Testing Ball-Shaped Wheels on an Omni-Directional Robot

in part one i designed a ball-shaped omni wheel that can drive in any direction it has one main driven axle which it's mounted on and two free rotating hemispheres which can move independently to allow rotation in the other axis this was inspired by a concept from goodyear for a ball shaped tyre which would allow a vehicle to move sideways while driving and also have a number of other benefits i based my design on some research from osaka university where a team had made a ball shaped wheel attached to an axle however we found that there is also a wheel in the middle of each hemisphere this is required to allow the wheel to move freely when the axis of the hemispheres is vertical because they cannot rotate in this direction the wheel also needs to stay oriented with the main drive axle so it always faces in the correct direction with the hemispheres rotating around it i made a test rig with three of these wheels mounted on it and i was surprised by how freely it ran so today i'm going to finish building the robot and add some drive motors so we can see how well it works in practice [Music] [Music] thanks to 3d fuel for the filament for this project and lots of other projects so check out my channel for more 3d printing projects and check out 3dfuel.com i've got three motors from gimson robotics in the uk and these are a 52 millimeter motor and this is the version with the 13.7 to 1 reduction i've printed pulleys for those motors and i've allowed a screw and a captive nut so we can tighten it up on the 12 mil shaft which has a flat on it so those seem to fit okay i've done this in quite a lot of other projects and i think they'll be more than fine for the load we're going to put on the motors each motor has a motor mounting bracket and i've made a little shim just so i can tension the belt correctly afterwards and make the shims bigger if i have to if the belts stretch and each of those screws down to the existing chassis the motors do have tapped holes in the front face but i've just opted to use a bolt to clamp them into that bracket which means i can move them backwards and forwards to get the belts perfectly aligned and of course there are three of those one to drive each axle of each of the omni wheels with the new mass of the motors installed on the robot i realize that the tpu ring i've got surrounding my little wheel is too flexible and that's going to crush binding on the retaining clip check out part one for more on the assembly of these hemispheres so to stop that happening i've replaced them all with just rigid pla ones printed in almost 100 infill ideally we'd keep those as flexible parts so the wheel can still grip but we need to back them up with something rigid there isn't clearance though in this design so ideally we need to redesign the whole thing but for now rigid parts will do for testing i 3d printed pulleys for the axles on the wheels i have a loud provision for a captive nut and another screw what i'm actually going to do instead is hammer in a hex spacer which is hex shaped into a round hole and that's a really tight fit so i think that'll hold fine then i can just do a nut up against it and that will hold it onto the mh shaft which i'm using as an axle and that's the same principle as holding the wheel on so the belt's installed and that seems pretty tight and i'll have no problem turning that wheel with a motor that's already geared and this is a 610 millimeter length five mil pitch nine millimeter wide htd profile belt on top of the whole thing i've made a round base which will allow us to mount instrumentation or the robot's body in the future so i think that's gonna make a pretty good robot base each motor has a motor driver which is a bts 7960 which will more than handle the current we need and of course there's one of those for each motor i'm going to be using an arduino mega to drive it and i've got an nrf24l01 radio chip attached i'll be using my universal remote which has another arduino mega another nrf24l01 and that's reading the joysticks and the switches and just sending the data straight over i've wired six pwm outs to the three motor drivers so we can drive each wheel in either direction as well as the power from a 3 cell lipo i'm using a usb boost bank to power the arduino so now we just need to work out how to code it up to operate those wheels but before we look at that it's time for a quick ad from the video sponsor which is fan homes build your own large scale replica of tony stark's legendary mark iii iron man armor fan home are a new brand dedicated to developing new collections and build up models from officially fantastic brands like marvel and star wars as well as providing fully illustrated magazines with inspiring content this stunning large-scale replica of iron man's armor is 100 accurate and officially licensed by disney each issue of this limited edition collection comes with pre-cut and ready to assemble parts including an easy-to-follow guide and step-by-step instructions all subscribers will receive amazing gifts during the subscription like iron man posters an iron man cap t-shirt power bank and backpack to celebrate the launch early bird subscribers will also receive a very special gift when you use my unique promo code bruton an iron man bluetooth speaker start your iron man armor or one of fan home's other exciting collections today use the link in the description box of this video to subscribe in your first package you'll receive two magazines and either two figures or two assembly stages with parts from the second package onward you'll receive three to four figures or assembly stages with their corresponding parts and magazines don't forget to use the link in the description to subscribe and use my unique promo code brewton to get your exclusive ironman bluetooth speaker for early bird subscribers driving forwards is easy because we can just move two of the wheels in one direction and ignore the other one rotating is also easy because we can rotate all of the wheels in the same direction and the robot will twist however if we want to drive directly sideways we need to get all of the wheels rotating at the right velocity that's pretty easy to work out though because we can just draw a right angle triangle with one side being where the wheel would be if it was straight and the other being where it actually is which is rotated 60 degrees then we can use trigonometry to work out the ratio in this case it's just a cosine of 60 degrees which is 0.5 so this line is half the length of this one that means that the wheels at an angle need to go half the speed of the one that's straight this may seem odd because they're not facing straight sideways so you'd imagine that they would need to run faster to keep up with the straight wheel but in reality the angle of these wheels causes the robot to twist in its vertical your axis so we need to run the straight wheel faster to untwist it so with that all coded up it's time to give it a test so rotation works okay with all those wheels rotating in the same direction but now let's try driving forward and sideways and that seems to work pretty well as well and also rotation will mix with those axes so we have full omnidirectional travel i'm pretty surprised how well this works on carpet with the small amount of ground clearance we've got on those little wheels on the ends of the hemispheres but that seems to work pretty well so it make quite a good domestic robot and i'm pretty happy with how that's turned out now there isn't much clearance on those little wheels and i was curious to see how well this would work on carpet so i'm going to try and align that wheel so it's perfectly underneath and try driving and seeing what happens so let's roll that wheel so the little wheels perfectly underneath on the trailing wheel and that seems to work well actually so pretty surprised by that but of course as soon as you change and move in another axis then it rolls back onto the bigger hemisphere so it seems to work pretty well the smooth floor is even better for that little wheel so we have even better clearance now with no brittles of the carpet sticking in there it's a bit noisier due to the rigid sections on the wheel but it runs perfectly well so this seems like it could be a good all-rounder for going around the house and doing general duties so i'm pretty happy of how this has worked out it'll be really good to make an autonomous robot out of this that can move omni-directionally and do general household tasks but how about dealing with some obstacles let's try and drive over some mains flex which i've put all over the floor those big wheels seem to handle it pretty well and the probability of catching it on one of the tiny wheels is quite low and even then it seems to work pretty much okay i'll just keep driving over it a few times just to prove the point how about some bits of metal well i suspect it will drive over okay although i could really do with some more grips on my wheels and of course it works better in the driven axis than the passive axis when we catch the back wheel when we're driving forward for instance probably if those discs i'd replace with rigid pla was still tpu it would be a bit better still and there's probably still some better redesigns that we can do with these wheels like removing the large gaps from between the two hemispheres but on the whole it's still better than my roomba what about a plastic box lid this is a bit trickier because it's got a sharper edge and without the grips on the wheels they don't really climb over it very well we'll keep trying though and see what happens hmm not much luck so far let's try again well we can just about get one wheel on if we hit it right but it seems impossible to climb over with two wheels and actually drive over it it is quite slippery though so again with more treads on the wheels made of tpu it'd probably work a lot better all together i'm pretty happy of how that's turned out and how well it runs on carpet as well as a smooth floor i was pretty surprised it works so well with those little wheels in the end and that ground clearance we got which is hardly any so i really like to turn this into an autonomous robot perhaps replacing my other little development platform for little ros experiments see if we can get it to navigate and move only directionally which would be quite a good thing to do we've got this platform on here so we could put something really useful on it like a kitchen bin and that's something that might come up in the future because we've got more projects like that coming obviously there's lots of improvements we should make to the wheels namely getting more traction by having more tpu sections on there probably redesigning it so that ring can be tpu perhaps even printing the whole hemisphere with dual extruder so it's entirely coated with tpu has some texture for traction the other thing is removing the gap in between the two hemispheres which is currently nearly 20 millimeters and the axle is of course only eight so it'd be good to get that to be much smaller perhaps we could just have an aluminium plate of about three millimeters that runs all the way through there and put bearing mounts on each end of that as well as the drive pulley so he could get that gap to be less than five millimeters which would help quite a lot on rigid surfaces but as i said i'm going to publish all the cabin code for this and you can find the link in the description to this video and it's entirely open source so if you'd like to support me through patreon or youtube channel membership then those links are in the description as well and patrons and youtube channel members can get access to all the videos up to a week early so click on that link if you'd like to and like the video and subscribe as well alright that's all for now [Music] you

Channel: James Bruton

Views: 767,471

Keywords: omni wheel, goodyear ball shaped tyre, making omni wheels, ball shaped wheel, 3d printing robot wheels, omni robot wheels, making your own omni wheels, omnidirectional wheels, innovative robot, futuristic robot locomotion, alternative wheel design, TPU robot wheels 3d printing, 3d printing tpu, how to make an omni vehicle, omni robot maths, how to use omni wheels

Id: zKLMCO0-How

Length: 12min 27sec (747 seconds)

Published: Tue May 25 2021