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:

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:

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.

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.

Printing on Kapton Tape

Nophead lent me some Kapton tape and I tried an ABS print on it last night:

It is an 8 hour print of a large part, it came out really well:

Although the part was much more firmly attached to the kapton than I've seen with PET tape, it still managed to lift the tape slightly at the corners:

I'd really like to eliminate this lifting if I can. It has not spoiled the printed part because as a percentage of the overall part size it is negligible. I'm going to try again with a higher chamber temperature. The above was done with a chamber temp of 42-45C. The tape though is great. It is 150mm which is exactly the width of my heated bed, so applying it is easy when I used the technique described below.This helps to avoid the inevitable bubbles when dealing with large adhesive tapes:

Bunged Up

Here's a video of my RepRap behaving as it should:



But for the last month or so I've been having problems. At random times the extruder started chewing filament instead of pushing into the heater. This of course resulted in failed prints. The first symptoms are particles of ABS accumulating on the idler bearing of the Wade extruder:

If allowed to continue printing, the extruder simply stops pushing ABS into the heater. On dismantling the extruder the hobbed bolt looks like this:

After cleaning with acetone it's pristine once again:

But after cleaning, sometimes I mange to get 2 or three large parts before another failure, othertimes it fails at the first print. I've tried reducing the flow rate of the extruder but this hasn't had any effect. The only consistent thing is that the print always fails on the second or third layer, never the first.

I got the nozzle from Wolfgang at RepRap Fab and I've bought a new one to see if this will improve things.

Buy Demand

I've posted on several forums that I'm open to suggestions for parts and kits to be available at www.tagbits.co.uk . One suggestion was for a Milestag CORE gun kit to complement the existing
Milestag UMT kit.

As I already had a design for the CORE module, I've added a CORE kit to the shop here.

Tagbits.co.uk launched

I've launched Tagbits.co.uk today. Basically I've made available all the Lasertag stuff I've been making over the last few months. Enjoy:

Tagbits

More Dome Bases

I've spent the last week or so testing my designs for different sensor dome mounts. These will allow me to mount Milestag sensors with sewing, velcro, press studs or 32mm elastic belts. These also have angled cable exits making it easier to get the cables out. I've had trouble getting the radius of the centre of the mounting screws correct, having cracked several domes but I've managed to fix this now and can get the domes realiably fastened to the bases 100% of the time.

The selection below is now available at www.tagbits.co.uk

New Sight

I've realised that some Milestag users prefer to mount an IR sensor on the gun itself (TonyC!). The problem with my existing design is that if the sensor is mounted forward of the sight, it is visible when looking through the sight.

To fix this, I've designed an M16 style sight raiser.This has been designed so that it can be fitted with either a picatinny rail or normal 'iron (ABS!) sights'. Looks pretty good on the CAD. Printing now...

In Focus

I've finally run out of the plano-convex lenses I bought last year from Surplus Shed. These were great as they had a 50mm or so focal length which resulted in a short IR focus tube. I've ordered some more lenses but these have a FL of 100mm, therefore I needed to re-design the focus tube of my tag guns.

I changed the tube design to be in two parts. One holding the LED mount, endcaps and focus screw. A second tube is designed to slide over the first, but also it can be lengthened/shortened or given a larger diameter to suit the lens being used.

I forced the two parts together in my carpenters vice.

 
The ridges produced by the RepRap process interlock providing a fantastic strong joint. No glue is needed, I'm not going to get these two apart in a hurry.

Here is a complete IR tube kit. These are now available at Tagbits:

Full Kit

Here is a photo of a complete kit of parts for a UMT based Milestag gun.  Apart from the 20mm barrel, all parts have been printed with RepRap. I'm quite pleased with the results. I'm able to manufacture parts that, once printed, can be assembled into a functional device within an hour or so. long live RepRap!

This kit, and its Milestag Core brother are now availabale at tagbits.co.uk

These parts come together to make this:

UMT Mk4

I've recently completed a Mk4 version of my RepRap'ed Milestag lasertag gun. This version has a a serially driven 4 x 7 segment LED display to indicate health/ammo which I got from RoboSavvy. This is driven from my homemade Milestag UMT PCBs. These have turned out really well. The only issue that I had was the corrupted display I mentioned previously. Here is a Mk4 complete with DIY acrylic dome sensors:

This has my new style muzzle flash suppressor attached. This differs from previous models in that it has side slots to allow light to show through:

More domes

I've almost completed my Mk4 RepRap Milestag gun and I needed to make some sensor domes with mountings that allow me to fasten the sensors to a baseball cap. I started out by maing six more domes from acrylic sheet as detailed here. To do this I modified the dome mount I made some time ago. I needed to modify the dimensions slightly as my domes have an internal diameter slightly larger than the ones I got from Lasertagparts. Here are the two parts:

Rather than potting the PCB and dome in place, my design uses three screws to hold it in place. This allows it to be dismantled for maintenance.

I SPI

I've been doing further assembly on my Milestag UMT PCB. I bought a serially driven 7 segment display module from Sparkfun. This module is the one recommended for use with the Milestag UMT board. It is used to display clip rounds remaining and life. However, I could not get the display to function correctly. I sometimes (about 80% of the time) got a corrupted display. I resorted to removing the PIC MPU from the PCB and wiring it up on a breadboard with just the display and run from a stabilised PSU. I still got the same results:

This should be displaying " 042". I made various attempts to fix it: Rewiring, shielded cable, more filtering caps, shorter sires. Nothing worked. I then noticed that when I picked the display up, it changed. I noted that this module has both SPI and TTL level serial inputs and when I touched the TTL input the display became corrupted. TTL level serial idles at logic 1, so I tied the serial input line high and I haven't seen any corruption since. The module accepts segment level commands. i.e. You can send 4 bytes of data representing the segments in each digit. Obviously the serial input was getting noise and this was being interpreted as a valid display command.

ABSsolutely fabulous

Now that I have my PLA extruder up and running, the acid test for me was the ability to switch between PLA and ABS easily. I swapped the extruders around in about 10 minutes. Most of this time was waiting for the heaters to get hot enough to allow me to remove/insert the filament.

With the ABS extruder in place, the first print I did came out perfectly without any need to re-calibrate. It's a picatinny rail sight mount for my Milestag lasertag gun.




Here it is sprayed up and with a sight mounted on my MK3, RepRap printed gun:







My wife is an avid photographer so I printed her one of kitlaan's lens cap holders.

It was printed with white ABS but I sprayed it black with the same paint I use for my guns. It came out very well.




The quick change extruder mount that I got from wolfgang has allowed me to change extruders without undoing a single bolt, and, more importantly, maintain calibration between changes.

Dome Goal

I got my homemade Milestag UMT board working this week. This has forced me to think about acrylic domes again. I bought 4 pairs of acrylic domes from LasertagParts whilst in the USA last year, but now I've used them all.

As mentioned previously my neighbour made me some dome molds from a weird slate/resin composite. These are just right but I needed to create a hole in a sheet of wood to allow me to force the soft acrylic sheet around the mold.

The problem I had was that the outer diameter of the mold is 36mm and the nearest hole saw I have is 44mm. A 44mm hole is too big to force the soft acrylic sheet around the bottom of the mold.

To solve this I drilled a 44mm hole in a sheet of 6mm MDF and then printed a bush to reduce the internal diameter of this hole. Here is the CAD:



And the printed part:



It has a flange at the bottom to prevent it from being pushed out of the MDF:



Top down you can see the diameter reduction:






I cut a second sheet of MDF to provide a flat surface to place the mold on. Here it is forcing 2mm acrylic, heated at gas mark 9 for 4 minutes, over the mold:



And with the forcing plate removed:




I'd previously sprayed the mold with PTFE to aid removal:



The molds have a threaded hole underneath. This allowed me to hold the mold in the vice whilst I gently prised the acrylic free. As this mold has a draft angle it came off quite easily:






The remaining problem was now the removal of the dome from the sheet. To do this I used my 44mm hole cutter on two 15cm square pieces of wood which I then placed on top of each other with the holes aligned. With the hole cutter in my drill press this prevents any downward force being applied to the dome, which might crack it. I applied very little force whilst cutting and I let the acrylic soften from the tool friction as this seemed to prevent cracking. I destroyed one dome by pressing too hard:



Here are sheet and dome after separation:



I cleaned the rough edges on my belt sander:



Here it is after grinding:




Total time is about 15 minutes, 4 of which is waiting for the acrylic to soften.

Can I repeat it? Of course!

These are now available at Tagbits.