Motors and Machining

Martlet 2 is powered by an O-8000 Pro150 Cesaroni motor. This is the largest certified motor available and, over the course of its 5.12s burn time, produces an average thrust of 8000N. We purchased the motor last weekend from Animal Motor Works and will be meeting it for the first time at BALLS.

Cutting some of the aluminium stock into a section that will remain in CUED and one to be sent to WPPE

Cutting some of the aluminium stock into a section that will remain in CUED and one to be sent to WPPE

In other exciting news all the aluminium stock is now out of the basement lab and being machined. WPPE are machining the various couplers, fins and the aft cone whilst the CUED workshop are kindly machining the fin can ( at a length of 480mm and with a diameter of 186mm it is Martlet 2’s biggest metal component).



Martlet 2 Body Tubes and Aluminium Stock

A couple of weeks ago we received the first components of the Martlet 2 airframe. These roll wrapped carbon fibre tubes have an inner diameter of 182mm and a 2mm wall thickness. They were bought ‘off-the-shelf’ from a UK company and look great!

Carbon fibre body tubes.

Carbon fibre body tubes.

Both need facing off to ensure the top and bottom surfaces are perpendicular to the rocket axis. One of the tubes needs to be cut down to 750mm for the motor section whilst the other is already at just about the correct length for the parachute section. If time allows then a thin layer of epoxy will be applied to the outside in order to get a nice smooth aerodynamic surface.

In addition to the carbon fibre tubes we have also got, as of this morning, most of the aluminium stock from which various parts of the airframe are being machined out of.


The raw material of the airframe

The raw aluminium stock consists of:

  • A length of 7.5″ OD x 3/4″ tube from which the fin can and the body tube coupler will be machined
  • A length of 7.5″ OD x 1″ tube from which the nose cone coupler will be machined. The extra 1/4″ is required to proved a surface that the Metron protractors located in the nose cone can push off from.
  • 500 x 1000 8mm thick aluminium plate which will be used to machine the rocket’s three fins.

We still need to get stock for machining the nose cone tip and the mirror shroud – though as these are much smaller parts the stock for these will most likely be obtained from CUED stores.

Now that we have the stock we can start getting components machined. Once the body tube and nose cone coupler are machined they can be sent straight to the anodisers. The fin can and fins, however, have to be welded together before a further set of machining operations can be performed on the combined unit. These machining operations are done in order to ensure that some of the machined features inside the fin can (such as the all important thrust ring!)  have the correct dimension and aren’t warped during the welding process. After this has been done the whole lot is sent to the anodiser for hard anodising. Hopefully this will all go smoothly and we’ll soon have pictures of the machined parts.