are attached to a mounting plate and glued to the inside of the eBay.

I do not use a "switch band", a short section of main body tube in the middle of the bay in which the switch access holes are located. Instead, I drill just both the ebay & main tube at the same location for the access holes. This gives more flexibility where to locate the switch.

If there is room, as in this case, I always use two altimeters for redundancy.

I use floating battery connectors, rather than fixed battery holders with buildt in contacts. That way, if the battery moves a little under acceleration, it the connector goes with the battery, and the battery doesn't unplug itself. I also mount the batteries through a cutout in the mounting sled and hold them in place with two thin aluminum sheetmetal covers. Being "in" the sled, the batteries are very secure, but are still easy to remove. Also, in smaller diameter rockets, centering the battery makes good use of the small available space.

I use u-bolts as opposed to eye-bolts to reduce the chance that the bolt unscrews itself as the rocket twists during recovery. Small stainless steel u-bolts are available from McMaster-Carr.

TR-1 eBay

I now 3D print my eBay sleds. They are not a structural or load bearing part of the airframe, so they do not need to be exceptionally strong. 3D printing allows incorporating all of the necessary features including standoffs to mount the altimeters, the fixed and removable battery covers, and allthread tunnels.

The TR-1 eBay uses an Altus Metrum Easy Mini altimeter. Since PerfectFlite Stratologger altimeters are no longer available, I have switched to the Easy Mini and have had no failures due to the altimeter. They are easy to use and reliable.

The TR-1 eBay also includes an RAF Datalogger board. This is the rocket I used to measure then side-to-side motion of the rocket to verify the rotational dynamic stability model (see the Rotational Dynamic Stability paper ), and the RAF Datalogger provided the gyroscopic and accelerometer data that was needed.

I now use binding posts to bring the electrical connection through the bulkhead and attach the ematch. I drill holes through the binding posts to allow the ematch wires to pass through and by positively retained by the binding post caps.

VTS-1 eBay

This is the eBay from my vertical trajectory rocket, VTS-1. The rocket is single deploy at apogee, separating the rocket into two separate sections, each with its own 4' parachute. The altimeter is attached to the front section, and the parachutes deploy from the rear section. The black powder charges are run on long wires past the parachutes to the rear of the parachute section. The second altimeter provides a backup charge.