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View Full Version : [Question(s)] Hello all - Some questions from a future rover builder (BrainStem and H-bridge related)



jafoca
07-21-2008, 02:54 PM
Hello All,

As you can see I am new here and have a couple of questions before I embark into my renewed robotics journey.

My goal is to eventually build a tracked robot that can be autonomous, and have built in telepresence features.

Some background:
I recently graduated college with a degree in CS and Business Management. I dipped my toes into robotics 5 years ago when I bought a Acroname BrainStem PPRK kit, but I don't remember much of what I learned from that.

So I have a few questions for you all, hopefully this is the right place to ask them!

Firstly regarding the Acroname BrainStem (version 1.0)
Is this a decent platform for getting started in robotics? I think that this is probably going to be insufficient for the purposes of my final project, however is it good enough to get going with? I guess my main concern is for ease of programming. If this is old tech that doesn't have anything going for it, I probably will upgrade off the bat.

Regarding motor drivers / H-Bridges:
What is the difference between an H-Bridge and an RC electronic speed control? Most controllers can easily control servos, so why not RC ESCs?

Regarding Acroname H-Bridges: Why are they so much more expensive compared to something like a sabertooth (80$)? acroname H-Bridge (http://acroname.com/robotics/parts/S24-15A-30V-HBRIDGE.html) for example is $120, and only 1 channel. What is up with that?

And lastly, here is my plan of attack for comment:
1. Fiddle with brainstem robot to get the hang of coding for the BrainStem
2. Work with sensors on brainstem pprk bot to get then hang of them.
3. Buy a cheap RC tank for conversion to robotics use
4. Buy some sort of H-Bridges / speed controllers to use with tank
5. Construct new bot around brainstem / sensors with h-bridges, attempt autonimous code
6. Figure out new controller platform that will allow expandability in terms of 802.11 networking, interface with webcam, etc.



I guess my last question would be if there is any one controller that is considered "The best" for rover type applications, that most people are using.

Thanks for any feedback, I know I have a laundry list of questions, however I think I have made them specific enough.

Thanks again

darkback2
07-21-2008, 08:11 PM
Ok...I should probably ask what your budget is before I do anything else. That said, have you checked out the track systems available on this website. The following seams like a pretty good track system to start from.

http://www.trossenrobotics.com/store/p/3181-Traxster-Robot-Chassis.aspx

As for controlling motors, I use the vantec RS21 ESP. It has two channels, so you can control two motors at once. The trick is to check and be sure that your ESC can take the voltage/amperage that your batteries and motors are generating. The other cool thing is that the vantec has motor mixing so you can control your two motors using one joystick.

The last thing you will need is something that puts out servo position signals. I looked up the brainstem unit, and if it is what I think it is, it is an entire robotic platform. If you wanted a tank tread version then you would be throwing a lot of bot away. You may want to check around this site for the various servo controllers. Also, I posted an extensive thread on a rover in the projects section.

http://forums.trossenrobotics.com/showthread.php?t=1439

Finally how big did you want to go? If you are building a larger rover you could use a laptop to control it. If not, then you may want to check out a microcontroller. There are some pretty cool ones on this site.

http://www.trossenrobotics.com/robot-parts.aspx

Hope this helps.
DB

Adrenalynn
07-21-2008, 09:31 PM
For the love of all that is holy, don't buy that traxis base. Sorry, DB - but I've been down the road with them. They have substantial track design flaws. Better to send him after LynxMotion's track base, or raw tracks to build his own.

Both the BaneBots and Sabertooth controllers have been good to me. At first blush, I don't see any advantage to the motor controller you linked, jafoca.

BTW: Welcome to the TRC!

jafoca
07-21-2008, 09:39 PM
Thanks DB,

To clear one thing up:
I have this (http://www.acroname.com/robotics/parts/R141-PPRK-BS-2.html) which is a robot kit featuring a BrainStem micro controller, 3 sharp sensors, and a very simple robot chassis.

I was thinking to get started on my project I could harvest the microcontroller and the sensors, if the brainstem is not a total piece of junk.

I have considered the traxxster chassis you suggested, but am concerned that the "abs" plastic treads will not suit my needs, hence looking more towards a modified RC tank that has rubber treads.

Anyhow, to answer a couple of your questions:
My budget at this time is $500 - could do more later probably.
My ideal size is what I think of as medium - slightly smaller than the size a laptop would need.

Thanks again!
nick

Adrenalynn
07-21-2008, 10:14 PM
have a look at LynxMotion's J5 base. It's only a couple hundred dollars and has awesome treads.

DresnerRobotics
07-21-2008, 10:30 PM
have a look at LynxMotion's J5 base. It's only a couple hundred dollars and has awesome treads.

That said, its also mostly an indoor unit and will not take shock very well. The mounting holes on the base are like 1/16 of an inch from the edge...

darkback2
07-21-2008, 10:41 PM
Sorry...I have no experience with the traxis base. Maybe a note should be shot over to Matt.

DB

jafoca
07-22-2008, 10:39 AM
So a little update:

The Lynx tracked base looks very nice, however it is also quite expensive, and no it does not look very rugged.

My thought is to use an RC tank for the base such as this (http://cgi.ebay.com/WSN-1-16-RC-RTR-RUSSIAN-T34-85-IR-BATTLE-TANK_W0QQitemZ320276015492QQihZ011QQcategoryZ44026 QQssPageNameZWDVWQQrdZ1QQcmdZViewItem)
That would offer a rugged platform I think.

Would a limitation be the lack of encoders on the motors? Encoders are used to synchronize the speed of the motors, correct?


I had another thought about controlling it: a mini ITX computer featuring a Intel Atom processor. Would this be a wise choice? I am thinking about THIS (http://cgi.ebay.com/Intel-D945GCLF-Mini-ITX-Motherboard-w-Atom-1-6GHz-CPU_W0QQitemZ220258175401QQihZ012QQcategoryZ131535 QQssPageNameZWDVWQQrdZ1QQcmdZViewItem) It would offer plenty of computing power, and offer all of the connectivity I could need, I think! I just have to figure out what to connect it to to control motors and monitor sensors...

What do you all think of those options?

Adrenalynn
07-22-2008, 10:58 AM
I think the problem would be carrying enough battery for the ITX Atom and the size of the board.

Why not a PicoITX?

jafoca
07-22-2008, 11:24 AM
I think the problem would be carrying enough battery for the ITX Atom and the size of the board.

Why not a PicoITX?

The atom is about as low-power as possible for an x86 cpu. The main reason for going with this over a pico is price, a pico ITX would cost over 2x as much!

I don't know exactly how to figure out if this would work, but I have a 12v 3300MaH lithium polymer battery pack from RC airplanes that I am thinking would provide good enough power to this motherboard. Any thoughts?

Adrenalynn
07-22-2008, 11:46 AM
The atom consumes about 4x the power of the PicoITX, so I'm not sure that's an accurate statement.

The Atom peaks at about 54 watts (13watts for the PicoITX) at 12v, so your 3300mAh, with a wide input power supply (important!) would provide about 3300/2 = 1650mAh useable

54*12 = 648mA draw

1650/650 = 2.5hrs maximum runtime. So figure 2hrs if that's the ONLY thing on the battery.

vs the PicoITX: 13*12 = 156

1650/160 = 10.3hrs.

If you're running a hard drive, or also driving your motors from this battery, other peripherals, etc - then obviously this substantially skews the numbers.

You can also use a substantially smaller power supply for the Pico which cuts your losses in power conversion as well [not taken into account here other than the /2 conservativeness.]

jafoca
07-22-2008, 11:58 AM
The atom consumes about 4x the power of the PicoITX, so I'm not sure that's an accurate statement.

The Atom peaks at about 54 watts (13watts for the PicoITX) at 12v, so your 3300mAh, with a wide input power supply (important!) would provide about 3300/2 = 1650mAh useable

54*12 = 648mA draw

1650/650 = 2.5hrs maximum runtime. So figure 2hrs if that's the ONLY thing on the battery.

vs the PicoITX: 13*12 = 156

1650/160 = 10.3hrs.

If you're running a hard drive, or also driving your motors from this battery, other peripherals, etc - then obviously this substantially skews the numbers.

You can also use a substantially smaller power supply for the Pico which cuts your losses in power conversion as well [not taken into account here other than the /2 conservativeness.]

Why thank you for your electronics wizardry! I can't go back in my education far enough to get those conversions from watts used to MaH etc, so really thanks!

And yes, you are correct about the Atom, I'm afraid. I just found a test where the atom micro-itx came in at about 50 watts under full load, and 30 watts at idle. Not good. Really, it is all to blame on the packaging.

The atom itself is supposed to use only 4 watts! But for the mini-itx system they used an old chipset + other board parts that add a TON to the power draw.

I will have to consider what my next move will be now, as the nano is too expensive to fit in my current budget. Perhaps I should go for something like Gumstix for an ARM based linux solution?

Adrenalynn
07-22-2008, 12:20 PM
Bah, my brain fell out and I fell into the milliamps vs amps thing. Really, I picked the wrong week to cut out the caffeine.

I did manage to keep my terms the same and they still work out though, thankfully. When I first read it I thought I was going to look like an idiot. ;) So you're welcome [huge sigh of relief]. I'm little Miss Ohms Law around these parts. :)

As far as the Gumstix or Hammer are an option if you're willing to live with the programming complications they add. Telepresence will be more complicated because you'll either be living with a wireless webcam and extracting the stream on a non-windows platform [generally with no documentation] or you'll be limited by what cameras v4l (video for linux) will support and the fight of getting v4l compiled and running on the Gumstix or Hammer might be substantial. Not sure if Dale (LinuxGuy) has attempted it or not.

JonHylands
07-22-2008, 12:58 PM
Using a gumstix isn't that bad. If we're using wifi cameras, you can decode that on your laptop. The gumstix has a wifi option, so you can talk to an application running on the gumstix with ease.

Alex
07-22-2008, 01:38 PM
Chiming in a little late here, I didn't notice anyone talking about the BrainStem. It sounded to me like you haven't tried it out much yet. I don't have any experience with it, but I had a friend that used it a few years back and he absolutely loved it. That was coming from an EE major in his last two semesters. Really smart guy too.

Then again, that was a number of years ago, so the BrainStem might be outdated, anyone? At any rate, if you're looking more at a PC based solution, then your BrainStem probably won't do you much good, except if I'm missing something obvious here...

jafoca
07-22-2008, 01:52 PM
Chiming in a little late here, I didn't notice anyone talking about the BrainStem. It sounded to me like you haven't tried it out much yet. I don't have any experience with it, but I had a friend that used it a few years back and he absolutely loved it. That was coming from an EE major in his last two semesters. Really smart guy too.

Then again, that was a number of years ago, so the BrainStem might be outdated, anyone? At any rate, if you're looking more at a PC based solution, then your BrainStem probably won't do you much good, except if I'm missing something obvious here...

Hey - Your not missing anything. Basically I am wondering if the brainstem will be a good learning platform, that I can upgrade from later on to something with networking and video capability.

Have their been any major advancements in hobby level robotics since I bought this brainstem 5 years ago, in terms of processing power or ease of programming?

jafoca
07-22-2008, 01:59 PM
Idunno, perhaps the power limitations of the mini-itx and the LiPO combination are acceptable?

The 53W is the peak power usage for the board, and I would guess that it would be running at less than 50% usage the vast majority of the time, so maybe it would average more like 3-3.5 hours of use on a charge for the board?

How did you derive the 3300mah/2 conservative measurement? I know that it is absolutely necessary to keep LiPO batteries at least at some base level of charge, so is this your way of approximating that? Not that I disagree, but am curious.

Adrenalynn
07-22-2008, 02:48 PM
Yup. The wide input power supply that you MUST use won't run below about 6.4v. The LiPOs maintain voltage with steady current dropoff so they're harder to approximate per-se, but I've yet to see a battery that can deliver more than 50% of its absolute flat rating and still hold its voltage up.

I was basing it from experience with about 5000 LiPO pack, 3.3v @ 1800mAh that we designed for GPS/Cell tracking devices.

jafoca
07-22-2008, 03:32 PM
Yup. The wide input power supply that you MUST use won't run below about 6.4v. The LiPOs maintain voltage with steady current dropoff so they're harder to approximate per-se, but I've yet to see a battery that can deliver more than 50% of its absolute flat rating and still hold its voltage up.

I was basing it from experience with about 5000 LiPO pack, 3.3v @ 1800mAh that we designed for GPS/Cell tracking devices.


by wide input do you mean something like THIS (http://www.mini-itx.com/store/information/M3-ATX-manual.pdf)? Accepts 6-24V input.

Adrenalynn
07-22-2008, 04:05 PM
Yup! Either the M2 or M3 should do it for you.

I like LogicSupply, btw: http://www.logicsupply.com/products/m3_atx

http://www.logicsupply.com/products/m2_atx

jafoca
07-29-2008, 10:34 AM
http://www.anandtech.com/systems/showdoc.aspx?i=3321&p=5

so the Asus Eee Box is an intel atom based desktop system.

This review clocks it in at 19watt power draw on full load.

I bet they are using the atom's mobile chipset in there which reduces the whole power load. That would be a good robot computer, however the thing is probably rigged to run on AC power, and it gets up there in price ($250). That is about the same price as a nano-itx.

Project is currently on hold. I don't know if I have the time, energy, or money to accomplish what I want. I was kindof hoping that this stuff was all easier to work with than it was 5 years ago, but I am not sure that that is the case.

Adrenalynn
07-29-2008, 11:00 AM
"at the outlet "

Georg Ohm called and asked me to kick the author's butt. I'll be back in a few minutes. ;)

Unless it's detailed somewhere in the article that I didn't see at a quick browse, it really means absolutely nothing. We really need a little more information before we can compare apples to apples. I didn't see how the current draw test was conducted there. :)

Five years ago, you'd have been dragging around 10 lbs instead of 1lb. That's a pretty good trade!

jafoca
07-29-2008, 12:01 PM
Five years ago, you'd have been dragging around 10 lbs instead of 1lb. That's a pretty good trade!


???

My guess would be that he used a "Watt-Meter" type device at the outlet. I can understand that that might distort the readings somewhat based on power source used, but would it not bias the readings upwards?

///edit

oh I bet you are talking about the computer parts weight, right?

Adrenalynn
07-29-2008, 01:20 PM
No, it wouldn't bias them upwards.

amps = watts / volts
watts = amps * volts

We're concerned with the actual DC wattage being pulled from our batteries. That dictates runtime. There's no enough information there for the "19 watts" to mean anything, really. More a measure of heat dissipation.

Yes, power for power, weight for weight, dollar for dollar, you're ten times better off today than your were five years ago.

LinuxGuy
07-30-2008, 02:31 AM
The atom is about as low-power as possible for an x86 cpu. The main reason for going with this over a pico is price, a pico ITX would cost over 2x as much!
You pay for the increasingly small size of these boards. There is a price for miniturization. :happy: There probably isn't much, if any, "dead" space on the pico-ITX board.

8-Dale