Ham Radio Rotators -Choices and Warnings

[@GordonHudson]

I have been around long enough to remember people using prop pitch motors as rotators. I actually feel quite lucky to have known so many people licensed before WW2 and getting to visit their shacks.

[@watersstanton]

Ah yes I remember prop pitch motors

[@KO4AYE]

Peter great video! Totally excited my engineer qeek, and its showing. Lets break down (no pun intended) why the position of a rotor motor on an antenna mast makes such a big difference in the torque experienced by the rotators stationary gearbox, especially when the wind blows. This is a topic that confuses a lot of people, so let’s address some common misunderstandings along the way. Torque Explained First things first, torque is a measure of rotational force. It is calculated by multiplying the force applied by the distance from the pivot point: Torque = Force x Distance This means that the longer the distance from the pivot, the greater the torque generated for the same amount of force. Think about using a wrench-the longer the handle, the easier it is to turn a bolt. While torque involves rotation, tension is the resulting effect: a linear pulling force that doesn’t cause rotation. When torque is applied by a motor to a mast, tension energy is stored in the mast until the motor stops. This is why the mast may appear to bounce slightly from side to side when rotation stops. However, when the motor is stationary and rotational force is applied at the top (e.g., by the antenna), the torsional force in the mast is amplified proportionally to the torque applied by external forces, such as the wind. The full effect of that torsional force is then transferred to the gearbox or motor via the mast. Common Misunderstandings Many people mistakenly believe torque and tension are interchangeable, but they are not. Torque is rotational, while tension acts in a straight line. The concept of a lever arm helps explain this: the farther the force is from the pivot, the greater the torque produced. This is why the position of the rotor on the mast is critical when discussing an antenna and rotor system. Using the wrench analogy. The longer the wrench (think about the length of the antenna) the greater torque (turning energy) gets applied by the motor or the wind. That energy is transferred into the bolt (think of the antenna mast) as tension. (Much like a ratchet wrench utilizing an extension) Analyzing the Rotor Position Rotor at the Bottom of the Mast When the rotor is mounted at the base of a 30-meter mast, the entire mast acts as a long lever arm. Wind forces acting on the antenna at the top generate significant torque at the gearbox at the base. Additionally, the mast will twist and store torsional energy, which can cause fluctuating forces that amplify the loading on the gearbox. This increased rotational force leads to higher stress on the gears or the motor, accelerating wear and tear. In extreme cases, if the forces exceed the system’s design limits, the resulting load on the gearbox can lead to catastrophic failure. Note: this is why if possible during a major weather event with high winds its good if you can to apply a "Mast Lock". This will keep any torsional forces from being transferred into the motor or gearbox, minimizing or isolating antenna system damage, if there is any. Rotor at the Top of the Mast When the rotor is positioned near the top, close to the antenna, the dynamics change. The lever arm-the distance between the point of force application and the gearbox-is much shorter. For the same wind force, the torque on the gearbox is significantly lower. With less mast length available to twist, there is reduced torsional energy accumulation, which means the gearbox or motor experiences smaller, more immediate forces. This configuration places less stress on the system and improves overall stability. As you eloquently stated Rotor at the Bottom: More torque due to a longer lever arm and greater torsional energy accumulation, leading to increased force on the gearbox. Rotor at the Top: Less torque and minimal torsional energy accumulation, resulting in reduced forces on the gearbox.

[@watersstanton]

Well, thanks so much for such a detailed and educational explanation, I am sure others will read it with great interest. It’s the kind of thing where you believe you know there is a danger of damage, but you don’t understand the me mechanics involved.Much appreciated.

[@JanJeronimus]

Great video. An important thing thar was not mentioned in this video : When expecting lightning do not only disconnect your antenna, also disconnect the rotator. Otherwise you can have via the control wires a point in you mast that can attract lightning and when lightning strikes it can destroy you equipment.

[@73deoldtimer]

Hi Peter, interesting presentation, thank you. I have been using the now obsolete Emotator 1200X for almost 40 years and did a complete rebuild 3 years ago. I agree with all you say and the best rotator is the one or two models from the range above that of the design minimum recommended for your proposed aerial array. It will be worth the extra spend in the long run and as you so rightly say, no getting cold and wet during a winter breakdown. Fortunately there is much information online concerning old rotators and spare parts are available if you search. 73, Martin GW3XJQ

[@watersstanton]

Thanks for sharing Martin.

[@on4mgy_radioamateur]

Again a great video Peter, thanks for that. I'm just using a folded X-beam wire antenna for 6 bands (20-6) Little windload and only 8 kg in total. I played on safe and mounted a G-1000DXC rotor under it. Should last forever. 73 de OO4M

[@watersstanton]

Sounds great!

[@David-hm9ic]

Thanks for this video! I had already purchased a Yaesu 450 for a hex beam based on the wind load rating of the rotator and the wind load of the antenna but still found the video interesting. Recently I helped install a hex beam on a big tower which provided great insight for my own project. Torque is not materially affected by the length of the tube between the rotator and the antenna as there is just not enough force applied on the system to reach the torque limits of the connecting tube. It is much better IMO to have a tube and thrust bearing than to mount the antenna directly to the rotator. The thrust bearing can carry all of the weight. It adds cost but it really helps the rotator do its job and it reduces wear. The ability of the rotator to start and stop the antenna (torque rating) and to maintain its position and tolerate wind loads are the most important factors.

[@watersstanton]

Correct, torque is no affected by length, but there is a significant magnification of transmitted force that is put on the rotator. Long screwdriver effect.

[@ralfkruse7565]

Hi Peter, my first rotator was a Stolle TV antenna rotator, I used it with 2 bearings, worked fine. 2m, 70cm, 23cm Yagis. When I wanted to install a 2m Dish ,plus Yagis, I changed to a Kenpro KR600 plus bearing. It worked for more than 35 years until a hurricane. Then he needed a Dentist. 2 teeth broken. Kenpro didn't exist anymore,so no new couronne. I scrapped it.😮

[@watersstanton]

Gosh, names from the past that I had forgotten!

[@andye2005]

Two dead rotators here, Daiwa DC 7011 Kenpro KR-400RC Turned out that the Kenpro uses exactly the same head unit as the Diawa. The problem is basically a poor if not incompetent design. There are NO end stop switches in the system, when the antenna hits the stops the motor keeps going and relies on a slipping clutch to save it. That does not work well and the motor burns out. These are 24V ac two phase motors you switch the phases to change direction. The advantage is that there is no electrical noise. The disadvantage is that spares are almost impossible to get now. (these are old rotators ) I have a long term project on the bench to rebuild them into something rather more robust, but as will all my projects other things get in the way 🙂 I see that the newer rotators now use a dc motor with limit switches that cut the power. So a much better design. The simplest roatator I ever had was for my 6 ele 144Mhz quad it was a couple of lengths of orange nylon garden cord tied to the ends. The strings came into the shack (bedroom) via the fanlight window So 180 degree rotation was easy. With a little practice I could let the antenna spin until the strings crossed and then the other 180 direction could be "beamed up" That worked really well for many years... Andy

[@Test-hw5fn]

Thanks for this Peter. Any thoughts on where on a pole you should place the rotator🤔

[@watersstanton]

At the top.

[@FNUKSTER1366]

Peter , have you been watching callum 's channel DX COMMANDER by any chance???

[@brianfields4479]

Why, what happened

[@gerardoppewal372]

I had a Channelmaster with thrustbearing to turn 5-el 6m, 9-el 2m, 19-el 70cm and an X-200 on top. Survived a gale 10 and worked well for over 10 years, with a little annual TLC. I figured I could thrash 3 of these for the price of one Yaesu, but I never did.

[@EssexCountyPhoto]

Great video, thank you! I'm very tempted to use a rotator... in my loft, to use with a magnetic loop! 😂

[@mariemccann5895]

Why not, that's a great idea for limited space.

[@brianfields4479]

Comments can be tongue in cheek, think twice about the expense, especially if a elevated vertical works just as well as a beam anyway. I did try a rotator on my vertical, but didn't get any gain. Hi. 73 mate.

[@thegingaman]

Thanks, Peter. thats a handy video 73

[@Colin_In_VK]

At least you call them by the proper name a 'Rotator' in the UK. 🙂

[@watersstanton]

Nice to hear!

[@leedeller1906]

Hmmm sounds like a dig at Mr Commander

[@brianfields4479]

Why, what happened.

[@qutips33]

good video and nice info. can you make a video about different loop antennas it would be nice 🙂 La2vla

[@keithjas25]

Hi Peter, not wishing to be rude but your screwdriver idea doesn't realy hold. Its the thickness of the handle that increases the torque. To give you an example of torque, it's force times distance or in old money, pounds per foot. Try pushing your front door open an inch from the hinges, then do so from the opposite end to the hinge, you will feel the difference of torque. Sorry if I am teaching anyone to suck eggs here, but thought it may help someone get the concept.

[@watersstanton]

Yes torque is easy to demonstrate. But there is an additional transmitted force. That is why we normally place the rotator at the top of the mast.

[@DavidCase-ov5uo]

I once had a auto rotator in my parents loft turning a 2 metre yagi. One day it jammed on the end stop, overloading the motor and getting very hot! Is was by chance that I went to the loft and smelt the heat. The rotor body stayed hot for a considerable time. Be warned! G4BTI.

[@watersstanton]

Good job there was no fire in the loft!