Remote Controlled Robots

[julia1]

Hi, I`m trying to make that $50 robot with remote controls but in the tutorial there is no suggestion of a transmitter or receiver (and I did read the RC page)
So I was thinking of buying the GWS GWT-4A 75Mhz FM Transmitter (http://www.robotmarketplace.com/marketplace_rc_radioGWT4A.html) and the GWS 4- channel R4PII 75Mhz Pico Receiver - Vertical Pin Model (http://www.robotmarketplace.com/marketplace_rc-receivers.html) and GWS crystals of the same channel.
Is this a good option? They seem to be the cheapest transmitter and receivers on the market (with dual axis sticks) and I`m in a low budget (I know more expensive systems would be much better). I suppose I can connect the two Hitec 311 servos and the Hitec 72MHz Rx battery box directly to the receiver and then everything will work right away without having to configure anything or use any adaptors, right?
I would just buy it all and test it but then if it didn`t work I wouldn`t have enough money to buy another transmitter/receiver. Thanks in advance.

[airman00]

Just buy a cheap R/C car and use the wires going to the motors for your purposes.

[paulstreats]

Just buy a cheap R/C car and use the wires going to the motors for your purposes.

exactly the easiest way to go

[julia1]

well I tried doing that, I bought a RC car hoping to find a receiver inside but there was only a battery box and microcontroller directly connected to two DC motors. So no receiver and no crystals (I opened the transmitter and there was no crystal in it, but it works on 27mhz, I didnt know it could do that without a crystal).

I really have no idea what you meant by 'use the wires for your purposes' --> how? I`m a complete beginner

Besides, those cheap RC cars dont have dual axis sticks on the transmitters. The left stick only moves back and forward, and the right stick only moves left to right, which means its too hard to use those transmitters with robots with differential drive. The RC cars with dual axis transmitters are almost as expensive as the GWS transmitter I mentioned, so I dont think it`s worth it (and I dont know if they have a receiver inside them, or crystals, so  I`d have to buy one to find out)
In the USA those expensive RC cars must be cheap, so I suppose you were talking about them. But I live in Brazil, so I guess that RC car solution doesnt work for me? Or maybe I dont need the receiver/crystals/dual axis transmitters and I can still use the cheap RC cars somehow? Please let me know.

[Soeren]

Hi,

[...] Is this a good option? They seem to be the cheapest transmitter and receivers on the market

The standard answer to such a question (good/cheapest) must be "rarely".

I`m in a low budget

A very good reason for going with cheap, but you have to go over what your needs are and then check if the RX and TX fulfill those needs (with a bit of overhead).

(I know more expensive systems would be much better).

Better in what respect, you should ask yourself.

I suppose I can connect the two Hitec 311 servos and the Hitec 72MHz Rx battery box directly to the receiver and then everything will work right away without having to configure anything or use any adaptors, right?

Wrong. you need to generate the proportional signals that the transmitter has to send and decode them at the receiving end.

I would just buy it all and test it but then if it didn`t work I wouldn`t have enough money to buy another transmitter/receiver.

Ample reason to fully comprehend what's involved to make a complete transmission - proportional coder, transmitter, receiver, proportional decoder.

A proportional system can be build from the ground up quite simple and cheap, for up to 9 channels.
If you want to go with ready made TX/RX modules, a simple proportional (de)coder can still be used.

[airman00]

This is what you should do:
Buy an R/C car
Disconnect the wires from the motors. You should have 4 wires in total.
Now connect your motors to the wires. Two wires per motor.
Now you have R/C. For differential drive you would just have the left side of the remote control motor 1 and the right side control motor 2.

If you have motors which require more voltage than the R/C car gives then you would use a circuit which has diodes and relays. The diodes only allow one relay to be switched per direction per motor. If you need info on doing that just ask and i will explain.

[Gertlex]

This is what you should do:
Buy an R/C car
Disconnect the wires from the motors. You should have 4 wires in total.
Now connect your motors to the wires. Two wires per motor.
Now you have R/C. For differential drive you would just have the left side of the remote control motor 1 and the right side control motor 2.

I haven't really looked for R/C cars, but from the ones I have experience with, they generally come with one motor for driving, one for steering.  The non-tiny ones anyways.  And this makes sense.  Realistic scale models of cars would look silly having four wheels and differential drive on just the back two.

But I could be wrong.

[h3ro]

You can try http://ashishrd.blogspot.com/2007/02/computer-controlled-rc-car.html?

[airman00]

I haven't really looked for R/C cars, but from the ones I have experience with, they generally come with one motor for driving, one for steering.  The non-tiny ones anyways.  And this makes sense.  Realistic scale models of cars would look silly having four wheels and differential drive on just the back two.

But I could be wrong.

I know that, sorry if I wasn't clear...

I am saying that you use your own motors and make it differential drive( no steering motor).
Wait a second, julia, why do you want differential drive anyway?

[julia1]

I couldnt really understand even half of what you guys said... I was trying to make the $50 bot but with remote controls, but the admin did not go into much detail about how to make bots with RC (even in the RC page).
In step two of the $50 bot, he said: "Since I had some basic RC equipment around, I made my robot temporarily remote controlled just for fun.[...] I attached a battery to the velcro, and put the receiver inside the bottle. Both servos were attached to the receiver."
So when I read this, I thought it was just plug and play. I thought I wouldnt have to configure anything, just plug the servos and the batteries into the receiver, and use compatible crystals in the transmitter and receiver.
I didnt mean to use a microcontroller, as I have no idea how it works (and I'd really like to avoid getting a microcontroller from an RC car, because then it would be almost like taking a pre-made rc bot and changing the chassis), so I'd like to start off just with servos/batteries/transmitter/receiver.
By the way, someone asked and I want differential drive because the bot will only have two wheels.

"A proportional system can be build from the ground up quite simple and cheap, for up to 9 channels.
If you want to go with ready made TX/RX modules, a simple proportional (de)coder can still be used." --> Is this some sort of hardware? I dont remember reading any of this in the $50 bot. Are you talking about Teleoperation? If so, it says in the RC page that its optional... If not, then what are you talking about? 

[Soeren]

Hi,

--> Is this some sort of hardware? I dont remember reading any of this in the $50 bot. Are you talking about Teleoperation? If so, it says in the RC page that its optional... If not, then what are you talking about? 

I thought you might wanna build the remote control link yourself since you talked about a particular transmitter and receiver . and since you mentioned "low budget", I told you it could be done for cheap.
Yes, it's hardware and no, I don't believe you'll find it on the mentioned robot page.

It sounds like you wanna make a ROV'er (Remote Operated Vehicle) of some sort rather than a robot (which by definition cannot be remote controlled/tele operated, since then it would be nothing more than a ROV with no autonomicy).

Yeah I know, many people confuse the two, but never mind that, tell us what you want to build, what it has to do, and how much of it you are able to construct by yourself and it will be much easier to give a good answer.

[Admin]

In step two of the $50 bot, he said: "Since I had some basic RC equipment around, I made my robot temporarily remote controlled just for fun.[...] I attached a battery to the velcro, and put the receiver inside the bottle. Both servos were attached to the receiver."
So when I read this, I thought it was just plug and play. I thought I wouldnt have to configure anything, just plug the servos and the batteries into the receiver, and use compatible crystals in the transmitter and receiver.

Hey julia1, sorry for being confusing on my tutorial . . .

Yeap its as easy as you say (I said?). The links you mentioned for the parts (the first post) are correct and will work. That GWS kit will have everything you need, is cheap, and good for beginners. Do not get that optional reciever battery however, its waaaaay overpriced. Look around for one that has at least 1500mAh, and dont pay more than $10 per 1000mAh.

Remember, if you ever need any parts, check here first:
http://www.societyofrobots.com/robot_parts_list.shtml


Also . . .

The idea that airman00 mentioned will also work, and be a lot cheaper, but also harder and wont work as nicely. It also wont work with servos, just regular DC motors - one for stearing and one for driving.

[julia1]

okay thank you for your replies, I'll go with the GWS transmitter/receiver, then.
But about using the cheap RC car (because Ive already opened one and now its impossible to get it back together and I want to give it some use).
I tried attaching the two DC motors to two cardboard wheels (with Scotch tape). I also made a castor (bottle). Well, it doesnt move because I think the motor is not powerful enough (but it worked with 4 wheels in the original car, and they spin when I hold the chassis in the air). So I was wondering, if I use two plastic wheels (I cant use the ones that came with the car because theyre attached to an axle, but i'd buy new wheels) and an omniwheel as a castor (less friction), should it work?
If not, would any of these motors work?--->
"Small Johnson" motor (http://www.robotmarketplace.com/marketplace_motorsmisc.html)
Speed-380 Motor (http://www.robotmarketplace.com/marketplace_motorsmisc.html)
I'm not sure what to look for because some motors say "brushed weapon" or "brushless weapon" (too expensive) or "We recommend using the Sprite-25 speed controller for this motor, or the AUX channel of your Ant 150 controller".
I was hoping to buy cheap motors from Robotmarketplace because I'll be ordering other things from them, and that way I'll save on shipping. But then again, if I can use the motors that came with the RC cars (by using actual wheels and a different castor), then I won't need to buy other motors.
Also, can I attach wheels to the DC motors through cardboard instead of aluminium? (I dont have a drill and I cant attach plastic wheels with scotch tape) And what is a "gear box" and how do I know if a DC motors comes with it? (I read about this in the Robot Chassis Construction section of the site). Thanks

[Admin]

I tried attaching the two DC motors to two cardboard wheels (with Scotch tape). I also made a castor (bottle). Well, it doesnt move because I think the motor is not powerful enough (but it worked with 4 wheels in the original car, and they spin when I hold the chassis in the air). So I was wondering, if I use two plastic wheels (I cant use the ones that came with the car because theyre attached to an axle, but i'd buy new wheels) and an omniwheel as a castor (less friction), should it work?

Well the problem as you said is that the motors are really weak. If you use really small diameter wheels it might work . . . As for omni wheels . . . no chance, too much friction.

I would just keep the parts around as scrap for the future. The remote control can also be attached to a microcontroller to remote activate stuff if you wanted, for example.

If not, would any of these motors work?--->
"Small Johnson" motor (http://www.robotmarketplace.com/marketplace_motorsmisc.html)
Speed-380 Motor (http://www.robotmarketplace.com/marketplace_motorsmisc.html)
I'm not sure what to look for because some motors say "brushed weapon" or "brushless weapon" (too expensive) or "We recommend using the Sprite-25 speed controller for this motor, or the AUX channel of your Ant 150 controller". . . . what is a "gear box" and how do I know if a DC motors comes with it?

First, dont buy a motor that doesnt have gearing unless it is a prop for a flying robot or a race car robot . . . Those motors operate at 10's of thousands of rpm when you probably wont want more than 200rpm max. What you want is high torque, instead. A gear box will be some large clunky thing attached to the motor (it would be obvious when you compare with and without). But most importantly, its the specs - rpm and torque (as well as voltage, etc).

To know exactly what will and wont work, this tutorial will show you how to calculate it:
http://www.societyofrobots.com/mechanics_dynamics.shtml
Robot market place is real good about mentioning motor specs for you to work with

Also, can I attach wheels to the DC motors through cardboard instead of aluminium? (I dont have a drill and I cant attach plastic wheels with scotch tape)

You can use whatever you want . . . but I'd still say plastic/aluminum is better
If you use cordboard, dont use the type from boxes. Use the flat sheet kind that isnt in layers.

[maverick monk]

Just buy a cheap R/C car and use the wires going to the motors for your purposes.

no, cheap rc cars use a single board, its got a controler for the servo ( which is usualy 5 wire instead of 3, a non-remible cristle, and the h-bridge all in one, this is bad.

as long as you dont need more then 2 fully directional channels, thats a great cheap controler, altho if you go to towerhobbies.com, i think it comes with the controler, reciever, and 2 servo's