Monday, August 21, 2017

Power/radio cables with over-moulding

I thought some folks might be interested to know how we are getting our cables fabricated, so here are some photos of the tool used for the low-pressure injection over-moulding that adds the red rubbery plastic over the connector and circuitry in the cable head.

First, here you can see a finished cable and the tool, which was designed and machined for us.  Unlike high-pressure injection moulding, where you can turn out multiple parts per minute, but the tool cost is tens of thousands of dollars, the complete tool design and manufacture cost here was only about AU$3,000 with our friends at Innovation Engineering.  The trade-off is that each part takes minutes to produce, instead of seconds. For now at least, that isn't a big problem.


Looking closer at the tool, you can see the big fat guide pins that hold it in proper alignment when assembled:

Then on the other half you can see this funny bar with the two brass pins.  This is removable, and held in with a couple of magnets.  It ensures that there are holes through the moulded body for the thumb-screws.  It needs to be removable, as you need to get the cable in and out of the tool.

Here is that same tool without it in place:

And here is the removable part itself. You can see here that it has the recess that fits snugly around the D-SUB25 connector, so that it doesn't get encased in plastic during moulding, but continues to stick out the end, as it needs to do, in order to be a useful cable:

Then finally, here it is all assembled (but without a cable inside):

As I have said before, it is so much easier to work with a company who is only a few minutes away, so that if there are problems, they can be quickly inspected and dealt with, and so that communications can be free flowing, so that everything goes well.

Now we are just waiting on the delivery of our next 45 of these cables, ready for our third trip to Vanuatu.

Monday, August 14, 2017

Assembling injection moulded Mesh Extenders

After various delays on various fronts, we now have in our possession enough components to assemble 40 Mesh Extenders, sufficient for the remaining activities for the Vanuatu Pilot.

Yesterday, the RFD900+ radios, antennae and Mesh Extender PCBs arrived:

 We already had the injection-moulded housings on hand (in the boxes behind the radios and PCBs):

First step of assembly is to fit the reverse SMA bulk-head connectors to the cases, and also install the o-rings.  While not particularly glamorous, this represents some number of hours of work to do.  Karthik, a work placement student, has been placed with us over the next few months, and gets to be the lucky one to do this task:

 The first afternoon's work, we have 16 units with seals and 2 of the 3 RSMA leads in place:

After these have been all prepared, we will then proceed with getting the firmware  on the PCBs, and radios and bulk storage fitted.

Our original plan was to use microSD cards, as they are lower power consumption than USB memory sticks, and probably handle power loss better than memory sticks.  However, there is a problem with the kernel driver for the microSD card interface, which we have yet to resolve, so we are probably going to stick with USB memory sticks for now. 

Fortunately we were able to get the USB port working in the Mesh Extenders, after a bunch of earlier problems with signal integrity of the USB data traces.

The only side effect is that we probably won't be able to reliably run these units on solar without a battery connected -- we'll find out for sure as we proceed with testing.

Thursday, August 3, 2017

Education in Emergencies challenge

Just a quick post to say that we have been short-listed in this challenge to find solutions for sustaining education during emergencies:

We feel that Serval is an ideal match for this use-case, especially if an online education system, like Moodle, were extended to support mesh delivery and interaction.

Please feel free to take a look at our entry, and hit the "love it" button, to help raise the profile of our entry.