How to tell if your treadmill is running too slow…..or too fast
This blog is about how to set (calibrate) the speed of a treadmill running belt. It assumes you have a basic understanding of treadmill control systems. Please note that these instructions apply specifically to DC motor systems in domestic grade treadmills – different rules apply for AC, commercial machines!
To change the speed you need to get inside the machine by removing the motor hood. Remember to disconnect the mains cord first and let the MCB capacitors discharge for about 3-5 minutes before poking your fingers in. Often there is a “speed” potentiometer lurking somewhere on the Motor Control Board (MCB) that you can use to adjust the running belt speed. This is normally a tiny blue square box with a screw head adjuster (see picture above) that can be turned with a small jeweller’s screwdriver. When setting the speed, I use a contact-tacho to measure the actual speed of the running belt. This allows you to set the speed fairly accurately and is perfectly adequate for most people. Incidentally, I got my tacho from Machine Mart http://www.machinemart.co.uk/shop/product/details/ct2-digital-contact-tachometer
There are 2 systems that treadmill designers use to determine running speed. One is called a closed- loop system and the other is called an open loop system. One is easy to adjust and the other is not.
On treadmills where there is no speed sensor such as Roger Black, Reebok and i-run, the control console has no idea what the actual speed is, since it has no speed feedback. All it does is pump out a speed signal to the MCB according to what the user chooses and hopes for the best. This is the open-loop system. When you change the “speed” pot setting on an open-loop system you’ll see an immediate change in motor speed according to how much you have turned the pot. It’s just like an old-fashioned volume control – you turn it up to go faster and down to go slower.
However, treadmills with a closed-loop system (ie. those with a speed sensor) will tend to auto-calibrate the speed, within reason, to maintain the actual speed set point which has been defined within the control console’s settings. These are not so easy to adjust because the settings are often burnt into software which you can’t change, or are hidden in an Engineering menu, which you can’t find.
On closed loop systems, when you step on the running belt you’ll probably hear the motor slow down due to the effect of your added weight, but listen closely………the speed will quickly and smoothly recover as the control console senses the drop in speed via the speed sensor and turns up the wick to compensate for your lardy proportions. In this case, the speed pot is there to provide a way for manufacturers to limit the maximum speed rather than for calibrating the speed. This allows them to match the MCB to the motor or in some cases It just allows a means for product differentiation – the higher the treadmill specification, the higher the speed pot gets turned up in the factory!
On some MCB’s you’ll also see a secondary potentiometer which is usually labelled as “torque”. You use this for adjusting how quickly or slowly the machine performs the auto-calibration. Set it too slow and the machine may never reach the required set speed but set it too fast and the machine will overshoot the set point and “hunt” (oscillate faster and slower around the set point without actually settling down).
A long-time, loyal customer of mine gave me the inspiration to write this post. He has 2 x treadmills side by side asked me to check the speed of them both. He was convinced one was running slower than the other. He was right! With my tacho, I measured about 10% difference between the two machines at the same indicated speed. Unfortunately, both his treadmills were closed loop systems and each time I adjusted the “speed” pot, the console would auto-calibrate to bring the speed back to what it thought was the true speed. Eventually, my customer and I decided that we would consider this discrepancy as an allowable error and we gave up. Sometimes life is just too short to get hung up about these kind of things (but it helps if you understand what’s going on)!