Replies to This Discussion

Permalink Reply by Michael Pursifull on June 24, 2012 at 11:00am

http://www.pololu.com/catalog/product/1248

https://www.adafruit.com/products/775

Happy hacking.

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Permalink Reply by James Printer on June 24, 2012 at 11:12am

Thanks Mike, that's perfect.

I never knew about slip rings.

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Permalink Reply by James Printer on June 24, 2012 at 2:37pm

PS is there any method available that would allow a range of speeds e.g. from 30 RPM to 300 RPM?

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Permalink Reply by Michael Pursifull on June 24, 2012 at 4:05pm

Those servos are continuous rotation, and vary their speed depending on how far away from the middle point the provided PWM value is. If it is above a certain value, it goes one way, below, it goes the other way. In the middle, it stops. The farther away from the middle point, the faster it goes. Unloaded speed of up to 70RPM when you use a 6v supply, up to 60RPM when you supply 4.8v

This is just one example, there are other servos like it if you need to vary your specs. At some point (80RPM?) it gets cheaper to use a different solution, but this is pretty easy and a modest price with simple control, and works directly with RC gear (TX/RX, you can use a pot or set up switch PWM values) or an Arduino or an APM.

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Permalink Reply by James Printer on June 24, 2012 at 4:14pm

Is it sensible to look at ESC's?

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Permalink Reply by Michael Pursifull on June 24, 2012 at 4:21pm

If you want very high speeds or want to use a step down transmission, maybe. Adds significant costs, and most off the shelf option will be in the thousands or tens of thousands of rpms, not tens or hundreds, if you just grab some at random. 

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Permalink Reply by Crispin on June 24, 2012 at 4:24pm

Google continuous servo mod. Takes any servo, 5 minutes and you good up go. Also speed is controllable.

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Permalink Reply by Michael Pursifull on June 24, 2012 at 4:28pm

Just check if the servo will support your rotation speed requirements. Most random servos will be just shy of hitting 60RPMs, and those spec'ed to hit 60RPM might not quite make it with a load. Which is why I chose one that is spec'ed for 70rpm. Since I'm guessing you might need to buy one, you might as well buy one that already does what you need, without needing to mod. But moding is fun, and if you are up for it, you can save some cash. Just get one that will be fast enough....

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Permalink Reply by James Printer on June 24, 2012 at 4:44pm

Thanks for your help.

Can you think of a way to maintain the same speed... I'm thinking if the batteries run down a little it will go slower, and ideally I would like some way for this to be maintained.

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Permalink Reply by James Printer on June 24, 2012 at 5:09pm

The continous servo is specified as moving fastest at 6V.

I am considering using a LM7086 voltage regulator and a 9V power source, and letting the voltage regulator output a constant 6V.

This should maintain a constant speed until the batteries run down significantly.

Can anyone see problems with this?

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Permalink Reply by James Printer on June 24, 2012 at 4:44pm

Ok checking out continuous servo mod, thanks :)

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Permalink Reply by James Printer on June 24, 2012 at 6:04pm

Meh just realised I'm going to need to use a Arduino controller to send PWM to this continuous servo. I only want it to go at full speed. Would connecting the PWM to DC to make it 100% send it at full speed?

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