throttle return spring

[topher]

wow what a response! So I think i am going to look at a better servo that has less resitance when powered off and use one of my thousand springs to shut the throttle (£1 spring set from a car boot sale years ago - looks like it was a good buy afterall!).

Thanks for all your input - its a good discussion thread!

One thing, when hot gluing your plugs into receiver, lay a piece of fishing wire in first, I found a pair of pliers and a pull makes it come off a little easier (on RC cars anyway!)

[ShinySideUp]

Isn't that the same as a spring on the throttle arm???

No. As has been mentioned there are drawbacks to the spring idea in that the servo also has to overcome the spring tension. Using an electrically-operated solenoid to control the fuel cut-off the spring tension is then not a factor.

[topher]

First off you have to find a servo that when powered off is very easy to move. The best two that spring to mind are the Futaba 9254 and the JR 8900 .

Are there any other servos that are easy to move on loss of power without breaking the bank or a particular type that are generally easier to move - i.e. brushless ones!

[Pabs]

Guys/gals,

Sorry to drag up an old thread, but what servo/spring combo is recommended for nitro models? I think my current analogue servos are too "strong" when not powered for a spring to return them to throttle shut-off position. However I don't want to spend big £££ on them as have several models I want to fit them to.

I think the spring around the carb is the method I want to follow - just not sure on where to get springs yet..
Thanks

[LaurenceGough]

I don't do nitro but perhaps one option would be a spring-loaded relay that would control the fuel flow. When you power up the receiver you also power up a fuel cut-off (such that fuel flow is allowed of course). Loss of power means loss of receiver and therefore loss of fuel supply with the inevitable return to earth. Just a thought.

Martin

Quick! Someone patent it haha.. Great idea.

Using rubber bands would not be a good idea as oil quickly deteriorates it but a metal spring is great for this purpose.

The CSM failsafe is a good idea mind you, keeping a reserve of power.

I'm really surprised at the amount of nitro flyers who don't have any kind of mechanical failsafe or means of cutting power if the RX power goes.

Edit: Old thread! Didn't notice...

[trillian]

I'm really surprised at the amount of nitro flyers who don't have any kind of mechanical failsafe or means of cutting power if the RX power goes.

Edit: Old thread! Didn't notice...

I think it's because of the statistical rarity of having a heli go AWOL due to a power loss. Usually they go down pretty quick. Maybe it's just pure luck but in all the time I've been flying, at 3 different clubs, I have never seen a chicken dance or a heli losing radio or power and going out of control.

If a chicken dance in the event of an otherwise normal crash is the worry then two things could help; 1. Very secure power setup from the RX battery through to the connections to the RX, preferably with redundancy in there somewhere. 2. Captive links on the throttle servo and carb so that (hopefully) the link will not come off.

The problem is that in a crash anything can happen and all bets are off. If a link comes off then the CSM device will do no good.

The extra strain on the throttle servo due to a spring may lead to shortening its lifespan and if the servo fails who knows what it might do. (I know Pete mentioned using a spring on fixed-wing aircraft but the throttle in that case is getting much much less workload than in a heli with a governor etc.) I'm just playing devils advocate here because we're talking about trying to insure for a very rare occurance and weighing up the danger of inducing another type of failure in doing so.

In all these years this obviously has never been seen by the manufacturers and top pilots as a problem that needs solving. No engine has been made with a spring fitted to the carb. No special throttle servo has been made with some kind of power backup and failsafe. To my knowledge CSM is the only company that has made a device specifically to address this issue. Surely if the sponsored pilots thought it was a pressing enough concern there would be something else on the market, something else in the design of engines or airframes or other electronics ?

[Pabs]

Interesting really - I suppose the technology progression bringing electric models up to speed has probably meant that there are less nitro models around these days? I don't know...
I just know that my biggest concern is to lose control of a model at any time, and so trying to avoid/lessen the chances of it happening really!
Lost control of a model last year, I think due to a failed battery, but luckily it was in a hover and so managed to catch the skid and bring the blades down into the ground to stop it from going awol.. cost a new set of blades and some minor repairs to linkages but would have preferred if I didn't need to get involved and could just have let it hit the ground itself.
Might just opt for a CSM then, but would prefer a mechanical solution.

[trillian]

Interesting really - I suppose the technology progression bringing electric models up to speed has probably meant that there are less nitro models around these days? I don't know...
I just know that my biggest concern is to lose control of a model at any time, and so trying to avoid/lessen the chances of it happening really!
Lost control of a model last year, I think due to a failed battery, but luckily it was in a hover and so managed to catch the skid and bring the blades down into the ground to stop it from going awol.. cost a new set of blades and some minor repairs to linkages but would have preferred if I didn't need to get involved and could just have let it hit the ground itself.
Might just opt for a CSM then, but would prefer a mechanical solution.

Yeah it's safe to say electric helis occupy a sizeable portion of the hobby now so different concerns apply with them.

One thing I was looking into was to have a completely redundant RX power setup for bigger helis. I spoke with both Fromeco and Duralite about running a setup with dual regs and Lipos and this will work so long as both are set to the same voltage. So if you have two separate power setups each with it's own connection to the RX it would be very unlikely to have a power failure. But this is not as practical on anything smaller than a 90 and even on a 90 size heli it's a few hundred grams of added weight.

I have opted instead for regulator setups with multiple connections to the RX or power buses for the servos etc. at least this eliminates the issue of a single failure point in wiring (the reg could still fail in theory).

Looking at all the various scenarios the best safety device would indeed seem to be a spring on the carb. With the right servo that will freewheel when powered down, this would theoretically cover more of the different scenarios than the CSM throttlesafe because the spring would work even if the link comes off or (maybe, I'm not sure in all cases) if the throttle servo dies.

[Pabs]

Yes - exactly, I figure a spring would be best option, and wrapped around the carb to close it would be a tidy install too. However, I don't know what servos I should look at to drive the throttle as said above, my analogue ones are very stiff to turn when powered off. Suppose digital is the way to go, but don't need a fast one (like you'd expect for tail) so don't really know which ones to look at.
Will have to do a bit more web surfing and see what I can find.

[trillian]

Yes - exactly, I figure a spring would be best option, and wrapped around the carb to close it would be a tidy install too. However, I don't know what servos I should look at to drive the throttle as said above, my analogue ones are very stiff to turn when powered off. Suppose digital is the way to go, but don't need a fast one (like you'd expect for tail) so don't really know which ones to look at.
Will have to do a bit more web surfing and see what I can find.

My favourite throttle servo (so far) is the JR 8231 and it has very little resistance when powered down so I think it would work in such a setup and the spring would not have to be very strong. The important points being that you want the lightest spring that will do the job (and hence a servo that freewheels easily when powered down) and you want to make sure there's no way something can jam or come loose / obstruct the linkage somewhere etc.

[cjcj1949]

I like the idea of a fuel cut off valve. It would take a while to work though. Closing the throttle quickly would be quicker, but some engines used to run on a bit from what I remember. Perhaps heli engines are better now. Shame my wife is anti nitro.

With the return spring you are assuming that the servo can be driven from the arm. It isn't guaranteed, especially if the fault is a stuck throttle or throttle servo.

[Pabs]

Agreed, but with the spring around the carb, it'd certainly stop any issues with broken linkage or loss of power - if the servo locks/seizes then you'd have no hope but I think this is a lot less likely than linkage breaking/falling off or loss of power to rx. No solution appears to be 100% fullproof, but a lot better than nothing at all.

[moyesboy]

My throttle return spring is still going fine.

I heard that nitro cars when raced have to have a throttle return spring, and their throttle must be wagging as much as ours.

I witnessed my own heli chicken dance. I saw a heli power itself toward the crowd at the 3D masters after a mid air, but it fortunately boom stuck and fell short. There are youtube vids of chicken dancing and several of helis flying away.

[trillian]

I witnessed my own heli chicken dance. I saw a heli power itself toward the crowd at the 3D masters after a mid air, but it fortunately boom stuck and fell short. There are youtube vids of chicken dancing and several of helis flying away.

We all know it does happen, just as we know Lipos and ESCs burst into flame sometimes. But my point still stands that it would appear, aside from CSM, the industry or 'community' doesn't see it as a common enough issue to address with specific devices or airframe / engine design changes.
The serious 3D guys that acknowledge crashing is inevitable at some point don't even appear to feel this is something to worry about, or surely there would be products by other manufacturers or commonly known mods made by the top pilots etc. (and by now those mods would be incorporated into the latest generation of airframes).

I'm not saying that some degree of prevention isn't worthwhile, because it could prove to be at some point, I'm just saying there must be a reason that the pros are not advising everyone rush out and do these things (because, despite the horror stories, statistically it is rare).

What worries me about the CSM throttlesafe is that you start to get an aweful lot of circuitry between the RX and the servo. Say you have a governor as well, then you now have two electronic devices in the chain. I have never personally heard of a governor malfunctioning and sticking the throttle open but is it not possible? Is it impossible for the throttlesafe itself to malfunction?

The spring on the carb is probably a safe bet so long as the servo will move easy enough when powered down, the spring cannot jam anywhere etc, but like anything it has to be done right or you risk inducing some kind of failure in the process of trying to prevent an otherwise relatively unlikely one.

[Pabs]

My throttle return spring is still going fine.

Hi Moyesboy - what servo are you using and do you have your spring wrapped around the carb? Thanks