Gates Engineering has provided EPI with the belt modulus which they use to calculate the stretch of a Pol圜hain belt in response to a given load. Using the Gates methodology and that modulus, we calculated the stretch produced by (a) 1619 pounds of tension applied to (b) a 62mm Pol圜hain GT-2 belt over a tensile span of (c) 19.75 inches. That stretch is 0.066 inches (just a hair over 1/16 of an inch). That stretch value (0.066") agrees exactly with the value which Gates Engineering calculates for the ProDrive system with 95 HP applied at 2168 RPM. It is a puzzlement how ProDrive comes up with a belt stretch value which is four times the REAL value. Anyone who has actually examined the system in operation system would realize that 1/4" of stretch is just not reasonable. Perhaps it is based on some fallacious observation taken from the misleading static display they had at Homer's-2004. That display consisted of two ProDrive sprockets (34 and 144 tooth) loosely attached to the side of a trailer, with a lever for applying torque to the driving sprocket. Of course, there was no preload on the belt. So when you applied 230 or so lb-ft of torque, the loose side of the belt sagged, mostly due to the movement of the large sprocket, which was loosely-bolted to the trailer. There was clearly no residual tension in the slack side of the belt, AND LOOK !, ProDrive proclaimed, "the belt does not skip teeth". The misleading part of this snake-oil demo is that if you were to try and transmit 230 lb.-ft. of torque through this drive dynamically (like at 2168 RPM, for example), with no preload on the system, you would certainly have tooth-skipping and horrible overloads to the shafts and bearings (not to mention to the belt).Īnd, of course, there was no mechanism in their demo to show the dramatic increase in SHAFT load caused by an under-tensioned belt. Recently, there have been two cases of the ProDrive belt fracturing across a single tooth root, as shown in this picture (Figure 1) of Mike Morgan's belt, which broke after slightly more than 3 hours of operation. Ardie Greenameyer's broken belt looked very similar to this one.ĮPI sent Mike Morgan's broken belt to Gates Engineering for analysis. Their opinion (a consensus of several knowledgeable Gates engineers) is that the belt almost certainly fractured because of being operated in an undertensioned drive system. They said there was clear evidence of the belt having skipped teeth, which severely overstresses the belt cords AND the shafts AND the bearings.Ī copy of that report from Gates is shown in Figure 2 below. (It has been edited to remove names and phone numbers. REMEMBER, Gates doesn't want their stuff on aircraft.) Recently ProDrive claimed they were sending Ardie Greenameyer's broken belt (the one being fixed at Homer's in July, 2004) to Gates for analysis. We really don't understand why ProDrive would send that belt to Gates for analysis, since they insist is not a Gates product. (BTW, Gates engineering has told us unequivocally that one ProDrive belt sample we sent them was indeed a Gates product, and they wanted to know why the Gates logo had been removed.) 3. Our contact in Gates engineering is one of the people responsible for the engineering manual. In July of 2004, he told us that Gates is in the process of updating their manual to reflect some of the new engineering data they have gathered from field experience with the Pol圜hain toothbelt. #Gates synchronous belt engineering calculator manual# One of the important changes is the fact that the maximum recommended tension ratio is being increased from 8:1 to 10:1 (That means the minimum allowable preload is LESS than before.
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