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mattmaho
11-30-2009, 01:42 AM
Hi,

I'm new here, so thanks for having me. I'm from a programming background and have absolutely no idea when it comes to electronics. I'd like to build a robot consisting of the following:

1 x VIA EPIA PX5000EG (http://www.via.com.tw/en/products/embedded/ProductDetail.jsp?productLine=1&id=472&tabs=1)

3 x Xbee Pro 60mW Series 1 with Wire Antenna (http://www.trossenrobotics.com/store/p/5827-Xbee-Pro-60mW-with-Wire-Antenna.aspx) connected to the VIA EPIA via 3 x XBee-Explorer-USB (http://www.trossenrobotics.com/store/p/5828-XBee-Explorer-USB.aspx)

1 x PhidgetStepper Unipolar USB 4-Motor Stepper Controlle (http://www.trossenrobotics.com/phidgetstepper-unipolar-usb-4-motor-stepper-controller.aspx)r (http://www.trossenrobotics.com/phidgetstepper-unipolar-usb-4-motor-stepper-controller.aspx) connected to the VIA EPIA via USB and running 2 x Danaher 42M100B2U motors (http://parts.digikey.com/1/parts/678364-stepper-motor-12vdc-3-6deg-uni-42m100b2u.html)

1 x PicoPSU 60W (http://www.mini-box.com/picoPSU-60-WI) connected to the VIA EPIA

So all up it should control 3 Xbees and 2 unipolar motors, all via USB.

My questions are regarding powering the robot:

1. The Phidget Stepper Controller has a separate power input to power the 2 motors. Is it possible to make a connection from one of the PicoPSU's MOLEX connectors to power the motors connected to the PhidgetStepper Controller?

2. My robot needs to run only for a couple of minutes before recharging. Would any of the following be suitable to connect to the PicoPSU for powering the robot?

a) http://www.batteryjunction.com/tenergy-11v-4400.html
b) http://www.batteryjunction.com/tenergy-96-hump-nimh-pack.html
c) http://www.batteryjunction.com/tenergy-31259.html

Thank you for reading my post, any suggestion are appreciated.
Matt

Adrenalynn
11-30-2009, 02:12 AM
Welcome to the forum!

The [email protected] is pushing it a bit, but the decently sized LiPo's should do it.

Just make sure you're using the "Wide Input" power supply and MOST IMPORTANTLY - you need some way to monitor the battery cell voltages. Draining a Li* chemistry battery too far is a Grade-A Bad Idea. (Unless it involves cutting it open and throwing it in salt water...)

mattmaho
11-30-2009, 02:37 AM
Thanks a lot Adrenalynn,

That helps a lot. I have no means of monitoring the battery voltage, so that excludes the Li* batteries. When you say [email protected] is pushing it a bit, do you mean the 9.6, the 4500 or both? Does it just mean the robot won't run that long or does it mean it won't even start up?

I did a bit of beginner's background reading and I think the 4500 correlates to how long the robot will run. Is this correct?

So I can use the MOLEX connector to power the motors, as long as I use the wide connector, i.e. the one that usually powers the 5.25" drives?
Once again thanks,

Matt

Acidtech
07-05-2010, 07:54 PM
Yes, the 9.6 part is the part he means you'll be pushing. The 4500 part is the MAH(milliamp hour) rating which generally indicates how long your robot will run. Eg 4500 about twice as long as a 2250. More specifivally 4500 means you can draw 4.5amps for 1 hour from that batter(after a full charge). Or 2.25amps for 2 hours etc...

mattmaho
07-06-2010, 12:46 AM
Thanks Acidtech,
For taking the time and explaining!

Stephen
10-29-2010, 12:24 PM
The [email protected] is pushing it a bit, but the decently sized LiPo's should do it.

Just make sure you're using the "Wide Input" power supply and MOST IMPORTANTLY - you need some way to monitor the battery cell voltages. Draining a Li* chemistry battery too far is a Grade-A Bad Idea. (Unless it involves cutting it open and throwing it in salt water...)

Hi Adrenalynn,

I'm currently thinking about moving from the NiMH battery packs to LiPo. I know TR has a selection of LiPo batteries and a decent looking charger. However, I know very little about battery tech at this time and so when I read your post I became a little nervous! I wonder if you could explain this a little more, and outside of a LiPo pack and charger (like those that TR sell), what other equipment I might need to purchase?

I don't mean to hijack this thread if my question appears off-topic here! Please let me know and I'll start a new thread!

Cheers,
Stephen

darkback2
10-29-2010, 12:57 PM
Hey Stephen,

I switched over to lipo's on my walkers. It is my understanding that lipos can deliver more power more quickly. I think nicads don't do as well at providing a lot of amps over a short period of time. I wouldn't worry too much about lipos provided you use the appropriate charger and keep the case intact. Outside of that my robot stops working or becomes sluggish when the voltage drops too low.

Yeah I think they can be scary, and teh charger is a bit intimidating, but you should be fine provided you follow the instructions.

Also I would love to see a project post about your robot. Seams you are teasing us by asking questions about it. Let the sharing begin.

Hope this helps.

DB

Stephen
10-29-2010, 01:20 PM
I switched over to lipo's on my walkers. It is my understanding that lipos can deliver more power more quickly. I think nicads don't do as well at providing a lot of amps over a short period of time. I wouldn't worry too much about lipos provided you use the appropriate charger and keep the case intact. Outside of that my robot stops working or becomes sluggish when the voltage drops too low.

Yeah I think they can be scary, and teh charger is a bit intimidating, but you should be fine provided you follow the instructions.

Hope this helps.

DB

This certainly does help DB. Thanks!


Also I would love to see a project post about your robot. Seams you are teasing us by asking questions about it. Let the sharing begin.

LOL! I will most certainly begin sharing my project, and soon too! But right now I have a dentist appointment to get to! ;) (No really, I do!)

Cheers,
Stephen

jes1510
10-29-2010, 06:04 PM
Generally, NiCAD's have a bit lower internal resistance than NiMH. That means that a NiCAD pack will deliver more instantaneous current. The downside is that they have severe memory problems and have to be charged and discharged properly in order to get peak life out of the pack. The "CAD" part of NiCAD stands for cadmium. Cadmium is pretty much outlawed under ROHS so most NiCAD battery packs will be going away.

NiMH (Nickle Metal Hydride) packs are like the middle of the road between NiCAD and LiPo. They don't have the memory problems that you get with NiCAD but they have a bit higher internal resistance meaning they can't deliver the instantaneous current that a NiCAD can provide. They also don't have the memory problems you get with a NiCAD so you can pretty much charge and discharge them willy-nilly without fear of damaging the pack. Cadmium is not used in NiMH so they don't have the ROHS restrictions you get with NiCAD.

LiPo is pretty much the "best" of the three batteries listed here. They have a very low internal resistance so they can deliver peak currents easily. They are significantly more efficient so you get much better life per watt used. They are extremely finicky when it comes to charging. If you don't follow the requirements for LiPo charging then there is a very real risk of the battery catching fire. Seriously. Using a well designed charger will minimize the risk to almost nil. They are also pretty particular about discharging. This is what Adrenalynn is alluding to above. If the cell voltage drops below somewhere around 3v per cell then the pack will probably not take a charge again. The damaged pack has a greater risk of catastrophic failure (fire) if you try to charge it. The stuff inside the pack will oxidize really quickly so a damaged pack can catch fire. If you put the pack in salt water for a while it will neutralize the battery so it can be disposed of safely.

Finally, never, ever, ever charge a battery unattended. Make sure someone is around and the battery is on something fire proof such as a ceramic plate when charging. This goes triple for LiPo's.

Stephen
10-29-2010, 07:20 PM
jes1510 - Thanks for the explanation regarding LiPo's. So prior to charging a LiPo pack it's probably best, as Adrenalynn mentioned, to check the battery cell voltages. Someone suggested in another thread/post the following item:

http://www.all-battery.com/valtagewattmeter01019.aspx

This or something like it is probably worth purchasing for a number of reasons, and checking LiPo's before charging being one of them I guess. (If I find that thread+post again I'll link back to it; I'm pretty sure it was part of a similar discussion.)

With the voltage and watt meter above, I'm also thinking I'll get the following LiPo battery pack and charger from TR:

http://www.trossenrobotics.com/store/p/6293-3S-11-1V-2100mAh-Pro-Lite-V2-20C-LiPo-Battery.aspx
http://www.trossenrobotics.com/store/p/6431-LiPo-Balance-Charger-Starter-Kit.aspx

I'll be able to charge my existing NiMh pack with that charger too... just need to figure out the connectors! (My NiMh has a standard Tamiya on it.)

Cheers,
Stephen

jes1510
10-29-2010, 08:11 PM
You should look and installing a voltage monitor on your robot. That should stop the machine or at least alert you to the voltages of the LiPo getting low.

Stephen
10-29-2010, 08:21 PM
You should look and installing a voltage monitor on your robot. That should stop the machine or at least alert you to the voltages of the LiPo getting low.

So something like this (http://www.batteryjunction.com/pcbfor7li181.html) or this (http://www.unitedhobbies.com/UNITEDHOBBIES/store/uh_viewItem.asp?idProduct=7223&Product_Name=Hobby_King_Battery_Monitor_3S) (links courtesy of mallster and Zenta respectively in this thread (http://forums.trossenrobotics.com/showthread.php?t=3780)).

The second one looks quite interesting actually!

Cheers,
Stephen

jes1510
10-29-2010, 08:35 PM
Yep! Just make sure a human is near by to hear the buzzer.

Stephen
10-29-2010, 08:45 PM
Yep! Just make sure a human is near by to hear the buzzer.

Hmm, I should plan on building a second robot just for this purpose!

Alright cool, thanks jes1510!