Author Topic: My Yard Robot Prototype (Read 10005 times)

ArcMan · « **on:** October 04, 2008, 09:19:15 PM »

A video of my yard robot prototype.

[youtube]fd2HH8mjC5s[/youtube]

Rebelgium · « **Reply #1 on:** October 05, 2008, 09:51:48 AM »

Looks like it has pretty decent power.

Wheelchair motors?
Howmuch battery life does it have?

ArcMan · « **Reply #2 on:** October 05, 2008, 10:04:08 AM »

Yes. I used 2 Merits wheelchair motors. They draw 11A ea full load. I have 32 AH batteries, so I estimate about 2 hours run time with a smaller load like a lawn mower or aerator.

ryan · « **Reply #3 on:** October 07, 2008, 11:22:54 PM »

Nice robot Arcman. Are you planning to include other sensors like sonar later?? What components did you used for the remote controlled system?

ArcMan · « **Reply #4 on:** October 08, 2008, 05:01:29 PM »

Thanks. Right now I'm thinking about tele-operation as my next step. e.g. mounting a wireless web cam and driving it from inside the house. My current radio probably doesn't have the range for that, so I will have to work on that one. Perhaps some fast socket connection over a 802.11g network. After that, I will probably look at an IMU and other sensors for autonomous operation. Sparkfun has an affordable IMU now. I saw an IMU-equipped robot navigate several hundred meters out and back in an outdoor setting and ended up within a few inches of where it started! It even had to go around a couple of trees.

Currently I'm controlling it via a standard JR Racing R/C car controller (which I'm holding in my hand). I've programmed a PIC 16F876A to convert the throttle/steering signals to right and left motor commands. I recently added acceleration limiting which greatly improved handling. The PIC commands the awesome Dimension Engineering Sabertooth drive which drives the wheelchair motors. The control system also features an E-stop circuit, which I've had to use a couple of times

ryan · « **Reply #5 on:** October 08, 2008, 07:15:10 PM »

What programming language did you used? A sabertooth r/c dual controller?

ArcMan · « **Reply #6 on:** October 09, 2008, 08:24:37 AM »

The PIC is programmed in the C language. I used the CCS C compiler. There's actually a good bit of floating point math going on to do the conversion from R/C throttle/steering to right/left motor drive. The Sabertooth drive is the 2X25 (2 motors @ 25A max.).

mhanuel · « **Reply #7 on:** October 20, 2008, 01:53:41 PM »

Very Nice,

Let me ask you, the most part of the weight resides above the swivel castor wheels, which are in the front of the robot. That means the motor need to push the load which could be a problem right?

Regards,

ArcMan · « **Reply #8 on:** October 21, 2008, 09:15:32 AM »

Actually, most of the weight is centered around the rear wheels - the motors and the batteries. After I mount the mower deck, it will be centered between the front casters and the rear wheels.

Of course, front and rear is relative when your talking about a differential drive bot.

ryan · « **Reply #9 on:** October 26, 2008, 07:30:01 AM »

To control the motors (for differential steering) with the Sabertooth, what did you used PWM? And how did you do that?

ArcMan · « **Reply #10 on:** October 26, 2008, 10:22:42 AM »

Basically, I convert incoming steering and throttle R/C pulses from my receiver into differential drive percentages. Those are sent to the Sabertooth drive via a serial line using their "simplified serial" protocol. My PIC also outputs 2 PWM pulses for use with other drives. There is also functionality for "radio lost" shutdown and acceleration control.

ryan · « **Reply #11 on:** October 28, 2008, 09:43:25 PM »

Hmm I'm using the PIC16F877A which has 2 PWM. I need my robot to move at 20 rpm but the motors I have got is 150 rpm at no load (parallax motor kit) and I need differential steering for the robot.What mode is best, for me as a novice, to set the Sabertooth to work with the PIC - Mode 1 Analog Input?

Admin · « **Reply #12 on:** October 30, 2008, 04:07:14 AM »

Quote

I need my robot to move at 20 rpm but the motors I have got is 150 rpm

You need the wheels to move at 20rpm, or the robot move at some particular speed? The mechanical way to slow your robot down is to reduce wheel diameter - and it gives the added benefit of boosted torque.

The Sabertooth can work with RC, PWM, serial, etc. Whats great about the RC mode is that you can use simple servo code and it'll work. But if you already got PWM working, I recommend using that more . . .

555 timer chip guy · « **Reply #13 on:** October 30, 2008, 09:06:24 AM »

I'm in FIRST Robotics competition and we are using sabertooth controllers this year.

ryan · « **Reply #14 on:** October 30, 2008, 09:08:50 AM »

I need the robot to move at 20 rpm...and the wheel diameter have to be 25 cm or 30 cm...but my motor is overated at a no load speed of 150 rpm

Admin · « **Reply #15 on:** October 30, 2008, 10:50:16 PM »

Quote

I need the robot to move at 20 rpm

But . . . rpm is not a measurement of velocity

the wheel diameter have to be 25 cm or 30 cm
I'm guessing those are the two wheels that you have? If your robot is too fast, use the smaller diameter.

Quote

but my motor is overated at a no load speed of 150 rpm

No load speed doesn't mean very much . . . got a motor datasheet with load/rpm curves?

Other options:
You can reduce the motor voltage, or use PWM to slow your motor down.

ryan · « **Reply #16 on:** October 31, 2008, 02:49:38 AM »

Hmmm the wheels I got with the kit is 16 cm diameter. I have to construct new wheels with a diameter of 25 cm or 30 cm so that there is space underneath the robot to fit in the mower blades and mower disk.

The parallax motor kit did not give any detailed specs of the motors. I got this graph from another forum:

ryan · « **Reply #17 on:** October 31, 2008, 02:52:14 AM »

Sorry Arcman for spoiling your thread

ArcMan · « **Reply #18 on:** October 31, 2008, 08:53:15 AM »

Damn you, thread hijacker!

Just kidding. I don't care. I'm glad my post spurred some discussion.

Rockyboy53 · « **Reply #19 on:** November 13, 2008, 09:31:56 PM »

How did you make the chassis? It looks like a plank of wood for a bench, but I can't tell. SWEET! Nice robot by the way.

Rockyboy53 · « **Reply #20 on:** November 14, 2008, 09:03:17 PM »

Quote

I'm glad my post spurred some discussion.

My bad, I guess that sentence was symbolic of "I'm tired of questions on this thread." Never mind...

...unless you want to answer my question (though I'm not directly requesting that)

ArcMan · « **Reply #21 on:** November 14, 2008, 09:49:33 PM »

I'm not sure what you meant by your second post... Anyway...

The chassis was made with 1.25" square steel tubing, 0.083" wall. MIG welded with the awesome Lincoln Electric 130T. I was sitting on the robot in the video to show the strength of that frame. Next year it will carry a lawn mower. I just C-clamped on that wood plank so I could ride it.

AdvsNoob · « **Reply #22 on:** November 24, 2008, 06:22:01 PM »

Good bot! Looks like you where having fun!

jfischer · « **Reply #23 on:** April 05, 2009, 12:48:59 PM »

I know this is a old topic, but is basically what i am looking to build, (unless some others might be able to come up with some better ideas)

I am in a wheelchair, and looking to build something that I can unload things onto out of my van (the bot doesn't have to be able to unload it, just carry things)

I have gravel and a slight downhill it needs to go down.

I have raced R/C cars and trucks for years, so don't think that will be a big issue with it, and would rather go with a wheel radio over the twin sticks.

I had thought of the idea of using motors and chain drive, but think that this might do the trick, only thing that kind of bothered me or concerned me was the motors look pretty close to the ground.

Any help or ideas would be appreciated. So I guess maybe it is time to look for some electric wheelchair motors, any out there know of any that are better then others. I have been in a wheelchair for 29 years. but am a T-5 para, and never used a electric chair.
Jeff

ArcMan · « **Reply #24 on:** April 05, 2009, 05:39:00 PM »

Quote from: jfischer on April 05, 2009, 12:48:59 PM

I had thought of the idea of using motors and chain drive, but think that this might do the trick, only thing that kind of bothered me or concerned me was the motors look pretty close to the ground.

Any help or ideas would be appreciated. So I guess maybe it is time to look for some electric wheelchair motors, any out there know of any that are better then others. I have been in a wheelchair for 29 years. but am a T-5 para, and never used a electric chair.
Jeff

Old topic, but I'm still working on it. If only my powers of observation were as keen as yours, I would have seen this problem during the design phase. But alas, I had to get it stuck in the mulch beds before I saw this. The photo below shows my new motor mounting orientation with my new 10" wheels. The ground clearance is much better. I will have a "yard test" in a few weeks.

I got these motors new on ebay.

jfischer · « **Reply #25 on:** April 05, 2009, 07:25:33 PM »

Wondering how the 10" wheels will work out for you? It looked like the others might have been 8" or so and I think in my yard that would have gotten hung up trying to jump from any concrete points to the gravel, or other places. Did you also add a inch or so height with the welded brace?

Anxious to hear how it works out and I will be looking around.

I don't think that radio you are using has the ability to mix channels on it, I have a old Futaba 3PK of which mixes pretty good, use it on a dual motor crawler and a Spektrum DX3R which has the ability to mix channels also, but doesn't do it as well as the Futaba. I would rather be able to use a good ESC for each motor, as I know the one truck I run now draws a ton, so it should have no problems with the wheelchair motors with them being geared down, but if worse came to worse I could buy a dedicated speed controller made for a bot that mixes.

But then again we are looking at 24volts here, so that might blow the idea on the R/C controllers, I know they will take 3s LiPo batteries with no problems, but that sure wouldn't be up to the voltage needed.
Jeff

Quote from: ArcMan on April 05, 2009, 05:39:00 PM

Old topic, but I'm still working on it. If only my powers of observation were as keen as yours, I would have seen this problem during the design phase. But alas, I had to get it stuck in the mulch beds before I saw this. The photo below shows my new motor mounting orientation with my new 10" wheels. The ground clearance is much better. I will have a "yard test" in a few weeks.
I got these motors new on ebay.

jfischer · « **Reply #26 on:** April 05, 2009, 08:03:52 PM »

I was looking at the 10" wheels you put on your project and they look a lot like any of the wheels you would get at Harbor Freight or any of those types of places

I know that most of those wheels just have a 5/8" bearing in them, did you take that out, change the hubs or what to be able to use a key in them, or did you use another method.
Jeff

ArcMan · « **Reply #27 on:** April 06, 2009, 09:30:52 AM »

Yes. Those are Harbor Freight wheels that originally had 5/8" ball bearings in them. I punched out the bearings and machined a hub from 1018 steel that press fit into the HF wheel hubs. The hubs have a (funky) 17mm bore to fit the motor shaft. Unfortunately, I don't have the ability to machine the necessary 6mm keyways, so I just put 2 6mm SS set screws in the hub that tighten down into the motor shaft keyways. Sloppy, but it works. The 6mm set screws fit snugly in the keyway.

jfischer · « **Reply #28 on:** April 12, 2009, 04:26:40 PM »

I have sent you a private message

Hope you had a good Easter, Jeff

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