Mecanum Advice Request

[jblay]

We are considering having mecanum this year and were wondering what the subtleties of it are. Anything and everything would be helpful such as what gear boxes to avoid, what ratios would be best or various problems with programing.

[Duke461]

Originally Posted by jblay

We are considering having mecanum this year and were wondering what the subtleties of it are. Anything and everything would be helpful such as what gear boxes to avoid, what ratios would be best or various problems with programing.

This is our (461) second year in a row that we are using mecanum; i don't know a whole lot about it, but i do know that:
Much better maneuverability
Less pushing force
Harder to program/longer
Problems can occur with a direct drive setup and thoughbox nanos, because it pushes the bearings with a force and direction they're not designed to take.
But all in all, if you're programmers and drivers are up for it, it is a great choice

[TubaMorg]

You ask a broad question with many details that is difficult to answer succintly. Specific questions are better in the forum format. However, there have been quite a few threads that address ALL of your sub-questions in some form or another. The technology hasn't changed since those discussions were posted. Also, there are a couple of white papers that discuss the physics behind mecanum drives.

[jblay]

Originally Posted by Duke461

Problems can occur with a direct drive setup and thoughbox nanos, because it pushes the bearings with a force and direction they're not designed to take.

We were considering using the nanos. Have you tried using them? What went wrong if you did?

[Red One]

Team 2950 used a 4 wheel drive combination of two Mecanums in the front and two Plactions in the back for a mix of great maneuverability AND traction in Breakaway last year. It worked out very well for us and could be good for your team as well.

[Chris is me]

I've heard good things about direct drive + Toughbox Nanos in mecanum drives, as well as regular Toughboxes.

[Duke461]

Originally Posted by jblay

We were considering using the nanos. Have you tried using them? What went wrong if you did?

Well, we haven't tested them out yet, but the mentors noticed that the bearings might not be able to take the 45 degree angle load from the direct mecanum drive, at least for the nanos. we aren't 100% sure yet, but it's definitely something to look into

[Dracon Phinex]

If you want an agile bot, go ahead. The team I'm with wanted to do mecanum wheels, but decided not to because of programing issues tied up in it. The ideas are great, but are not very good for newer teams. The frame might have to modified in order to do this.

[Dad1279]

Last year 1279 used 8" mecanums, direct drive to long output shaft nanos, 12.5:1. We used a bearing on the other side of the long shaft.

My suggestion is get it done ASAP, so the driver(s) have time to train, and programers have time to program it. We actually built a test bot using a second set of Mecanums, using a 3/4" plywood base fot driver training and programming.

[jblay]

Originally Posted by Dad1279

Last year 1279 used 8" mecanums, direct drive to long output shaft nanos, 12.5:1. We used a bearing on the other side of the long shaft.

My suggestion is get it done ASAP, so the driver(s) have time to train, and programers have time to program it. We actually built a test bot using a second set of Mecanums, using a 3/4" plywood base fot driver training and programming.

We are planning to do the same thing except with a legit second drivetrain.

Our plan is to use the 6 inch mecanum. Is the 8.45:1 ratio to slow? I know that mecanum is inefficient and will lose some of that speed but how much?

[Chris is me]

Originally Posted by jblay

Our plan is to use the 6 inch mecanum. Is the 8.45:1 ratio to slow? I know that mecanum is inefficient and will lose some of that speed but how much?

Nope. For reference, 12.75:1 with 6" wheels is ~9 feet per second.

[BigJ]

If you have an algorithm that translates in every direction the same, you will get about 71% ( sqrt(2)) of full power from your motors when going forward with no other modifications. 1675 usually includes a "beast mode" for going stright forward/back with 100% power.

[Duke461]

Going on the topic of bearings, and this might sound like a stupid question, are spherical bearings ever used (as opposed to the traditional ball bearings)? and if so, what are the pros and cons respectively?
thanks
-duke

[Jogo]

Originally Posted by BigJ

If you have an algorithm that translates in every direction the same, you will get about 71% ( sqrt(2)) of full power from your motors when going forward with no other modifications. 1675 usually includes a "beast mode" for going stright forward/back with 100% power.

Can you further explain this? Why would you only get 71% when going forward?

[Creator Mat]

If you are direct driving a mecanum drive or any drive for that manner, make sure you support the shaft in two places. If you don't you'll bend your shaft and destroy your drive train. The tough box series from andy mark does have two support points internally and you can get away with no external supports on the shaft for short distances. However if you use an extended shaft you'll just kill the gear box and the shaft if there is no support on the other end of the shaft. My team used mechanum last year and used the P80 gear boxes with an extended shaft. It was extremely efficient, had good mount points for the encoder, and we had no problems. Hope this helps