HOW TO FIT ELECTRIC GATES: Rear Bracket Geometry for Swing Gate Motors.
Hello and welcome to a new series of articles published by SEA UK showing you how to fit an electric gate system. In today’s article we are going to discuss how to set up the rear bracket geometry for an above ground electric gate Ram. Our method is simple and easy to follow and can be applied to any manufactures product, so you can get it right every time.
Gate rams are one of the most effective gate systems when fitted correctly, but if you get the rear bracket position wrong you will have a system which either works badly with no power, is dangerous or can be easily damaged.
There are 3 important elements which we must discuss before we go into detail about how to fit an above ground swing gate system:
- Gate/Motor Centre of rotation is the point which the gate or motor rotates around. This will always be in the centre of the gate hinge or at the back of the motor where it is pined or bolted to the rear bracket (see Figure 1 to 3 below).
- Stroke length is how much a gate motor can change its total length by, we will talk more about the importance of this later on.
- A and B measurements play a crucial role in correct installation. They can be quite hard to explain but the 3 diagrams below will show how to find the A and B measurements. Figure 1 and 2 show examples of standard inward opening gates but Figure 3 shows an example of an outward opening gate, notice how similar it is to Figure 2.
A Basic Installation Example
To successfully fit any piston or ram type automatic gate system you must first know the operators Stroke length. The Stroke determines the A and B measurements which can be used. In order to achieve the most control over each gate leaf you must take the stroke length in millimetres, subtract 20mm and the resulting measurement can then be divided by 2. These become your A and B measurements. Let’s use a the SURF 250 gate operator, which has a Stroke length of 400mm as our example. 400mm – 20mm = 380mm, 380mm/2= A: 190mm & B: 190mm.
A longer Stroke Length allows for more adjustment when fitting. With the Surfs long Stroke Length you could subtract 15mm from each end of travel giving operator a total piston stroke of 370mm; when split between A and B, this gives 185mm to each. Now there is extra margin to fit the operator comfortably and still have strong leaf locking, as in the figure 8 example below.
When A and B are not balanced?
A lot of problems can arise when the A and B measurements are too different. First let’s look at what happens when there is a relatively small imbalance. Returning to our previous example, what would happen if A is larger than B? In Figure 6 the A measurement is 210mm and the B measurement is 160mm. An imbalance will cause the operator to speed the gate up as it approached the open position and as the gate returned towards the close position it would lose momentum, reaching the close point with very low power (this can cause problems with electric locks).
If the reverse is true and B is large than A the gate operator will be moving faster as it comes to the close position, carrying more momentum but will be slow when opening and sometimes may not fully open. This can lead to unsafe gates, see the example in Figure 7 above. There will be situations where these imbalances cannot be avoided, but if installers are aware of the way a gate will change, measures can be taken to minimise the negative effects.
Extreme problems caused by poor geometry.
When the difference between the A and B measurements is too high, or when very little of the operator’s stroke length is used you will find that the operator will move very fast but with very low force, or the operator will not move at all. As well as this, operators will be vulnerable to excess forces and could be easily damaged by a person or even the wind.
In figure 8 below a very small A measurement and a small B measurement has resulted in the gate operators having low power and low resistance to excess forces. This is because the combined A and B measurements only uses a tiny fraction of the operator’s total Stroke Length.
However, if the A measurement is still small but the B measurement is extended to use the full piston stroke there will still be a significant problem. In Figure 9 above, the A measurement is still 80mm, but B has been extended to use the remaining 300mm of the 380mm available. Unfortunately, because the front and rear bracket rotation centres are in line, causing the operator to be parallel to the gate, the operator cannot pull back. In this configuration the operator will also be extremely poor at resisting excess forces. Remember for a Ram type operator to move a gate there must be a triangle and in figure 9 the triangle is non existent.
Finally, if the A measurement is large but the B measurement is small, the Motor will hit the gate as it opens. This problem is usually spotted early on site and so very few people report this, but we think it is still worth mentioning here.
In conclusion for perfect geometry and a flawless ram operator installation simply find the operators stroke length, subtracted 10-15mm from each side and divide by 2. The resulting number will be you’re A and B measurement which you can use to find the correct location for the motor centre of rotation relative to the gate centre of rotation.
If you have any questions feel free to contact our technical team, or leave a comment below.