4WD + WiPort

Lynxmotion Rovers, Sumo, and Tracked
1

I just “found” these forums, so I apologize for emailing tech support directly.

I have the full autonomous 4WD kit, SSC-32 servo controller, and the WiPort kit from WiBotics. I’m using this all for a grad course project to demonstrate “communication & mobility” - i.e. controlling a robot thru WiFi. I’m no expert in robots and would put myself at a low-ish intermediate level (definitely not a complete newbie).

My Question(s):

How do I connect the SSC-32 to the Scorpion and Bot Board?

I’ve been scouring the website and all I can find is the wiring scheme for the hexpod. Should I just use that and wire the I/O ports for only 2 inputs? I’m at loss here, the project is supposed to be “simple” – hence the reason I bought a kit and didn’t build the robot from scratch.

Thanks,
– Kristine Vacola, B.Sc.(EE)
[email protected]

2

Hi Kristine,

I found this electronics guide for the mini atom bot board:

lynxmotion.com/images/data/abbpdf02.pdf

it’s in information -> electronics guides -> bot board

The wiring diagram on page 9 is for connecting the bot board to a scorpion to drive a 4WD with 3 sharp sensors. I’m not sure where the SSC would fit into this as you didn’t specify if you’re putting an arm, a pan-tilt assembly or gripper, etc on the bot.

The wiring diagram on page 5 combined with the one on page 9 might be what you’re looking for.

I’d love to hear about your project as well as what graduate program you’re going through (communications track?). The project section is a nice way to keep the community up to date on your project, hehe 8)

Regards,

Mike D

3

Hi Mike,

I don’t have anything special on the bot except for the WiPort (i.e. no arms or anything … just the bot). I haven’t hooked up the sensors yet, and honestly I didn’t want to because the bot was gonna just be controlled via WiFi.

So, what you’re saying is that I can control the DC motors of the 4WD bot by kinda melding page 9 with page 5?

Once the thing looks a little better I’ll post some pics to the projects area.

I’m a master’s student with (sorta) a Biomedical edge, however I’m starting to lean towards communications.

– Kristine

4

Hi Kristine,

I’m pretty sure you don’t need the SSC-32 at all to control the DC motors, I had thought you got the SSC for an arm attachment or other servo assembly. If that isn’t the case then I think all you need is page 9.

Basically, if you read through the scorpion description on it’s spec page, it requires a 21-22mS period PWM signal with a 20mS off-time and an on-time that swings from 1.0mS to 2.0mS, with 1.5mS being dead stop, 1.5<t<2.0 causing forward motion and 1.0<t<1.5 causing reverse (well, it all depends how you hook up the motor and which way is left, right, etc) - the furthur you are from 1.5mS (in either direction) the faster it goes.

[if anyone has better experience with the scorpion please chime in, I haven’t gotten mine in the mail yet]

Biomedical? Cool! Rutgers had a very up and coming biomedical engineering program while I was attending, heck, my BME friends knew more about electronics before I did. I would love to go back to advance my degree, but, work…hehehe)

Mike

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Hi Mike,

First off, thanks for getting back to me so soon … I really appreciate it. I plan on working on the robot tonight … so if you’re gonna be online we could communicate a little more directly thru MSN.

I was told by someone at WiBotics that I would need the SSC-32 to interface with the WiPort because it doesn’t have direct outputs to DC motors. However, the WiPort’s GPIO lines could control the DC motors directly by simply switching the motors on and off – pretty crude and the control would be limited.

What do you think?

– Kristine

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No. those GPIO lines are like most and will source somewhere around 25ma. If you try to drive motors directly from them the most likely outcome will be frying the WiPort. You’ll need an H-Bridge like the scorpion.

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So feed the GPIO lines into the Scorpion (which I have) and then Scorpion to the BotBoard? I’m guessing I treat the GPIO inputs into the Scorpion as if I was connecting an R/C to the Scorpion (like they show in their documentation)?

Question: how “rough” is the control if I use just the GPIO lines from the WiPort instead of the SSC-32?

– Kristine

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Hey Kristine,

I’m at work right now but I thought I would chime in while on my lunch break.

What I would do is hook the wiport up to the ABB (which uC did you buy? Atom Pro 28?) as inputs, then use those inputs to control output PWM waveforms to feed into the scorpion. It would take some tweaking to get a good input/output mapping but it shouldn’t take too much empirical data.

I’m off at 5:30pm EST, maybe we can work on this tonight for a bit.

Mike D

PS reading through a little bit, you might not even need the ABB, it depends on what the WiPort I/O outputs. If you can get some documentation on the wiport (I looked at the website briefly last night after football) I might be able to piece things together.

9

I did buy the Atom-28 (it’s the one that comes with the autonomous kit for the 4WD-1). I’m at my day job right now, but I plan on working on my robot after about 7:15pm Central (I’m in Winnipeg, MB, Canada). Where are you located?

I guess I should get on and order a battery pack – didn’t exactly do that when I ordered the bot. Is there one in Digi-Key that I could order? I prefer to stay with a Canadian distributor, it’s a lot easier for me to order them and they I don’t pay duty or have to wait a week for it to clear across the border. (Although the CDN dollar is doing pretty darn good right now!)

– Kristine
([email protected])

10

Kristine,

Mike lives in New Jersey.
(He and I met at the South Jersey Robotics Group.)

For battery packs…
well, you could go to just about any local store and pick up some rechargable NiMh batteries.

You’ll need to get battery holders from Radio Shack (or the Canadian equivalent), though.

However, I’ve had quite a bad experience with home-made packs, so I recommend buying one.

Digikey…
Yep, there’s a ton.
Search for “battery”.
Under the “battery assemblies” heading, click on “Nickel Metal Hydride”.

You’ll want a pack that’s 7 or 10 cells (depends on your motors).
That equates to 8.4V or 12V.
If I were you, I’d shoot for nothing lower than 1500mAh.
The more mAh, the merrier.
However, the more mAh, the bigger your battery will probably be, and thus the heavier.
You’ll probably want to stick to AA or SC (Sub-C) cell-types, to keep that weight at a minimum.

By the way… I’m also using the WiPort, although it’s for a servo project (a Humanoid Biped).
I haven’t used the GPIO for anything, yet; I’ve pretty much just stuck to using a TTL Serial Port to create a virtual bridge between my computer and the bot’s electronics.

This isn’t going well, though, as I haven’t been able to get it working.
Either this or next week, though, I’ll be going down to the SJRG again, and, hopefully, the guys will help me get it running.

I’d like to hear how your project progresses.
Please keep us updated.

^.^

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Hey Kristine (and hi Nick!)

I’ll shoot you a PM with my windows messenger ID thingy, we can go over your project tonight if you like, I’ll be messing around with my eyecon.

Yay! My lynxmotion order got shipped today =D

Mike

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Just a quick shot of the bot so far from my Samsun A920 phone. (1.3MPix)

http://home.cc.umanitoba.ca/~umvacola/robot.jpeg

– Kristine

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Kristine,

Just FYI, I found out through a convoluted set of emails with David (the guy behind www.wibotics.com) that the GPIO pins function at a rate of about 10,000 bps.

He implied that rewriting the firmware to make the GPIO pins a priority would increase that rate.

You might want to talk to him about that if you run into issues with data lag.

For now, though, I doubt that you’ll have problems running at that speed, since your only sending instructions.