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Author Topic: Custom Servo  (Read 2622 times)

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Offline PolemusTopic starter

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Custom Servo
« on: April 01, 2009, 12:28:21 PM »
Hey guys / girls?

Is it possible to take the circuitry of a normal servo, rip it out and add it to a stronger dc motor?

i dont know servo's that well but i think they all make use of dc motors.

Thanx   ;D ;D ;D

Offline Razor Concepts

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Re: Custom Servo
« Reply #1 on: April 01, 2009, 01:17:24 PM »
The circuitry probably cannot handle a bigger motor.

A simpler solution would be to just make a servo yourself - motor driver, motor, and a encoder/potentiometer.

Offline offy

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Re: Custom Servo
« Reply #2 on: April 01, 2009, 01:27:15 PM »
The circuitry probably cannot handle a bigger motor.

A simpler solution would be to just make a servo yourself - motor driver, motor, and a encoder/potentiometer.


You don't need an encoder or potentiometer unless you care about the angle it is at. If it is just for drives, you will only need it to go forward and backwards unlimited until a sensor tells it to do other wise. So if it is for something other than drive, you will most likely need the encoder or potentiometer.

Offline PolemusTopic starter

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Re: Custom Servo
« Reply #3 on: April 01, 2009, 01:33:14 PM »
ah great, i only need it to go forwards backwards, and stop,

thanx alot

Offline Razor Concepts

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Re: Custom Servo
« Reply #4 on: April 01, 2009, 01:44:09 PM »
In that case all you need is a simple motor driver - I would reccomend the SN754410.

Offline PolemusTopic starter

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Re: Custom Servo
« Reply #5 on: April 01, 2009, 02:02:36 PM »
i just realised that what i wanna do is way more complicated.

My robot is running on a track, i need it to stop automatically at certain spots, (but that needs to be pre-programmed), i then also need to move it back and forth on the track(remotely).

why do i say its more complicated? well..... how on earth is the robot going to know what its current position is and how far the next position is? also...... how do i account for wheelspin?

eish... as far as i know... with full h-bridge i can measure distances traveled, but that does not account wheel spin (this little bugger needs to go fast so pull off will cause wheel spin).

I have a 100 meter track, so i guess i can use lazers to judge the distances from the two end of the track, this will give me the ultimate position of the bot. I can then do some calculation based on that.

questions:

1) does anyone know of a better solution?
2) is lazers the way to go, or is there a better method of judging distance? (GPS wont work cause its enclosed in a building)
3) does lazers cover 100m?


any suggestion?

Offline SmAsH

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Re: Custom Servo
« Reply #6 on: April 01, 2009, 02:26:13 PM »
for the problem you may be able to use a wheel encoder. im not too sure about the laser question as i have no experience with them. but im pretty sure gps would work inside??? and yes lasers can go VERY far but they are also very dangerous (and expensive for a decent one)
Howdy

Offline PolemusTopic starter

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Re: Custom Servo
« Reply #7 on: April 01, 2009, 02:48:11 PM »
gps needs line of sight, this bot needs to sit in a building, couple of floors down in a basement...


the wheel encoder looks like a pretty neat device, but yeah, one of the downfalls, as posted here http://www.societyofrobots.com/sensors_encoder.shtml, it comes down to counting distance based on revolutions.... my robo is gonna take off like a bullet... well... almost...

wheelspin will occur at some stage, and the distances will inevitably be out.

but thanx for that tip wheel encoders.

Offline SmAsH

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Re: Custom Servo
« Reply #8 on: April 01, 2009, 02:56:50 PM »
well if you can estimate how long the spin lasts you could use a delay to only take readings after the spin has finished? how accurate does it need to be?
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Offline madchimp

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Re: Custom Servo
« Reply #9 on: April 01, 2009, 03:07:53 PM »
Well if it's on a track does it have wheels other than the drive wheels? You could put the encoder on the wheels that aren't being driven should eliminate the wheel slip throwing your encoders off.

Offline PolemusTopic starter

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Re: Custom Servo
« Reply #10 on: April 01, 2009, 03:15:37 PM »
The the bot "DVB" will be running back and forth on the track (100 meters long) for months on end, the track can have up to 30 designated pre-programmed points, so accuracy in the loooooong run is paramount.

I did some reading on the IR range finders, sounds perfect, as "DVB" will run in an enclosed 20x20cm box that stretches 100m, and IR is more accurate over long distances. The box it's enclosed in will also be empty(no obstacles).

Using one IR on each side (front/back) of DVB will allow me to alway use measurements based on the IR that stretches the furthest, this way i should be able to make use of the most accurate reading?


madchimp: it only has the drive wheels


Offline PolemusTopic starter

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Re: Custom Servo
« Reply #11 on: April 01, 2009, 03:23:29 PM »
Well if it's on a track does it have wheels other than the drive wheels? You could put the encoder on the wheels that aren't being driven should eliminate the wheel slip throwing your encoders off.

This is a actually not such a bad idea, i can modify the bot and add another wheel (with a tensioner pressing against the top of the track), and add the encoder on that wheel... but once again, if the added wheel slides at any stage, it can cause problems, and this device is based on the accuracy of its current position on the track.

I could also potentially make the track like a saw blade, and get the wheels designed to to fit like gears on the track, this should illuminate the whole bloody problem, but my previous experience with similar tracks showed me that it causes vibration and thats not good for the bot if its running like that for months on end



Offline Soeren

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Re: Custom Servo
« Reply #12 on: April 01, 2009, 04:52:50 PM »
Hi,

[...] this should illuminate the whole bloody problem,
Perhaps, but it won't eliminate it.

You could (=should) mark the spots on the track (where you want to stop) in a machine readable form. Any dead reckoning method will accumulate errors.
At the very least, return to one of the track-ends every now and then to give it a clean start.

An extra wheel with just a modest amount of friction, held to the ground with (a) spring(s), will have no reason to skip, skid or slide, but markers on the track will be the only way to ensure months of precision.

Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline Trumpkin

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Re: Custom Servo
« Reply #13 on: April 02, 2009, 08:08:42 AM »
You could also have a bump on the track where you want to stop and have a tactile sensor sense when you hit it.
Robots are awesome!

Offline Razor Concepts

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Re: Custom Servo
« Reply #14 on: April 02, 2009, 10:27:30 AM »
Rangefinders mounted on the track so when the bot passes by, the rangefinders communicate wirelessly to the bot telling it where it just passed?

Offline PolemusTopic starter

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Re: Custom Servo
« Reply #15 on: April 02, 2009, 03:42:06 PM »
just goes to show... ask and you shal recieve.

thanx for all the options people, its highly appreciated.

Hi,

[...] this should illuminate the whole bloody problem,
Perhaps, but it won't eliminate it.

You could (=should) mark the spots on the track (where you want to stop) in a machine readable form. Any dead reckoning method will accumulate errors.
At the very least, return to one of the track-ends every now and then to give it a clean start.

An extra wheel with just a modest amount of friction, held to the ground with (a) spring(s), will have no reason to skip, skid or slide, but markers on the track will be the only way to ensure months of precision.



thanx soeren... i decided to make use of your suggested solution ... atleast now i can tell it to "reset" everytime it passes this sensor... and it save alot on costs aswell.


 


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