OFF ROAD EQUALISING HITCH

Submitted: Tuesday, Jul 01, 2003 at 23:02
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Further to my earlier postings regarding an off-road equalising hitch, David Pentreath has now agreed to my describing his most interesting new mechanism.

Briefly, an equalising hitch is essential on any but a very light trailer if it is attached to a towing vehicle such that its weight is carried behind that vehicle's rear axle.

The problem is not that the trailer depresses that vehicle's rear suspension (because that can readily be fixed by stiffer springs etc), but that its weight acts as a lever to lift the towing vehicle's front wheels - thus reducing their grip on the road. If the vehicle sways at the same time, front wheel grip may be lost and the rig is likely to jack knife..

To see how an equalising hitch works, visualise a rigid beam that is rigidly attached along the whole length of the rig - from the rear of the van to the front of the towing vehicle. Now, no matter how much weight is placed on the front of the 'van - and thus the rear of the towing vehicle, the front of the towing vehicle cannot lift.

This would in fact be a good equalising hitch except the rig is likely to break in half over bumps, and will only move in a straight line..

So we insert a pivot (i,e, the tow ball) to allow the rig to bend in the middle for cornering. We also make the beam springy (to allow the rig to flex over bumps etc).

This removes the problems of a rigid beam but still ensures that weight pressing the towbar down does not lift the front of the towing vehicle.

This is how a normal equalising hitch works - and it's fine for normal road use.

There is however a big problem off-road in that if the towing vehicle is traversing (say) a deep creek crossing, the towing vehicle may be climbing up the far side wgilst the 'van is still going into the gulley.

The towing vehicle and the 'van are now at one considerable angle - and this causes the springy hitch bars to have to deflect to a hugely greater extent than was intended.

The greater the spring bars are deflected the greater the loads imposed on whatever they are attached to - and in the above scenario the bars may break, or the towbar be torn off.

Until now there has been no solution to this - except to continually connect and disconnect the bars. This is quite a problem with tracks such as the Cape Leveque Road (my home patch!) that has many sections that enable a comfortable and safe 60 km/hr plus, but also deep dips etc. Many outback tracks are like this.

What David has done is to retain the existing equalising hitch principle, but has cleverly modified it such the hitch maintains constant (but readily adjustable) 'lift' on the equalising bars such that the stress on the equalising bars remains constant regardless of the angle between the towing vehicle and the 'van.

The hitch works by having a smallish airbag that is connected to a larger air reservoir. The small airbag expands and contracts vertically to raise/lower the 'van ends of the equalising hitch bars. (The rig is levelled by adjusting the air pressure.)

As the rig traverses dips and rises, the corresponding upward and downward movement of the bars will vary the pressure on the air bag.

This will cause it to expand or contract accordingly and as this air bag is interconnected to a much larger air reservoir, the overall system pressure will remain substantially constant.

The overall effect is that the lift transmitted via the equalising hitch remains more or less constant regardless (within very wide limits) of the angle between the towing vehicle and the ''van. This is in total contrast to a conventional hitch in this situation - where the lift off the bars, at the more extreme angles may even lift the rear wheels of the towing vehicle off the ground (assuming nothing breaks beforehand).

David's hitch also has an ingeniously simple but very effective way of allowing independent movement of the arms, (but maintaining correction) during roll.

This hitch apears to be a very elegant but eminently practical approach to what has previously been quite a major problem when towing heavy trailers over rough going. I wish I'd developed it myself!

I need to add that this is perforce a theoretical assessment, but as the operating principle is so simple there seems no reason at all why it would not be highly effective in practice.

David has been using his own BT as a test bed and has some very dramatic pix of the hitch in action.
I need to stress I have financial interest of any kind in this project, nor am I accepting payment for this assessment.. I'm simply very pleased to see such a long-standing problem apparantly solved.

Finally, to those hopefully few remaining people who believe that one of Newton's more dramatic Laws are circumvented by buying several tonnes of BT - please do think again - because others have to share the road with you.

I will attempt to post a few pix of the hitch on this site.
Trusting this is of interest
Collyn Rivers
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Reply By: Deleted User - Tuesday, Jul 01, 2003 at 23:04

Tuesday, Jul 01, 2003 at 23:04
Damn!

Third para from end of the above - should read
I have NO financial interest etc!!
Collyn
AnswerID: 559078

Reply By: Noosa Fox - Tuesday, Jul 01, 2003 at 23:05

Tuesday, Jul 01, 2003 at 23:05
I bet you would like to have a financial interest in it though, Collynn. If David has done his homework with the patent right and this takes off, he might be buying a new Bushtracker soon.
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Reply By: Deleted User - Tuesday, Jul 01, 2003 at 23:06

Tuesday, Jul 01, 2003 at 23:06
Brian

Yes indeed! - But my credibility as a writer in this field precludes any financial interest or involvement in anything commercially related to what I write about.
Collyn
AnswerID: 559080

Reply By: Bushtracker Buck & Babe - Tuesday, Jul 01, 2003 at 23:07

Tuesday, Jul 01, 2003 at 23:07
Dave, any idea how much approximately it might sell for? Angie
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Reply By: Deleted User - Tuesday, Jul 01, 2003 at 23:08

Tuesday, Jul 01, 2003 at 23:08
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Reply By: Motley - Tuesday, Jul 01, 2003 at 23:09

Tuesday, Jul 01, 2003 at 23:09
I had the opportunity today to see in real live action, the Off Road Equalising Hitch which David has developed. Corrected a little mistake - I meant to say I would NOT have tried test with a HR Hitch - Sorry David I went to Davids's place so I could see EXACTLY how the thing worked. David put it through its paces by reversing the caravan up a 45 degree embankment - on an angle! I'm damn sure that I would not have tried it with the Hayman Reece gear in place! Once I saw the hitch in action and fully understood how it operated, it's a simple, elegant solution. What I guess it means is that you can have all the benefits of a sound equalising system without the problems of using it off-road - continual hitch/unhitch, potential failure etc. Definitely worth considering and when David comes to Cania Gorge I'm sure there will be interest. Like Collyn, I have no commercial interest in this development just admiration for savvy innovation.
Motley

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Reply By: Deleted User - Tuesday, Jul 01, 2003 at 23:10

Tuesday, Jul 01, 2003 at 23:10
Angie, In C&M magazine in June it says Kit price to come in just above $1500 mark and the second part of the kit to get bars above A-frame will be POA. In my experience POA can mean two things .... one ... it's expensive and two ... each individual application is different with a resultant price difference. To quote a pollie ..... in the fullness of time we will all know POA ! [wink] Anthony
AnswerID: 559084

Reply By: Deleted User - Tuesday, Jul 01, 2003 at 23:11

Tuesday, Jul 01, 2003 at 23:11
Hi Angie , The hitch sells for basic price of $1700aus . The load hitch bar attachment is extra , and is most suitable to the old type bushtraker coupling if they are still available By the time your van is up to this stage Dave should have all the different options worked out. .. Will be taking our van with the hitch to Cania Gorge so you can get all the feedback from there. Dave is computer illiterate so he is much happier putting pen to paper or ear to phone as communication medium than trying to deal with the internet. regards Joan
AnswerID: 559085

Reply By: Deleted User - Tuesday, Jul 01, 2003 at 23:12

Tuesday, Jul 01, 2003 at 23:12
Looking at what set-up would be required to use this WDH extension. Doubt that Jockey wheel could be left in it's "travel" mode as it would probably foul on the rig. If necessary to take off, looking at bracket behind stone guard. Could some of you that use weight dist hitches describe your arrival/departure routines? Specifically, on arrival, do you apply hand brake; chock wheels; undo the hitch chains; drop jockey wheel; undo electrics & chains; move vehicle; remove & store hitch?? or some different order of battle? I'm trying to work out how awkward it will be to fit the jockey wheel with all that extra ironmongery hanging about. Thanks Griff
AnswerID: 559086

Reply By: Noosa Fox - Tuesday, Jul 01, 2003 at 23:13

Tuesday, Jul 01, 2003 at 23:13
Griff, It is best to try and park on a flat surface. If you have strain on the coupling from screwing the van around to get next to a concrete pad etc or if it is on a slope and pushing forward or back from vehicle, then it becomes a lot more difficult to remove the pin. With my setup it is necessary to swing the jockey wheel down so that the handle doesn't fowl the WD bars. If the wheel is wound down then it takes strain off the WD bars and you don't require as much effort to remove /install them. If on a slope I put the hand brake on, if on flat I then wind the jockey wheel up or down first until the pin will turn and can be removed easily. The Maco Mule power wheel locks in place when the handle is in the vertical position so this is an additional safety feature. Once the pin is out I make sure the van is secure by handbrake, then remove the safety chains and wiring plug. This way if it was going to roll away from vehicle it can only go as far as chains allow it to. So far the van has never moved after applying hand brake. It would be advisable to always unhook van on sloping land so that it is sloping towards the vehicle. By doing this it is much easier to move it down hill on power wheel to connect up, than going up hill to vehicle. When removed from vehicle I then do another check of levels with spirit level, put the support legs down and chock the wheels.
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Reply By: Deleted User - Tuesday, Jul 01, 2003 at 23:14

Tuesday, Jul 01, 2003 at 23:14
Did David & Joan make it to Cania? Any more reports on this unit? Griff
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Reply By: Noosa Fox - Tuesday, Jul 01, 2003 at 23:15

Tuesday, Jul 01, 2003 at 23:15
Yes, they made it to Cania, Joan had to return home while David has left the van at Cania for a few weeks while he travelled to Cairns. His van is now called BOGETTE, as it was the smallest van at the gathering. His invention is well thought out and should work well but without backing of some big company that can push it, it will probably end up being another great invention that doesn't go far. (personal opinion only) Anthony had a good look at it and may be able to give some details on it. Brian.
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