Drills and Batteries

Why Do We Need New Batteries?

One requirement of the New Zealand cavers, was that we use 10 mm through bolts. This requires the drilling of about an 10 mm diameter, and about 60+ mm deep hole. This was a relatively unusual requirement - UK and European exploration usually takes place with 13 mm threaded self-drilling 'Spitz' or 8 mm through bolts.

Our Experience

Over the last five years in Slovenia, we have had considerable (positive!) experience with modern lightweight pneumatic drills. There we have built around the 'Bosch Uneo' for deep underground work, which is just 900 g once you remove the internal batteries (really quite difficult), and uses a non-standard 'SDS-quick' chuck. The pneumatic action (and general torque) of the drill is relatively weak. This is actually a benefit, and it seems perfectly matched to drilling 8 mm diameter in Limestone - you can easily hold an Uneo out at full reach and drill a straight hole. The drill is designed to run off an internal collection of 4 lithium cells in series (14.4 V), and was found to be intolerant of anything much below ~12 V.

In 2011, we bought a Makita BHR162Z bare drill (no batteries), upon a recommendation that these were lightweight and efficient, and noting that it used the same battery voltage (14.4 V) as the Uneo. These drills have a much stronger pneumatic punch than the Uneo (capable of large diameters in limestone), and have a standard SDS+ chuck (i.e. cheap drill bits). This drill we found to be extremely easy to modify - there's actually two spare binding posts to attach the external fly lead to! This drill we mainly used on the surface in Slovenia, as it is so much more bulky and heavy than the Uneos. Jarvist also borrowed it for the 2013 cave diving expedition to Mexico, where it was used as one of the 3 identical drills to rebolt the cave to - 800 m, though there it was used with genuine Makita batteries.

On the original recommendation from Dave Wilson (and after watching the initial 'Molex' type plug spark & smoke!) we used Anderson-type 30 A connectors to wire everything together. These are extremely well fitting bits of technology to drilling underground. There is a large leaf-spring contact, the design is Hermaphroditic, and it seems extremely tolerant of mud. The contact is very positive, enough so that it doesn't disconnect accidentally, but instantly uncouples if a drill or battery is dropped.

Around our Uneos and the Makita we built up a collection of NiMh Sub-C cell batteries. These had made up by the manufacturers (Component Shop UK) with Anderson pole connectors, and were relatively cheap and of moderate capacity. NiMh is a relatively simple battery technology, and has no serious safety issues

During our long Slovenia expeditions, we collect power with solar panels, storing them in lead acid batteries, which works as a 12 V buffer before we then use this energy to charge the drill batteries with a 'hobby charger', as well as our AA batteries for caving (and sound systems, GPS etc.), dedicated helmet battery packs, and USB (for the increasing collection of gadgets that people have!).

New Technology

Of course the big breakthroughs in battery technology have been in Lithium ion. In particular, there are now large Lithium Ion Polymer packs available for the hobby community (powering everything from electric remote control planes to electric bicycles). These are much more fiddly to charge, requiring careful balancing of the voltages of the individual cells to avoid damage, and offer a definite hazard in terms of being a fire risk when charging.

A well protected battery

However, we didn't want to be the Guinea Pigs on this one, and so over the last few years, other than ensuring that the new Hobby Charger we bought could balance charge lithium polymers, we watched from the sidelines as other's innovated.

In particular, York University had an expedition to Montenegro over the last few years. They had a much lighter base camp in the hills than we did in Slovenia (they flew in rather than drove), were typically in the field for fewer weeks, and were doing a lot of surface based shaft bashing.

Our New Technology

Faced with similar logistics we came to the same conclusion: it doesn't make sense to take solar panels or a generator, better to take a stash of batteries, to effectively import the bolting energy within their charge. So how many batteries did we need?

There was no point having the power to drill more holes than we had bolts to place. Similarly there are 'rules of thumb' for the number of fixtures required per length of rope, for which a rebelay every 10 m is usually a pretty good metric. Of course, this only covers the exploration of a given cave - when 'shaft bashing' on the surface, you reuse the same rope in lots of different locations. The logistics of the expedition also suggested that there would be the opportunity to recharge (in the car) at least some of the batteries halfway through.

Based on the York data, and our own experience in Slovenia, we would expect 20 8 mm throughbolts from each battery. This hopefully corresponds into about 12 of the 10 mm throughbolts we are expected to use in New Zealand.

Six batteries should provide for 72 bolts, without recharge. This is sufficient to consume 720 m of rope, enough for a pretty sizeable cave, and a lot of shaft bashing.

We read the York information (and acknowledge some extremely useful & informative discussion directly with Mark Sims), but decided that we didn't need any limiting resistance, in spite of the nominal 14.8 V of the Li-ions. The Makitas are extremely simple, it's a carbon-brush-commutated DC motor with a FET-based variable power supply - the same technology as in the original Bosch GBHs that revolutionised bolting in the early 90s. These were often used 'over volted' from 24 V with an extra cell or two to compensate for long leads and dirty connectors, to no seeming damage.

So we bought six batteries, and a set of Anderson 30 A connectors. The leads come with some bullet-type connectors, which we substituted for Anderson.

This required some very careful work, and fairly sophisticated soldering - as you're working on live Lithium packs which would happily self-immolate if you short circuit. The wires from the packs were cheap Aluminium (copper is expensive), which was too thick to fit in the 30 A Anderson sheaths. However, the relatively long leads and silicone insulation meant that the wires could take the heat.

The working method was:-

  • Separate plugs (with scissors)
  • secure one wire to the rear of the battery with electrical tape
  • wire-cut (with a sharp pair of pliars) the connector off
  • use a sharp penknife to slice ~5 mm of the silicone insulation, remove
  • gently fold back ~40% of the wires by separating the bundle of very fine aluminium
  • gently twist the remaining wires to hold them as a bundle, and slip inside an Anderson connector
  • flux the whole lot
  • apply soldering iron to the front of the Anderson connector with a blob of solder as thermal contact
  • you can see the point at which is the solder is wicked down the connector
  • you can now feed in solder from the base of the Anderson connector until you see the wires are saturated
  • snap on the plastic Anderson housing, swap which lead was taped down & repeat with the other!

Our current Hobby Charger is the iMAX B6 'little blue box'

Our batteries were 5000 mAh 4S1P LiPos, from HobbyKing

Jarvist Frost