Thursday, 19 January 2012

New DIY UMT design

I've modified my Milestag UMT design to correct a problem with the original.

The problem is that the muzzle flash LED is wired in parallel with the infra red LED:

This is an issue because the forward voltage of the IR emitter is 1.35V, and that of the muzzle flash LED is 2.1V. This results in the muzzle flash illuminating far below its potential.

My new design has two outputs, one for the IR LED, and one for the muzzle flash LED. Both are driven from the same MOSFET but the current limit resistor is dedicated to the IR LED:

The muzzle flash LED will require its own current limiting resistor, but this matches the original Milestag design.

Here's the PCB, it will be available as a kit at TAGBITS in a few weeks:

Wednesday, 18 January 2012

Bugdet Milestag- Continued

I've been continuing the development of my budget Milestag gun kit. This is designed to have a single sensor on the gun body to reduce the cost of the unit. Initially I've concentrated on the sensor electronics. I've created a kit to make a Milestag sensor:
Here it assembled. Surface mount components are a lot easier to solder than through hole:
This needs to be mounted in a sensor housing that can be fitted to the breech section of my Tagbits Guns, I've designed a special mount for this sensor type. I'll be building the gun in the next few days:


The Milestag CORE and UMT PCBs use 0.1" Vero connectors. These are a pain to use in quantity as every cable has to crimped manually. I've started using AMP 0.1" IDC connectors instead. These are much faster to wire:
A friend of mine uses fine snipe nose pliers to force the wire onto the connectors. I found this unsatisfactory so I made myself an IDC crimp tool from a M8 bolt:
This pushes the cable into the IDC connector nicely:

Monday, 16 January 2012

Battery Cover

Whilst getting ready to try out my single sensor Milestag gun I decided that I needed to re-design the battery cover on the gun body. Previously this had been quite thin and had chamfered, circular tabs that were proving difficult to print as the filament often failed to adhere to the layer below as the radius increased with the chamfer:
I redesigned the cover to have rectangular tabs. These should be easier to print with a chamfer:
I then subtracted this shape from the gun body, and increased all the edges by 0.2mm in size to allow for a good fit.
As the gun body is quite large, it takes a long time to print so I cut out from my model the part I was interested in and printed that:
I then printed the new battery cover:
The new cover slots nicely into the body cut outs and does not need any finishing to make it fit:

Thursday, 12 January 2012

Sensor PCBs 2

I've just taken delivery of my Milestag Compatible sensor PCBs:
I'll be making these available ready made and in kit for at Tagbits in the next few days.


I've just included Vishay TSOP4856 sensors at Tagbits

Wednesday, 11 January 2012

The Full Monty

Here is a pic of my RepRap complete with heated chamber, acrylic door and filament spool holder. It's printing a grip section from one my Milestag guns.
At the bottom right you can see the hot air gun that I use to maintain the chamber temperature. I keep the machine in my garage and it struggles to get up to temperature with heat from the heated bed alone.

Monday, 2 January 2012

Second Sight

I've been asked by several people whether it would be possible to mount a sensor on the gun bodies sold at Tagbits so I re-designed a sensor mount to fit onto the forestock section. When fitted with a 3 way milestag sensor this should allow for a low cost solution, but will allow body mounted sensors to be added later if required:
Here's a view looking down on the Milestag Gun
Here is the printed part fitted with an acrylic dome:
The underside has been modified to ensure the dome mounting screws and M3 nut are flush:
Here is the part on one of my Mk4 guns:
Looking at the height of the dome on the CAD model, I was concerned that the dome might obscure the optical red dot sight:
A rather poor camera shot down the sight confirms this. The bright dot is the 'red dot' of the sight:
I am going to have to re-engineer my picatinnny rail mount to be higher. A second sight.

2012 Spares

After my extruder mount failed the other week, I declared that I needed to stock up on spare parts for my RepRap. I've printed this set of bits which is all but one of the components that I have identified as critical.
After printing the missing part I'll have a full set of spares. I really need to have pairs of some of these fittings though, namely the bar and linear bearing clamps as it doesn't really make sense to replace one of these in isolation.