pic: Recycle Rush Re-design Part 2

[mman1506]

Originally Posted by GeeTwo

That would be "leaving the downstroke unpowered", which has been considered and largely discarded. Unless you have a separate mechanism to engage and disengage from the tote, your downstroke will have to work against some sort of spring action to get around the top edge of the tote. For reliable action, either the down stroke needs to be powered, or a spring return is needed, or the carriage must be heavy enough to force through the ratcheting action.

That's not hard. The weight of the shaft alone will probably be enough to overcome the friction of the cylinder. Anyway Ari423's reasoning for not powering the downstroke was not due to friction but due to the solenoids switching restrictions (what I'm questioning).

[Ari423]

Originally Posted by mman1506

That's not hard. The weight of the shaft alone will probably be enough to overcome the friction of the cylinder. Anyway Ari423's reasoning for not powering the downstroke was not due to friction but due to the solenoids switching restrictions (what I'm questioning).

Well the reason I gave was solenoid switching restrictions, but it was actually more than that. We did devise a method of dealing with the solenoid. When we tried using in without any down pressure, it worked but it was painfully slow when only lifting one tote. Gravity just wasn't strong enough to overcome the friction (granted we also had a pulley system to make sure both sides were the same height that could have added some friction). We settled on about 15 psi of down force, which was below the rated min pressure but it worked out ok. Perhaps with a strategy where you lift 2 totes minimum you can get away with a lower pressure or even no pressure.

[Chris is me]

Originally Posted by Ari423

Well the reason I gave was solenoid switching restrictions, but it was actually more than that. We did devise a method of dealing with the solenoid. When we tried using in without any down pressure, it worked but it was painfully slow when only lifting one tote. Gravity just wasn't strong enough to overcome the friction (granted we also had a pulley system to make sure both sides were the same height that could have added some friction). We settled on about 15 psi of down force, which was below the rated min pressure but it worked out ok. Perhaps with a strategy where you lift 2 totes minimum you can get away with a lower pressure or even no pressure.

You definitely either have too much friction, or you have the wrong flow control valve installed. This is a great application for one-way flow control valves, which restrict air going in but not out. My team had a stacking mechanism that would quickly and easily lower itself even without the weight of any totes on it; unless you have an extremely inefficient system this should work fine.

[Ari423]

Originally Posted by Chris is me

You definitely either have too much friction, or you have the wrong flow control valve installed. This is a great application for one-way flow control valves, which restrict air going in but not out. My team had a stacking mechanism that would quickly and easily lower itself even without the weight of any totes on it; unless you have an extremely inefficient system this should work fine.

I can't quite speak for the mechanical aspect of the system, as I had no hand in that. I only worked on the control aspect of the system. And since I'm the only member of my team on CD, I don't expect we'll ever get a good answer as to why our system had so much friction.

I was under the impression that one-way valves were illegal. Is that not true?

[GeeTwo]

Originally Posted by Ari423

I was under the impression that one-way valves were illegal. Is that not true?

In 2015, Rule R66 F allows (among other things) flow control valves as pneumatic components. Festo's page of one-way flow control valves describes the same thing Chris is describing - allowing free air flow one direction, throttled flow the other. There does not seem to be a rule allowing check valves, which allow air to travel in one direction but completely prevent airflow in the other direction. Apart from the interface between an external compressor and the robot, it is difficult to come up with an application for a check valve that complies with 2015's rule R78, which has been a game rule for some time:

Originally Posted by 2015 Game Manual

R78 Any pressure vent plug must be:

• A. connected to the pneumatic circuit such that, when manually operated, it will vent to the atmosphere to relieve all stored pressure in a reasonable amount of time, and
• B. placed on the ROBOT so that it is visible and easily accessible.

If the compressor is not used on the ROBOT, then an additional pressure vent plug must be connected to the high-pressure portion of the pneumatic circuit off-board the ROBOT with the compressor (see R68).

[GeeTwo]

Originally Posted by Ari423

Also for the OP, if you do decide to go with pneumatics as GeeTwo suggested, you can move the PCM onto the tethered bot. Then you can decrease the tether to two wires (power and CAN). The power wire has a pretty low amperage when not running a compressor, so if you make it a big-ish wire you shouldn't see too bad of a voltage drop.

I wanted to share my reasoning for putting the PCM on the robot side. Either way has benefits and costs relative to the other.

• The way I set things up, all of the wires carried simple DC signals that switched on the order of a second. CAN carries rather faster switching, so I wanted to leave it just on the main hull. I've since checked CAN lengths, and you should be OK running from one hull to the other, and even back. However, to simplify things and reduce losses, I would use an external terminator on the stacker end rather than bring the line back to the robot for termination at the PDB as most teams usually do.
• I didn't want to run CAN down the tether, because it's inherently more vulnerable. I was worried that if something happened to the tether, the whole robot might freeze up. If you are using PWM for motor control, this may not be an issue for you.
• I didn't want to run compressor power down the tether. There are workarounds, including a spike relay on the main hull side, and using a "tether bypass" when filling the tanks*. Still, much less current is required to power a compressor than some CIMs.
• Note that even with the PCM on the stacker hull, any limit switches or other sensors (except the pressure switch) still have to go back to the 'RIO. Limit switches and thoughtful design can significantly reduce the amount of air needed.

* I haven't found any rules in 2015 that would have prohibited making internal electrical changes (e.g. disconnecting the tether and wiring directly across it using molex or Anderson power poles) during pressurization process. Just make sure you put things back! The more steps in a checklist, the more likely something will get missed.