Lipo's and regulators

[rep001]

Hello Just ordered my ,and a friends Robonova last night and am all excited so i thought i should start talking to people at least until the boxes arrive.I dont see many people using lithium polymer cells is there a reason for this?I have read the recent posting of someone that has just changed but not much else is said.The cells now are very good and certainly up to the loads that we would require as 20c is becoming the norm.Also do people know that there are voltage regulators available from most electric flight shops that support 2,3 and 4 cells packs and also lipo savers that cut the voltage if it fails below the safe 2.9 vpc.Im no expert in this area, just wondered ???
There is some great info on this forum so thanks in advance to you all and hope to speak again.
Regards
Rep001

[subpilot]

I may be wrong but I think you will find that the regulators you are talking about will only support a light load (the receiver and a couple standard servos) and would not be able to drive 16 high power servos.
Robonova typically idles at around 1Amp (just standing around). When all servos are stalled it will draw up to maybe 5A. That would be a pretty extreme situation. I think saying 2.5A average for a fully active robot would be about right. So a 2000mAh 20C pack would be way overkill. You can get away with a 1000mAh 5C pack but that wouldn't gain you much other than weight savings.
I think people haven't jumped on board the LiPolys because of the requirements for a special charger, under voltage shut off and a voltage reg. As a minimalist thing you could have your voltage sense routine shut off power to all servos when the batt voltage drops but it's risky. Better to have a regulator with an undervoltage lockout.
I had tried using a TI TPS54350 switcher but it is limited to 3A out. It does not like the load the Robonova presents. Not sure why but it doesn't like it. It's a shame since the evaluation module can be had from TI for $10 and it's really small. There is talk of a 5A version but so far it's vapor ware.

[RubikCube]

Subpilot,
Do you think this power supplies will be sufficient for ROBONOVA's current requirement ?

http://www.roboticsgroup.com/products.asp?id=22

[subpilot]

I think RGi-SDPPS-1 is marginal and may well not work. It is also a bit too large due to the big caps and euro connector.
I have an Intersil ISL6420Eval board but haven't tried it out. http://www.intersil.com/data/an/an1159.pdf
They are free from Intersil but are a bit too large. You may be able to hack it down to a more reasonable size but I'd try it out first.

[bauermech]

UGH!

I just blew my 6v regulator and my plane leaves for RoboGames in the morning! 10A max, but w/ the HSR-5995TG servo, along with the 19 HSR-8498HB's, I'm pretty sure I peaked it. The 5995 has a max Amp draw of almost 5A by itself! I doubt it makes it there too often, but I had enough servos nearly stalling that it knocked it out... yikes!

I just bought an emergency "MPI Miracle-Switch". It is 10A continious/20A peak deal w/ your under-voltage bypass and caps etc.... and of course, the 6.0v regulator. I'm tearing it apart now to solder on my battery and output leads. I need to finish my robot's routines... this is gonna' be close!

I've got two 7.4v 1900mAh 16C LiPo's wired parallel. Oh yeah!

With the Ni-MH's I was getting about 15-20min. max play-time, but w/ these suckers I'm doin' somewhere around an hour and a half - two hours.
I have two 7.4v 1320mAh Li-Po's as programming time bats and emergency back-up.

I still don't have a under-volt cut-off, but wired in a LED volt indicator w/ real-time current draw (pre-regulator). It's mighty accurate as long as I keep an eye on it, when it hits red, time to charge!

For a charger, I picked up a DC-DC Celectra 1 to 2-cell Li-Po charger for $20 bucks. I rigged up a 300w computer power supply (rated for 9A max) to give the 12v 5A DC source I needed for the charger. Saves me from having to pop the hood of my car to charge my Li-Po's

What am I doing typing? I've got a LOT of work to do! (whip-sound) 8O

[subpilot]

Good luck Matt. Hope you manage to get it all together in time. Hate being under the gun myself. I'll be looking for you at the show.

BTW, Got my grippers and they look great, thanks