Hitec HSB-93XX and HSB-94XX series servos information- PAD - RC Groups
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Jul 21, 2017, 01:25 PM
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Hitec HSB-93XX and HSB-94XX series servos information- PAD


Some of the information surrounding these servos seems to be unclear, let me clear the confusion. First off, let me start by saying there is no need to get overly complicated with these servos and the PAD (Power Absorption Device). This is a simple device that is provided with the HSB servos (Hitec RCD USA Inc customers only) to make them entirely compatible with whatever system you are using.



Benefits of Hitec HSB-93XX and HSB-94XX series servos:

-Extremely powerful brushless motor designed by Steve Neu
-Ultra efficient circuit design
-Constant holding power, no fade under load
-Torque does not change with voltage, only speed
-Super long life electronics
-Steel and Titanium geartrain options

Now, there are some side effects that come with these servos, namely because of the regenerative function that is built into them (as part of their ultra efficient operation). This is where the provided PAD comes into play. This PAD is designed to absorb the backfeeding power coming from the servo and eliminate any sort of inconsistent operation you may experience.

What does the pad look like:



How to use the PAD:

The PAD is very simple and easy- all you need to do is plug it into any open channel on your receiver and it will do all of the work of absorbing the excess current for you. We recommend 1 PAD for every 3-4 servos depending on the application. For 3D airplanes, I suggest 1 PAD for every 3 servos, on sport airplanes you will be fine using 1 PAD for every 4 servos- Do not use 1 PAD for every servo!

If there is no open port on your receiver (or channel expander) for the PAD then you can utilize a Y-harness, or solder the PAN in line between the servo and receiver at any point. Any way you deem fitting is perfectly acceptable so long as the PAD ties into the positive and negative lead between the receiver or servo.

How to tell if you need the PAD:

The HSB servos will tell you if they need the PAD. Tell tale signs is if the servo overshoots center but promptly returns to it- there is no risk to your other electronics otherwise. If the servo seems to exhibit these characteristics then simply use the PAD to solve the problem. That's it, nothing complicated. Please keep in mind there is no set number of degrees the servo may overshoot, it's completely random.

Devices that typically require the use of the PAD:

-"PowerSafe" type receivers
-Electronics Speed Controls with built in BEC's
-Standalone BEC's
-Voltage Regulators
-Battery sharing devices or switches
-Certain fail-on style switches

There is no exact list of what specific devices require the use of the PAD as the list would be ever expanding at the rate new hobby items are introduced to market. The above list is more of a guide to better educate yourself on whether or not a PAD would normally be required- some of these devices do not mind when power goes back and forth so this is something you will have to test on your own to ensure you won't have any problems. Like mentioned before, if the servo seems to overshoot center, try using the PAD.

How to mount the PAD:

You can mount it however you see fit. Typical materials is velcro, double sided tape, zip ties, electrical tape, etc. just whatever you decide is the best way to secure them within your aircraft or vehicle.

Is the PAD absolutely required:

No! The PAD is absolutely not required in many of instances, this is why you have to do some testing on your end to ensure that you don't need the PAD. If you do need the PAD, then don't sweat it.

Is there any reliability issue with the PAD:

There have been zero reported instances of PAD failure even in extreme 3D applications, out of countless tens of thousands of HSB servos sold.

What to do if you are still uncertain or unclear on the use of the PAD:

-Panic

Okay, no don't panic. We are always here to help as best we can with whatever questions you have or if you just need clarification on something. I will leave this thread open for the posting and discussion of this topic- please keep it on topic, any unrelated posts will be removed.
Last edited by Xpress..; Jul 21, 2017 at 05:40 PM.
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Jul 21, 2017, 04:25 PM
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Thanks for the information on the PAD. I was going to buy some HSB servos a few months ago but decided not to purely because I didn't completely understand the details about using the PAD.

Unfortunately, now that I understand them, I doubt I will use a Hitec servo requiring a PAD. More complexity is always bad in my opinion. I rarely have open channels in my Rx and I don't like to use Y connectors - something else to fail, more weight. As a 3D flyer who often buys high end servos, if these HSB servos could have been designed without requiring a PAD and they would still perform as well, minus the regenerative feature, I would probably buy them.
Jul 21, 2017, 05:37 PM
Xpress..'s Avatar
There were a lot of options considered but ultimately it was decided that the servos would just not be the same without the way the circuit is designed now. It may seem like another component to fail but out of the tens of thousands of HSB series servos sold, not one single report of any PAD's failing have ever surfaced. Zero risk of reliability issues with their design.

If no open channel then they can be soldered inline between the receiver and servo, which is another common practice. You're definitely missing out on how amazing these servos really are by not trusting the design- remember, we're industry professionals who specialize in servo technology

As an example, here are a number of airplanes being flown on HSB-9380TH servos (randomly picked from YouTube):

NORTHWEST RC 3DHS Edge 540 V2, GP-123, Hitec 9380 (3 min 53 sec)


EF EDGE 540 88" (0 min 29 sec)


Krill 35% Extra 330SC maiden (5 min 38 sec)


I also run them in my personal airplanes, bone stock out of the box. So really, there's no reason to fear the PAD- again, it's not a complicated subject, if you need it then plug it in, if you don't need it then don't use it


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