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Futaba A700 Advise needed

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Futaba A700 Advise needed

Old 01-03-2020, 05:34 AM
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kevinthoele
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Default Futaba A700 Advise needed

I am putting together Skymaster 1 7 3/4 F4 and using Futaba A700 as a single elevator servo. I have heard that I need to use possibly two leads with Ys at each end for the current??? Or possibly heavier gauge wire for extension. The lead will be pretty long back to the tail.

Using power box and high voltage to servo

Thanks
Old 01-03-2020, 05:49 AM
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Auburn02
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There is an advisory from Futaba to add a capacitor when using with SBus and on a long extension with multiple servos on it.

https://futabausa.com/a700-pdf/

In other words, if the A700 is on a long lead but fed directly from your receiver/powerbox, you should be fine. But if you're using SBus and the A700 is sharing a hub and thus a power lead from the rx with other servos, use the capacitor.
Old 01-03-2020, 10:02 AM
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Dave Wilshere
 
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Kevin

I have a customer we put 8x A700 in a CARF Pitts S12 with a Moki 300, we have been giving it some for over 4 hours flying now with no issues! Powerbox Royal SRS supplying the power. He also has a 3.3m CARF Yak 55 that we swapped out another brand of servos and the feel was improved.
Don’t see an issue if you use decent wire.

Dave
Old 01-03-2020, 10:18 AM
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FenderBean
 
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I think the capacitor is more for guys who are running large 3d planes with a tone of servos. I seriously doubt its an issues with jets and even more so with any kind of power system.
Old 01-03-2020, 11:51 AM
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Ad Clark
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Thanks for the information Dave
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Old 01-03-2020, 01:48 PM
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tassos p
 
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I'm running 7 x HPSA-700 on my F-104 connected on Powerbus on the PB Royal without an issue.

In fact I would summarize my conclusions to:
1) This is the strongest servo I've used to date with 74kg*cm (1,027oz*in) - no issue to manage any surface
2) This servo consumes less than half of power vs its predecessor and with double the torque. In one flight with 7 servos working I consume ~150mAh per battery
3) This servo has no slope - no play vs other Futaba top range servos that have some slope.
4) You do not need any capacitor if running directly on a PB
5) Operating voltage 4.8-8.4V
6) SBUS programmable
7) Brushless motors - last forever basically

I still cannot believe how much technology is packed in this little device - really amazing job by Futaba

Install them with confidence and enjoy flying them.

Tassos

Old 01-03-2020, 09:06 PM
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kevinthoele
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Thanks for all the replies. I will install and fly with confidence with powerbox and 18MZ
Old 01-04-2020, 06:28 AM
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David Gladwin
 
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The following may help for those guys using or about to use these servos.

The following is a summary of the advice I received from Colin Strauss of the UK Futaba distributors, Ripmax.

It may help !

These new servos employ new technology to deliver the very high power with relatively low power consumption. In the main, this is achieved by a new type of Futaba motor which receives a very high current pulse at the beginning of servo movement but which current reduces as the servo arm rotates. This means that the ENTIRE power supply to the servo must be able to handle the start current which can be very high without resulting in a drop of voltage to the receiver and gyros etc.



Should a voltage drop occur it could result in the receiver and any gyros etc., rebooting. A reboot could lead to very high start currents again as the servos restart, causing another voltage drop and potential reboot and so on………… !



So, when using dual battery supplies it is essential that they can supply the high start current, at high speed, without a significant voltage drop. The use of voltage regulators is not recommended as they can often be slow to react and Futaba recommends direct feed from 2 cell Lipo or LiFe batteries of sufficient capacity, say, for two 700s 2Ahs. These batteries should be of low internal resistance to enable high current delivery and minimal voltage drop.



Further, it is recommended that if more than 2 700s are used on electric aircraft with a BEC then separate power supplies should be used for the receiver and servos, not least because some receiver components could not cope with the high currents and the use of 10 or more of these servos is discouraged, again current related. The use of fuses in the output to servos should be avoided due to high start currents. Futaba further recommends that installing several servos on a single S bus cable should be avoided as standard cables are unlikely to be able to handle the high currents. A further recommendation is the possible use of an external capacitor to cope with the high current peaks of the servos at startup.



Examples: 2 A700s can draw a continuous current of 15-20 amps with peaks of 40-45 amps so that a 2 cell LipO or LiFe battery is the minimum.



Now, a lot of these recommendations sound rather severe but it is the IMAC type of aircraft with multiple servos and large surfaces, frequent rapidly reversed, where problems might arise, and which will be overcome if the Futaba recommendations are adhered to.
Old 01-05-2020, 04:04 PM
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Originally Posted by tassos p View Post
I'm running 7 x HPSA-700 on my F-104 connected on Powerbus on the PB Royal without an issue.

In fact I would summarize my conclusions to:
1) This is the strongest servo I've used to date with 74kg*cm (1,027oz*in) - no issue to manage any surface
2) This servo consumes less than half of power vs its predecessor and with double the torque. In one flight with 7 servos working I consume ~150mAh per battery
3) This servo has no slope - no play vs other Futaba top range servos that have some slope.
4) You do not need any capacitor if running directly on a PB
5) Operating voltage 4.8-8.4V
6) SBUS programmable
7) Brushless motors - last forever basically

I still cannot believe how much technology is packed in this little device - really amazing job by Futaba

Install them with confidence and enjoy flying them.

Tassos
Hi
I will be using only 1 HPS in my AW F104. 2 HPS seems a bit overkill, plus I don't like the AW balancing system for the elevator.

My major concern is the distance from the Powerbox to the elevator servo that is arround 2,5 meters or 100". This is a huge distance..... I ma using 0,5 mm2 section cable

Br
Nuno
Old 01-06-2020, 08:36 AM
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mikes68charger
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I have 2 of these big bad boys in the tails of my1/2 scale Christian Eagle, Huge elevators, lots of weight, and vibration of the big ZDZ210 twin. These gears and power are still tight after 1 year of flying. I add one of the futaba capacitor's to my set up for peace of mind but I have no concerns.
Old 01-06-2020, 11:44 AM
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tassos p
 
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Originally Posted by jetnuno View Post
Hi
I will be using only 1 HPS in my AW F104. 2 HPS seems a bit overkill, plus I don't like the AW balancing system for the elevator.

My major concern is the distance from the Powerbox to the elevator servo that is arround 2,5 meters or 100". This is a huge distance..... I ma using 0,5 mm2 section cable

Br
Nuno
Hi Nuno,

I don't use the AW balancing system for my elevator, I have installed a custom mechanism that can never fails (similar to the below picture but with a sliding ball bearing).

Also I'm running POWERBUS cables which can manage big amperage as they're 1.5mm2. Then I use Powerbox Powerbus to BUS adaptor which can manage 20A per outlet. After the flight the consumption is 150mAh and max consumption around 4.1Amps, biggest consumer being the flaps, not the elevator.

I agree with you 2.5m of 0.5mm2 cable may not be able to manage this servo. I'd only use Powerbus to manage this servos.

I'm super happy with these, I will start using them everywhere now, in all my planes.

Thanks, Tassos









Old 01-06-2020, 10:09 PM
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Dave Wilshere
 
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The biggest thing is one servo does not have the support, servo case, servo output spline and servo gears. Always use two on all flying tails like this.
Old 08-15-2020, 07:28 PM
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are you guys changiung some thing in the servo setup to use on jets.. or using the standart setup?
Old 08-15-2020, 10:29 PM
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olnico
 
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Originally Posted by David Gladwin View Post
Examples: 2 A700s can draw a continuous current of 15-20 amps with peaks of 40-45 amps so that a 2 cell LipO or LiFe battery is the minimum.



Now, a lot of these recommendations sound rather severe but it is the IMAC type of aircraft with multiple servos and large surfaces, frequent rapidly reversed, where problems might arise, and which will be overcome if the Futaba recommendations are adhered to.
Thanks for the feedback.
However I doubt Futaba would sell a device able to consume 15-25 A continuous, feeding on a connector rated for 3A max.

PS-70400-001.pdf

We have done many tests with 0.1" connectors ( JR and Molex ) and 3A is indeed the threshold when the plug starts to heat up. So if this servo would really be using 15-20 A continuous, I'd be really worried.
I am more encline to believe the statement from Tassos, showing a total max current draw of 8 A from two regulators for 7 servos.
This would put the servo at an average draw of 1 A with possible peak of 3A, right on the limit of the plug.

Note that we are in the process of fitting an industrial project with 15 of these servos and we will have test bench data on this product with a couple of months from now.
We will use a high frequency amp meter to check the pulse current at start.
Old 08-16-2020, 01:08 AM
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Please remember, the figures quoted above are not measured by me, they are in the notes sent to me by Ripmax, the UK Futaba importers.
I have lots of current draw data from models using Weatronics receivers which measure currents.
On large models such as my Airworld and SkyGate Hawks. Typical total current is around 3 amps with spikes of upto around 8 or so, when flaps are running, but these are very short term.
Due to CV I have not yet flown models with these servos to make comparison, but if, anything, I expect the current draws to be lower with these new servos so I am using them as dropin replacements for conventional servos such as JR 6311s with no change to wiring.

Theres certainly no need to worry about the gears on this servo. I checked gear metal spec. which includes a stainless steel final gear, against the Vickers and Rockwell hardness scales. The 700 is absolutely tops and will probably have the least wear of any servo.

That said, I WAS surprised that these very high power servos are supplied with standard plastic output arms!

Last edited by David Gladwin; 08-16-2020 at 03:49 AM.
Old 08-17-2020, 08:02 AM
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kevinthoele
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On my F4 I am using 1 on the elevator. Power box is saying max draw was under 3 amps. I have cycled on bench for a while and all looks good. I am ready to do maiden at this point. Using 2 Jeti receiver packs 5200
Old 08-19-2020, 10:02 AM
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Check the servo arms carefully on the A700. The 25t spline is smaller than many and the Savox arm particularly is very loose without the clamp done up,,,and the arm still rocks opposite to the split clamp!
We have seen that arm lose its splines on an aerobatic aeroplane...



Old 09-06-2020, 03:38 PM
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Oh wow, that might be perfect, it's 70kg and has a way larger travel range than the servo we have, and it's cheap. We could probably work with that form factor too. Thanks a lot!





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Old 10-13-2020, 06:18 PM
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You are using the servo direct from the box with factor setup? or change something?
Old 10-15-2020, 05:16 AM
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Originally Posted by heraldoboldrin View Post
You are using the servo direct from the box with factor setup? or change something?

Hi
Looking forward for the same answer. I guess it depends if its a flying stab or not. Dampening factor should not be the same
Old 10-15-2020, 01:15 PM
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Dave Wilshere
 
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All of the units I know are from the box
Old 10-15-2020, 03:25 PM
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Originally Posted by tassos p View Post
Hi Nuno,

I don't use the AW balancing system for my elevator, I have installed a custom mechanism that can never fails (similar to the below picture but with a sliding ball bearing).

Also I'm running POWERBUS cables which can manage big amperage as they're 1.5mm2. Then I use Powerbox Powerbus to BUS adaptor which can manage 20A per outlet. After the flight the consumption is 150mAh and max consumption around 4.1Amps, biggest consumer being the flaps, not the elevator.

I agree with you 2.5m of 0.5mm2 cable may not be able to manage this servo. I'd only use Powerbus to manage this servos.

I'm super happy with these, I will start using them everywhere now, in all my planes.

Thanks, Tassos

HeyTassos can you show more of this crazy linkage set up? It seems it is clever in a way that I don't understand..
Old 10-15-2020, 03:28 PM
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Originally Posted by kevinthoele View Post
On my F4 I am using 1 on the elevator. Power box is saying max draw was under 3 amps. I have cycled on bench for a while and all looks good. I am ready to do maiden at this point. Using 2 Jeti receiver packs 5200
Sounds good, what arm are you using? I usually use swb but I have not tried this new servo yet, thinking of putting it in a high powered bvm phantom
Old 10-17-2020, 08:12 AM
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Dave Wilshere
 
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This is the Savox arm he used...not suitable for main controls. Sloppy fit on the spline and brittle.



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