Hi forum,
I know everybody has their opinions on what kind of holonomic drive is best, but what are the pros and cons of each type? Specifically, I am interested in the specific differences between an X-drive and a mecanum drive.
Thanks!
Thanks Cody!
No problem.
Something else our team has looked at besides the force and speed difference is the ability to integrate the rest of the robot onto the chassis. For our case this year we felt it was better to use the X-Drive for mounting a middle post cube arm on due to the front motors being further spaced out for cub and post clearance. We felt it was better to use the mecanum on our dual jointed arm skyrise bot due to allowing for a more narrow base. We felt it better to use an H-Drive for our linear lift bot due to having a stronger support in the middle to use for mounting. Personally I would always recommend a mecanum due to my square personality and it’s better applications in FRC, but to each their own.
As well as the information in the table Cody posted, another thing to consider is how fast the rollers have to move relative to how fast the robot is moving. The faster your rollers move, the more energy you will lose to friction between the rollers and the wheels.
By this measure mecanums are better when going forward, X-drive is better when going diagonally and mecanums are significantly worse when strafing.
I’ve had an x drive this whole year. It is amazing especially when in pushing matches with other robots. Since strafing with the x drive is basically the same as driving forward, we are able to our- power other drives without an x drive.
We have a 4 motor x drive with high speed internal gearing on the smallest (2.5"?) Omni wheels.
They’re 2.75".
Does anyone run a mecanum drive with turbo-geared 393’s? We we’re thinking of going that route, but worried about the effect on torque, particularly when having to push things around with our heavy elevator lift.
How many motors are you using on your drive? I wouldnt even try that with 4. Speed motors would probably give you plenty of speed and power.
How do macanums work with high speed motors? We are currently using omnis on high speed, and a wheel in the middle, but as far as strafing this isn’t the best option, and leads to inconsistent autonomous programs.
If you have a light robot it works well. If you’re heavier you might try custom ratios with sprockets.
You’ve described an H-drive which is usually the best holonomic drive performance wise. I have an H drive and its relatively consistent. If you’re having problems, maybe start another thread (so we dont hijack this one :D) and the community can help.
Luckily there are no problems as of yet, and our robot is very light-weight. I’m just considering making it better at strafing, which we are considering macanums for
I running 269’s on it(at the time of assembly they were the only ones available to us). And even being able to mount them depends on our mentor’s approval. Anyways, you really do think speed gearing is substantially enough?
We are running a 2:1 standard 4 motor 393, so 40 RPM less than the turbo gears, light weight robot (13 lbs.) mecanum drive and have ran into PTC trip issues if we strafe too much during the match. Personally I wouldn’t recommend using the turbo in a competition robot that weighs more than 10 lbs.
I’m don’t know that much about your teams situation, but if can get 393’s, you will be in a much better position. The speed gearing would be plenty assuming you have a light robot. Our Toss up robot was ~24 lbs and ran 1:1.25 as our drive ratio on 4 motor mecanum drive and had to be extremely careful not to overheat our drive.
From what I’ve seen of Skyrise so far, speed is not vital. I’ve used a turbo drive (on 2.75" wheels) and have not benefited as much as I originally thought I would have from the speed. Reliability and stability are much more important.
Bottom line, depending on your robots weight as well as other factors(do you have 393’s, how slow is your lift), you probably want either speed gearing (1:1.6) or a custom ratio with sprockets (1:1.5, 1:1.25, 1:1.2, etc.). Do remember that getting to a post in a second and waiting an extra 6 for a lift to go up isn’t very efficient. Match your robot system’s attributes.
Mecanums aren’t known for strafing abilities, they are usually used because they are the easiest holo drive. That being said, if it works for your team, awesome, best of luck.
One of our teams is using a x-drive with high speed 393’s and the smallest omni-wheels. Very nice setup. Very good speed, good power, no tripping of PTC’s.
I personally do not like the mecanum wheels. They are WAY to heavy and wide. I have never thrown them on the scale, but I would guess that two mecanums weigh almost as much as 4 omni wheels. That extra weight only leads to problems. Your poor motors have to overcome that momentum with every single change in direction. Also, the width of the mecanums makes your entire chassis larger than it really should be in my opinion.