Latest Project 1

Several years ago, the service department of a transport company in Budapest asked me to calibrate their balancing machine. It was an old balancing machine type AM-1000W from the GDR. Many years ago we made a computer controlled balancing unit for it, because the original measuring unit broke. I listened to their problems, looked at the balanced rotors and learned about their balancing method. The balanced parts they repaired in the service were the rotors of the drive motors of old city streetcars. Three different types were repaired there. Most had the same balancing problems. It seems that the designer-designers of the motors of streetcars at that time wanted to make the shortest motor possible. They liked to put the bearings inside the commutator and fan, thus making balancing more difficult. When we put a rotor on the balancing machine, we want to turn it around the original axis of rotation, which means that we need to support the axis in the place of the bearings. With the balancing machine they had, it was not possible. Even in no other universal balancing machine they could support the axle where it was needed.

At the service the workers tried to solve the problem with an extended sheathing of the axle. The minor problem was that these took a long time to install. The bigger problem was that despite the seemingly successful balancing, most of the motors failed the last check because they were unbalanced. After some rehearsals, they came to the conclusion that after disassembling and reassembling the extensions, if you first disassemble them, then reassemble them, you will measure a completely different unbalance, so the already balanced rotor will be unbalanced again. So they concluded to recalibrate either the machine or their electronic device. I checked both the machine and the device and they both seemed to be working properly. So this was not a calibration problem/failure.

When I saw these large extension shrouds welded together from several pieces, I thought about them not having the same axis with the bearing locations. This assumption was not easy to prove even with the help of an indicator clock. I took a rotor with me, and we tried to put it in our workshop on one of our balancing machines but without an extension shroud. Some of our balancing machines are very flexible, the roller pair support can be removed and changed.

We made 2 pairs of special displaced roller pairs and we were able to use them to support the rotor at the bearing locations. We balanced the rotor. When this was installed in the machine, it was no longer unbalanced, the vibration was very low. So our method was correct, but this could be used on a special balancing machine. After a short time, the bosses of the transport company understood that for balancing the rotors they needed a special balancing machine, which could also support the axles of the rotary bearings with unusual construction. They ordered the machine from us, so we designed a new balancing machine for them. The machine was belt driven and we made special shifted roller pairs for 3 different rotors. Because of the shifted roller pairs, the weight of the rotor created an asymmetrical load on the support points of the balancing machine. We modified these support points to be able to bear this load. This special balancing machine made balancing much faster, (you didn't have to mount an extension shroud anymore) and every balanced rotor is flawless even during the last engine tests. If you ever come to Budapest and ride on an old tram and you don't feel any vibration of the engine, please, think of me.

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