input on a mosfet in a p90

[Cloven]

I got a KA P90 lightly used last year, and of course it had the problem with getting stuck mid cycle on semi on anything less than 11.1v. I've researched that to the ends of the earth and know the cause. Full auto any battery (tested 11.1, 9.6 and 7.4) and it cycled with no problems, on semi with 11.1 it cycled relatively normally, anything less and it felt like the motor was struggling to turn and often get stuck mid cycle if I let go of the trigger too early. I figure this winter during the down time I'll show it some love and give it a mosfet. My question is specifically regarding how that would affect the cycling to trigger pull time. I know the addition of the mosfet would take the strain off the trigger contacts, but would it cause more complete cycling on the smaller voltage batteries with a quicker trigger pull? I'm not looking for a high ROF, field is semi only so I'm not pulling the trigger 15 times a second but still want response better than having to hold the trigger down the full cycle. Since I'm popping it open anyways I'll shim it and adjust the AOE to help with smooth operation, but if the motor itself was causing a high drain that smaller voltage batteries couldn't keep up then I'm not certain if it would still get stuck mid cycle even with the addition of a mosfet on <11.1v. I know the Titan mosfets have a "cycle detection" function but that's way out of my budget, I was looking at the gate units. Maybe the best would be add a mosfet and only run 11.1v? Hopefully that's clear enough. Thanks.

[RainyEyes]

For better cycling your best bet would be to focus on the battery and wiring first and then make way for the more expensive upgrades like a MOSFET. Are you using lipo batteries or nicad? Tamiyas or deans/variants?

I notice a huge difference between deans and lipo batteries compared to their stock counterparts.

[Cloven]

The plan will be to go 3s lipo on deans.
The gearbox itself is tamiya at the moment, came with some 9.6v nihm but used a 3s lipo after a few games realizing the nimh didn't have enough muscle.
Again on full auto it would shoot fine regardless of the battery voltage so I don't think there was a ton of friction or resistance somewhere that it had to overcome first...and doesn't seem likely it's a weak motor.

[ccyg8774]

Originally Posted by Cloven

would it cause more complete cycling on the smaller voltage batteries with a quicker trigger pull?

It would, in a way, by putting less resistance in the circuit compares to trigger contact. So your motor will get slightly larger current (assuming everything unchanged) and being able to pull the spring slightly faster. The difference is small in most cases.

Have you tried to do some cleaning, shimming and regreasing to the gearbox before?
(I know you don't think there was a ton of friction but some friction is enough to make the issue you had. )
Have you checked if your trigger contacts have a lot of deposite building up?
Does your wire or connector get hot much?
Is there any parts not stock? What spring does it have?
If you think the current drain is too much for the battery, you may also need a RC watt meter (www.dx.com/p/183523 ) to diagnosis it.

The thing is, the issue you described shouldn't happen even with 9.6V or 7.4V. Instead of "cover it up" with 11.1V or advanced MOSFET, it would be better to find out the true cause of it.

[RainyEyes]

Your motor might be weak but it might also be attributed to Tamiyas. I noticed MUCH better trigger response once I switched to a 7.4v lipo 2 cell battery on deans than tamiyas. The battery also lasts longer on deans rather than tamiyas just because of the extra surface area for contact.

If you're going the 3 cell lipo route with deans I highly recommend rewiring the whole thing even if you don't go on a MOSFET. Grab some nice 16 gauge wiring and wire them to deans and your motor might be able to get some new life. If you continue using what sounds like stock wiring with tamiyas and a high voltage lipo you might as well replace the motor now since it will be toast after a few mags.

[lurkingknight]

basic fet and rewire is going to help. p90 contacts are getting harder to find so there's no reason not to put in a basic fet.. they're 35$

the motor will not melt with tamiya connectors and 11.1.. the tamiya connectors will melt because of tamiya connectors and 11.1. They are the highest point of resistance, then the trigger contacts.


You still have to hold the trigger down for a full cycle. Most computerized mosfets do not have a cycle complete feature.


Also, you need to educate yourself better. a MOSFET is NOT a fire controller.

A FIRE CONTROLLER is not a MOSFET.

A fire controller and mosfet are two separate things that can be built as one.

There are currently no reliable firecontroller mosfet that fit well in a p90. A gate merf might fit but that thing is huge and doesn't have cycle completion.

If you want to hold the trigger for less time, you need to speed the cycle speed up.

[Kos-Mos]

Originally Posted by lurkingknight

basic fet and rewire is going to help. p90 contacts are getting harder to find so there's no reason not to put in a basic fet.. they're 35$

the motor will not melt with tamiya connectors and 11.1.. the tamiya connectors will melt because of tamiya connectors and 11.1. They are the highest point of resistance, then the trigger contacts.


You still have to hold the trigger down for a full cycle. Most computerized mosfets do not have a cycle complete feature.


Also, you need to educate yourself better. a MOSFET is NOT a fire controller.

A FIRE CONTROLLER is not a MOSFET.

A fire controller and mosfet are two separate things that can be built as one.

There are currently no reliable firecontroller mosfet that fit well in a p90. A gate merf might fit but that thing is huge and doesn't have cycle completion.

If you want to hold the trigger for less time, you need to speed the cycle speed up.

Does have it.

Also, I did not read your thread before replying to your PM.

I would suspect a worn motor. KingArms stock motors are not known to be efficient or reliable. A good high torque neodyme motor would definitely help your issue, regardless if you use 7.4 or 11.1 and a FET or not.

I ran some P90s for a while, and 7.4 should be plenty enough to cycle properly. I also suspect your gun as other issues than Tamiya connector and 9.6v NiMh battery.

[Cloven]

Thanks, that helps. Because there's basically three parts to making it go, battery, contact path, then motor, I wasn't sure if I go and do the first two but the last is really the issue, if I'd still have problems with it getting stuck mid cycle in the end. The trigger contacts on these dual stage triggers are obviously a known issue, but I wasn't sure if KA motors were known to not exactly be the best. I gamed an ares km09 this summer and had good results, I'm a taller guy with longer arms so using the P90 feels like I'm really choked up on it but I'm still a sucker for bull pups and would like to get it more reliably operational so I could take it out more. The only thing that wasn't stock on it was it had a tight bore barrel put in it. The trigger contacts don't look like burnt toast black, but there definitely is a little bit of fouling on them. Comparing the feel of the cycle, the km09 on 11.1 was zippy, where as the p90 felt like it had a long way to go before it got out of that dead space and I could safely release the trigger for a new shot. Talking about it now it sounds like if I went with a high speed motor then it would help increase that cycle so that it's basically done sooner, cut off and contacts be darned.

[ccyg8774]

You can get a simple (homemade) IRLB3034 based MOSFET. That take the resistance of the trigger contact out of the question. That is also never hurt to have whether the problem is the trigger contact or not, expecally for a gun with hard-to-buy (read: not V2 or V3) trigger contacts.
After that you can see whether it is a weak-old motor or friction on the gears.

[ThunderCactus]

you'll get better results with a high torque/low speed motor and low ratio gears.
high speed motors run fast, but they get real shit efficiency under heavier loads.
a high torque motor will get up to it's lower max rpm much faster. And (especially if you're doing lots of semi auto) will be much easier on the battery, and not wear out as fast as a high speed motor.

Don't feel like you NEED to run an 11.1, in some builds a 7.4 can be pretty darn quick as well.