Brushless motor reducing fps considerably. Is it too fast?

[SmoothboreSten]

A few months ago I got an E&C M110A1 (basically an HK417) and while the body is great I've had to do a lot of work to get it to perform like a DMR.

This week I've tried putting a brushless motor in and the performance dropped, quite significantly and I can't really under stand why. With the stock motor I'm just about reaching 300fps using 0.43g but with the brushless motor it drops to 240fps. I recorded the gearbox firing without the body, and the piston is travelling the full length so I don't think it's short stroking.

Any ideas what might be causing it?

 

[EDcase]

It's possibly so fast that the cylinder can't fill with air before firing?

 

[Skara]

Tappet timing is off and brushless motors are VERY good at exposing it

What happens is that the tappet plate gets picked up before the piston ends its travel against the cylinder head. Have a look at how piston, sector gear, delayer and tappet plate work with each other and you'll understand what I mean

 

[SmoothboreSten]

So having watched this video a few times and getting a better understanding of how the Tappet plate works I think you're almost certainly right I'll have to open my gearbox up again and see how mine specifically is behaving.

Easy to see how if the motor was unexpectedly fast the main spring could beat the spring on the tappet plate to the finish line. For the moment I may just make do with the existing motor and use the ETUs pre-cocking to get better trigger response. But I'll buy a stronger tappet plate spring and the next time I need to tinker with it I'll give it a go.

Will update when that happens, thanks again guys.

 

[Skara]

Easy to see how if the motor was unexpectedly fast the main spring could beat the spring on the tappet plate to the finish line.

Not quite.
When the piston is released the tappet plate is already forward, pushing the nozzle into the hop rubber thus creating air seal.
If you pay attention to the placement of the sector gear cam in relationship to the tappet plate's pick up point you will notice that there isn't a whole lot of space left.
This is standard for every single aeg on the market due to where the tappet cam on the sector gear is located. Some of the newer gear sets have an advanced cam position to slightly delay the whole nozzle cycle and avoid the issue you're experiencing.
On stock guns you won't really notice it because even on a hefty battery the rate of fire will rarely reach 20 bb/s and if it's above that, more serious issues will present themselves anyway.

I suggest to take a look at the delayer chip and modify it to remove any chances of early tappet plate engagements..

 

[SmoothboreSten]

I think I understand now. The term "early tappet plate engagement" confused me, as the problem it causes happens at the end of the firing cycle. It's so early it starts before its finished firing the last shot.

Interestingly the stock gears have a delay chip on them. I only replaced the stock gears as it seemed to be the general consensus for the E&C replicas, but they're still steel and seem good enough.

I'll investigate the timing with both sets when I get a chance. I'd like to avoid cutting the tappet plate if possible as I don't really have the means to do a precise job of it.

 

[ButcherBill]

I know SFA but the easiest way to fix the issue is to put the previous motor back in.