pic: Potential Off Season Drive

[kk052]

Originally Posted by cad321

Yes after all of the comments I have seen above (including yours) I will almost certainly be converting the design for a 4in mecanum. More pros than cons (cant see any cons at the moment).

there are issues with 4 in machanum, as far as i know vexpro is the only place to sell FRC ones, and they had serious issues with wear and functionality if you are going to try 4 inch wheels you should make the wheels vary easily replaceable (between matches you should be able to easily replace one, and you will probably want to make sure you can replace two in five minutes).

[Electronica1]

Originally Posted by kk052

there are issues with 4 in machanum, as far as i know vexpro is the only place to sell FRC ones, and they had serious issues with wear and functionality if you are going to try 4 inch wheels you should make the wheels vary easily replaceable (between matches you should be able to easily replace one, and you will probably want to make sure you can replace two in five minutes).

You have to remember, vex knows this is an issue. I am going to assume the people at vex are going to find a way to fix this for next season, so it might not be a problem.

[Ether]

Originally Posted by Electronica1

You have to remember, vex knows this is an issue. I am going to assume the people at vex are going to find a way to fix this for next season, so it might not be a problem. (I could be wrong)

http://www.chiefdelphi.com/forums/sh...19&postcount=6

[cad321]

Ok, so I have made some revisions to the initial design and am happy about most things but the pistons. In order to prevent having to re calculate the positions of the hard stops, I kept the stroke of the piston the same (1.5") and extended the rod length. My concern though is whether or not the pistons rods will flex under the load of having to lift the bot in the air. Here is a photo of the current setup:



Also, if you'd agree that this warrants concern, what might you suggest as a solution? I'd like to keep the single piston per side to help with keeping weight down and I can't think of a workaround at the moment (perhaps I need more sleep)

Just as an update to the revisions made:

1) Spread the wheel modules apart by 4.5".

2) Swapped the toughbox mini's over to a custom stackerbox.

3) Final speeds of 8.5fps on traction wheels and 21fps on mecanums.

4) Swapped to 4in mecanums, mecanums on the pivot with traction on the outside.

5) Ensured that the pistons now have enough force to lift bot.

6) Taken 1.25" off the top of the side plates to make them 5" (the height of bumpers).

All of the following modifications leads to a loss of 10lbs, totaling in at 40lbs. The only downside I see at the moment to these changes is that by going with the custom spinboxes over the toughboxes, is that I can no longer add 4 775's for more torque if deemed necessary.

Also, on a bit of a side note, does anyone have an idea of when Vex will be re-releasing their 4in mecanums?

[Greg Woelki]

Originally Posted by cad321

The only downside I see at the moment to these changes is that by going with the custom spinboxes over the toughboxes, is that I can no longer add 4 775's for more torque if deemed necessary

Adding 775's to the drivetrain may not be such a good idea anyway. The RS-775 is cooled by a fan on its shaft, so when it stalls or is under high load it stops being cooled and will burn out much faster than a CIM or Mini-CIM, which use their high thermal masses to keep from burning out.

Your drivetrain is power limited in high gear so stall and near-stall conditions should be expected at some times. If you want better acceleration in high gear then you should consider an option that would allow you to add Mini-CIMs.

[cad321]

Originally Posted by Greg Woelki

Your drivetrain is power limited in high gear so stall and near-stall conditions should be expected at some times. If you want better acceleration in high gear then you should consider an option that would allow you to add Mini-CIMs.

This Is something that could still be done with the toughbox mini. They have dual cim mounts. The way I would have incorporated 775's is by using a cim-ile gearbox from vexpro. However yes, I had forgotten about the posts I had read about this topic and the 775's might not be the best idea for continuous use.

[cad321]

Just in case anyone was interested, here is the step file with my current revisions.

[matthew_martin]

This year, my team used a modified Octanum Drive that we called the "Dragonfly." It also used 6" AndyMark HD Mecanums mounted on the outside of the modules with 4" x2" Colsons on the inside of each module. We had no issues with being passed onto our medallion wheels, and with a Vex Pro Ball Shifter with a CIM and a Mini-CIM driving each module,we had more than enough power to spare.

The thing that worries me about your concept is the placement of the pistons that actuate the modules. You could easily bend the shaft or just have one side of your robot on mecanum and the other using traction just from another not hitting you hard and pushing. We had one piston actuating each module with both the pistons on one side mounted to a machined aluminum block.

Our not was an expensive, power hungry monster, but it did its job, and it did it WELL. Here is a link to the CAD files.
And here is a picture of our competition bot! Good luck!