Motor choice and encoder choice.
Hello,
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I'm trying to build a line following robot and I'm having a hard time deciding what type of motor to use. I'm using the BASIC Stamp 2 as my brains and it will be able to update the robots speed, direction, etc. about 10 times a second - which is adequate.
·
Anyway, the problem is that I need so way of making the robot move pretty fast because it will be in a line following race. However, I need some position feedback control and other environmental control except where the line is because the course is on a sloped hill with two severely sloped drops in which the robot will most likely accelerate greatly.
·
So, my current options are:
·
I have a 1.5A dual H-bridge to drive the motors (geared up ones)·with current sampling and constant current control, however I think I might need some kind of encoder for speed feedback. However, any encoder I use will need to have its own separate co-processor because I can't devote time from the BASIC Stamp to maple motor speed data.
·
I also could just use two servos. But I don't know if they will resist acceleration and be fast enough to get me through the course the fastest.
·
I'm trying to cut cost - current I'm working with a robotics club that has a load of old servos and old motors and other electronic equipment - that being said I don't wish to buy too much stuff.
·
So, any ideas? Does anyone know which type of motor to use?·
·
Thank you for your help,
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Nyamekye
·
I'm trying to build a line following robot and I'm having a hard time deciding what type of motor to use. I'm using the BASIC Stamp 2 as my brains and it will be able to update the robots speed, direction, etc. about 10 times a second - which is adequate.
·
Anyway, the problem is that I need so way of making the robot move pretty fast because it will be in a line following race. However, I need some position feedback control and other environmental control except where the line is because the course is on a sloped hill with two severely sloped drops in which the robot will most likely accelerate greatly.
·
So, my current options are:
·
I have a 1.5A dual H-bridge to drive the motors (geared up ones)·with current sampling and constant current control, however I think I might need some kind of encoder for speed feedback. However, any encoder I use will need to have its own separate co-processor because I can't devote time from the BASIC Stamp to maple motor speed data.
·
I also could just use two servos. But I don't know if they will resist acceleration and be fast enough to get me through the course the fastest.
·
I'm trying to cut cost - current I'm working with a robotics club that has a load of old servos and old motors and other electronic equipment - that being said I don't wish to buy too much stuff.
·
So, any ideas? Does anyone know which type of motor to use?·
·
Thank you for your help,
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Nyamekye
Comments
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- Stephen
If you know you will experience 3-D terrain, you want adequate (but not excessive)·ground clearance and a 3-point suspension (ie, two-wheel differential drive and a single skid/caster to avoid loss of traction by one drive wheel lifting up.
The Stamp is "single thread" and can only do one thing at a time, so encoders would require more processing power. I would pursue a solution without them and spend most of your time on positioning, reading, and interpreting data from·your line sensors for highest vehicle speed.
My·suggestion is to forego encoders entirely and·use worm drive gears on your wheel drives instead of traditional spur gears.·See·http://www.pololu.com/catalog/product/69·· and http://www.pololu.com/catalog/product/73.·Although they are not as efficient power-wise, they are self-locking and will not coast when your motor is switched off, even if torque from a steep downhill is applied. Of course, your wheels can always slip in an extreme case, but all is lost at this point anyway and encoders wouldn't help. Alternatively, use a standard gearbox with a very high gear reduction ratio to reduce the downhill torque effect. See a good selection at http://www.pololu.com/catalog/category/34, some of which can be assembled in several various gear ratios, including one already set up for differential steering: http://www.pololu.com/catalog/product/114.
In general, smaller/lighter/simpler is better when speed is the goal. Have a look at the tiny new 3pi robot from Pololu. Info & vids at http://www.pololu.com/catalog/product/975
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·"If you build it, they will come."
Take a look at the Wheel Watcher.
http://www.nubotics.com/products/ww01/index.html ·
It's an encoder that you can put on a servo and a plastic Boe Bot type wheel.· They also include some sample programs for the Stamp and most other controllers so it's very easy to use.·
You can take the electronics out of servos and run them as gear head motors at pretty high voltages, like 12 volts.· They tend to blow up or melt at around 14 volts.·· Lube the gears well.
Daryl
http://www.pololu.com/catalog/product/993
and they are fast! I used them with these wheels http://www.pololu.com/catalog/product/1090 and they have a tooth system inside the wheel designed for a sensor see http://www.pololu.com/picture/view/0J813
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Nyamekye