Bowden cables for the robot arms? Will it work?

hello and welcome to my channel it is very important to keep the weight of the robot arm as low as possible especially the weight of the wrist of the robot arm the lighter the wrist the more payload you can use and this is because the torque is equal to the weight times the level and the wrist can have quite high level especially in this position and that's why the weight of the wrist is very critical usually the heaviest parts of robot arm are motors and gearboxes and so it's really good idea to put these motors and gearboxes somewhere close to the shoulder or even in the shoulder and one of the simple way to put these motors and gearboxes in the shoulder is to use building cables you know this cable which used on the bicycles for the brakes so the idea for today's video is to build the wrist with the bowden cables with the motors which are going to be apart from the wrist and to see if this system works properly and if it's acceptable for the robotic arm let's get started this is a button cable which i'm going to use this is standard bicycle building cable for the brakes as you can see like this it works perfectly fine but i think it's not so obvious that it's going to work perfectly fine for the robotic arm and let me explain you why first of all when there is a lot of bending in this bowden cable the friction in the cable and the housing becomes quite important so here it's very easy to slide this cable in and out with very little friction but for example in this cable when there is a lot of bending it's already quite difficult to pull it and push it so this is a potential problem number one and now let me illustrate the potential problem number two so for this i'm going to fix this end of the bowden cable so i'm fixing the cable to the housing so i'm just going to hold it like this and now i'm going to move this other end and let's see what happens with this part i will try to hold it still so when there is a lot of bending it contracts and when i straighten it it expands and it contracts and expands quite significantly actually i think this could be a really big problem so for example let me bend it like this and let's put it here to the zero and here i'm going to fix it and now i'm going to um unbend it and you see it moved almost one centimeter this is really a lot so when i bend it again it's zero yeah i think this will make it unusable but anyway i'm going to assemble this wrist and we will see if these problems are real problems or just my imagination i have designed everything in fusion 360. this is the output the yellow piece this output has the bevel gear over here which is connected to this bevel gear and this red part is basically one of the pulley so bowden cable is going to pull one or another side of this pulley and another pair of bowden cables is going to pull one or another side of this gray pulley which is going to move the output so basically this pulley is last axis and this pull is the axis just before the last one and also in this design i have made the hole to pass the cables from the end effector to the base of the robot and in order to move this bowden cables i have designed bowden driver over here and it's basically using the stepper motor nema 17 with the planetary gearbox which is fixed in this part there are pulley over here which is going to pull one or another bowden cable the bowden cable is tensioned with these two blocks and i also made a cover in order to make everything pretty and now the quick add from the sponsor of today video phantom world it's a compact and stylish warrant which has a special mechanism to access your cards they have three sizes and plenty different finishes phantom r wallet has screw holes where you can mount various accessories like coin holder cash holder key holder id tracker etc or you can even design and 3d print your own accessory all this gives you a lot of possibilities for the customization you can find more information following the link in the description to this video and this is how i use my phantom wallet i have bolted this water to my iphone case and this is very practical whenever i need the phone i need my water and whenever i need my wallet i need my phone and it works perfectly well don't forget to use coupon code screentip for 10 off [Music] now i think it's time to start the assembly these are the 3d printed parts which we are going to use and these are my stepper motors with planetary gearboxes by the way all these parts was 3d printed in the orientation which they are now laying on the table and this is a big part for the wrist really huge one 22 hours of print for the print i use the standard settings and the support only on the build plate and before starting the assembly i need to clean the parts meaning that there is a small holes in these parts for the cables and the cable does not pass in this hole and there are two reasons for this first of all in the cable there is a blob at the end which i need to file so the end of the cable is a little bit larger than the diameter of the cable itself and the second reason is 3d printing because these holes are 3d printed in these layers the top of this hole is not really perfect let me make a drawing to illustrate this ideally this hole should be round but in reality because we 3d printed this piece in this direction the hole is round on the bottom and on the side and a little bit like this on the top and so we need to correct this part and for this i'm going to use the blades for the thread saw because they're really flexible and so they can go easily through this hole so basically i need to take a hole i need to take this piece shape it a little bit in the curved like this and now it can go inside this hole and so basically like this i can correct this hole and by the way it's very easy to eliminate this blob by filing it with the dremel now i need to repeat this on all four cables and to take care of the four times two eight holes i have corrected this holes really just by tiny amount and now it works so it means i can put the cable over here somewhere and it passes through and the other end of the cable looks like this so it's going to be blocked over there now i need to do the same on this pulley and we need these three pieces for the axis i'm really happy with this design because the layers the in this direction so in the direction of the axis in the xl direction and so basically these three pieces make a perfect cylindrical axis and before assembling this axis we need to put the nuts in these holes so like this when the x is assembled we can screw something over here for the axis we need 6707 bearings now our pulleys goes on the axis and another bearing goes over here and on top we need to put this spacer great the second pulley goes on the other side with its own second bearing and with its own spacer again the fit is quite tight so you need to apply some force and this is how it looks two pulleys and this axis runs quite smoothly so i'm really happy with this so far next we will put this assembly over here i'm trying to keep the axis vertical like this the embedded nuts are not going anywhere now i will put the cables to the appropriate holes over here two holes here and two holes there so let's start with this cable because it runs on the outer side now the bowden tubes this tube has a lens 55 centimeters and now this cable goes inside and on this side i'm going to secure it with a bigger clamp and before we continue i would like to make a small test with a bowden cable my idea now i'm going to put this tube straight fix one side over here like rigidly fix it and see what happens when i will bend this bowden cable and to fix this cable i have plenty possibilities because i bought all of this in my hardware local store because i was not sure what would work the best yeah so now cable is straight here no gap so i'm just pull it like this and now i need to tighten these nuts so as you can see over here there is no any gap and here i fix it and so this end over here is seven centimeters and one millimeter so let's try to bend it ah first of all it's way more difficult to bend it you can easily feel that it became more rigid over here i have the one where the end is not fixed and this one is really easily bended no problem and this one is quite rigid actually now let's try to bend it in some excessive way oh yeah it's super rigid and i think there is a lot of force over here so now when it's straight and there is a gap this gap so now the question where this gap came from i think the cable moved inside this bracket or the bottom tube became shorter or the cable became longer let's break it and in order to check this let's check that this distance let's check the distance over here again and now it's six centimeters point seven millimeters six point seven and this end stop moved by uh four millimeters and this is quite impressive because i tighten it really well this is definitely going to make a problem so this problem is basically comes from the fact that button cable when it's bended it's longer so when the bottom cable is like this the straight one it has a certain length and so let's look at the parts of this bowden tube so when we bend this tube it's going to be something like this these gaps over here will appear and will basically the increase the length the middle length of this bowden tube and i think this is a problem anyway let's continue with the assembly over here we need to install the output piece this one so for this piece i need these beadings this is 6710 bearing now these yellow pieces they go inside over here and on the opposite side and afterwards we can install it just need to align everything cool now over here we need to install embedded nuts and to secure the output with the screws there is no big backlash between output and this gear this is good so now the wrist is assembled and we should take care of the other sides of the bowden cables and the other sides of the bowden cables are going to be driven by these stepper motors so for this so first of all we need this piece and we need to install embedded nuts in these four holes now this piece goes on top of our stepper motor and we secure the stepper motor with the four screws over here on our pulley first all four embedded nuts goes here just like this and now maybe you notice that this inner diameter is way bigger than the shaft of our planetary gearbox and this is because i'm going to use these colors and i hope thanks to them this entire pulley piece is going to be stronger i need to align the screw holes with these holes and this one goes on the another side over here and from this side i'm going to use the screw with the head and from this side i'm going to use the headless screw but quite long one and this is because otherwise i don't have the place for the cables i made the hole is quite tight because all the torque is going to be held by these two screws i will use such pieces at the end of the bowden cables to make everything pretty the next we install the cables in this pulley so we need to push the cable through this small hole which i think should be kind of tricky but doable before installing this cable i need to put the washer this washers they're going to be used in order to pinch the cable between them now this pulley goes on top of our motor with the reducer like this and in order to fix the bowden tubes originally i plan to use this system with two brackets like this one so these brackets they have this screw and nut like this this one goes on top and through these two holes i can unscrew this screw and like this i would be able to tension the cable so let me show you this cable goes here this one goes on another side and afterwards i can tension these cables with this screws it seems like a good solution but it's not going to work because of our test which we made so if i will make this entire system rigid so with this rigid screws in this case when i will try to bend the bowden cables some pieces are going to fail so instead of using this rigid screws and this rigid piece i'm going to replace this screws with the springs and this should work but we will see and these are my new pieces with the holes for the spring so this piece goes here the nuts goes on the opposite side now the springs i can put either two over here and here or four over here i have made the holes to assist the assembly like this during the assembly the springs are not going to fly anywhere now it's assembled before securing these sides of the cables we need to align this pulley with this one so basically when this one in the middle this one should be in the middle too i have not yet tightened the pulley to the shaft of the reducer and so now i can rotate this pulley freely and our output moves cool now i have tightened the cables with one screw for each cable afterwards i will tighten also the second screw for each cable now i will release these two screws and like this these two springs they going to tension the cables and if i'm happy i will cut these cables and fix them with the second screw it's tensioned this entire system with the springs does not work perfectly well because when i try to rotate this pulley its entire block moves and there are a lot a lot of friction in the system let me fix this piece there are a lot of frictions yeah it seems like button cable sucks so now you can check the output and i will try to rotate this pulley it works but i need to apply a lot of force like a lot really a lot enormous amount of the friction and now i will untightened this screws so now our springs are going to work and it makes everything even worse you see yeah this design is bad i don't like it i have assembled the second piece so the second stepper with the pulling but this time i put extra grease lubricant inside these bowden tubes and i hope that probably it is going to reduce the friction but the friction is still very high by hand it's uh looks like it's the same like here so lubricant does not help and this is because uh initial cables they were already in the lubricant so this extra lubricant which i put have not made any difference but nevertheless i have two assembled so the problem that if i fix this block in this case i will have the problem when i will bend these cables by the way these cables are quite rigid now and if i don't fix this block in this case i have this problem the ideal would be to restrict the motion of this block just to allow to move it parallel like this but prevent the tilting this would be perfect but it's not easy to do cheaply and in the small space and if i release the tension so for this i need to press the block and to fix it with the screws so now the tension is released and now it's very easy to move this pulley there is no much friction no problem at all now let's see what's going to happen here when i'm going to bend these button cables so now i'm bending it and you see these blocks they move they move inside so this means that you really need to keep these springs otherwise you will break something when i bend this cable the motion is mostly parallel of this block because all the cables they bend more or less at the same way so what i can try to do is to put these covers and like these this covers they're going to limit the motion of this block so the block will go easily parallel but it will be a little bit more difficult for the block to tilt and maybe this will help i have connected our steppers to the electronics to drivers to the stepper drivers because i cannot move this pulleys when the cover is on and it's going to make everything a little bit more fun by the way this is electronics from the old project it has the drivers power supply for drivers power supply for arduino arduino mega switch and two joysticks now the pulleys are fixed to the shafts and let's try to move them you see what happens so in this range the output does not move at all now let's try to solve this problem by installing these colors and i'm going to fix these covers with the screws one two and over here three and now let's see how it works now so i will check that these screws are not tightened they should not in order to allow this block to work and let's try it kind of works a little bit better [Music] [Music] now let's try to bend it the cables are super rigid [Music] i wonder can i move it and bend it at the same time [Music] again no problem this works check the motion of these blocks when i'm going to bend the building cables so you see when i bend the cables this block and this one they go inside and only thanks to our springs this mechanism is not broken because of this motion my overall conclusion button cables are not really good for the robotics at least when you use them like this and there are two main problems first problem is friction when the cable is tensioned the friction is really high the second problem which we kind of solved deals with the fact that when you bend the bowden tube the effective length of this bottom tube increases and yes we solved this and it kind of works but i personally don't like this solution okay this is all what i have for you today please like this video please subscribe to this channel huge thank you to the people who support me via patreon and via youtube channel membership hear their names their support is crucial for the existence of this channel as usual stay safe good luck with your projects and see you next time you

Channel: Skyentific

Views: 66,960

Keywords: robotics, Bowden cable, robot joint, robot actuator, robotic actuator, robot arm, robotic arm, robotic joint, 3dprinted, 3d printing, diy, Arduino, 3d printed

Id: ahSS5HUylT8

Length: 21min 19sec (1279 seconds)

Published: Tue Jul 06 2021