Pallmann Cobra Design Evolution

By Simon Gallaway of Ultimate Floor Care​

How old is your Pallmann Cobra? Chances are, if it’s nearing 10 years old, or it has “Frank” written on it in bold, or any of the colour scheme is green, there is a suite of parts upgrades that can improve its reliability and performance, making your work more efficient, and minimise the time it takes to do that whole sanding job.​
You see, belt sanders are not and could never be ‘finishing’ sanders; After the Cobra has done the donkey work of cutting back the gouges, scratches, lumps, humps, and bumps, it still needs finishing with a rotary machine.​
But, think about this. The smoother you can get your Cobra to leave the floor, the less time it will take to finish it with a rotary sander.​
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Now, apart from good operating practices outlined here: Pallmann-cobra-09-classic-belt-floor-sander
the quality of floor finish after using any belt sander, will depend how flat the drum touches the floor. If it cuts deeper on one side than the other, just think how much extra time it will take with the rotary sander to take off all those slanted ‘lawn mower’ like cut lines.​
The angle of the drum on the floor is controlled by the wheel height adjuster, so what holds the wheel height adjuster in a particular position? Well it’s a combination of aluminium and steel parts under the Cobra. You can get some idea what they look like if you lean you Cobra back on its handle, or tip it sideways for a Classic, and look at the underside.​
A modern one looks like this:

The older Cobras had a similar arrangement, but the parts have differences. Lets list the main differences:​

1. The main spindle that the whole wheel carriage rocks up and down on is now made of a solid bar of steel. The old ones were thin hollow tubes… And they are prone to bending easily. Compare these two old and new ones. 

  

Each end of that spindle holds a part of the frame that holds the wheels. So when the spindle bends at one end, it’s not going to hold the wheel  at that end to the same height, and the drum height will fall on that side, and the rest you know, but they are . How badly do you think this old one affected the machine’s performance?​

2. The aluminium frame that holds all of the wheel components is now cast aluminium (think cheese crackers – they never bend, they’re either whole, or broken). Cast metal generally doesn’t do much bending. It tends to go from good, to breaking if it’s subject to enough force. So one day it would be perfect, them someone rolls the Cobra harshly over some very bumpy concrete with its heavy motor still in it, breaking the wheel frame, and the next day it’s blatantly obvious that something’s wrong. You ring Cameron or me here at Ultimate Floor Care, and strap your Cobra to a pallet. We arrange for its collection, I do my magic on it, and you get your Cobra back perfect again. ​

But, the older wheel frames were extruded lengths of aluminium (think rolled pastry before it’s cooked, or piped icing on a cake) welded together. See photo.

How, extruded metal tends to bend more, gradually, without breaking. So when exactly are you going to get to a definitive point in time when you know something is wrong? And how many jobs are you going to struggle through, taking more time, with a Cobra that’s not broken, but not as well tuned as it could and should be, before you’re sure something’s not right? ​

This is what happened to the early Cobras and it’s why Pallmann developed the material of the wheel frame from extruded  aluminium to cast aluminium.​

Take a look at the three next photos that show how the old ones twist and bend:

  

Finally, this leads us to the addition of a spring to the mechanism that adjusts the right wheel. It looks like this, tucked away above the wheel and its rocker arm.

 The reason for this is a little obscure. The best Cambridge-based Pallmann service engineering minds (that’s Terry Guilford and me) put together their collective intellect, and came up with this:

Without this spring, if you were picking up the Cobra to lift it out from a bunded storage area, the wheel would droop through the rest of its available travel, unconstrained by the weight of the Cobra in one direction, and the limit of the wheel height adjuster in the other. It could potentially catch on upwardly projecting items, making the action more awkward. Pallmann likely didn’t want it to feel like it wasn’t properly fixed in place when picking it up. Certainly it didn’t look good when it happened.​

 

So, unless you know your Cobra is fairly young, next time you have it out to do a job, or look for clues as to what maintenance it might be calling out for, tip it to look underneath, and see if the wheel carriage parts look like the older type.​

Even if, and especially if, it is the newer cast aluminium type, I would leave you with this take away:​

The cast aluminium frames tend not to bend, but are easier to break. I have had to replace them on several machines after someone has dropped the Cobra harshly while lifting in or out of a van, and rolling it harshly across a bumpy concrete floor. ​

So they do give the machine improved and dependable performance when working in their native environment, but do remember to ease them gently in and out of the van. Better still, leave the wheel lever down and the drum on the ground (with an old belt on it for protection) when lifting