Maxstoke

ebay is full of offers for Tower Pro SG90 servos or try some of th eonline sellers.  Giantshark is one, although not a patch on its predecessor Giantcod.

Welcome to the fun-packed world of servos.

 

ebay is full of offers for Tower Pro SG90 servos or try some of th eonline sellers.  Giantshark is one, although not a patch on its predecessor Giantcod.

 

That's where I got mine. Didn't know that MERG actually sold servos.

 

Make that sure your supply can chuck out a reasonable level of current - servos can draw a fair bit for brief periods and if your supply can't handle it then the controller electronics run out of elecricity, which in my experience is one cause of servo glitching. I have a bench supply and things are OK with a 1.5A limit but if I drop the limit to 500mA (plenty for the steady state but not for the peaks) then things become rather more unpredictable.

That's where I got mine. Didn't know that MERG actually sold servos.

 

Make that sure your supply can chuck out a reasonable level of current - servos can draw a fair bit for brief periods and if your supply can't handle it then the controller electronics run out of elecricity, which in my experience is one cause of servo glitching. I have a bench supply and things are OK with a 1.5A limit but if I drop the limit to 500mA (plenty for the steady state but not for the peaks) then things become rather more unpredictable.

If you look in the kitlocker, under 'accessories' - that's where you find the servos.

 

Thanks for the info re; power consumption. I had not anticipated that, but as there are only four turnouts that would be individually operated that peak consumption would not be excessive.

 

 Now for the tech bit... you have a bench supply at (I assume 12V) and capable of 1.5A Yes?,  How do you limit it to 500mA?

Richard

Don't need to limit the power supply, it will be fine at 1.5A.   The Servo4 device will only draw 500mA, so you could run three of them from the power supply.

 

 

BUT....  You need a setup device as well to use the Servo4, or it does nothing.  

 

The cheapest setup device is a serial lead to your computer (assuming it has a serial port, or you have a suitable USB-Serial adaptor).  Once the settings have been made, disconnect the lead and done.  This requires some software running on a PC to make the settings.  Various options exist on the MERG website, and one day they will have the stuff properly organised so it is easy to find.

 

The other setup device is the servo-settings box, which is another MERG kit.  This is a stand-alone box of gubbins which you temporarily connect to the Servo4 to make the changes.

 

There is another way, but only for the somewhat insane... The PIC (processor) can be programmed with the settings required directly into its EPROM.  Requires a PIC programmer.   The other two options are a lot more sensible and cheaper !

 

 

- Nigel

Thanks for the info re; power consumption. I had not anticipated that, but as there are only four turnouts that would be individually operated that peak consumption would not be excessive.

 

Now for the tech bit... you have a bench supply at (I assume 12V) and capable of 1.5A Yes?,  How do you limit it to 500mA?

 

I think the main issue is when more than one servo moves at the same time. Bear in mind that this can happen when you switch the power on so one possibility is that if your supply can't handle it then it could turn a power-on glitch from being just audible into a big jump.

 

As Nigel says, you don't need a current limit - I just happen to have a supply for which I know the limit. Normally it would be a good thing for preventing electrical damage but in this case I think it's counterproductive.

 

What you do need is enough amps - all supplies have a limit whether you like it or not. I've had glitching with a single MERG board with 4 servos attached (or even just two servos) when using a 500mA limit. The glitching vanishes immediately when I switch the limit on my supply to 1.5A.

 

You probably don't want to go down this road, but since you asked... my bench supply was built as an electronics project a looong time ago. It uses an L200 variable voltage regulator and is adjustable from 3V-30V. The same chip does the current limiting and can be arranged to provide different limits - in my case 500mA and 1.5A.

 

BUT....  You need a setup device as well to use the Servo4, or it does nothing.  

 

 

The cheapest setup device is a serial lead to your computer (assuming it has a serial port, or you have a suitable USB-Serial adaptor).  Once the settings have been made, disconnect the lead and done.  This requires some software running on a PC to make the settings. 

 

That's what I use (eBay again). The main drawback is that you need to cart a laptop around if you want to adjust your servo speed and movement range. The other snag is that the USB adapter driver isn't too well written so if I forget to close the programming software before I unplug the lead it crashes my laptop.

 

Regards, Andy

Don't need to limit the power supply, it will be fine at 1.5A.   The Servo4 device will only draw 500mA, so you could run three of them from the power supply.

 

 

BUT....  You need a setup device as well to use the Servo4, or it does nothing.  

 

 

 

 

- Nigel

Hi Nigel,

 

I have the setting kit, and PC software/leads too (just to cover my options). I'll leave the PIC programming deal on the shelf for now!

 

Andy- Thanks for the info- 1.5A supply it is then.

The servos arrived yesterday- and to my great  relief, the servo driver board and setting device all seem to work... next step is to link it all together.