AM servo delayed or no shifting

[haroony341]

working with a rookie team this year, we decided to go with the Gen 2 AM 2 speed servo shifters. 2 years prior while working with 341, i worked with the pneumatic shifters but because of weight, 2234 wasnt able to have a pneumatic system. during the build season we were able to get the servos working but had trouble on our last day of testing before ship. the right side's servo didnt seem to be powerful enough to shift. it can be seen struggling. at chesapeake, our first regional, i switched out the servo. but it still need help. using a 2 stick tank drive, we had to shake the joystick to help the servo shift up. we added grease, it got a little better but still have delay issues. there is about a 2-5 second shifting delay of both gearboxes. we also have issues where it will shift when we are tethered but doesnt always work through a radio connection when we are on the field. does anyone have any suggestions we can try when we get to atlanta? could it be a programming problem?

thanks in advance

[Hieb]

It could be a programming problem, although without seeing the code I couldn't really say for sure. One thing to check is the charge on your backup battery. The servos are powered by the backup battery, so when it is run down they don't shift well. From 2014s experience, the AM servo shifters worked great with no noticable delay in the shift. And if it does turn out to be the state of the backup battery, consider the charging circuit from IFI--that way you make sure you are running off of a full charge when you need to shift.

[haroony341]

Originally Posted by Hieb

It could be a programming problem, although without seeing the code I couldn't really say for sure. One thing to check is the charge on your backup battery. The servos are powered by the backup battery, so when it is run down they don't shift well. From 2014s experience, the AM servo shifters worked great with no noticable delay in the shift. And if it does turn out to be the state of the backup battery, consider the charging circuit from IFI--that way you make sure you are running off of a full charge when you need to shift.

generally how long does a backup battery last? we waont be able to make the circuit in time, also, what is the best method of charging the batteries? i know you can just leave them on the charger for an extended period of time.

[Alan Anderson]

Originally Posted by haroony341

generally how long does a backup battery last?

If you're using the camera, not very long. Using this year's yellow battery, we'd get less than a half hour of total time before the camera got flaky, and the servos lost strength shortly afterward.

also, what is the best method of charging the batteries? i know you can just leave them on the charger for an extended period of time.

Do not leave them on the "charger" supplied in the 2007 Kit of Parts! It is certain to overcharge them, and likely to damage them. The best method is to use a true charger designed for a 7.2v NiCd battery pack, like the ones supplied in 2006 and 2005.

We use the IFI-approved (but not IFI-supported) on-board charging circuit. It's very liberating to not have to worry about charging the backup battery. This is likely to be especially important at the Championship, as the RC will stay running on backup power for quite some time after the main breaker is switched off following a match, and the long walk back from the field means the pit crew won't be able to notice it and shut it the rest of the way down quickly.

[Mark Pierce]

Originally Posted by haroony341

generally how long does a backup battery last? ... what is the best method of charging the batteries?

The useful charge on a backup battery varies a lot based on usage. we're not using a camera or servos this year and we could run all weekend on a single charge, last year's lasted about two or three matches, (a servo and a camera).

We've had good luck using the pre-2007 chargers. If you don't have one available, stop by Team 85's pit in Archimedes. I'm pretty sure we still have two in the tool box (on it's way south already). It's quite easy to monitor the backup battery voltage on the operator interface. We like to see a voltage of 7.8 volts before starting a match.

[Tom Line]

We went through camera battery issues as well.

We had problems with the IFI circuit. We had the program set up to charge when the battery dropped under 7 and to stop when it was over 8.5 (at least I think that was my last code, I'd have to check). It will attempt to charge the main battery with the small one when the main voltage gets low. We actually had many instances where our little cruddy yellow batteries were drained from a full charge by the main battery during testing from the IFI circuit.

Likewise, they don't take much charge to begin with, and the supplied chargers will nuke the battery if you're not carefull.

We ended up removing the charging circuit from the robot in annoyance.

A much better solution, if you can can stand to part with $30, is to go to radio shack and pick up one of the 7.2 hi-amp hour batteries for radio control cars. They come with an auto-sensing charger. Then use the yellow battery for testing, and the hi-amp battery for competition. The charge on one big one easily lasted us an entire day of competition running only the camera.

One other thing. We found that if you push reset on the robot controller after killing main power, it will stop pulling from the backup battery as well.

[efoote868]

We used the AM servo shifting, and didn't have any problems.
When we wrote our code, we didn't bother trying to find the value which made the servo shift left or right... we went with 0 and 255 (if the servo didn't shift immediately, the I in its supposed PID loop would take care of it).

Best of luck!

[haroony341]

thanks for all the replies!

is there anything else we can do to help it along mechanically? or should the light grease and making sure the backup battery is good be enough?
also, what could be causing the shifters to work while tethered but not on the field while in play?

[Bharat Nain]

Our team bought higher quality backup batteries which last longer. There are other threads suggesting different batteries. We use servos for our brakes and they(ifi batteries) wear out after about 4 or 5 matches. Good luck.

[haroony341]

Originally Posted by Bharat Nain

Our team bought higher quality backup batteries which last longer. There are other threads suggesting different batteries. We use servos for our brakes and they(ifi batteries) wear out after about 4 or 5 matches. Good luck.

how long is the recommended charge time? i know you cant leave them on for too long

[Bharat Nain]

Originally Posted by haroony341

how long is the recommended charge time? i know you cant leave them on for too long

I don't know what the recommended charge time is because I do not take care of the backup batteries. However, once the charge of the battery reaches around <7.2v to around 8v you know it is fully charged. Perhaps someone on your team can experiment and find out approximately how long it takes.

[Greg Marra]

Originally Posted by haroony341

how long is the recommended charge time? i know you cant leave them on for too long

You can purchase a "smart" battery charger that uses a microprocessor to monitor charging and will not overcharge or damage your battery. I don't know what the model 177 uses offhand is, but some googling would turn up potential models. Feel free to visit us in our pit in Atlanta to ask.

Originally Posted by Qbranch

hey on the backup battery problem you could consider soldering up the IFI suggested onboard backup battery charger, found on this link.

it charges the backup battery off the main, but has a diode so that if the main is lower then the backup, then the source for the RC's power is the backup battery alone.

-q

Careful with this circuit. Lots of people who know more about electrons than me were questioning its performance at the beginning of the year, and I don't know if FIRST or IFI has made any modifications to improve it. Generally, my experience is that if you switch out your backup battery once or twice a day you'll be fine.

[Greg Needel]

Originally Posted by haroony341

also, what could be causing the shifters to work while tethered but not on the field while in play?

check and see what variables you have assigned before and after auto mode and that they are consistent. Because when the RC changes modes from auto to teleoperated, it will keep the last given assignments. I would just check your code and see if you have anything in the base code that gets re-assigned in the auto mode. A good way to test this would be to run the routine with a dongle in the same order that the field works.

Disable, Auto, Disable, Enable and see how that works when you are tethered.



*excuse the fact that I may have worded things wrong as I am not a software guy. I am re-stating the solution to a problem we experienced this season.

[Conor Ryan]

Also make sure you have a good electrical circuit, a bad wire could be the root of all this. How did you run the shifters much before you started having problems with them? If you did with no problem, before hand check and make sure everything is symmetrical on each side from a mechanical aspect, you might have a buildup of gunk on the shifter shafts, also check to make sure nothing is inside the dog gear itself. Its more likely that you'll have a mechanical problem here over a programming or electrical issue.

[les chortos]

We had similar issues - but we found as the gear boxes were shifted more and used more -some of the rough "machining " burrs and such came off and they worked pretty consistant. From what I saw you need about 1-2 hours of driving on the chassis and a lot of up and down shifting to "break them in" - also the battery issue caused us grief. - you definitely need lots of juice if you want them to shift 10-20 times during a match. - we also programmed a slight delay 100 milliseconds 1/10 th second from the time the shift button was pressed to the time the gear would shift. - this would remove the load from the 2 gears in mesh and give the servo an easier - lesser load - to overcome when shifting. Basically if you were in a tough pushing match (low gear) and wanted to shift to high gear- the servos need to over come the gear loads- it would be very hard to do. - but by adding a delay in the motor power- it relieves the gears loads and thien slips into gear smoothly. - try it.- ask your programmer- to add a .100 second delay in power to the drive motors. pwm=127 or "0 rpm" . shift servos- then add power again. it should slip into gear within 1 or 2 eye blinks and go - it will appear to be seamless and not slow you down much- if at all.

good luck!