Power supply?

brandong

I was wanting to replace the AA battery holder that comes with the BoeBot with a rechargeable 7.2V battery pack.·

··· I have·3 queations about this...
1. Is this safe to do (will it damage my robot)?
2. If safe, what amperage/mAh should i be looking for?
3. Where would i be able to find the barrel connection to wire it onto the battery pack (do i have to buy another AA battery holder and destroy it)?

If anyone knows something about this your·assistance would be greatly appreciated

Thanks,
Brandon


·

SRLM

1) It's safe
2) Anything works, but the higher it is the longer your battery will be able to power the BOE
3) I made one using a Tamiya connector to attach to the battery, and a 9v battery clip from Radio shack to connect to the BOE.

allanlane5

I believe the 'barrel connector' is a standard one from Radio Shack -- 5 mm / 2.1 mm, I think -- Parallax people could say.

Edit:· Ah!· That's right, 5.5 mm/2.1 mm.· That's the ticket.

Post Edited (allanlane5) : 12/8/2008 11:13:32 PM GMT

PJAllen

Radio_Shack has the connector (plug)·for the BoE's DC/coax jack.

http://www.radioshack.com/product/index.jsp?productId=2103614
·

Mike Green

Don't use a battery pack rated for more than 7.2V though. The servo motors have small brush DC motors inside and the brushes will wear more quickly than normal with voltages above 7.2V. Also, the Boe's regulator will gets hotter the higher the voltage is above about 6V. 6V to 7.2V is really the best supply voltage range for an unmodified BoeBot.

GWJax

If you want to use a larger battery pack you MUST have a 5v external regulator in circuit and a heat sink on the LM7805 5V reglator. I had found this out the hard way but I did not burn out my chip thank goodness. so if you don't have an external power supply for it then do as Mike had said NO more than 7.2V on these chips.

Jax

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If a robot has a screw then it must be romoved and hacked into..

MSDTech

One other option is to use a BOE-Boost and AA rechargables. I'm using 5 AA's rated at 2500 mAh and the BOE-BOT runs great. The only problem I've run into is that the chargers always want pairs. As a result, I have two full sets of batteries. Once both sets are exhausted I can then load the charges and bring them all up to power.
The BOE-Boost requires no wiring changes, as it tucks into the existing battery pack.
http://www.parallax.com/Store/Robots/RoboticAccessories/tabid/145/CategoryID/22/List/0/SortField/0/Level/a/ProductID/455/Default.aspx

brandong

Thank you all for your helpful advice. Im looking at a 7.2V 2000mHA Rechargeable battery pack made by Tenergy that should fit right where the battery holder goes. When i do mount this up to the BoeBot will i want to switch the servo power selector to Vdd and regulate the power to 5V or is the unregulated 7.2V supply acceptable...got the impression that it was, just wanted to double check?
Also, MSDTech, do you think that i would be better off with the Boe-Boost, as far as power longevity, compared to the power source ive mentioned above.

Again thanks,
Brandon

GWJax

If you connect it to the regulated stamp 5V be sure you don't go over the max current for the stamp, if you're not sure connect the servos to the unregulated power supply of the batteries.

Jax

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If a robot has a screw then it must be romoved and hacked into..

allanlane5

Yes, the 7.2 volt battery can be used to drive the servo units directly. It's a little "hot" for them -- they're designed for 4.8 to 6 volts -- but it shouldn't reduce their life too much.