Replacing the battery to Li-ion

[mic2]

Guys,

Notice the lighter of the body the better performance it can be. Especially if you want it stand on one leg.

I am thinking of replacing Li-Ion battery to the robot to lighten the body weight, but most of the Li-Ion battery standard voltage is 3.7V so if I put 3 of these 3.7v into to a pack then the total voltage will be 11.1v (too high), if 2 of 3.7v is 7.4v (too low) hence the original battery pack is 1.2x8=9.4v at 2400MAh.

My question is, would the CM5 ok to work with 11.1V?

Thanks
Mic.

[JonHylands]

The CM-5 runs just fine on 11.1 volts - the power brick when plugged in provides 12 volts. I run my system at 12 volts (including the AX-12 bus power) all the time.

- Jon

[mic2]

Cheers Jon.

[StuartL]

Do be aware when you do this that Li-Ion battery pack output voltages vary significantly. Make sure you monitor/limit the pack voltage. 3 cell packs seem to be able to get as high as 14-16v!

[billyzelsnack]

Charging any sincle lipoly cell above 4.2V is dangerous. Any reasonable charger would never charge it that high. So a 3S pack should never be above 12.6V.

I think the biggest concern with using lipoly batteries is over discharging them. Discharging a cell below 3.2V seriously effects it's lifetime. Actually.. The common wisdom is really to never suck out more than 80% of the battery capacity (mah). 3.2V is just a rule of thumb.

[mic2]

Guys,

I have successfully upgraded my Bioloid to Li-ion battery. That gives lighter weight as well as unbelievable longer operating time.

Initially I have used 3S twin pack 2900 mA which can give non-stop moving almost 1 hour operating time!! So I have decided to use only 3S single pack to give half of the operation time i.e. 30 mins. Because that should be good enough for me. Before the upgrade, I was content with just 8 mins.

The only concern is that I have to get one circuit board to control its over discharge but it looks like only the US sell it.

Is there any change I can monitor one of the servo voltage e.g. once the voltage drops down to 10 V, and then call a function to shut down itself?

Mic.

[StuartL]

Is there any change I can monitor one of the servo voltage e.g. once the voltage drops down to 10 V, and then call a function to shut down itself?

The Dynamixels themselves monitor the voltage. Look at a register read of 0x42. Resolution is 0.1 volts.

[BillB]

Wow - 8 mins to one hour change. This is impressive. I definately need to make this upgrade.

Could you tell me where you got the voltage regulaton cuircuitry from?.

[Voelker]

Hi, It seem that you are not using Li-ion battery but Li-po (Lithium Polymer). This is very different as Li-Ion battery can not deliver more than a few mili-amper. Li-po can deliver up to 25A but need a good regulator. Li-po are well adapted to robot, but are very fragile and can take fire when bad used.

[BillB]

Li-po are well adapted to robot, but are very fragile and can take fire when bad used.

Question:
The dangers of not charging properly are well documented, but I can't find anything that describes the effects of shock. My robot is always falling over - is the shock caused by a falling robot (falling from standing position) enough to make the battery dangerous? Bear in mind that through its life time the Robot & battery will fall many, many times.

[Voelker]

The battery is made of three layer : cathode and anode separated by Li+. If a shock occurs and the anode and cathode are short circuited the battery can take fire. If you are using multiple cells in parallel you need to have a circuit that equilibrate charge and discharge because if cells doesn't have the same voltage they can take fire.

[PeterW]

I have for the past couple of years used LiPo batteries in antweight combat robots. We have robots with big spinners that can smash robots apart or throw them hard against the Policarb arena cover. I have seen batteries smoke when physically cut or spiked by a weapon but never through impact. The main reasons for failure are over charging or over discharging when the battery starts to puff up and becomes useless.

[PeterW]

I was just looking at the LiPo cells offered on the Robosavvy site and they quote a continuous discharge of 2C which is only 4 amps on the 2000mah cells. Is this correct as the ones I use in the antweights are normally 15-20C on cells as low as 250mah and you can get upto 35C on larger capacity cells.

[savuporo]

You could try A123 lithium phosphate M1 cells too, very high 10C discharge, lower specific energy than LiPos. They have 3.15V nominal voltage
http://www.slkelectronics.com/DeWalt/index.htm

quite a lot of RC hobbyists now use these

[PeterW]

Yes I have looked at those for the combat robots as they are inherently safer when damaged but they have a metal case and weigh much more. The two 1000ma LiPo packs I have, although not the best you can get now, are 10C and they only weigh 65gms each.