Weight Capacity: (based on my notes after talking to an engineer
This is the maximum weight that the machine will support on the plate.
There are three variations on the weight capacity as specified by manufacturers, and it is very important that you know which one you are being presented. They are:
1) The weight that the plate can support before the device fails mechanically. For example, powered off, the weight will break the plate mechanism.
2) The weight that the plate can support while operating.
3) The weight that the plate can support while operating within the stated specifications.
For example, a spec sheet might state that it produces a maximum amplitude of vibration of 1 inch, and supports a maximum weight of 500lbs. However, you may find that it cannot fulfill these specifications at the same time. (for example, it can produce 1 inch of vibration, but only with a weight of 100lbs, and it can support 500lbs, but at this weight will only produce vibration of 1/4 inch. Some manufacturers will actually provide this information, but most will supply maximum specifications in isolation of one another, which I believe is misleading to a point.
Bottom line: More weight capacity will cost more, so only buy what you need. Also be certain to compare specifications of performance at the actual desired weight capacity.
As a rule of thumb, only buy what you need. Take into account your own weight and any static weights that you might use on the plate.
Under 100 lb people
If you are 100 pounds or less, you can get by with a motor that is 1 hp or less. Most of the machines under 700 dollars have motors that are in this range. Although they are capable of lifting much heavier weights, almost all the G force is sacrificed and the more people weigh over 100 pounds with this cheap of a motor, the more it will simply feel like a over-sized foot massager, just vibrating without really much G force. If you are under 100 pounds, I do sell machines that will simply do no more than what I would expect from this range. As long as you don't expect it to do more than just vibrate if you are over 100 pounds, you should be happy. Not much horsepower is needed for weights under 100 pounds. If you are going to get a motor at 1HP or below, please make sure its direct current, not AC. Also, do not expect a very long plate. Typical machines are 200 watts max.
100 - 150 lb people
In this range, a 1.5 HP motor is sufficient and the closer you are to 100 the more you can get away with less wattage. 1.5 HP motors usually come in 200, 300 and 500 watts. If you are closer to 150, a 300 watt , 1.5 HP motor would strain less. Anything less than a 1.5 HP motor for people close to 150 will still lift them but the G force is drastically diminished. A 500 watt motor wouldn't give hardly any strain and a 300 watt would be sufficient. 200 watt is pushing it but if you didn't stand near the edges and were doing static exercises at higher speeds, it can work. 500 Watt motors have come down in price and the price you used to get a 200 watt machine you can now get a 500 watt machine.
150 to 200 lb people
In this range, most people usually have about 20 to 30 pounds to lose or have bone issues that call me. Most of the people that call me are usually in this weight range. If the primary purpose is lymphatic drainage, what to look for is how low of a hertz the plate will move and how many G forces will it deliver at the lowest rate. If you are close to 200 pounds, and you expect the machine to deliver enough G forces to drain the lymphatic system, a 2 HP motor is the only one I have found to reach the low frequencies as this requires power and not momentum on a fast moving plate. If a person weighs close to 200 pounds and the reason is bone density concerns, the low end is not as important. A 1.5 HP motor is fine. Only at the low speeds do you need a more powerful motor. A 1.5 HP motor with 500 watts would be fine for people that are up to 200 pounds. A 2HP would be probably be better if the focus was more on lymphatic drainage but for general exercise and everything but lymphatic drainage, this is fine. You just lose a little of the "pop" at the acceleration that you would get with a stronger motor.
200 to 300 pound people
If you are over 200 pounds, although a 1.5, 500 watt motor is still sufficient to lift someone, having enough copper windings to deliver 2 HP will make the ride smoother, make less noise, and feel more stable. A 200 to 300 pound person should be able to stand near the tippy edge of any size plate with 2 HP and 500 watts. A lower wattage model can still work but might have a slight strain if standing too close to the edge. Many recent machines have 2 motors and instead of having to turn up the vibration really high, the 2nd motor (we call it a spiral motor) gives the plate an extra vibration front and back along with left to right vibration. Also, on linear models, some have different mechanisms of moving the plate up and down. Some feel more like a push and others a pop. Either way, if someone is over 200 pounds, I would almost always recommend a 2 HP models with no less than 500 watts.
Remember, the larger the motor, the less the motor has to work to deliver higher G forces. For example, a car with a V8 engine has to work less hard than a 4 cylinder car to reach the same speed. The same with motor. If you want a motor that is no bigger than a coke can that has a 2 HP rating or you want one that is bigger, with more copper windings and more electric potential, the less it will have to strain and the longer it should last you. A 2 HP motor with 300 watts will have to work harder than a 2HP motor that has 500 watts. If you tried both side by side you would notice the difference in feel and sound.