Geelong Motorsport Club - Mounting items in a cockpit.

An article by Peter Lawrence, Manager Technical Services CAMS.

When I raised the idea of an article about mounting items in cockpits with some of my staff I got a wry grin or two ... won't go there.

Time and time again, the CAMS National Office is asked to produce a rule about how to mount items in cockpits, in particular two items: Cameras and Fire Extinguishers. Mostly these requests come from scrutineers who have seen what can only be regarded as poorly executed mountings, but when they ask the competitor to “fix it” are told “Where does it say that in the Manual?”

The CAMS National Technical Committee revisited the matter at its August 2006 meeting, and like all previous times, found great difficulty coming up with a universal prescription for either cameras or fire extinguishers. The issue is extremely complicated by the sheer diversity of cameras, fire extinguishers and cars in use.

The standard generally accepted is that any object located in the cockpit must be capable of withstanding an acceleration of ‘25g' where ‘g' is the acceleration due to gravity. The actual force acting on the mountings however is the product of that acceleration and the mass of the object, so logically a heavier object will require a stronger mount than a lighter one. To put that into perspective, seats and safety harnesses are tested to 25g with a 75kg dummy although to be realistic most safety harnesses can resist loads more than twice that. I am only aware of one instance where a harness broke in a collision, but in this incident the impact was so severe as to have been un-survivable anyway

Hand held fire extinguishers pose quite a hazard in the cockpit if not mounted securely and so we must consider how to safely mount them. A typical fire extinguisher holding 0.9kg of extinguishant weighs around 1.5kg and using our 25g model it must therefore be mounted to withstand a 38kg force in any direction. A 2.0kg extinguisher in a rally car is obviously twice as heavy with twice the strength requirements. A typical bracket as supplied with one of these extinguishers is designed to mount the unit on the wall of a house. Such brackets are mostly plastic and have some sort of simple ‘over centre' latch on a single strap. There must be some doubt that they will hold the extinguisher in place in any sort of serious impact. What makes matters worse is that the straps are quite often offset to one end, quite logical for a vertically mounted extinguisher hanging in your kitchen.

However, to simply specify that a metal bracket is used is also not in itself sufficient. A metal bracket may be stronger, but if the extinguisher is not tightly held, or if the bracket doesn't have some form of end support to stop the extinguisher sliding out sideways, then it is no better. It is for these reasons that it is difficult to make a ‘one rule fits all' prescription. How the bracket is mounted to the body is also important. Self tapping screws or pop rivets can be used to mount the bracket if done with great care, but again bolts with washers and self locking nuts provide greater security

The following recommendations are therefore made:

• Use a steel bracket with some form of support to prevent sideways movement;
• Use two straps that go behind the steel bracket and tightly hold the extinguisher;
• Use at least four 3mm bolts (or two x 5mm) with load spreading washers and locknuts; and
• Orientate the extinguisher across the car rather than longitudinally

In relation to the other bugbear, video cameras, many of us like to record our own ‘in-car' footage. I have many hours of the stuff, and it can be a training tool and cheap data logger as well. However like the fire extinguisher, they must be mounted securely to withstand a potential impact. There are basically two types of systems in use - the camcorder and the separate camera/recorder. From a safety perspective, CAMS encourages the use of lightweight/lipstick cameras feeding video to a recorder fixed to the floor of the cockpit in a sealed box. These tiny cameras can weigh only 50g or so and can be held in place safely using little more than race tape. There are companies in Australia who specialise in these systems. With these systems you can also have multiple cameras on one recorder for a full front/rear/whatever coverage of the cars.

The traditional camcorder is still commonly used as they are widely available, and whilst they have certainly come down in size they can still be relatively heavy. Mounting any such camera using only the 1/4” tripod hole on the bottom is insufficient. This threaded hole is there to hold the camera onto a tripod, and may not withstand any sort of significant impact.

If you wish to use a camcorder it should be mounted in some sort of cradle/box unit. A complete box made from 2.5mm aluminium alloy will generally suffice so long as the box is mounted securely to the car. In most cases this can be to the diagonal member of the safety cage. Whilst there are proprietary clamps available, a clamp fabricated from two exhaust clamps can be entirely satisfactory

It maybe desirable to use a cradle rather than a full box. The base of the cradle should be from 5mm alloy with returns on each edge to locate the camera laterally. You will then need some form of strap over the camcorder to hold it in place. Two or three heavy duty cable ties (at least 5mm in width) can be used as an alternative to a fabricated alloy strap.

Whilst I am discussing things mounted in the cockpit, I might briefly touch on seat mounts. A typical aftermarket seat bracket is made from 5mm or 6mm alloy. If you are using the type with slotted holes, make certain you have a good quality washer on the outside. Also remember that there should always be at least the same width of material on the outer edge of a hole as its thickness. We had an unfortunate failure of a seat mount last year. One of the mounting holes had been filed out to fit the production mounting holes on the floor pan, leaving only two or three millimetres of material between the hole and the edge of the mount. In the collision, this thin piece of alloy tore open resulting in the seat coming partially adrift.

Remember in a rearwards collision, the only thing restraining you is the seat. If it or its mounts break, you are going to hit whatever is behind you, generally the safety cage.

One last thing: with one exception, never mount your harness to the seat or its supports. The exception is where the manufacturer mounts the lap belts to the seat, and you use the manufacturer's original and unmodified mounting brackets.

Responsibility:

I have added this postscript just to reinforce one thing. It is not the responsibility of the event scrutineers to ensure that your camera, extinguisher, seat or harness is safely mounted. Scrutineers can only check for compliance against known standards, beyond that they can advise based on their experience. Every car is different as is every driver. You, the entrant, are expected to know your car better than anyone else. If you are not sure, consult a qualified engineer.

CAMS Magazine Spring 2006

Peter Lawrence

Manager

Technical Services