LiPo Battery Option / Regulator Option and Run Time...

[PaulL]

I found this:

http://cgi.ebay.com/Intellect-7-4v-2200 ... 518c892769

And I was wondering if anyone had any experience with this battery. I intend to run this in my RN-1, with a Roboard on his back (the black casing will need to be modified / replaced). Not sure what to expect from my RN-1 for typical current draw, does anyone have numbers using the standard walk, standing, etc? Trying to get an idea of runtime.

From the looks of it, the size should be a perfect fit inside his battery compartment with no modifications, and should go up to his head screws on the inside (I have no servo for head movement yet, was thinking about a small "lazy-susan" type bearing and a small micro servo like an HS-55 with sprung movement in his chest to rotate- doesn't need any force for head movement, it's just for aesthetics anyway).

Now for a regulator, I was looking at this:

http://www.sparkfun.com/commerce/produc ... ts_id=9275

It's rated at a 5.5vDC maximum voltage output, and it has a 93.6% efficiency rating at 5.0v out, and is rated at 6A. I don't know if 5.5v is enough to run the roboard at a half volt shy of 6.0v, but if it works, this seems perfect. I'd rather do this than a regular regulator, as the efficiency gain over a regulator would seem to be well worth it.

Using some math:

7.4v Lipo at 2.2Ah = 16.28 Watts of available power for an hour.

After efficiency loss in the DC to DC converter of 93.6% using the 5v figure: 15.23808 watts of available power. At 5.5 volts, that's 2.77 amps for an hour.

With a 6 volt "regular" regulator, the available power would be 16.28 Watts, minus efficiency (calculated as 6v/7.4v, 1.4v lost as pure heat) over an hour, leaving 13.2 watts of available power. At 6 volts, that's 2.2 amps for an hour.

Is my math right? If it is, and I can get the Roboard running off this DC to DC converter at 5.5v, it's a done deal.

Does anyone see any drawbacks with this setup?

Thanks,
Paul

[PaulL]

In looking through the datasheet for the regulator, it seems I'm looking at 93.6% MINIMUM for the voltage and current draw I'm talking about, and the output can be trimmed over 6v. This DC to DC converter (regulator) is a done deal. Same for the batteries, going to buy two and give them a try. I have a Schulze ISL6-330D that should charge the LiPo's OK. Longer term, I'd like something more automatic for a charger. I'd like to have my RN-1 head back to his charging station when his batts get low, and have his station consist of a couple charge paddles (at his feet, or where his arms can reach) and have him couple himself to the charger by himself.

Paul

[PaulL]

I have the DC to DC converter trimmed to 5.98 volts (yes, it will trim to this voltage, and higher if I tried, though it is not in the datasheet), and it does run the Roboard and a Hitec HSR-8498HB servo using a 12v source. Success so far! I trimmed it with a 10k multiturn potentiometer (5k would've been better with finer trim, but it's what I have on hand that is tiny enough not to make the board any taller), to 1.092k ohms. In the future, I'll be powering and running all of the servos through some of his "stock" moves to prove this out completely. My batteries from overseas have not yet arrived, or I would have it running off LiPo instead of a bench power supply. Again, this DC to DC converter seems to run the Roboard just fine.

[PaulL]

Further Info, I have run the video card on the Roboard with a servo using this DC to DC converter, and so far, so good- it works. Gets a little warmer off my current 12v supply, but still waiting on overseas batteries.

[limor]

Hi, I was wondering how it went with the lipo batteries , DC-DC, and Robonova. Did the battery come with some low-voltage cutoff? what charger do you use ? any other experience you care to share regarding lipo with RN1 ?

[PaulL]

Hi Limor,

I did receive the batteries, and they fit with room to spare on the sides. I have since swapped out all my HSR-8498HB's with HSR-5498SG's, so my current requirements have increased. I think I'll need at least two of these DC to DC converters to handle the 5498's, if not one for each limb. I'll have to keep you posted as I go. For now, I plan on using a Schulze ISL6-330D to charge one cell at a time, but that's temporary. I need a newer charger to handle the center tap for the 2c LiPo cells.

This battery is the perfect size to fit in the RN1's battery compartment, but if you have a head servo mounted inside under the head, it would not fit. I plan to mount a head servo elsewhere. I have moved from working on hardware back to software (still have a ways to go with software), so I don't have info regarding the whole beast up and walking around with DC to DC converters, the new LiPo's, and the Roboard. I will definitely post here when I do!!!

I had an idea that I need to look into a bit more. I would like to implement a "High Power" versus "Low Power" mode, or even be able to adjust to anywhere inbetween. Right now, I plan on running the Roboard right from the batteries, and use the DC to DC converters for the servos only, but I may devote one converter to Roboard. I might end up with a custom circuit board with 5 of the DC to DC converters on it, but that's hard to say until I get Roboard running my RN1.

I do have an almost complete "stock" RN-1 since I swapped out nearly all of the parts (only missing screws for the top plate where the head attaches), and I may try the DC to DC converter in it w/ LiPo and post results back on that. My "main" RN-1 as of now isn't very stock anymore.

I will post back when I have some feedback on this setup, but as of right now, I simply haven't got it all wired up yet (all of the servos in an RN-1 running off the DC-to-DC converter and the new LiPo batts).

Paul

[limor]

Using the sparkfun DC-DC regulator was quite original of you.
So how do you manage low-voltage cutoff? do you make the blue head LED blink blink through the RN1 software or does the battery come with a low-voltage-cutoff circuit ?
low voltage with LiPo can have undesirable effects..

[PaulL]

Thanks! The DC to DC regulator seemed like a good idea at the time. "Regular" regulators waste a lot of power, I wanted to drop the voltage more efficiently.

I plan to use my Roboard's ADC to monitor voltage levels on both cells, I'm not using my MRC-3024 at the moment. But, reading the voltage of the battery like in the default program and using a pin to control the DC to DC converter (It has something like an "output inhibit" pin) would probably work to power it down using the MRC3024.

Take Care,
Paul

[Sazabi]

On my RN with Roboard I use two Li-Po of 1900 mAh and 7.4V connected in series without any converter. Roboard capable to work on 6-24 volts and Hitech servoes "eat" 7.4V also (max voltage for max power on them).
The only thing I use to prevent critical discharge for Li-Pos is Li-Po Alarm with buzzer (kind of this one http://www.laureanno.com/RC/picaxe-simplevolt.htm). So it's really hard to miss discharge level.
It drains more on higher voltage, but since battery capacity in increased for about 4 times than stock RN battery, it should be able to run at least the same time stock nova had.

[Kelpy]

On my RN with Roboard I use two Li-Po of 1900 mAh and 7.4V connected in series without any converter. Roboard capable to work on 6-24 volts and Hitech servoes "eat" 7.4V also (max voltage for max power on them).

Hi Sazabi.

I have a bog standard RN, but I do have quite a few 7.4V Li-Po's (from my RC Helicopters). Would it be safe to use in the RN without any other precautions? Having a greater mAh capacity, I'm hoping for longer running times.
Also, you say you have 2 in series. Where have you mounted them?
Another thing, I'm not familiar with the plug/socket for the battery. Are there any adaptors available, do you know?

Thanks.

(sorry to 'borrow' your thread, RN1AsOf091407)

[Sazabi]

Hi Kelpy,

You should check battery discharge current, to make sure it will not burn under load (I don't remember exactly, but mine give around 10C discharge current, so it's ok to load almost all Nova servos at a time). Also, check you servo props to insure they capable to work on 7.4V (but stock Nova servos do, I know).
I'm currently reworking Nova's frame, so haven't mounted them anywhere yet.
According to plugs - I've cut standard battery plug and soldered tube ones, they allow fast and simple connection/disconnection in case of emergency (anyway, there is an on/off switch, placed between batteries and servo/roboard).

[Kelpy]

Thanks for that, Sazabi. Mine are standard servos and the lipos are rated at 10c with 15c burst, so just got to decide where to install them now (and put suitable plugs on )

[engineer]

the connectors for the batteries is sold at digikey electronics the part #'s are Housing A30499-ND @ $.31 ea, contacts A30501-ND @$.27 ea, header connector (for charger) A30511-ND @$.14 ea. I use them for making nimh 1600 mah packs that weigh the same as RN'S stock packs and don't change the balance very much, since I also have two gyros, a head servo, bluetooth reciever and the accelerometer stuffed inside RN-!

[Kelpy]

Many thanks for that, engineer. I'll have a look now.
Yes, I can see why your RN eats the juice!

[Bicgatepc02]

I read some older posts on the forum about an open source controller as an alternative to the MR-C3024 but it didn't look like anything ever came of it. Do you know if anyone has successfully replaced the C3024 with something that I might be able to communicate with a bit quicker?





















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