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Offline GravitonTopic starter

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RC Robot
« on: December 08, 2007, 03:23:11 PM »
Hello,
I am new to robotics, and I have decided to start by making an RC robot. I have found this kit: http://www.robotshop.ca/home/products/robot-parts/communication-control/rc-communications/gws-dream-starter-gwt-4a-4-channel-fm.html
which includes a transmitter, receiver, and 4 servos. I am not sure if these servos rotate continuously (I know of others, but I want to buy this kit). I have looked at the 'how to modify a servo' tutorial and I'm not sure if you need a mircrocontroller to do so (the tutorial makes references to them). Also, on the site I have specified, there are some grip/claws that have servos included; could I control one of these with a transmitter?
Thanks

Offline HDL_CinC_Dragon

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Re: RC Robot
« Reply #1 on: December 08, 2007, 05:22:32 PM »
Not many servos come already modified for continuous rotation so It would be safest to think they are rated for only 90 degree travel

You can use a micro controller or you can build a simple circuit that outputs a frequency that tells the servo to stop (I think 1400 uS tells servos to turn to zero location) and use that for the signal rather that the micro controller. You can pretty easily make one using a 555 timer. Just google "555 timer circuit" for an easy to follow schematic diagram for one. Youll most likly find ones for blinking LEDs. Replace your servo with the blinking LED in the circuit and your good to go :) Make sure you pay attention to the frequency of the pulses its sending out.

And yes, you can control as many servos as your receiver and transmitter has channels...
If im not mistaken you can control multiple servos on one channel with the help of a micro controller... only 95% sure on that one :P
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Offline cooldog

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Re: RC Robot
« Reply #2 on: December 08, 2007, 06:42:32 PM »
ya you can get a haress (i think is called a y harness) so the you can put 2 servos on 1 channel and they will turn the exact same. geat for 4wheel drive robots
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Offline HDL_CinC_Dragon

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Re: RC Robot
« Reply #3 on: December 09, 2007, 12:04:58 AM »
yeah the only reason I didnt suggest a Y-Harness in the first place is im not sure if hooking up the two servos without a power amplifier (such as an MCU) would deteriorate the signal at all... I dont know.
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Offline GravitonTopic starter

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Re: RC Robot
« Reply #4 on: December 09, 2007, 10:48:26 AM »
Would you need a Y-harness for a two-wheeled RC robot with differential drive?

Offline ed1380

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Re: RC Robot
« Reply #5 on: December 09, 2007, 10:53:02 AM »
no. the y harness sends the same sigral to seperate servo's. on a diferential drive robot you'll need each servo to get seperate messages if you want to be able to steer
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Offline cooldog

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Re: RC Robot
« Reply #6 on: December 09, 2007, 04:37:59 PM »
ya but if you want differental drive with 4 wheels you can use 2 servos and a y harnes on 1 side for 1 ch on the reciver then do the same for the other side for a different channel
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Offline ed1380

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Re: RC Robot
« Reply #7 on: December 09, 2007, 05:01:47 PM »
that'll work
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Offline cooldog

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Re: RC Robot
« Reply #8 on: December 09, 2007, 05:29:29 PM »
for moding the servos you don't need to build the circut it is just if you don't have a reciver and transmitter just plug the servo into the reciver and it will turn to 0
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Offline bukowski

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Re: RC Robot
« Reply #9 on: December 11, 2007, 10:42:44 AM »
Watch your trim settings on your transmitter.

Also, if you want to skip modding the servo, you can buy one from paralax already modified for continuous rotation for ~$12 ea.

Offline ed1380

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Re: RC Robot
« Reply #10 on: December 11, 2007, 03:25:10 PM »
or put resistors instead of teh pot and you won't need to glue anything
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Offline GravitonTopic starter

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Re: RC Robot
« Reply #11 on: December 19, 2007, 07:34:21 PM »
Hello again,
I've ordered some parts (2 continuous servos, 2 regular servos (for the claw), a claw, receiver, transmitter, etc.).
However, I am having some problems. I ordered this package for the transmitter, receiver, etc. : http://www.robotmarketplace.com/marketplace_rc_radioGWT4A.html
Being as neglectful as I am, I forgot to purchase the battery pack for the receiver, and instead I bought the 5V regulator. I am not sure how to utilize the regulator, so I am looking for some guidance. Also, I am having problems with the receiver (from GWS Model R4P 2) as I do not know how to turn it on ( the instructions say to turn the receiver on last, but I can't even find the switch). I also can't find the spot to put the crystal into the receiver. Please give me any guidance and any other tips for problems I might encounter.

Thanks again

Offline Trumpkin

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Re: RC Robot
« Reply #12 on: December 28, 2007, 06:06:03 PM »
the reciever might not have a switch on mine you just plug in the battery and it turns but I do not have the same reciever either.
Robots are awesome!

Offline GravitonTopic starter

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Re: RC Robot
« Reply #13 on: December 30, 2007, 01:07:36 PM »
Hello again,
I've almost finished my robot. The receiver is accepting the signal, but I have a few problems. First of all, for some reason, the antenna on the transmitter (fully extended) has to touch the antenna on the receiver for anything to happen. Also, no matter what I do with the transmitter, it only causes the servos to 'twitch.' In other words, the servos move forward, and then back. Finally, if I wiggle the antenna (on the receiver), if it moves, or occasionally by itself, the servos twitch by themselves. What should I do?

Thanks again

Offline cooldog

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Re: RC Robot
« Reply #14 on: December 30, 2007, 04:08:48 PM »
check the batteries
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Offline GravitonTopic starter

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Re: RC Robot
« Reply #15 on: December 30, 2007, 05:12:23 PM »
I've checked the batteries in the transmitter (I charged them) and I also tried switching the batteries that I hooked up with the receiver (4 NiMH 1.2 V AA batteries in a battery holder) already with other batteries, and nothing seems to work.

Offline Admin

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Re: RC Robot
« Reply #16 on: January 14, 2008, 09:28:30 AM »
Did you get it to work?


Is the frequency for the receiver crystal the same as the frequency of the transmitter crystal?

Offline SmAsH

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Re: RC Robot
« Reply #17 on: January 14, 2008, 08:59:06 PM »
yea ive had that problem before with rc kits...never resolved them
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Offline GravitonTopic starter

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Re: RC Robot
« Reply #18 on: January 17, 2008, 06:41:18 PM »
Did you get it to work?


Is the frequency for the receiver crystal the same as the frequency of the transmitter crystal?
I haven't gotten it to work, and I'm not really sure what to do.
Also, I've never found a place to put the transmitter crystal into the transmitter, oddly enough. I've read through the manual and haven't found a place to put it. Nonetheless, the transmitter is 75Mhz and the receiver crystal is 75Mhz, so I guess that's why it's somewhat working (more specifically, the servos move slightly).

Offline cooldog

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Re: RC Robot
« Reply #19 on: January 17, 2008, 08:22:45 PM »
thw servos moving slightly is probebly radio interfirence
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Offline paulstreats

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Re: RC Robot
« Reply #20 on: January 17, 2008, 08:40:40 PM »
Is the receiver supposed to work with servos? Some of them are set up to use motors on some channels.

Offline SmAsH

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Re: RC Robot
« Reply #21 on: January 18, 2008, 04:57:25 AM »
Is the receiver supposed to work with servos? Some of them are set up to use motors on some channels.
he has a point. i have seen several cases where they were on a channel that only supported dc motors. you should check it out on google.


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Offline garriwilson

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Re: RC Robot
« Reply #22 on: January 18, 2008, 08:53:47 AM »
You said you didn't put in the crystal into the transmitter, right? So how do you expect it to communicate with the receiver unless they are in physical contact? I need to go right now, but you can search on google how to put in a crystal. If you don't get results I'll try to do a search after school.

Offline Admin

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Re: RC Robot
« Reply #23 on: January 20, 2008, 05:51:37 PM »
I second what garriwilson said.

That servo jitter is caused by random electrical noise.

 


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