ball shifter vs wcp ds
 

we are doing west coast 6*6 drive train
we were thinking about using 2 cims(maybe 3 but probably 2)and a shifter on the middle wheel and using chains for the other 2 wheels
what is your expirence from both? and what are the pro's and con's u found i each of them?
and about 2 or 3 cims(if 3 cims then also single speed is an option) how muh is the diffrence?

Re: ball shifter vs wcp ds
 

Hi! 3061 built a belt-driven west coast drive last year around the WCP-DS 3 cim shifters, so I'll try to answer some of your questions.

Using your gearbox to direct drive the middle wheel, and running chains/belts to live axles at the ends of the robot, is part of what makes a west coast drive a west coast drive.

Our experience with the WCP ds boxes was very positive. You have to locktite every bolt to ensure that the vibration does not loosen them. We failed to do that and one of our gearboxes threw a CIM. We were not able to replace the damaged gears but they still ran fantastic for 2 competitions and hours of offseason drive.

There are a few differences between a 2 and 3-cim. 3-cim drives have to be careful not to brownout the control system or blow the main breaker at high speeds. They accelerate much faster for a given robot weight, and allow for a faster top speed. I'd reccomend gearing for about 8 and 15 fps in a 3-cim (higher than 15 is ok for high speed if you have current draw limiting software). 2-cims are a safer option- they are very hard to mess up.

Re: ball shifter vs wcp ds
 

I would recommend belts over chain. Direct drive the center wheel with a gearbox and 2 or 3 cim motors and connect the outer two wheels to the center wheel with belts. A wet coast drive is a great choice.

I would recommend using 2 sims and not 3. Using 3 sims would be a little overkill, and has the possibility of burning our electronics. ( a lot of amp use all at the same time) Cim motors also use a lot of electricity, causing your battery level to drop faster. This could result in a brown-out.

Good luck this season and have fun!

Re: ball shifter vs wcp ds
 

Of course we need a wet coast drive for the water game! :yikes:

But in all seriousness, why belts over chain? We have never used belts (never in our team history), and are considering wcd, so is there any particular disadvantage for chain?

Re: ball shifter vs wcp ds
 

You can find pages and pages of arguing for chain drives vs. belt drives. Each can be done effectively as long as teams prepare properly.

This isn't true. As long as your electrical system is wired properly the snapaction breakers and main breaker should protect everything from dangerously high currents.

OP, I recommend you read through this thread before trying out a 3-CIM drive:
http://www.chiefdelphi.com/forums/sh...light=tripping

Also, search through the forums here for team's experiences with 3-CIM drives. They can be very effective and somewhat beneficial, but only if implemented properly.

Re: ball shifter vs wcp ds
 

The thing to make sure of with belts is that you have a precise tensioning solution - like a versablock- in mind.

3 CIMs will not burn your electronics and in fact takes load off of each individual controller in a pushing match at a given speed. That said, make sure not to try and push things in high gear - you'll blow the main breaker.

Edit: Monochron beat me to it! :P

Re: ball shifter vs wcp ds
 

I am just speaking from my experience. Using 6 (3 on each side) cims all at once uses a lot of power and amperage. This puts a lot of strain on your PDP and I have burned one out.

I prefer belts over chain because in my experience chains losses more over time than belts do. Both will loosen with use but chains seem to loosen faster and require more work to keep them tight. Either one will work though. Some people prefer belts and others prefer chain.

Re: ball shifter vs wcp ds
 

I want to bring this up simply because I have not read much on this exact thing. Although belts with the WCD are quiet and smooth, your bound to put yourself in a bad repair if one breaks. From our experience, we had to have a second gearbox ready when using cots transmissions with belts because you cant just put a new belt through metal. We have on the other hand, broke chain and been able to rivet a new, pre-made, chain section in without removing a thing. This might not make a difference when you have 15 minute breaks, but between finals 1 and 2...it is a huge thing.
That being said, we now love WCD and are continuing to try new things with it. Good luck!
-Ronnie

Re: ball shifter vs wcp ds
 

That's a very good point. In my experience I have never had a belt break, although it is good to have a easy way of fixing it if a belt does break.

Re: ball shifter vs wcp ds
 

I have no experience with the VexPro Ball Shifter, so I won't go over that.
I have had plenty of experience with misaligned axles and sprockets, wobbly bearings, etc.

WCP's gearbox is designed such that if it's mounted on the centerline of a 2x1" rail, it's really hard to mess it up, no matter how much you over-think the drive train design. The mount holes of the WCP block for the output shaft have to be fairly precise, but the outer two mount holes have some tolerance.

When combined with the VersaBlock kit sliding bearing block, you can make a precision WCD drive train without the frustrating time wasting mumblings that come with messing up a non-DRO manually milled part by 0.03". Note that you want the WCP gearbox to be on the centerline of the rail, as the VersaBlocks have the "wheel drop" built-in to their design - the wheels mounted to these are raised by 0.06" (which, by the way, means you can place a precision-aligned raised wheel using just a hole saw).

As for chain vs belt - the WCP gearboxes have appropriate space for chain, but I don't know if they can do belts without some modification. The WCP gearboxes also come with wave washers to dampen axial vibrations which cause chains to pop off under a variety of loads. CAD it out first if you have your heart set on belts.

Re: ball shifter vs wcp ds
 

It is incredibly unlikely that your PDP burnout was caused only by amperage strain from 6 CIMS. It is important that the OP knows that.

Re: ball shifter vs wcp ds
 

^ This. I won't speculate as to what caused the failure, but remember that the FRC control system's main breaker is designed to blow before the amperage gets high enough to damage anything else. You will blow the main breaker or 40A breakers before you do damage to your system.

Re: ball shifter vs wcp ds
 

After talking extensively with several teams who run 6 CIM West Coast Drives, this is what I've found out:

1) It's not a problem anymore, but the CRio had a minimum voltage shutoff (under 5 volts). One team changed this down to a more manageable number and had no problems whatsoever with brownouts.

2) The most important thing to watch is the current. At the moment, my team has code written that detects if the current draw to the motors is over a certain interval that would also blow a breaker. If this happens for a certain period of time (it's something like 1 or 0.5 seconds) the motors automatically shift down and stay there.

3) If 6 CIMs is too much voltage, you could always swap out 1 or 2 with mini CIMs. They have the same rpm, just less torque.

Speaking as a driver, though, the 6 CIMs are well worth the risk once you get out on the field and can push people around. Just make sure you have easy access to your drivetrain in case anything breaks. Didn't do it last year and ended up spending over an hour to change a blown CIM.

Re: ball shifter vs wcp ds
 

How exactly did that team change the brownout voltage of the cRIO?

Re: ball shifter vs wcp ds
 

This is still a problem. The RoboRIO cuts the PWM/CAN outputs below ~7V, which can happen quite frequently under certain conditions. See: http://www.chiefdelphi.com/forums/sh...d.php?t=131593