Author Topic: New guy robot questions (Read 4907 times)

Spiffyguy · « **on:** February 29, 2008, 08:12:10 PM »

Howdy folks. New guy here. Let me start by saying thanks right off the bat for all the great information on this site. I am learning quite a bit. I have decided to start learning to make a robot. I have been learning a little C/C+ but I have nothing to really program. So I figured I would learn how to program a robot. I am still very new to electronics, I can solder and have a basic understanding but I an not well versed in schematics and such.

So here is my plan. I want to create a wheeled robot that will be able to do a variety of things. I will start with the simple and work towards the more complex. The basics would be to move and avoid obstacles. The more complex would be to maybe do some terrain mapping? or track through an obsacle course to a certain object. I have a bunch of RC car parts so I am going to use them. Once the car is moveable then I can look into adding on some electronics that will perform my tasks.

As any new guy I have questions. As I am progressing through the myriad of car parts, all from about 15 years ago, I am trying to think of what is best to use. I have a few electronic speed controls and one mechanical speed control. I am not completely sure if they work at this point. I have forgotten most of my RC wiring skills so I am having to learn that too. I am thinking that a mechanical speed control will be easier to use since it is just a servo to move the control. But I have heard that if you run a mechanical speed control at a low speed it can burn it up. So question number one is: mechanical or electronic speed control.

Power wise I was planning on using an RC battery to power the car motor. The brains could be powered by a separate battery pack. This should also isolate the powerful motor from the delicate electronics. I don't think the extra weight of the 2nd battery pack will effect the vehicle. Question two: Will the 4 wheel frame make it more difficult to control the car once it has obstacle checking electronics on it. It won't turn on a dime like the small bots that have no turning wheels.

I am starting to work in sketch up to figure out a good design for placement of all the components. I am also interested in the Arduino boards. I may try to integrate a USB connection to help out with programming.

Anyway I am sure I will ahve a ton more questions as I progress but any thoughts would be great. Design is key obviously and any input helps out.

Thanks
Spiffy

AndrewM · « **Reply #1 on:** March 01, 2008, 10:12:45 AM »

1) If you have it, use an electric speed controller. You will have better response times, use less energy (at least on the controller side), less likely to overheat (if I remember from my RC days correctly) thus a longer lifespan, and you don't have to waste a servo.

2) Yes. Most of the simpler designs make use of two motors/servos for locomotion and control. You just turn on each motor in turn at a certain speed to control movement. With a four wheel design using an RC car (assuming a single motor differential gear box) you now have to control the speed (and they have a tendency to keep moving even once the motor is stopped) as well as the turning.

Spiffyguy · « **Reply #2 on:** March 01, 2008, 11:44:17 AM »

the reason I was planning on using a turning wheels in the front is I was hoping to have the car be able to navigate outside. I am not sure that would be possible if I used the rear wheels to set the direction. Don't think it would track well. I might be wrong though so that is why I am asking. What is the main reason people use servos as the wheel motors? Cheap and easy to use? I have 3 motors, and I am pretty sure at least two of the work lol. If I used a motor for each drive wheel how big of a pain is it to sync them up to do the steering. I have a couple electronic speed controls that I could use, provided they work correctly.

AndrewM · « **Reply #3 on:** March 01, 2008, 12:10:52 PM »

There are a number of reasons for using servos for robot drive, the first being that they are very easy to control using PWM from an mcu. Motors require some sort of H-bridge to provide control, which can get complicated for beginners to work with. Another reason is that because of the gearing in servos, they tend to not roll on their own, so turning off the servo equates to a relatively short stop. Speaking of gearing, servos have it built in, and while you can get motors with gearing designed into them (gearhead motors), they become more expensive than a servo.

If you can get your drive wheels to turn at the same rate (a single motor with differential gear box, or using two motors with pwm control from an h-bridge), the only turning your platform would do is by the front steering wheels. As you said, it won't turn on a dime, but it would work relatively easily.

Spiffyguy · « **Reply #4 on:** March 01, 2008, 11:35:19 PM »

I think I will work with the $50 tutorial and start expaning off of that. Couple questions of course.

I am planning on buying the ATmega168 chip. Is there any thing I should be concerned about using this chip in the project. Gist I get is this is a better chip that the ATmega8 due to the higher memory but the max I/O pins is different on the atmel website. That is why I ask if it changes any thing.

I am going to order up the AVR ISP2. I will certainly have to ask before I solder on the program headers though. since the ISP2 has different connector.

airman00 · « **Reply #5 on:** March 01, 2008, 11:55:30 PM »

yes some changes have to be made if you will be upgrading

http://www.societyofrobots.com/step_by_step_atmega168_swapout.shtml

Spiffyguy · « **Reply #6 on:** March 06, 2008, 02:46:39 PM »

one more quick question. I have gotten all my parts together. I still need to get a battery pack. I figured I could just stop by the hobby store and get one and a charger. They didn't have anybody useful that could help. Seemed to get confused when I told them I wanted a 6V NiMH pack and a charger. SO I guess I need to order one online.

I am looking at this one, http://www.onlybatterypacks.com/showitem.asp?ItemID=10406.7 but I am not sure of the discharge amps. this one is 3 amps but they have a 1700mAh one that is 20 amps. Being a noob I am not sure which one I need to get.

would this be ok for a simple charger? http://www.onlybatterypacks.com/showitem.asp?ItemID=10031.12 or would I need to go buy something a bit more expensive. I know that is an over night charger which is fine for me.

Sorry for the questions but I don't want to buy the wrong thing.

Thanks

Admin · « **Reply #7 on:** March 09, 2008, 02:41:21 PM »

Quote

I am looking at this one, http://www.onlybatterypacks.com/showitem.asp?ItemID=10406.7 but I am not sure of the discharge amps. this one is 3 amps but they have a 1700mAh one that is 20 amps. Being a noob I am not sure which one I need to get.

Im actually using that exact battery right now on a robot arm I'm working on (that uses 5 servos). You basically need a discharge of at least .5A per motor. So 3A will work, no problem.

Quote

would this be ok for a simple charger? http://www.onlybatterypacks.com/showitem.asp?ItemID=10031.12 or would I need to go buy something a bit more expensive. I know that is an over night charger which is fine for me.

yeap that will work, but will take ~30 hours to recharge your battery . . . a bit too long . . .

This is the charger I am using:
http://www.onlybatterypacks.com/showitem.asp?ItemID=10085.12

It takes less than 3 hours on the 1A setting (the 2A setting didn't work correctly for this battery on that charger).

Spiffyguy · « **Reply #8 on:** March 09, 2008, 04:23:54 PM »

thanks for the reply. I will get those ordered up then.

Spiffyguy · « **Reply #9 on:** March 09, 2008, 04:52:00 PM »

oh what connector do i need to get? There is a ton listed on that site.

Spiffyguy · « **Reply #10 on:** March 10, 2008, 08:13:01 AM »

i guess let me rephrase that. I need to get the jr/hitec/airtronics one but the site states that the battery side is male and the charger side is female. in the $50 tutorial doesn't the battery connect to some male headers. so wouldn't I want the battery to have female?

pomprocker · « **Reply #11 on:** March 10, 2008, 12:36:24 PM »

The Hitec male connectors look just like the ones you see on the end of servos which slide onto the male headers like a glove. Definitly get the battery side one.

Here is some good pictures of the hitec male and female, and futaba.

http://www.servocity.com/html/servo_connectors___pins.html

Spiffyguy · « **Reply #12 on:** March 10, 2008, 03:40:27 PM »

after looking at those pics I will get a the femal end for the battery and the male for the charger. Seems like the most logical. Just wasn't sure what type of connector to get. Thanks again.

pomprocker · « **Reply #13 on:** March 10, 2008, 07:30:23 PM »

get the kind they recommend for battery and charger

Spiffyguy · « **Reply #14 on:** March 10, 2008, 08:03:20 PM »

they show the male for the battery and female for the charger. If the headers on are male that isn't going to work. The $50 tutorial shows the charger with a male end as well. That is why I asked. don't want to spend 50 bucks on a battery and charger and have to change things after I get them.

pomprocker · « **Reply #15 on:** March 10, 2008, 08:30:58 PM »

yes it will trust us.

the male headers on the board dont have a housing. so the male hitec connector will slide right on. when they say male they are just refering to the actual housing, not the actuall pins sticking out. the male hitec connector still receives the pins inside of it. kind of confusing i know. inside the female hitec housing are pins sticking out. so you would not be able to connect it to the male headers on the board. the pins in the female connector are just sheathed by the housing.

Spiffyguy · « **Reply #16 on:** March 10, 2008, 09:16:39 PM »

ahh ok good thing I asked then. I will order it up tomorrow and get rolling on it.

Admin · « **Reply #17 on:** March 15, 2008, 02:10:34 PM »

Quote

the male headers on the board dont have a housing. so the male hitec connector will slide right on. when they say male they are just refering to the actual housing, not the actuall pins sticking out. the male hitec connector still receives the pins inside of it. kind of confusing i know. inside the female hitec housing are pins sticking out. so you would not be able to connect it to the male headers on the board. the pins in the female connector are just sheathed by the housing.

I dont quite understand what you meant above, so I'll just say it summarized:

In the $50 Robot tutorial, I used a battery with a female connector (female cause it has holes in it), a charger with a female connector (but I stuck header pins into it to convert it into male), and on the circuit board I used male pins (cause they are pointy, hehe).

Spiffyguy · « **Reply #18 on:** March 15, 2008, 02:28:23 PM »

ahh ok. I ordered up like the website said. i think the charger is male. no worries. I will get it to work.

pomprocker · « **Reply #19 on:** March 15, 2008, 05:15:33 PM »

Quote from: Admin on March 15, 2008, 02:10:34 PM

I dont quite understand what you meant above, so I'll just say it summarized:

The connector you have on your battery I am pretty sure is considered male because while the pins go inside of it the connector housing itself is phallic in nature

whereas the charger side, while the pins stick out they are hidden by the connector housing which i think is considered female because of he fact that it accepts the male connector inside of it.

So when you put the two together a connection is born

Like this drawing here, you can see the pins sticking out, but they are sheathed by the housing. This is considered a female hitec connector.

[img width= height=]http://www.batteriesamerica.com/Image11.gif[/img]

So you would NOT plug the female connector onto the male headers on the PC Board because they both have pins sticking out.

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Author Topic: New guy robot questions (Read 4907 times)