Second Year Problems - Response

[drdanielfc]

This is an unofficial response to this thread which was posted in the official answers section. Ordinary users cannot respond in that section.

I am currently in my second year with implementing the VEX Robotics into my classroom. Last year was a trial year of just getting adjusted to the kits and learning how to build and program them. This year I ordered new motors, batteries, structural pieces and VEXnet keys for all four of my robotics kits.

My class this year just finished building their Protobot and we are trying to do a competition right now but we are having no success. Problems are the only things that are occurring.

This sounds an awful lot like our first year :o

Motors are dying, running slow, not strong enough to lift the arm.

This is usually because you are putting too much strain on the motors. You may want to consider using a different design for the arm or gearing for more torque.

Some helpful links:

1. Motor Overheating Info
2. Lift Designs
3. Gear Ratio Tutorials

A common problem for newcomers is forgetting to use a bearing flat on the axle to the motor. This significantly reduces the amount of friction the motor needs to overcome. Not sure if this is your issue but just throwing it out there.

Batteries are constantly dying, even though they were fully charged.

An excessive load on the motors can kill the batteries very rapidly. A 393 Motor can pull up to 4.8 amps when stalled (ie given full power but not able to move). According to some battery load tests, this means that with 2 strained motors, you’ll be encountering issues after like 2 minutes with the 2000mAh batteries.

Also, it is not unusual to have to change batteries fairly often. We use the 3000mAh and generally change them after every 1-2 practice matches. In other words, 2-4 minutes of use.

The biggest problems seem to be the connection status with the VEXNet controller and the Cortex. All the robots will only hold a connection for a few minutes at most. The VEXNet light is constantly flashing Green on the controller and Cortex. I have tethered them, switched keys and tried to reconfigure them. None of these solutions have worked.

Most likely related to the battery. VEXNet is infamous for behaving poorly without enough voltage. You may want to try using a 9V battery backup as it helps with intermittent connection issues.

Also, we typically don’t run our robots connected to vexnet for “a few minutes.” You should really only use vexnet for when you need to run the robot wirelessly and turn the robot off while working on it. We also use the orange tether cable for just quick tests where we don’t need the wireless.

It is too early in the year to be getting this frustrated with the kits so any suggestions or answers would be greatly appreciated. Thanks.

Robotics is extremely frustrating. Our first year we didn’t score a single point in any competition and the second year we had countless problems. I realize it seems like “I have so many problems now, I’m just gonna have more later,” but really it’s more like:

1. Tons of issues at the start
2. Most of the issues get fixed, everything works fine
3. Nothing works at competition

I very well may be wrong on some of this but fixing these problems is where I’d start. If you have pictures of the robot, we would be more than happy to point out specific things we notice may need changing.

I hope you get this all squared away and have an excellent season!

[Team80_Giraffes]

In addition to those great suggestions…

You may want to invest in a battery beak. This can tell you spent batteries that don’t hold a charge any longer. Misuse of the fast setting can make batteries not hold charges as well. Batteries were described to me once as an art, not a science.

http://www.crosstheroadelectronics.com/Beak.html

It’s over $120 though.

Also, we too have problems with too many wi-fi signals in a small space with metal rafters and roof bouncing signals all around. Limiting the wi-fi of cell phones in your class and other wi-fi signals might help. Vexnet is on a very common negotiation channel for wi-fi. This is why they say no wi-fi at worlds I believe.

Lastly, do you encourage using rubber bands to assist the lifting? Even the protobot arm might like a helping hand. Skipping comes from not bracing well enough. Friction creates general malaise in lifting ability. Bent shafts create more frcition too. Friction is always a bear to deal with.

[edjubuh]

The biggest problems seem to be the connection status with the VEXNet controller and the Cortex. All the robots will only hold a connection for a few minutes at most. The VEXNet light is constantly flashing Green on the controller and Cortex. I have tethered them, switched keys and tried to reconfigure them. None of these solutions have worked.

This may also be an issue related to the program you’ve loaded on. If it’s not in the correct mode, the robot will automatically time out after a few minute in order to simulate competition.

If the 9V battery doesn’t fix the VEXNet issue, try running the robot as you normally would, but using the USB cable, rather than wireless. If the robot still stops operating after a couple minutes, then you might also want to post your code and what programming environment you’re using (easyC, ROBOTC, etc.)

The suggestions you’ll see above this post (and likely below) are blanket recommendations we’ve seen from newcomers. In order for us (the VEX Forum community) to better help you, I’d recommend posting some pictures of the robot so we can take a closer, more informed recommendation.

[Ephemeral_Being]

Another thing about VEXnet keys; they’re fragile.

We were talking to the field tech support guy (sorry, I can’t remember his official title. Incredibly helpful, though) for our division at Worlds because our Keys would not stay connected during a match. We were literally spending 15-20 seconds of each one waiting for the keys to talk. It turns out that any sort of banging at all is enough to cause them to begin to loose connectivity. We kept ours stored loosely in the lid of a toolbox, and apparently the sliding around they do there is enough to cause damage. Something like a 7-9% error rate is acceptable, and when he was testing them we were at 40-60%, I think is what he said.

Ship them in. VEX has a process where they will test your keys to determine if they are broken. If so, most commonly they will replace them at no cost to you other than shipping. It takes a few weeks, but it’s a great help.

As for your motors burning out, show us the mechanism and we can offer more help.

[jpearman]

To add a little more

Motors are dying, running slow, not strong enough to lift the arm.

The motors are doing too much work and tripping either their internal PTC or the one in the cortex.

Which motors do you have? What configuration are you using on the arm, what is the gearing, how much are you trying to lift? Photos would help.

Batteries are constantly dying, even though they were fully charged.

Which ones do you have? I find that a standard VEX 3000mAH battery is good for 10-15 minutes of use, sometimes longer.

The biggest problems seem to be the connection status with the VEXNet controller and the Cortex. All the robots will only hold a connection for a few minutes at most.

May be environmental, any changes at the school? WiFi blockers? Other sources of RF interference (microwave ovens) ? Have you tried swapping keys around? sometimes I find that just swapping the two keys between joystick and cortex actually helps (which doesn’t make any sense I know).

The VEXNet light is constantly flashing Green on the controller and Cortex.

err, it’s supposed to, that’s normal (when using VEXnet). You can see this in the first post (first example) of this thread.
https://vexforum.com/showthread.php?p=326053#post326053