I just completed modified tractor puller using Vex , Meccano , and a weed eater motor .
Every thing works great with one exception . As soon as I start the 2-stroke motor the servos get the jitters .
Any ideas on a solution .
meccano man,
My first guess is that you have an electromagnetic compatibility (EMC) problem between your spark and your servos. If you can’t put more distance between them (or, at least, between their wires), I suggest you try shielding.
If you have some flexible metallic conduit or flexible metal jacket cable (just the jacket, remove the conductors) around, you could try running the spark wire through that. If not, you can always try wrapping aluminum (“aluminium”, perhaps, because you said “meccano” and not “Erector” ;)) foil around the wires (and servos) as shielding. Remember, though, that for shielding to work you need to ground (earth) it to the electrical system.
If you’ve used a common electrical system or a common ground for the engine and the servos, separate them.
If none of that suffices, you may need low-pass filters that will permit the servo control signals but block the high frequency noise from the spark circuit.
Happy Hunting,
Eric
Yep, the spark plug is producing radio interference, especially on AM channels. I’m pretty sure Vex uses FM, but it could still be affected by the spark, so you should try doing what esklar said and shield the engine from the electronics and radio system.
Thanx for the help guys
i think I have a handle on the problem now 'cept for one thing
The sheilding I’m going to put high tension lead on the spark plug I can ground to the engine block .
But where would I ground the sheilding on the Vex components ??
To the best of my knowledge both electrical systems are isolated from each other .
The engine electronics are self-contained although the engine mounts could provide some continuity to the tractor frame .
And as far as I know, ( you guys are the Vexperts this is where I need your help), the vex components would be isolated from the tractor frame in that the housing on the microprocessor , the radio receiver , and the servos are all plastic and the battery pack plugs directly in so I don’t see that there is any continuity to the tractor frame . And I am not aware of any ground connection on the vex components
All that being said , the servo I am using for the throttle. there wasn’t room to use the little plastic cludge, that vex provides so there could be continuity
through the throttle cable , do you think this could cause a problem?
I have a couple of other things I want to try, along with the shielding, and I will let you know how I made out in a couple of days.
Knowing that the servos and motors have plastic gears tells me that no, there probably isn’t any electrical connection between the servo and the throttle cable. Even if there were, I don’t see how there could be a problem, as the throttle cable connects directly to the carburetor, so I couldn’t imagine a problem coming from that. If you have your spark plug shielded (I now remember what the spark plug would be called in this case - a spark gap transmitter) then I see no reason to shield the vex controller side of this. I think the problem here all has to do with radio interference, and not any poorly insulated connectors. However, if there is a loose connection, the rattling caused by the engine could cause eratic operation.