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ralsobrook

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Posts: 12
Reply with quote  #1 
This year our hub (Dallas) decided to permanently disable the "fast" setting on the battery charger, a decision that I'm sure will cut down on overcharging and damaging of batteries. We certainly appreciate the time and effort put in to these modifications, and understand that they should improve battery life in the long run.

My team is concerned though, that in the final rounds of competition, our batteries will not have enough time to recover their power between matches if they're charging on the "safe" setting. I'm quite positive there's not a single team out there that would want their robot running on anything less than full power when it matters most.

I would suggest (or rather beg for) one of the following solutions:

- That teams be provided with a "fast" charger during the final rounds

                                               or

- Supervised fast charging of the batteries in the final rounds. Perhaps teams could be given a fresh battery at the on-deck table to use in that match, and turn back in to be recharged thereafter. 

Not sure if this situation applied to every hub, but I wanted to post here in case it did.

-Thanks as always!

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jgraber

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Posts: 112
Reply with quote  #2 
Is your team concerned enough to do any mathematical modeling?
Or to do experiments to test the implied hypothesis?
That type of data and the consideration of the practical safe limits of battery capacity and recharge time, vs the efficient operating range of the motors and servos(the components with the highest and controllable current draw) as an additional (but implied) engineering constraint, would look great in the engineering notebook.  (oops 12 element sentence, I'll try again in bullet list format)

- motors and servos draw the most current (my hypothesis, I haven't measure the CPU current)
- the current draw of motors and servos is controlled by the torque required
- torque requirement is a function of: 1 the design of the robot, 2 the driving style, 3 software aids for driving style
So max robot current draw  vs battery capacity vs recharge time is an avoidable problem. (another hypothesis)

Everything below looks great in a BEST engineering notebook,
because it resembles real engineering process and constraints in product design.

- mathematical modeling of maximum or expected current consumption of BEST robot components when used as directed
- test results to do a reality check on the mathematical modeling
- Hypothesis and experimental results to test a hypothesis
- using the either the experimental results, or the mathematical modeling, and stating them in terms of 'an engineering constraint to be met' fits really well into the EDP (Engineering Design Process)
- describing how the robot physical design was changed to improve the metric of battery current consumption, with before and after test results
- describing how the control program has features to reduce needless current consumption, without significantly impacting performance, with before and after test results


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ralsobrook

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Posts: 12
Reply with quote  #3 
We are indeed, and some such experimentation is in progress. We had not thought of using software to help with this problem, but we will certainly look into that too. Our initial hypothesis was based purely on experience in past years, but we do understand that math and science are quite handy in situations like this. This experimentation will take some time on our part, so, hypothetically speaking, should we find evidence that validates such concerns, could we expect something more than a good write-up in our notebook(i.e. one of the aforementioned suggestions)?
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jgraber

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Posts: 112
Reply with quote  #4 
Sorry I missed your response for a while,  feel free to ping me in email if I take more than a day to respond.

   Someone raised this issue to management of BRI national, which pinged me for my side, which I detailed.
I await their guidance.
[edit: guidance arrived promptly, I'll provide Fast enabled chargers for regionals]

Google drive link https://drive.google.com/open?id=0B3kaaE-o2YLKRlctLWJHZWdhRVE
 is a spreadsheet model showing that 2 half-charged batteries starting semi-finals,
with an 18 minute gap between semi-finals and finals, should be sufficiently charged by a 1Amp Safe mode.
  You might play with the model and see which you would prefer,  I haven't checked myself.
A  two batteries that meet min spec of 2.0 AH capacity, and a FAST mode enabled charger, or 
B two new batteries, probably 3+AH capacity, and a SAFE mode charger.

I am easily swayed by evidence, if you have any of the usual scientific kind,  
 test procedure described sufficient for duplication, 
 sample size > 1,  all that usual engineering stuff. 

I'm also open to refinements of my simple theoretical model, such as 
- SAFE charge rate is different than 1 Amp
- Charge efficiency is less that 1 Amp input for 1 Hour yields less than 1 AH utilization increase
- Other values for Average AH utilization.
- amount of overhead AH utilization wasted during idle time waiting for match to start.

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