: Rotors for OTA: Channel Master, Nexxtech/Archer, Yaesu, Hy-Gain, Others
2011-02-03, 09:49 AM
I concur with using a ham rotator. My G-450 has given me flawless duty since 2002. Granted it's not turning a big 5-element 20M monobander but it has survived over eight years on the tower.
I would be nice if a wireless remote could interface with the controller somehow. I know some models do allow computer control so if one was ambitious one could possibly rig something up to their HTPC.
Having said all that my two year-old 9521 has worked fine in this cold weather.
2011-02-03, 01:07 PM
Also check with the local ham radio groups to see if any swap meets are coming up - great way to find rotors and other stuff. ;)
2011-02-03, 09:34 PM
I would appreciate comments on the following Hypothesis
That the frozen rotor problem is caused by excessive voltage drop on the control cable when trying to start the motor.
- cold temperature causes increased resistance in the bearing grease
- Increased bearing resistance causes increased current draw required to start the motor
- increased current draw causes excessive voltage drop on the control cable and the motor cannot start due to insufficent voltage
- Locked motor rotor current draw is 5 times normal running current draw - which is typical for an induction motor
Using a formula to estimate voltage drop of Voltage drop(%)=(K*P*L*I)/A **
K=specific resistivity in ohms-circular mils/foot or 11 for cooper wire
P=Phase constant or 2 for a single phase, 2 conductor circuit
L=wire run in feet
I=Current in A
A=wire area in circular mils
The control wire for the CM rotor appears to be AWG #20 that has an area of 1020 cmils
Assume that the normal running current is 1 A at 18 Volts
Assume that the control cable run is 75 feet
This would result in a normal voltage drop of 1.6% or 17.7V at the motor.
If one assumes that in winter, more current is required to start the motor because of the stiff grease and the rotor locks and is drawing 5A instead of 1A, the voltage drop is becomes 8.1% reducing the voltage to 16.6V at the motor
My hypothesis is that 16.6V is not enough to start the motor and hence it is frozen.,
If this is true, the cure is to replace the control cable with a wire of larger gauge, or, to run two lengths of cable in parallel doubling the effective area of the wire. Of course, replacing the 20 gauge wire with one of 16 gauge (typical outdoor extension cord) would have a similar effect
This would halve the voltage drops and maybe result in sufficient voltage to start the motor when the grease has become stiff.
Is anyone who has a frozen rotor in a position where they can test this by either replacing or paralleling their control wire with a larger wire?
** formula and values for the various constants are from "Pocket Ref" 2nd edition, Thomas J. Glover, sold by Lee Valley Tools
2011-02-03, 09:51 PM
Is anyone who has a frozen rotor in a position where they can test this by either replacing or paralleling their control wire with a larger wire?Been there... Done that. I switched from 22 to 18 gauge wire, (130') and it made no difference. It was only after switching to the 30V controller that my rotor will turn in sub freezing temperatures.
2011-02-04, 07:25 PM
A bit more information:
I have an older [at least 20 years] CM rotor hidding in the basement. I connected the newer 18V controller to it, with just 3 feet of wire. The unit seemed to function just fine.
I then put the rotor in the freezer for a few hours, and repeated the same test. It would not turn.
2011-02-04, 08:20 PM
strange, mine's a hand me down, probably early 1990's vintage
and it works just fine. Even in that sub-zero deg F we had recently.
This is the first winter I've had it up, but haven't had it seize once.
Admittedly it doesn't stay synced (a diff flaw altogether) with the controller, but it does work.
Did it take longer to thaw out than the porterhouse steak:)
PS - I'm not even using real rotor cable either. I'm using the control cable that you'd find
on a C/Ku Band Satellite Ribbon Cable. The smaller control cable that normally runs the dinky little polarotor
servo motor of a Chapparal C/Ku feedhorn. Works just fine.
2011-02-04, 08:31 PM
The steak takes bit longer to defrost. LOL!
Which controller are you using? What is the output voltage?
2011-02-04, 08:38 PM
Never even bothered looking till u asked,
it's CM9510A, 30 Volts at 1 Amp
2011-02-04, 09:48 PM
Is it just me, or does there seem to be a 30V vs 18V pattern here folks?
2011-02-04, 10:12 PM
Sounds good to me.
Don't they need to paired up also?
Like ya can't just use the 9510A I have with a Motor that was designed for the lower voltage controller, or can you?
I'm just guessin cause I'm not familiar with 'em enough to know, but the newer controller with the remote and LED display must be the lower voltage ones u guys are talkin about?
If it was a frozen grease, subsequent rotor lock, voltage drop issue..
wouldn't someone have taken one apart by now, cleaned out the factory grease and lubed it up with something else,
suitable but a lighter weight lube. Like a lithium grease used on turntables, VCRS or sumthin...
Might be worth a shot.
In fact, I recall, before I put mine up, it was given to me in a frozen, locked condition from sitting on a roof for years, unused. Wouldn't budge with no load.
That was the first thing I did. Took it apart to free it up. Cleaned up all the old grease the best I could (alchohol solvent), and replaced it
with a white lithium grease (what I had laying around). Then ran it thru it's paces on the ground to work it in.
Not sayin that'll fix an 18 volt guy, cause I don't have one but ya never know till ya try...
2011-02-04, 10:28 PM
ya can't just use the 9510A I have with a Motor that was designed for the lower voltage controller, or can you?3-wire rotor control circuits are very simple, so you could do it with 3 relays and 2 power supplies. When the 18V controller is applying a voltage to one of the conductors, it trips a relay that applies 30V to that direction. It would work vice-versa too (30V controller to 18V rotor).
Controller Wire A ----18V---->Relay>----30V----> Rotor Left
Controller Wire B ----18V---->Relay>----30V----> Common
Controller Wire C ----18V---->Relay>----30V----> Rotor RightIn either case you could probably use just one 30V power supply with the 18V stepped down and split off from it as long as it provides enough current for everything.
2011-02-04, 11:30 PM
2 phase AC motors are inherently low torque devices, geared down considerably. I'd suggest that the thick grease + a marginal supply voltage (18V) would cause it to not have the torque required to move in colder weather. (As some members have seen)
The only problem with applying more voltage to the windings is that the current might be too much for them, an easy way to check this is to measure the resistance of an 18V motor vs a 30V motor. If they are same, or close, then applying 30V to an 18V unit should be fine.
If it's considerably different, then a little more investigation needs to be done, perhaps a voltage somewhere between 18 and 30 can be safely used.
2011-02-05, 01:24 PM
iblackford keep in mind that TV rotors don't use conventional electric motors:
2011-02-05, 03:24 PM
Indeed, as my post indicated:
"2 phase AC motors..."
i'm well aware that rotors don't use conventional motors. However, the concepts are still similar...you have current passing through a winding, producing Torque. This torque can be increased by increasing the drive voltage. The only limitation to this is that the motor windings use a certain conductor size, which limits how much current that they can safely handle.
2011-02-05, 04:24 PM
Thanks, it is important to clarify that.
2011-02-05, 05:31 PM
For whatever it's worth, both the new motor and the older one are reading about 8 ohms across any 2 connectors.
2011-02-05, 06:16 PM
That seams to answer it then, I'd say if the winding resistance is the same, than you are safe to put 30V to the 18V motor.
Remember, if you're using the digital controller, the 5V regulator may need extra heatsinking to handle the increased supply voltage. From the circuit that I saw, the rest of the circuit should be able to handle the increased voltage.
2011-02-06, 08:47 PM
Well fuctionality of my CM rotor returned with the warmer weather -2c.
2011-02-06, 09:47 PM
The rotor here is drawing 790 mA AC from the #1 Terminal of the CM 9510A controller (30 VAC), Outside Temp 29 deg F. For kicks, wait for a really cold morning (Tue,Wed,Thur from forecast), and see what it draws. Might be interesting to compare to someone's 18 V unit that's freezin up...
2011-02-07, 09:37 PM
In theory the slower the motor turns the more it will draw. Any time as motor is prevented for spinning at rated rpm it draws more. Like peak loads during start up. So Iíll bet I know what the test result will be.