Piston not travelling all the way forwards?

[Boo-Sabum Ben]

Finally managed to upload this to YouTube!

It definately completes the cycle, but brings the piston round about a 3rd of a cycle back again each time on semi!

http://www.youtube.com/watch?v=cEnoX...e_gdata_player

[humphriesryan]

Re: Piston not travelling all the way forwards?

I told u what it is bud try a standard bat or add mosfet

[Boo-Sabum Ben]

I really don't believe its the battery. It didn't do this on the same battery before I opened it up!

[rossy02]

Re: Piston not travelling all the way forwards?

More than likely a worn cut off lever imo.

[Stones]

Re: Piston not travelling all the way forwards?

maybe it's just a lazy piston.

[Bachelarius]

Im not surprised its doing ot. You shimmed and possibly lubed it, so there is less mechanical resistance in the gearbox. Less power is being wasted so the gears get more power, less friction and thus more momentum. All you are seeing is a bit of overspin.

To remove it, you need to re-introduce that resistance in a controlled manner.

The current accepted method is to add a heavier spring and lower the fps via short stroking the sector and piston and correcting the aoe, which will also extend the life of the piston. Bare in mind that you will need to somehow adjust the bolt resting position to compensate for the aoe fix as well on a blowback. Annoying, i know, but thats the ideal fix for this issue.

The 'cheat' fix is to add a braking mosfet, which adds resistance electrically via the motor, but leads to excess heat and motor wear.

[Boo-Sabum Ben]

Oh, so it's not a cut off lever problem then? Is it a common issue?

If its not causing an immediate issue I may leave it until after the weekender

[B.E.N.]

Re: Piston not travelling all the way forwards?

I'm with Bachelarius on this. It's not an uncommon problem, in fact I wouldn't go as far as saying it's an issue at all... Apart from starting the motor in a loaded position, it will actually increase your trigger response as you are half way to being pre-cocked!


Personally I'd get an ASCU V2 in there and never have to worry about it again, plus your MP5 will be burst-moded super trigger responsed and will be able to rock an 11.1V LiPo with no worries.

[Boo-Sabum Ben]

Okay then chaps! Whilst doing the video I was starting to think ooooh I'm on the way to making a TW5

I'll not worry then and leave it, it's only a lender and back up so not worth dropping all that cash in it!

Thanks peeps

[Kaladyr]

Re: Piston not travelling all the way forwards?

I'm following with B.E.N., it's not really a problem at all. Whacking in a decent MOSFET with active braking will eliminate it, a higher torque motor might help too, but other than shortening your spring life marginally it really isn't actually a problem.
Personally I'd recommend waiting for the BTC Chimera over an ASCU, but it's ultimately all much of a muchness, you could even use far cheaper MOSFETs for similar effect.

I do, however, need to pull up humphriesryan on half of his contribution to this thread, purely because disinformation in threads where people are seeking information is a terrible thing. If you state something as fact on forums, all too often, people with little knowledge themselves will take it as fact even when it's a load of bull.
"Some motors can't handle the higher power". The motor is what determines the amperage draw from the battery, a battery will never force more amperage on a motor than the motor wants. In voltage terms you would be correct, but that is a slightly different argument and, again, a 7.4v LiPo isn't going to be too much for anything but the very worst of motors. A high C rating battery actually won't over-run a motor so much as allow the motor to run to it's potential, it's when you combine that with higher voltages that you can start to introduce problems for the motor.
Also a pure MOSFET wouldn't solve the problem at all, in fact in it's purest form it would make the situation worse as it removes yet more of the resistance of the circuit and provides a greater degree of the current from the battery direct to the motor, what you would need would be an "Active braking" MOSFET, but specifics here are key.
Information without the correct detail and qualifiers can be significantly worse than no information at all.

Anyway, as we've concluded. It's almost certainly over-spin, a higher-torque motor or a MOSFET with active braking should solve the problem, but it's not so much a "problem" as an annoyance anyway.

[Boo-Sabum Ben]

Re: Piston not travelling all the way forwards?

not to worry guys, somehow, it solved itself after a mornings playing!