Hi All,

what is the difference between tx's that have "analog trim" vs "digital trim"? (specifically, this is listed as one of the differences between the Futaba 6EXA and the 6XAS in the product guide using the compare and contrast function) It would seem that digital would be better, am I correct in assuming this? And if this is true, why is the 6XAS the more expensive radio since it has analog trim?

auto5man

Digital trim can mean two different things, though one meaning is a lot more common.

What it normally means is that instead of having a mechanical lever that moves to "trim" or adjust the center point of the sticks, there is a little button or knob instead. You tap it one way or the other to trim the plane, but the knob doesn't actually move.

The big advantage to digital trims is that since the lever or knob never moves on the TX, you trim the plane in flight, and forget about it. The trim setting is stored in the computer's memory, and it won't change when you turn the radio off and turn it back on.

On analog trims, you have a mechanical lever that moves to set the trim setting. The problem with this is that if you turn off the TX, and then bump the trim levers, the plane will be out of trim the next time you take off. You have to do something manually to re-center the trim levers, so that the plane is trimed for straight and level flight with the trim levers in the center positions (which is the ideal situation).

Another drawback to analog trims is that if you have multiple models on the radio, if one plane requires 3 clicks of downtrim to fly level, and the other requires 5 of left aileron, then you have to remember this, and reset the levers when you switch from model to model. On a digital trim system, the trim settings should be saved with each model, so the plane is always trimed out, and it's harder to take off with a model badly out of trim.

Some people prefer the feel of mechanical trims (me among them), and there are some radios that have the feel of mechanical trims, but have a way to "save" and re-center the trim levers to avoid the problems with knocking the levers out of possition.

First the basic answer:
An analogue trim is an actual lever on a ratchet that you slide to one side or the other to obtain the desired trim.
A ditital trim is just a rocker switch, as you move the switch to one side or the other you will hear 'beeps' from the Tx to indicate movement and there should be a graph on the Tx LCD to indicate the position of the trim.

Before the advent of computer radios, the norm was to adjust the pushrods on the plane after each flight so that the trim levers could be returned to the centre position. You could easily knock the trim lever and not remember where it should be. Also, if you use the Tx for multiple planes, the trim would be different for each plane unless you made the appropriate adjustments to each plane after every flight.

I recently got a 6XAS (it was being sold off at the LHS) and it is an older design radio with analogue trims, so the original radios probably had the problem described above as the TX could be used with 6 planes. Futaba probably added the software at a later date to store the trim positions. You have to go into a menu to do this and then set the actual trim lever back to neutral. Not really an ideal solution.

With digital trims on more modern radios, the trim positions are automatically stored when you make any changes, so there are no problems with the lever getting kocked or the position not being saved. The trim will be correct for each model if you switch planes.

The 6XAS is still more expensive than the 6EXA because it offers more features. I don't know the specifics but the 6XAS offers PCM and programming for heli's for example.

For the control surfaces, I think the digital trims are a better solution, and certainly better than the half-ar**d bash Futaba have done with the 6XAS.

Digital or analogue trims on the throttle are a whole new subject.

I've got the XP8103 which is also an old design, but at least JR updated the trims to fully digital with the exception of the throttle. I used to have a digital throttle on my XF631 with a throttle cut button, but I like having the analogue throttle trim on the XP8103...

Btw, the reason I perfer analog trims is that I find it easier to trim a plane that is really out of trim. It takes too long to feed in a large trim value with digital trims, at least on the radios I've used, IMHO. But, I also test fly more planes, and many of them are hand-launch combat planes, so trimming in a hurry is something most guys never deal with, but that I do quite a bit.

Most guys do prefer the rocker switch digital trims on flight surfaces. I'm an oddball that way . Throttle trim is a more mixed bag.

Oh, one cool thing that some radios offer on digital trims is the ability to adjust the trim sensitivity. My Polk, for example, has analog-style levers, but is actually a digital trim internally. I can set the trims up to make a "click" more or less sensitive. On really touchy models, where one click can go from too much one way to too much the other, it's really nice to be able to make a "click" result in a smaller servo movement. I'm sure other digital trim radios have this feature, but I've never heard of it on an analog trim radio.

And, it's always worth noting that all radios, and trim levers, still resolve the final servo position in to a series of "steps", either 512 or 1024 from end-to-end. So, if you're wondering if the receiver can tell the difference, it can't, it's all the same to the RX.

I can see that quickly flipping a manual trim lever can be a lot quicker than waiting for the beeps on a digital trim. My XP8103 has the selectible trim sensitivity, but then you lose the resolution if you turn it up and it's at system level so it affects all models.
Therefore, you need to go back into the menu to reduce it again to get back the 'normal' amount of resolution you'd need for fine trimming. In this case, manual trims are definitely better.

One other thing I noticed recently is that the servo end point adjustment or ATV affects the amount of trim you have. If you reduce your control throws by reducing your servos travel to 50% for example, you also reduce the amount of movement that occurs when you use the trims. I discovered this after running out of trim movement for the ailerons on my Tiger Moth. I don't know if this also applies to manual trims.

The ability to store the trim settings in the computer has been around longer than the "digital trims"

The Futaba Super 7 series specificly... (average of about 15 years old... some of these radios are approaching 20 years old now) has the anolog trim levers as with a non-computer radio... and has the ability to remember where the trim was... so you can just press a couple of buttons and store it, then recenter the trim levers. (and... all planes in its memory can be flown with the levers centered for normal level cruise.)

I see an advantage to anolog trims for in-flight trim changes in different flight modes... a few clicks up-trim at take-off and you can take-off hands off the right-stick as long as there isn't a strong cross-wind to deal with. The analog trim on throttle is great... so you can have trim and stick down for engine kill, trim center and stick minimum for normal idle, and trim full and stick minimum for engine start.

No matter if you have the digital or the analog trims... you SHOULD readjust the mechanical linkage to center the trims, centering the SERVO for normal level cruise.

Computer radios can make you lazy about proper control system setup. Getting lazy about that can cost you an airplane.

Thanks everyone for the replies. Slowly I am learning more and more about this hobby. I think I would prefer analog trim as a beginner because its simpler, and then once I'm more experienced and working with several different planes then the digital might be preferable.

auto5man

figured out some really handy programming last night for my 9c. you can use the side slider thingys as trims for whatever control surface you want! Just program them as a control with reduced control percentages, 35% work ok for my plane. instant trim! and easier to get to also.

tiggerinva,

That's interesting about the trim sensitivity on that radio. The Polk has it setable seperately for each of the 4 channels (actually, maybe not throttle, haven't checked), for each model. But yeah, it does mean you can run out of trim.

It also makes sense that the trim would follow any expo or endpoint/ATV settings you have, most trims are set up as a percentage of the stick travel, not servo travel, so yes, you wind up reducing your trim's effectiveness. You could get it back by making the trim lever more sensitive on some radios though.

In general, if you find yourself reducing throw that much using ATV or whatever, you need to go adjust the linkage and come in a hole on the servo or out on the control horn. You should always try to use full travel of the servo. My rule is, anything more than +/-20% means that my linkage needs to "change holes" somewhere. The reason behind this is that you get better control resolution and therefore better precision this way. (This sometimes shows up when a plane can't be trimmed level, one click either way is too much, etc)

In theory, I agree with FHHuber as well, that you generally want to adjust your linkages so that the trimmed neutral of the servo has the pushrod and servo arm at 90 degrees, so you get equal travel in either direction. (Unless, of course, you want more throw one way than another. I sometimes set up elevators or ailerons this way.)

You can adjust the trim sensitivity on the 9C, as well.

Andy