Tm MP5 30rps build

[sj_asc]

Re: Tm MP5 30rps build

It's not an issue, The Tappet cam always engages the Tappet before the sector teeth meet the piston, there will be slight ovwrspin after cut off which is inevitable with higher cycle rates unless you run an active braking mosfet (which for the same of heat build up is something that you want to avoid unless absolutely nescessary).

[Sitting Duck]

Re: Tm MP5 30rps build

it's fine, you will get a little more over-run but as long as she don't double fire you will be fine
the piston head should still below the port - just fire 2 shots on semi at end day to ensure she parks ok

remember most batteries can have 1v extra or a touch more fresh off of charge too so that will affect ya rof
also burst rate on lipo's can make a big difference, usually a min of 20c - well I aim for 25c or up to 35c
but you can feel the difference in 20c vs 25c and obviously get more response on 35c but I don't go mental nutz myself

a higher spring and short stroking will help to stop over spin at a higher rate but tbh see how she goes
the shs torque motor has plenty in her and there may have been some faster options but for a good all rounder that motor is gonna do ya proud

plus 25-ish is nice rof - you won't notice a few more really and keeping it in moderation should mean she lasts a good long while
rather than something bust/strip sooner rather than later

sure you can check in higher juice but think 24/25 is quite a nice speed without appearing like a trigger happy overkiller showing off
(yeah it is nice to go past 30 or even 40 but though it feels good for a laugh - it does look a bit ott trying to over compensate for something)
yes I have a few higher guns but mid twenties is plenty really imho

nice steady build, good response - now get out there and use the damn thing

[Dude666fx]

Re: Tm MP5 30rps build

I know I could get quite a bit more out of it if I went lipo but it was more an experiment to see what could be done without one.
Really happy with all of fact it feeds well as it's a pain to strip over other guns to readjust the gb again.
315fps is about right as 325 in the m16 with the barrel difference plus people shouldn't get to mad being hit on that rather than 350.
Plus the burst fire mosfet works with the other mosfet so I can keep it controlled between 2-10 rounds per pull I was worried one mosfet would conflict the other but it all works really well.
Considering it was 12rps before and it's now double that happy days.

Next game is ucap bunker 29th plus got a tracer unit to try out too so hopefully some nice steady star wars style laser beams.

I feel like I've learnt a lot from all this and understand how things work a lot more now thanks guys your legends.

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[Dude666fx]

Re: Tm MP5 30rps build

One more question guys my Swiss cheesed piston arrived it is pretty light if I used that with my set up with the m100 spring (Untrimmed) I should get a bit higher rps? Probably would go ahead and short stoke it by 2 teeth to get the desired fps as it's a pain stripping the mp5 right down and reassemble to find it chronos too high.
Not gonna do it now for a while as want to see how it performs over the next few games for now.
Just got me thinking when i read an old hi rof thread on here.
The m120 I have in there is so cut it just sits barely pushing on the piston and spring guide handy when putting gb back together but don't think it's bringing the piston back as quick as it could.
Also got another m120 with just a coil removed but i think it would drain the battey too quick and take a ton of short stroking.
But then again short stroking = less strain on the motor= less battery juice used?


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[Sitting Duck]

Re: Tm MP5 30rps build

Short stroking don't save juice

Reason being from standstill the motor has more work to do from still pulling back a higher spring with less of a "run up" so to speak like trying to do a long jump with a shorter amount of space....

Short stroking on a normal spring will save juice but you lose aprox 15fps per tooth. This is a rough guide as each build/gun is different plus your spring or old m120 is already trimmed. Also the way irregular springs are fitted will produce different results
So it is not so easy to predict final fps unless you build very similar specs with same stuff and barrel lengths

On top of all that the 13:1 ratio is placing more work on motor, think of it as now it is doing a hill start...

Now add in a beefier motor, imagine now you have gone from a 1.3ltr car to a 2.0ltr and also now doing hill starts.
Yes that SHS will draw more juice/petrol that before, so extremely unlikely batteries will last longer especially when you are firing out more rounds per second.

Whatever you do, look into 25c lipo's 7.4v rather than nimah's, for tweaked setups lipo's are the way to go.
Try/borrow a 7.4v and think you will see for yourself.
Do not just chuck in 11.1v, it will very very likely PE, and though Life batteries come in @9.9v they have limited range/sizes and lack the raw punch or burst ( C ratings ) you have available in the 7.4v lipo's

[Dude666fx]

Re: Tm MP5 30rps build

Ok so m100 was doing 345 -350fps in the mp5 plus spring bearing guide 10-15fps then short stroke 2 teeth minus 30 fps possibly 330 final fps?

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[Sitting Duck]

Re: Tm MP5 30rps build

Ok so m100 was doing 345 -350fps in the mp5 plus spring bearing guide 10-15fps then short stroke 2 teeth minus 30 fps possibly 330 final fps?

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Yeah that sounds feasible to me......

Lighter pistons are normally for returning piston asap to avoid PE rather than altering rof, a few gms in piston weight is nothing really to a beefy motor pulling back a mofo spring that nearly has ya eye out...
A few grammes won't change owt just to ensure it returns in time and don't get mangled up on sector

There will come a point at say 25 - 28rps that she may start to over run
And 30-35 PE WILL happen....

So you reach a certain point where you have to decide just how far you go. With them gears she could be OK at about 26rps maybe 28, but the double firing should also be taken as an early warning of PE if you keep turning up the juice in its current state

So unless you like stripping her down again keep it in moderation for now.

PE is not a bad thing if plastic piston teeth strip.
But using a full metal rack there is no weak point.
So if PE takes place you have metal pinion, metal gears, metal rack - nothing will give so next time you open box up you could be looking at a boned set of gears/motor/piston -even more damage

So go easy n see how she goes

[Dude666fx]

Re: Tm MP5 30rps build

Tbh I don't think my soldering is the best have got a lot better but there's a lot of breaks and connections that probably don't help had to extend the mosfet trigger wire and another section where the wire is just soldered to another with shrink wrap over for protection. Do think there would be a 1-2 rps increase from that m100?

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[Sitting Duck]

Re: Tm MP5 30rps build

Trigger wires probably wouldn't matter much of a toss for resistance..
Main wires to motor maybe but not a major difference unless we are talking a few ugly breaks badly done.
If you got 16awg then there is not a massive difference using much thicker like 14awg and when I soldered wires direct to motor on v3 it wasn't a massive noticeable gain

You can't really do this on v2's

If you got decent fet, decent wire like 16awg with deans then you ain't gonna pull out much more really

If say you at 25rps to get 2.5 that is 10%
Or 1.25rps if gaining 5%

When you dump small tamiya, thick wire & fet you would seek to gain maybe 15% with those 3 above

To gain a further 5% if you rewired in just 1 thick posi and 2 thick neg wires to fet, resoldering the motor connectors - yeah maybe 5% gain

But 10% nah can't see it, if you push 40c lipo's perhaps but on ya nimah's nope it won't regain anything like that

[Dude666fx]

Re: Tm MP5 30rps build

Well had a bit of a problem when doing another rof test 3 days before the game was a break in the wiring somewhere and ended up tearing apart all the work over two days to find and fix it lol.
Anyway got it sorted and was very happy with the results throughout the day averaged 24-25rps had it set to 5 rd bursts on the Hicaps and 3 on the midcaps which worked really well. Was worried the battery was gonna run out early on (9.6v 2000mah) but actually did the whole day/1600rds apx. The response on semi was very satisfying although most of the day was on burst as the site allowed it and was trying out tracer rounds for first time which was pretty cool affect with the increased rof.

[Sitting Duck]

Re: Tm MP5 30rps build

Glad you got it sorted.....

wiring and messing about so much with ya box for shimming & gears & springs
it was bound to be a bit scrappy with all that pulling apart

eventually you find a nice technique for wiring in fet's - proof of pudding is
bet if ya did another box it would be so much easier and neater and a lot quicker
(bit like IKEA or MFI furniture - 2nd/3rd one is a breeze but first one is some bad mofo)

anyway - get blasting more bb's - it is the only way to see how good she is
happy shooting

[safgg]

Re: Tm MP5 30rps build

Some of those will rip the crap out of a virgin stock gearbox.

[Sitting Duck]

Re: Tm MP5 30rps build

Some of those will rip the crap out of a virgin stock gearbox.

A fair amount isn't stock, shs gears, the shs torque isn't ultra ultra fast motor, steel rack lightened piston etc....

If corners of shell radius, sorbathene pad to help absorb impact then really there isn't a great deal more you can do. Bushings instead of bearings or at least under the gears (spur + bevel a must coz bearings really go under these)

Worth remembering the Tokyo High Cycle's are often short stroked to improve ROF and at 25rps I think it is a good sensible build without going too nutz

Gearbox shells can degrade over time and the high quality pot metal can break at front or trigger switch stop in v2's plus running any box faster n faster will mean it will wear quicker.

But if you want a toy gun to last then either leave it stock or better still hang it on ya wall as an ornament.

[Dude666fx]

Re: Tm MP5 30rps build

Thanks sitting duck don't think the chap read the start of the thread or the complete thread.
Yes I haven't short stroked it yet or used the pre Swiss cheesed piston as it is running happily as it is for now as things need replacing will probably use them then but for now want to use it as much as possible before taking it apart again lol.

[safgg]

Re: Tm MP5 30rps build

Some of those will rip the crap out of a virgin stock gearbox.