Alex K Posted May 23, 2021 Share Posted May 23, 2021 (edited) Hello fellow gripsters! Since I live in Germany, and the closest place where I could rate my grippers is pretty far away (and seems to be inactive), I have tried various methods to measure the RGC Rating of my grippers at home. In the end, I built my own accurate RGC device on my balcony but before that, I had developed a small tool for approximating the rating of grippers without actually closing them. In this thread I would like to explain, how it works, and tell what the ups and downs of it are How does it work? It's quite simple, actually. The precise RGC Rating of a gripper depends on incredibly many factors, like for example anomalies/imperfections within the torsion springs, the friction within the spring, axial torsion of the spring (since we don't have an ideally flat spring and it rotates throughout the ROM) and many others. However, we can just try and assume for the sake of simplicity, that we only work with two main influence factors: the spring's torsion stiffness and all of the different moment levers within the gripper (which vary in a surprising manner even amongst the best gripper manufacturers). The calculations behind the algorithm are based upon lots of trigonometry, mechanics and torsion spring formulas. How is it used? A few accurate calliper measurements have to be performed (they are all shown in the sketch in the Excel sheet), plugged into the tool (the values in Bold), and it gives you the expected RGC Rating with those parameters. That's pretty much it Important: the spring diameter has to be measured within the spring winding instead of the usual measurement point near the leg. This is due to the fact that the formulas all work with the spring winding diameter, and it turned out to be a slight bit smaller, when comparing it to the diameter at the leg point (where the wire is straight). Note: Since there is no account for friction phenomenon in the algorithm, the best results are achieved when comparing the numbers to grippers with oiled springs. What are the challenges of this method? Mainly, inaccuracies within measurements. For example, the torsion spring's stiffness depends on the spring wire diameter to the 4th power. This means that even the slightest inaccuracies in the measurements (we're talking 0,01-0,05mm) could yield an RGC Rating that is a few lbs off. However, this challenge can be overcome by taking as many measurements of the spring diameter at different points within the winding as possible, using an accurate measurement tool (a typical calliper will do). I usually tried to see which number appeared on my calliper tool most of the time throughout the measurement. Plugging it into the algorithm yielded a result which was very close to my actual RGC gripper rating. Another challenge would be of course the other factors, like gripper handle spread decreasing after a few closes, and the other mechanical phenomenon mentioned above. However, in the end all of my RGC values ended up being pretty close to my real life measurements - some within half an lbs. I would like to share my findings with the GripBoard forum community, to allow folks like me who didn't have any convenient opportunity to get their grippers rated to at least know roughly how tough their grippers are. At this point I would also like to mention, that no algorithm can fully replace the accuracy of an RGC measurement performed by professionals, and that this tool is just a concept of mine which probably still has plenty of work to be done with it. I added a mm/kg and an inch/lbs system so that everyone can use it conveniently! I hope you guys enjoy it, and I am very open to any questions or improvement suggestions from your side RGC approximation tool (Version 1).xlsx Edited May 23, 2021 by Alexander Koss 2 1 Quote Link to comment Share on other sites More sharing options...
pancho_grip_lift Posted May 23, 2021 Share Posted May 23, 2021 10 hours ago, Alexander Koss said: Hello fellow gripsters! Since I live in Germany, and the closest place where I could rate my grippers is pretty far away (and seems to be inactive), I have tried various methods to measure the RGC Rating of my grippers at home. In the end, I built my own accurate RGC device on my balcony but before that, I had developed a small tool for approximating the rating of grippers without actually closing them. In this thread I would like to explain, how it works, and tell what the ups and downs of it are How does it work? It's quite simple, actually. The precise RGC Rating of a gripper depends on incredibly many factors, like for example anomalies/imperfections within the torsion springs, the friction within the spring, axial torsion of the spring (since we don't have an ideally flat spring and it rotates throughout the ROM) and many others. However, we can just try and assume for the sake of simplicity, that we only work with two main influence factors: the spring's torsion stiffness and all of the different moment levers within the gripper (which vary in a surprising manner even amongst the best gripper manufacturers). The calculations behind the algorithm are based upon lots of trigonometry, mechanics and torsion spring formulas. How is it used? A few accurate calliper measurements have to be performed (they are all shown in the sketch in the Excel sheet), plugged into the tool (the values in Bold), and it gives you the expected RGC Rating with those parameters. That's pretty much it Important: the spring diameter has to be measured within the spring winding instead of the usual measurement point near the leg. This is due to the fact that the formulas all work with the spring winding diameter, and it turned out to be a slight bit smaller, when comparing it to the diameter at the leg point (where the wire is straight). Note: Since there is no account for friction phenomenon in the algorithm, the best results are achieved when comparing the numbers to grippers with oiled springs. What are the challenges of this method? Mainly, inaccuracies within measurements. For example, the torsion spring's stiffness depends on the spring wire diameter to the 4th power. This means that even the slightest inaccuracies in the measurements (we're talking 0,01-0,05mm) could yield an RGC Rating that is a few lbs off. However, this challenge can be overcome by taking as many measurements of the spring diameter at different points within the winding as possible, using an accurate measurement tool (a typical calliper will do). I usually tried to see which number appeared on my calliper tool most of the time throughout the measurement. Plugging it into the algorithm yielded a result which was very close to my actual RGC gripper rating. Another challenge would be of course the other factors, like gripper handle spread decreasing after a few closes, and the other mechanical phenomenon mentioned above. However, in the end all of my RGC values ended up being pretty close to my real life measurements - some within half an lbs. I would like to share my findings with the GripBoard forum community, to allow folks like me who didn't have any convenient opportunity to get their grippers rated to at least know roughly how tough their grippers are. At this point I would also like to mention, that no algorithm can fully replace the accuracy of an RGC measurement performed by professionals, and that this tool is just a concept of mine which probably still has plenty of work to be done with it. I added a mm/kg and an inch/lbs system so that everyone can use it conveniently! I hope you guys enjoy it, and I am very open to any questions or improvement suggestions from your side RGC approximation tool (Version 1).xlsx 133.34 kB · 6 downloads Hey Alexander, how are you? Your method looks really interesting. I'd like to try the calculator, but I have one question, what do you mean by measuring the spring within the spring winding? May I ask you for a photo or video, so I could measure my grippers in the same spot? Thank you in advance! 1 Quote Link to comment Share on other sites More sharing options...
Alex K Posted May 23, 2021 Author Share Posted May 23, 2021 1 hour ago, pancho_grip_lift said: Hey Alexander, how are you? Your method looks really interesting. I'd like to try the calculator, but I have one question, what do you mean by measuring the spring within the spring winding? May I ask you for a photo or video, so I could measure my grippers in the same spot? Thank you in advance! Hello! Sure thing, I'll show it based on my CoC#3.5 (pretty easy one according to RGC measurement and algorithm - around 171lbs). As you can see, in the "insertion point" of the spring the diameter is 7,41mm, while within "the spring itself" it drops to 7,33mm. This seems to be the case with all of my grippers, some varying just a bit and some more (like my #3.5). I suppose it has something to do with the spring's production process. The calculation seems to be the most accurate when using the measurements within the spring (so, in my case, where the wire's diameter is 7,33mm), this is also backed up by the equations used for the calculations (they assume an idea spring with the same diameter everywhere). I hope the images help a little more 1 1 Quote Link to comment Share on other sites More sharing options...
pancho_grip_lift Posted May 23, 2021 Share Posted May 23, 2021 1 hour ago, Alexander Koss said: Hello! Sure thing, I'll show it based on my CoC#3.5 (pretty easy one according to RGC measurement and algorithm - around 171lbs). As you can see, in the "insertion point" of the spring the diameter is 7,41mm, while within "the spring itself" it drops to 7,33mm. This seems to be the case with all of my grippers, some varying just a bit and some more (like my #3.5). I suppose it has something to do with the spring's production process. The calculation seems to be the most accurate when using the measurements within the spring (so, in my case, where the wire's diameter is 7,33mm), this is also backed up by the equations used for the calculations (they assume an idea spring with the same diameter everywhere). I hope the images help a little more You made it clear! I'll try it in my grippers Quote Link to comment Share on other sites More sharing options...
Alex K Posted May 23, 2021 Author Share Posted May 23, 2021 Just now, pancho_grip_lift said: You made it clear! I'll try it in my grippers Curious to find out if the measurements end up being close like mine or not Enjoy! 1 Quote Link to comment Share on other sites More sharing options...
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