| T.R | Title | User | Personal
Name | Date | Lines |
|---|
| 1329.1 | I'm just a bundle of help. No ? | ELMAGO::TTOMBAUGH | A Fistful of Epoxy | Wed May 22 1991 16:37 | 8 |
| It is technically possible to change 4 wire servos to 3 wire operation
and it used to be done back in the days when both types were on
the market. I long ago lost or threw away the documentation that
showed how to do it. My Heathkit servos wore out before I ever
got around to trying it.
Again, I'd be cautious about using them in an airborne system.
Terry
|
| 1329.2 | 4th wire == center tap | POBOX::KAPLOW | Set the WAYBACK machine for 1982 | Wed May 22 1991 19:57 | 4 |
| The 4th wire on old 4 wire systems was a center tap from the
battery. theoretically, all you would need to do is to buss these
(usually) white wires together, and provide the extra tap from the
center of your battery pack.
|
| 1329.3 | | ELMAGO::TTOMBAUGH | A Fistful of Epoxy | Thu May 23 1991 11:09 | 6 |
| Glad to see someone remembers the 4th wire function. I've been
wracking my brain since yesterday.
So what you're faced with Jacques, is to break into your battery
pack in the center, add another wire, and use the old Heathkit plug.
Terry
|
| 1329.4 | I've got a box full also | ZENDIA::REITH | Jim Reith DTN 226-6102 - LTN2-1/F02 | Thu May 23 1991 11:31 | 7 |
| Yep, center tapped batteries. As Charlie Watt pointed out to me back
when I WAS considering getting my two Heathkit's 1991 ready, if your
battery pack ever loses a cell, the voltage imbalance will probably
drive all the servos to one extreme. Not a pretty failure. I gave up on
the conversion idea. The three wire servos are a lot more tolerant of
bad cells but this can lead to usage of packs with a weak cell. Another
reason to check/cycle your packs to know what you're flying.
|
| 1329.5 | 4-wires to 3-wires means different electronics. | HPSRAD::AJAI | | Thu May 23 1991 13:05 | 24 |
| I think the original question was if the 4 wire servo could be
converted to 3 wires.
If you don't change the electronics inside, the answer is NO!
As others have pointed out, 3 of the 4 wires are +V, -V and GND, with
the 4th wire providing the reference pulse. The transistors in the
servo circuit (NPN, PNP), and the grounding scheme is designed taking a
dual supply into consideration, so you can't wriggle out of it easily.
The design of the electronics is much easier if you have a dual supply,
but what with the advent of ICs, the extra circuitry needed to deal
with a single supply doesn't take up any more space (practically
speaking).
If you really want to mess around with the guts of it, you could try
using a Signetics NE 5xx (sorry don't remember the number - been over 7
yrs since I played with this). However, you would be hardpressed to
achieve the reliability that is available with SMD (surface mount
device) parts, and automated soldering, given the hostile, vibration
prone model aircraft environment.
ajai
|
| 1329.6 | Center tap battery packs | DAVE::MITTON | DECnet is not just for Ethernet anymore | Tue May 28 1991 20:58 | 22 |
| Having brought my old Heathkit system back to life last year,
I think I have the schematics on the servo electronics if you are
interested. Heathkit's technical support line is willing to make
copies of the on-file old manuals for a nominal charge. ($.05~.10/page)
Yes, the fourth wire is the battery pack center tap. I rebuilt my own
recvr and xmitter battery packs from single cells soldering them
together and jamming them in the old dissected cases. In retrospect, I
should have just used an ordinary four cell battery holder, added a
wire, and taped the batteries in. Then I could pop all the cells and
discharge/recharge them in parallel in an ordinary recharger.
I use it in an old car system. If I ever get serious about racing,
I'll just drop it and buy all new electronics. The reliability
of my system has never been good (though I have found and fixed
some bad solder joints in the xmitter recently) and the size of servos
these days is amazing.
Dave.
If you give up on it, give me a call. I could use the spare parts!
;-)
|
| 1329.7 | OUTCOME | POLAR::SIBILLE | | Wed Jul 24 1991 11:54 | 9 |
| I've decided to give it another try and try to keep them complete. So
I replace all the batteries with new one and charged them. The system
seems to work fine now exept that some of the servos move rather
slowly.
I still have the manual and I will try to correct the problem. Thanks
to all for your info. I'm planning to use the system into a race boat
that I designed and never tried yet.
Jacques
|