We finally received the HS-5745 servo amps. This will make it possible to make the monster servos many have asked about. The servo has a stall current of 4.8amps, but I’m not saying this amp will be able to deliver 4.8amps continuously! The dead band is 2uS and the valid pulses are from 1100uS to 1900uS with 1500uS as center.
Does the shaft encoder need to be a 5k pot, or can it be any generic 0V to 5V analog signal?
I’d think any 0-5v signal should work. Remember, a pair of 2.5K resistors can be substituted to give a continuous rotation servo on a servo hack.
But you need to “close the loop” for a servo.
Alan KM6VV
This is a nice addition to the LM line of products. Finally I will be able to create a beefier servo for my pan/tilt systems. I assume the servo controller can be swapped for any RX? Either way, I could always just use the SSC-32 or ABB…
I ask because I am considering alternate encoders.
The pot on the servo will function happily from 0V to VS. The MAE3 will function only at 5V.
Which is why I was asking, is it a 5V analog signal, or are you stuck with a resistor based voltage divider?
I looked at the MAE3. I don’t see why it wouldn’t work. All the servo amp should want is a 0-5v analog signal.
We put 5V across the pot, the output of the pot is thus 0-5 V. The MAE3A (analog output) essentially does the same.
Should be a nice improvement. Let us know how it works out!
Alan KM6VV
Am I understanding this correctly? The HS-5745 can be used to provide precise positioning of a larger DC gearmotor? Use an input signal from an SSC-32 or a TX/RX radio, place the 5k ohm pot on the output shaft of the gearmotor and I can flip a car over? 
If you have a motor at 6v up to 4 amps continuous…than ya!
Jim,
Does the pot have to be exactly 5K or will, say, 10K work as well?
Regards,
TCIII
Because it’s just used as a voltage divider 10k would be just fine.
Increasing the resistance range might reduce the useful rotation range of the pot if both pots have the same range of rotation.
Huh?
It’s a voltage divider. The output voltage will be the same no matter what the resistance of the pot is. The higher resistance value could possibly impact the functionality slightly if it were an analog servo, but even then it would be minimal. The input impedance of the A to D on the microcontroller is really high.
Hi Jim,
Thanks for the response. Much appreciated.
I suspect that the higher resistance will mean slightly less resolution as the 10K pot impedance change per degree of shaft rotation, and the corresponding change in the output voltage per degree of rotation, is higher than that of the 5k pot.
It may depend on the resolution of the microcontroller’s ADC in relation to the output voltage during pot rotation.
Regards,
TCIII
Still not seeing it. All pots have roughly 270° of rotation. If one end is ground and the other is 5vdc, then the voltage will range from 0vdc to 5vdc in those 270°. At 135° it’s 2.5vdc. This is true for a 500 ohm pot and it’s true for a 1meg ohm pot. I don’t see how the value of a pot will effect the output when used as a voltage divider.
Are you guys pulling my leg cause I’m on vacation?
Hi Jim,
Your right about the voltage change per degree. It is the same for either pot. I forgot that the current flowing through the 10K pot is 1/2 that of the 5K pot, for a given voltage, so the voltage per degree stays the same even though the resistance per degree of the 10K pot is double that of the 5K pot.
Regards,
TCIII
Is it the voltage or is it the current that is important in charging an RC circuit in the servo chip (assuming the chip uses an RC circuit)? Just doing some holiday hanger flying.
In this case the pot is feeding an analog input in the processor. I’d have to see the schematic of the analog servo to know if the value of the pot would imact it’s operation. I’l see what I can find.
The below would make for a good practical comparison between the two pot values.
radioshack.com/product/index … Id=2062354
radioshack.com/product/index … Id=2102789
Sorry, I’m at a loss as to what I’m supposed to be comparing here. I have a very good understanding of the difference between two pots of different values. 
I have found a couple hobby servo schematics and believe they’re using the pots as voltage dividers feeding high impedance op amp inputs. In fact one end of the pot is labeled V-ref. I don’t believe the pot value will appreciably effect the analog servos operation. 
Hi Jim,
I have to agree with you. It looks like they are keeping a constant voltage across the pot since one end is hooked to V ref. Only a change in pot position will cause a voltage change on the wiper. Instead of an ADC, they may be using a simple comparator circuit that moves the motor shaft in the direction that will null out any difference between the pot wiper voltage and the pwm commanded position.
Comments?
Regards,
TCIII
