The geometry of those wheels is interesting. I just spent a few hours investigating using OpenScad.
Wow, thanks for this insight ceptimus. You know on a flat surface, there is very little contact at any one time. These must use a lot more energy than a regular wheel set-up.
Wow, thanks for this insight ceptimus. You know on a flat surface, there is very little contact at any one time. These must use a lot more energy than a regular wheel set-up.
I assumed the same thing but Rich convinced me otherwise.
If the wheels are used just to propel the vehicle forward, you don't loose any of the wheel's motion to the rollers.
While speed isn't lost, I bet Mecanum wheels don't provide as much traction as many other wheels.
Not sure why "very little contact" equates to using a lot more energy. It is actually the other way around. Think of tires. You want them inflated so that the contact patch is as small as possible to be most efficient.
Tractive force is another matter, and difficult to compare. The Vex Mecanum wheels have sufficient traction to stall the motors that I use - 53:1 gear motors. My robot is moderately heavy so if it were to be built lighter then I am sure the motors could cause them to break traction much more easily. As it is I am not wanting for more traction.
On loose surfaces the Mecanum will have a disadvantage due to the small contact patch, but on soft surfaces some advantage is gained back by the "knobbiness" of the wheels. In regular applications, you will not see a significant traction or efficiency disadvantage by using Mecanums. Of course they don't roll as smoothly as regular wheels and they also have a moving contact patch which will make accurate odometry more of a challenge.
If you have a 3D printer you can use a 'mirror' function to print both handed wheels. You have to print 14 of the half-rollers for each hub and you need 14 M3x30 socket head cap screws and 14 plain M3 washers per wheel. I designed the hub to take a 5mm shaft with M3 grub screw holes for retention. A Nema 17 stepper motor fits snugly inside the 'dish' on one side of the wheel formed by the projecting rollers, which means the wheel can fit close up against the motor without having a long unsupported motor shaft.
I've not actually printed these wheels myself yet, so I don't know how they perform.
What type of filiment do you plan on using, maybe ABS for the hub, and something else for the rollers.
One thing you have to think about,
Is the plastic suitable for tire use? If it doesn't have some grip, you could end up with flat spots.
What do estimate cost per wheel including hardware, no motor?
I've only ever printed using ABS or PLA. My printer is capable of using other filaments that may be better for the rollers, but I've never tried those. It will be very cheap, quick and easy to print out new rollers, and replace worn or broken ones - or even a complete new set - so I'm not too bothered about wear initially, providing the wheels actually work!
I've ordered some motors and stepper drive units to build a new robot that uses these wheels. I got the lowest cost ones I could find which means I have to wait a few weeks for them to arrive from China - but that gives me chance to write the control code. I'll post a video if and when I get the robot working. I expect that will be in June or July.
Comments
Wow, thanks for this insight ceptimus. You know on a flat surface, there is very little contact at any one time. These must use a lot more energy than a regular wheel set-up.
I assumed the same thing but Rich convinced me otherwise.
If the wheels are used just to propel the vehicle forward, you don't loose any of the wheel's motion to the rollers.
While speed isn't lost, I bet Mecanum wheels don't provide as much traction as many other wheels.
Tractive force is another matter, and difficult to compare. The Vex Mecanum wheels have sufficient traction to stall the motors that I use - 53:1 gear motors. My robot is moderately heavy so if it were to be built lighter then I am sure the motors could cause them to break traction much more easily. As it is I am not wanting for more traction.
On loose surfaces the Mecanum will have a disadvantage due to the small contact patch, but on soft surfaces some advantage is gained back by the "knobbiness" of the wheels. In regular applications, you will not see a significant traction or efficiency disadvantage by using Mecanums. Of course they don't roll as smoothly as regular wheels and they also have a moving contact patch which will make accurate odometry more of a challenge.
If you have a 3D printer you can use a 'mirror' function to print both handed wheels. You have to print 14 of the half-rollers for each hub and you need 14 M3x30 socket head cap screws and 14 plain M3 washers per wheel. I designed the hub to take a 5mm shaft with M3 grub screw holes for retention. A Nema 17 stepper motor fits snugly inside the 'dish' on one side of the wheel formed by the projecting rollers, which means the wheel can fit close up against the motor without having a long unsupported motor shaft.
I've not actually printed these wheels myself yet, so I don't know how they perform.
What type of filiment do you plan on using, maybe ABS for the hub, and something else for the rollers.
One thing you have to think about,
Is the plastic suitable for tire use? If it doesn't have some grip, you could end up with flat spots.
What do estimate cost per wheel including hardware, no motor?
Looking forward to updates on your project.
I've ordered some motors and stepper drive units to build a new robot that uses these wheels. I got the lowest cost ones I could find which means I have to wait a few weeks for them to arrive from China - but that gives me chance to write the control code. I'll post a video if and when I get the robot working. I expect that will be in June or July.