Problem with Propeller BOE reset

bellshapedhead

Last weekend I bought a new Propeller BOE from a local store (Micro Center) with the intention of replacing the original basic stamp BOE. Since I was not familiar with the Propellor, I followed the initial training information on the learn.parallax.com site. I ran into problems when I started trying to run the Test Full Speeds spin code:

OBJ

system : "Propeller Board of Education"
servo : "PropBOE Servos"
time : "Timing"

PUB Go | i

system.Clock(80_000_000)

servo.Set(14, 200)
servo.Set(15, -200)
time.Pause(3000)
servo.Set(14, -200)
servo.Set(15, 200)
time.Pause(3000)
servo.Set(14, 0)
servo.Set(15, 0

When I run the above program, the Prop BOE seems to execute only the first two servo statements and the pause, then it resets and repeats the first two servo sets and the pause then resets......indefinitely. This occurs with the the Prop BOE pwr switch is in position #2.

If I add the following code (with references to the pin object)

pin.High(9)
time.pause(200)
pin.Low(9)
time.pause(200)

to the end of the program and run it with the pwr switch in position #1, the program runs till completion and pin 9 lites after approximately 6 seconds (the delay). It does not appear to reset in this case

I suspect that something is defective with the board but is there way to perform a definitive test? If anyone out there has any ideas it would be appreciated.

jazzed

Do you have fresh AA batteries in your BOT?

Mike Green

What happens is that the servos draw a lot of current when they're starting up and you're trying to start up two of them. If the batteries are marginal, that will cause the output voltage of the battery pack to drop below the point where the BOE's power supply can keep the Propeller working and it resets, thus starting the program over again after a few seconds. The few seconds gives the batteries time to come up in voltage ... and the whole process starts over. Using switch setting #1 disconnects the servo motors and the Propeller itself doesn't draw that much power, so the program finishes.

bellshapedhead

Thanks for the responses. The batteries are new AA batteries and I have tried two new sets (batteries purchased recently). I am assuming that the Propeller BOE should work from the same source as the original (which is the way it is set up) (6.0v). I have also run the test using 4 NiMH batteries (5.0 v). Same results.

I performed two additional tests this afternoon.

Removing one servo connection and running the same program causes the second set of servo commands to be executed and the program appears to terminate (since the led flashes). However the servo never stops after executing the second set of servo set instructions.

I have moved the server connections to all of the servo pins 14-19 and I have used servos from two other BOE Bots. All have exactly the same effect.

What am I missing?

bellshapedhead

Follow-up..... It appears I must have run into a batch of bad batteries. I ran out and bought a new set of batteries shortly after dinner. After my last post I went to my workbench and replaced the *new* batteries in the boe-bot with the NEW batteries I had just bought. Problem is now gone.

I guess i know where I will be buying my batteries from now on! Sorry to bother you guys.

One final thing... Should I be able to run the drive servos and a ping sensor servo off of the same set of batteries or should I look to a different power solution?


Thanks again

Mike Green

I don't have access to the source files at work for "PropBOE Servos" or "Propeller Board of Education". I assume "PropBOE Servos" is a modification of "Servo32v6" or something similar. Make sure you've called the initialization method before you call servo.Set(). "Timing" may also need initialization. The advice to check your batteries is sound since it's often the cause of the kind of behavior you're seeing. I'll have a look at the code in a few hours if no one else has been able to help you by then.

Duane Degn

I use this Li-Ion pack with my PropBOE-Bot but I'd think four NiMH AAs should be okay.

One problem I've found when using four NiMH AA cells is the voltage can drop over time making navigation difficult.

With my CheapBot, I used four Li-Ion AA and a 5V regulator so the servo speed would be consistent from one run to the next. I'd think the regulator on the PropBOE might take care of the voltage regulation for you but I still think four NiMH AA cells is on the low end of acceptable power for your robot.

Mike Green

Four NiMH AA cells are a little pokey for a BoeBot. Their nominal voltage is 4 x 1.2 = 4.8V. I would use 5 cells (5 x 1.2 = 6.0V). Parallax sells a single AA holder that wires in series with the standard 4-cell holder. I bought one similar single AA holder from RadioShack for my BoeBot and glued it on the top of the platform in the rear over the pivot ball.

Servos can draw up to 1A or so when starting up or under heavy load. 2A is a big load for AA batteries even though the current drops quickly as the motors begin to move. Parallax's LiIon Pack is great and mounts (tightly) in the space under the BoeBot in place of the standard 4-cell holder. I recommend it, particularly if you're going to use your BoeBot a lot.

The Propeller BOE is designed to be able to supply two servos at least in addition to the circuitry on the board. Normally, when you add a PING))) and its servo bracket, the PING is not used at the same time as the wheels because you don't want the BoeBot to be moving significantly while you're trying to measure distance, so the current drain is that for two servos at a time plus the BOE.

Ken Gracey

You could call us and order one of these 5-AA packs http://learn.parallax.com/node/183 or get the 7.2V Lithium Ion rechargeable. Then you'll have more than enough power. Here's the link: http://www.parallax.com/Store/Accessories/PowerSupplies/tabid/165/ProductID/782/List/0/Default.aspx?SortField=ProductName,ProductName and here's an example of it in use http://learn.parallax.com/project/juke-bots-propeller-robots.

A bit more voltage, current and capacity will make your robot projects so much easier. These servos can pull up to a half-amp if you've got two drive servos and one for the Ping))). And the Ping))) can be a bit of a pig as well. Just stuff the system with power and put this problem behind you.

That's my suggestion.

There's a whole lot of great stuff in store for Propeller Boe-Bot owners in the future. Can't say more. . .

jmg

bellshapedhead wrote: »

I am assuming that the Propeller BOE should work from the same source as the original (which is the way it is set up) (6.0v). I have also run the test using 4 NiMH batteries (5.0 v).

A simple sanity check for Suspect-Power issues, is to run TWO battery packs :
One powers just the CPU, and the other powers the Motors.
If that gives a large difference and a clean-up in behaviour, you know it it Load/Vcc interactions.

bellshapedhead

Thanks for all the feedback everybody. I think I'll order the 5 pack first. I have dozens of 2500mAh NiMh AA batteries that I need to put to use.

Phil Pilgrim (PhiPi)

In my experience, if you buy batteries from Costco, stay away from the "Kirkland" brand. They just don't seem to last as long as Duracells. I still have a few of the Kirkland AA's, but I never put them in anything that has a higher-than-average current or lifetime requirement. The extra money for "real" alkalines is well spent, IMO.

-Phil

NikosG

Hi,

I had similar problems with batteries. To make things better I asked from a local shop to make for me a pack from 6X1.2 v researchable batteries. I asked them to arrange the batteries in appropriate way in order to fit perfect on Prop boe’s chassis. (as you can see I have made a “Π” holder in order to adapt the pack into the chassis.



On the existed hole of the chassis I also added a small on off switch. For the charging I don’t remove the pack from the robot. I use a charger and a homemade connector in order to connect the batteries pack’s cable with the charger.


Edit: I'm looking forward to see what Ken has made for us with the news accessories for the Propeller Boe-Bot!