Longest servo motor cable

markuster

Hi,
Just to know if I can move a servo motor with a basic stamp but
the distance between the Basic Stamp and the servo will be about 40 feet.


If not , I could know how can I do that.
Thanks, Mark

$WMc%

This can be done but its hard to give a HOW-TO with out knowing the size of the servo and its voltage.
'
Is it just a simple Parallax servo that would plug into a BOE board or similar board?
'
Can you remote mount a power supply?
'
A little more info would help your post!

markuster

Yes,

It is a simple servo from Parallax. I will use batery power @ 6 Volts . And I want to use
a Basic Stamp 2. I don't know if it is better if I use a Propeller in order to have
more length.

The power supply will be near to the microcontroller but the servos will be installed at
40 feet. I can't remote the power suply.

Thanks, Mark

W9GFO

We've used about 10 ft long standard servo cables (22 ga I think) without issue. The longer the cable, the more the voltage will be dropped. Use a larger gage to keep the voltage drop to a minimum.

The Propeller Chip runs on 3.3V, the BS2 is 5.0V. For the purpose of getting the signal to the servo, there is no advantage in using the Propeller Chip.

GordonMcComb

Rich mentioned voltage drop but there's also capcitance issues, which tends to round off the edges of nice square waves. The net effect could cause more than a little jitter in the servos. You could always test it of course, but for overall economy and reliability an XBee link might be preferable if you're running more than one or two servos. Cost for a pair is about $40, not including carrier boards. You said "servos" (plural) so I assume multiple 40-foot runs for each servo, and if you use good wiring and connectors you could spend $40 right there.

Even at the default 9600 baud for XBee you could pass simple servo control commands from a host processor to a sub-processor, which is the one directly connected to the servos.

You don't even really need a sub-processor or XBee. Parallax makes a nice Propeller-based servo controller that operates up to 16 servos. You can control position and transit speed. Your BS2 can easily communicate with the servo controller. At least with this approach you'd only have to invest in one high quality low capacitance 40-foot line. That's a lot for TTL serial, but if you were willing you could put in line drivers on each end. And of course you could still use XBee. (If the 40 feet is through walls go with the high power version.)

Use a separate shielded line for your power, no matter which way you end up going.

On Rich's comment "there's no advantage to using the Propeller chip" note he's referring to the signal-passing capability. So you know, there are many other advantages, such as being able to control more servos, and having much more control over the speed of servo transit times. Freely available servo objects for the Prop make working with multiple servos dead-bone easy.

-- Gordon

Beau Schwabe

I've made 20 ft runs with standard CAT-5 cable. At the servo, you need a decoupling cap (at least 1000uF), and at the signal OUTPUT (closest to the micro controller) you need a series resistor (at least 4.7k) to prevent any RF that would be acting on the 20ft (or in your case 40ft) antenna from entering the microcontroller.


Reference this thread...
http://forums.parallax.com/showthread.php?80452-Stamp-controlled-Laser-Pointer

erco

Shielded audio cable might work too, grounding the outer shield will suppress RF pickup.

LoopyByteloose

I suspect that the twisted pair in the CAT-5 is just as important as the shielding.

40' is a bit long without some way of boosting and enhancing the signal. Couldn't an RS-422 driver and receiver extend the distance. After all, if you use CAT-5; you have extra pairs of wire to power a chip near the servo and 6VDC is likely to drop nearer to 5VDC that the reciever chip would use.

erco

@markuster: Lots of informed speculation here. What did you find out? The simplest way is to just try it and see. Did you?