Buying a battery for the diddyborg

Submitted by jonapap on Mon, 03/14/2016 - 16:21

Forums:

I am looking to switch from the AA batteries to one battery for the diddyborg. I have a hard time finding how much voltage I need. From the Picoborg reverse specifications, it seem I can have a bettery between 6-25 V, am I right?

cleric boomer

Tue, 03/15/2016 - 12:12

Hi Jon

I am currently in the process of setting up a 4S LiPo battery, these run at 14.8v nominal.

I am using a DiddyBorg Red edition which uses 12v motors rather than 6v.

So if I am correct, and I am sure PiBorg will correct me if I am not. And if you have the standard DiddyBorg with 6v motors.

You could use a 2S Li-Po battery (which is 7.4v nominal), or if you need a little more power, 3S (11.1v nominal).

When I was researching batteries I was advised to go for the Li Po batteries rather than NiCad, NiMH or any of the other standard re-chargables due to the number of cells needed to make up the battery, which then transposes into a heavier battery pack.

The 4S battery pack I have weighs in at a hefty 420 grams, but the other battery types are even heavier.

a 2S weighs in at 119 grams
a 3S weighs in at 224grams

You will need appropriate wires and battery connectors.

And LiPo batteries are not the cheapest. This is definitely a case of pay as much as you can. Get a decent, trusted brand. I have seen 4S for less than £30, although I decided to pay £54 fror the battery. I don't want a fire in the house when charging it. Just cause I wanted to save a few pound.

The big thing about LiPo battery packs is that you MUST have a balanced battery charger, and keep an eye on them whilst they charge. They have been known to burst into flames (worst case explode). I charge the various LiPo's I use (model power boats) in a specialized charge bag.

I hope this helps

Chris

piborg's picture

piborg

Tue, 03/15/2016 - 11:22

The voltage range you will need is between 7-25 V.
This is because the BattBorg requires at least 7 V to generate the 5 V supply for the Raspberry Pi.

We would recommend using more than 7 V to ensure a regular supply to the Raspberry Pi when the motors start to draw power, more than 8 V would be ideal.

cleric boomer

Tue, 03/15/2016 - 12:13

I would go for a 3S LiPo, rated at 11.1v, you pick your current rating, but the higher the better.

lars_the_bear

Tue, 03/15/2016 - 12:50

Can you recommend something specific, since you seem to know about this stuff? I guess I would need a compatible charger as well.

Best wishes
Kevin

cleric boomer

Tue, 03/15/2016 - 13:37

Hi Kevin

This is my personal preference.

I only know something about this as I have a power boat that runs a brushless motor, and therefore requires LiPo batteries.

The battery packs I use for the boat are 2x 2S (7.4v), and boy does it fly (and it has a couple of times!!), I think the max is 45mph, which for a 2 1/2 foot model is quite impressive.

I have only ever used Overlander brand LiPo batteries, and purchase mine from a specific shop. You can have a look at their website and see if your local RC model shop sells them.

Going from my research on battery packs and power requirements of the DiddyBorg:

For the standards DiddyBorg a 3S (11.1v) battery pack is the way to go

http://www.stevewebb.co.uk/index.php?pid=OLSKU2570&area=BATTERY

As I have indicated I have a 4S (14.8v) for my "Blushing" Red DiddyBorg, and I purchased a 4250mAh pack. £54. Not cheap, but I decided to go the whole hog.

LiPo need something called a "balance charger" as each of the cells need to be charger at exactly the same rate.
I have different make of balance charger, but I am tempted to purchase this which matches all my LiPo battery packs.

http://www.stevewebb.co.uk/index.php?pid=OLANDERSKU251&area=CHARGER

Just recommending Overlander as I have experience of them, I cannot comment on other brands.

But as I indicated before, due to the nature of LiPo battery packs, I would never go the cheap option.

I hope this helps

Chris

lars_the_bear

Wed, 03/16/2016 - 07:21

Thanks.

sigpaw@hotmail.com's picture

sigpaw@hotmail.com

Tue, 04/12/2016 - 17:37

I'm also using a 4S 5000mah LiPo batttery pack. I had to make a new power cord using 12 AWG and a HXT 4MM connector. One word of warning, I STRONGLY reccomend you place a 10A fuse inline in the new power cord!

Images: 

cleric boomer

Wed, 04/13/2016 - 12:14

Thanks for the thought Sigpaw.

How long does you 5000mAh battery last running the Diddy Red?

I have to be honest I did not consider using a fuse.

As the Reverse board can provide 10A in total (5A per channel) would it not be better to have a slightly larger fuse?
I know a 10A fuse won't blow at 10A, but I don't want it blowing if it is drawing the max current the Reverse board can safely handle.

PiBorg,
What are your thoughts on this?
10A or higher

Thanks

Chris

piborg's picture

piborg

Wed, 04/13/2016 - 13:28

We would suggest sticking with 10 A.

If everything is okay and the PicoBorg Reverse is handling the supply it should limit its draw to the 10 A maximum anyway by reducing the power output to the motors.
The trouble is when the power desired is too much for the board to handle quickly enough.

A typical 10 A fuse will take brief spikes beyond 10 A, it should tolerate a reasonable amount of power spiking from changing motor speeds.
On the other hand a 13 A fuse would allow more that 13 A through briefly, this could do damage to the PicoBorg Reverse.

The usual rule of thumb here is that you can easily replace a fuse with a larger value if it seems to be blowing when it should not.
On the other hand a problem the fuse fails to handle is usually serious and cannot be fixed by buying another fuse :)

sigpaw@hotmail.com's picture

sigpaw@hotmail.com

Wed, 04/13/2016 - 18:12

That's a GOOD question. :-)

Multi cell LiPo's have to be handled gently (in more ways than one). As stated elsewhere they require a cell balancing charger. Also during discharge it is wise to monitor the individual cells. Most all packs have a cell balancing connector. The industry wires these in a standard way (thank heavens). I use an external, programmable doodad to monitor the cells in my pack during use: http://www.amazon.com/Battery-Tester-Voltage-Buzzer-Alarm/dp/B005GJCJOA/...

If you like, you can unsolder the buzzer and connect it to a GPIO pin (via a voltage divider).

My goal is to be able to run the unit 12 hours on a charge. But I will also be managing movement and activity during that 12 hour period. I will be using my Diddy as more of a "mobile sensor package". With more emphasis on "Sensor" than "Mobile". ;-)

cleric boomer

Wed, 04/13/2016 - 14:00

Hi PiBog

Thanks for the quick response.

I was out at luch, looking at various types of fuses and fuse holders. I never realized there were so many options!!!

So I am looking at a 20mm in-line fuse holder, and I will wire it to the switch (live wire) then to the Reverse board.

I will have a look to see if they sell 20mm standard blow fuses, if they don't, would you suggest a fast-blow fuse over the time delay/sow blow type?

Thanks

Chris

piborg's picture

piborg

Wed, 04/13/2016 - 14:56

I would recommend trying the fast blow fuses.

The trouble with the slow-blow is that they may react too late for digital electronics.
The trouble with the fast-blow is they are much more likely to blow around short power spikes.

If you use the fast-blow and avoid harsh speed changes then everything should be quite happy.

sigpaw@hotmail.com's picture

sigpaw@hotmail.com

Wed, 04/13/2016 - 17:51

I took a liking to this one: https://www.radioshack.com/products/radioshack-30a-12-24vdc-mini-blade-i...

Rated at 30A it should easily handle 10A. I like the fact it is water proof as well as the LED light.

On other comments...

One can only hope a fast blow fuse is quick enough to protect your digital electronics. If that is your goal I would recommend a current monitor and a crowbar circuit.

My primary concern for everyone, was the battery. Once you start adding an "upgraded" battery you introduce some danger. Modern LiPo batteries are capable of 20-30C. For a 5A battery, this means instantaneous pulses of 100-150 AMPS! When shorted LiPo's "like" to burst into flames, burning your home down in the process.

Please be cautious folks, "Its all good fun till someone puts out an eye". :-o

cleric boomer

Thu, 04/14/2016 - 11:15

Would an RCD style device be better then? If so do you have any suggestions?
I was planning on a fast blow in-line fuse at the minimum, following from the advice here. Also a large bag of spare fuses!!!!

I was looking at the monitoring style devices, I will definitely get one now, Amazon have loads of them.

I have a little experience with LiPo batteries, and have a healthy caution/respect of them.

I use them in a model power boat (2x2S LiPo's) I have an appropriate balance charger and also a charge bag.

In fact I am considering a couple of the charge monitors for those batteries in the boat.
Definitely getting a couple for the Diddyborg, one to mod for the Pi, and the other just to sit and alarm until the modified one is ready.

sigpaw@hotmail.com's picture

sigpaw@hotmail.com

Thu, 04/14/2016 - 15:48

That's getting a bit too complicated for my purposes. Hopefully the Pico will be able to handle a small, short term spike. My original intent was to protect the battery against accidental shorts.

The protector has been a welcome addition and at £1.67, it's hard to justify not having one. ;-)

cleric boomer

Fri, 04/15/2016 - 12:26

The RCD was just a thought, and a question.

I have bought a 20mm in-line fuse holder, and 10x 10A quick blow fuses. Which should be sufficient.

I am off out tomorrow to buy the battery connectors, wire and whatever else I need to wire the 4S battery up to the BattBorg and Reverse board.

Via a key switch fand in-line fuse.

On top of that I have the shut down switch made up and ready to fit and add the code lines.

PiBorg's comment re controlling the speed change (and therefore the current flow) has made me think. Is it possible to have that controlled software wise (using PWM possibly?)? Sort of along the lines of keeping speed increases down to a reasonable level. Maybe like fly by wire. Pilot pushes joystick forward and the software tells the engine what to do, but keeps it from exceeding the limits.

I know nothing of python programming and getting the DiddyBorg was a massive leap into the programming side. So I can have an automouse DiddyBorg, whizzing around the house taking appropriate readings.

I really hope I have some time this weekend to make some progress.

Getting a little fed up with seeing poor Red sitting half completed on the table.

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