What is Cycloidal Drive? Designing, 3D Printing and Testing

hello dan here from howtomechatronics.com in this video we will learn what is cycloidal drive how it works explain how to design our own model and 3d print it so we can see it in real life and better understand how it works a cycloidal drive is a unique type of speed reducer which provides very high reduction ratio with compact but robust design compared to conventional gear drives like spar or planetary it can achieve much higher reduction ratios of up to 10 times in the same space or stage in addition to that it features virtually zero backlash higher load capacity rigidity and high efficiency of up to 90 percent these properties make the cycloidal drive suitable for many applications where positioning accuracy and performance are important such as robotics machine tools manufacturing equipment and so on let's take a look now what's inside and how a cycloidal drive works a colloidal drive is composed of five main components a high speed input shaft an eccentric bearing or cycloidal cam two cycloidal discs or cam followers a ring gear with pins and rollers and a slow speed output shaft with pins and rollers the input shaft drives the eccentric bearing and the eccentric bearing drives the cycloidal disc around the internal circumference of the ring gear housing the eccentric motion makes the cycloidal discs teeth or lobes to engage with the rollers of the ring gear housing in a way that they produce reverse rotation at a reduced speed if we take a closer look here we can see how the eccentric bearing is actually pushing the cycloidal disc against the ring gear rollers because of the unique disc shape and the position relative to the ring gear rollers we can see that as the eccentric bearing progresses the disc lobes in front of the rotation won't be able to pass or jump to the next ring gear roller but instead it will slip or roll backward this behavior is what actually causes the reverse rotation of the discs in general there are one less cycloidal lobe on the disc compared to the number of rollers on the ring gear housing this makes for one full rotation of the eccentric bearing the cycloidal disc to move only a distance of one loop from this we can see that the reduction ratio depends solely on the number of rollers on the ring gear for example here we have 12 rollers on the ring gear which means 11 lobes on the cycloidal disc and that's a ratio of 11 to 1 or 11 times slower output speed the reduced rotation is transmitted to the output shaft pins through the holes of the cycloidal discs there are two cycloidal discs placed 180 degrees out of phase in order to compensate the unbalanced forces caused by the eccentric motion and provide smoother operation at higher speeds the name cycloidal drive comes from the profile of the disk which in turn comes from a cycloid but more on that in the next section of the video where we will design our own cycloidal drive so now as we know how a cycloidal drive works we can move on with designing our own model which we will be able to 3d print it if we try to print this demo example it might work but it will fail quickly as the 3d printing material is not strong enough to withstand the forces and friction that appear in the gearbox the critical parts here are the rollers that are usually bushings which is a great option if the materials are metal but with a pla material we will have to use ball bearings instead having that in mind here's the cycloidal drive that i designed and uses ball bearings for the rollers when designing a cycloidal drive there are four main input parameters that define its size and shape and that's the ring gear radius it's roller radius the number of these rollers and the eccentricity before i explain my approach of designing this gearbox let me give a shout out to solidworks for sponsoring this video have you heard about the 3d experience world an annual event organized by solidworks 3d experience world 2022 brings a vibrant community of designers engineers entrepreneurs and makers together to learn meet one another share knowledge together on newest technologies and best practices this year you can experience the event both virtually and in person life in atlanta georgia in both settings you will be able to enjoy the networking opportunities technical how-to sessions new technology announcements and much more it's an awesome way to break into the trades or sharpen your skills if you are already in the industry be sure to register today at solidworks.com 3dxw2020 underscore how to make and use code 3dxw2020 how to make to get 50 of your in-person conference pass if you are not able to travel to atlanta you can attend virtually for free personally i'm looking forward for this awesome event don't forget to check the links in the description and register today once again big thanks to solidworks for sponsoring educational content like this alright so let's get back to topic now and explain my approach of designing this gearbox the first thing that i defined was that i wanted 15 to 1 reduction ratio for this gearbox which meant that i needed 16 ring gear rollers so i draw a sketch in solidworks with 16 rollers around the circle then i chose to use bearings for the rollers with 13 millimeters outer diameter now according to these two parameters i was able to define what size should the ring gear pitch diameter be i set it to 90 millimeters the eccentricity value should be smaller than half of the roller diameter and i chose to use a value of 1.5 millimeters now that i have the four main input parameters we can draw the shape or the profile of the cycloidal disk as i mentioned the disk profile comes from a cycloid which is a curve traced by a point on a circle as it rolls along a straight line without slipping or its variation an epicycloid which is traced when rolling on a circumference of a circle there is another variation called epitruchoid where the tracing point is at a distance from the center of the exterior circle and that's what the cycloidal disk profile is actually based on for drawing such a curve we can use these parametric equations here but there are also other parameters to include in them such as the roller's diameter and the eccentricity this complicates the things a little bit but luckily there was a great document written by omarionis for the solidworks education block where he combines all of these parameters in a single x and y parametric equations now in order to generate the profile we can simply use the solidworks equation driven curve tool insert the two equations appropriately and that will generate the cycloidal disk profile of course for the input parameters we should insert our values also note that the curve won't be generated if the t parameters are from 0 to 2 pi or 360 degrees so we need to set the t2 parameter a little bit short of 2 pi and then generate the curve with a small gap which we can connect later using a simple spline now that we have the main parameters for our cycloidal drive defined the rest is just finding technical solutions for how everything will be connected again considering that we are using not so strong 3d printing material i designed the shafts of the rollers to be supported on both sides as well as the input shaft and the output shaft the input shaft is made of several sections and supported with two bearings within the output shaft the output shaft is also supported with two bearings within the housing so to recap the work of this gearbox the input from the motor is transmitted to the eccentric input shaft which drives the cycloidal disc around the gear ring the produced reverse motion of the cycloidal disc is transmitted to the output shaft through the output shaft rollers and that's it now let's 3d print it and see how it works in real life you can find and download the 3d model as well as the stl files needed for 3d printing the parts on the website article when 3d printing parts it's important to use the whole horizontal expansion feature in your slicing software usually the holes of 3d printed parts come smaller than the original size so with this feature we can compensate for that and get accurate dimensions which is very important for these parts i set mine to 0.07 millimeters and a horizontal expansion feature which can compensate for the outer dimensions of the parts to 0.02 millimeters of course you should do some test prints to see if that values will give you the best result on your 3d printer so here are all of the 3d printed parts as well as the bearings and the bolts needed for assembling the cycloidal drive i started with inserting the ring gear pins to the housing these pins accommodate the ring gear rollers or the bearings but they are just six millimeters in diameter i wasn't sure better they were strong enough not to break under the load of the cycloidal disc therefore i made them hollow and inserted into them three millimeter metal shafts which i had laying around this way the pins will be strong enough for sure of course there are smarter solutions for this for example we could use m6 bolts instead but what i don't like about this is that the m6 bolts are slightly smaller than six millimeters so the bearing would wobble ideally we could use a proper six millimeters rod which is actually easily available to buy even with this particular size of 35 millimeters i will put links to them as well as all other components needed for this gearbox on the website article once we have all the pins in place we can insert the bearings in this order a 7 millimeter distance ring a bearing then three millimeter distance ring a bearing and another seven millimeters distant ring the cycloidal disc should now fit in this ring gear that we created and if we try to rotate the disc with an eccentric motion by pushing it to the sides while rotating the disc should start rotating reversely next we can assemble the input shaft which is made of four sections in each section we need to place a bearing and some distance rings and because of the eccentricity we won't be able to do that unless the shaft is made in sections for connecting the sections together i'm using two m3 bolts which go through all of them we can note here that the holes for these entry bolts are made slightly smaller than the m3 bolt so that the bolt will make a thread into them and have tighter fit here's how the shaft should look like when assembled but i actually had to insert the cycloidal disc as well as now i couldn't do it so i disassembled it and assembled it again with the disc inserted as well i continued with assembling the output shaft here we need to install the output rollers or bearings and we do that in similar way as shown for the ring gear rollers a 6 millimeter pin with 13 millimeters bearings and some distance rings inserted through some 20 millimeters long m3 bolts when inserting these output rollers through the openings of the cycloidal disc it's important to position the two discs relative to each other 180 degrees out of face to help with this i made a small holes on both discs 180 degrees out of face so we just have to match them and we are good to insert the rollers through please note that this is a bit tight fit but if the hose dimensions are accurate we will be able to fit them now we can secure these pins to the other flange on the other side but for that purpose first we need to install some threaded inserts into the flange i'm using threaded inserts in order to make the whole assembly more compact so once the input and the output shaft are assembled together we can install the whole assembly into the housing to a bearing with 47 millimeters outer diameter then we can install one more bearing like this in the front of the shaft and insert the housing lid in place this is also a tight fit as all 16 pins should fit in their housing lead slots so we probably have to use a bit of force to insert the lid in place on the back side of the housing i installed some m4 threaded inserts and then secured the lid and the housing together with some 40 millimeters long and 4 bolts and that's it if it's fair to say just take a look at this beauty i really like how this cycloidal drive turned out clean design with nothing popping out of it nevertheless now let's attach a motor to it and see how it will work at the back side of the input shaft i installed few more threaded inserts so i can easily attach various shaft couplers to it for testing this gearbox i will use a nema 17 stepper motor so i attached a suitable 3d printed shaft coupler to the input shaft i secured the stepper to a 3d printed mounting bracket and inserted the motor shaft into the coupler and secure the mounting bracket to the housing one last thing is to install some threaded inserts at the front of the output shaft so we can attach things to it here's the final appearance of this cycloidal drive in combination with a nema 17 stepper motor but of course we can use any other type of motor here and there we have it in motion to be honest i was really surprised how smooth the output of this gearbox turned out from the front we can see both the input and the output shaft rotating at the same time in opposite direction and with speed difference of 15 to 1. i was also able to run the gearbox without the front lid and so we can see everything explained previously in action the motion of this cycloidal drive is simply mesmerizing at the end i made some tests to check the gearbox performance one more thing to note here is that the cycloidal drive is also big drivable which can be a good feature to have for some applications so here i'm measuring the force this gearbox can produce at a distance of 10 centimeters i got a reading of around 26 newtons which translated to torque is about 260 newton centimeters and this nema 17 stepper motors which is 34 centimeters long is rated at 26 newton centimeters that means that we've got torque increase of around 10 times with this cycloidal drive that's efficiency of around 66 percent considering that the reduction ratio is 15 to 1 and in ideal conditions we should get 15 times torque increase nevertheless that's still a great result considering that everything is 3d printed with a budget 3d printer and the parts are not that accurate as we could get it with some pro printers or cnc machines in case of all metal gearbox i also made some accuracy tests which also showed good results i would definitely use this type of gearbox in future videos when making some robotics projects i hope you enjoyed this video and learned something new don't forget to subscribe and for more tutorials and projects visit howtomechatronics.com

Channel: How To Mechatronics

Views: 12,306

Keywords: Cycloidal Drive, Speed reducer, Gearbox, Gear drive, How It Works, How to design, 3D Printed, 3D Model, Designing cycloidal drive, cycloid, speed reduction

Id: OsS9-FzKN6s

Length: 16min 35sec (995 seconds)

Published: Sun Dec 19 2021