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Rapidstrike pusher over running

 
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Rapidstrike pusher over running
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TheDon808
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Joined: 16 Mar 2017
Posts: 16
Fav. Blaster: Stock Stryfe
Location: Bristol



Post Rapidstrike pusher over running  Reply with quote
So I've just spent all evening playing with motors, brushes and a rapidstrike in bits for my first phase of my first mod. After working out the circuit for the pusher and then wiring it up to the rev switch?!? I finally got it wired up OK  and it worked like a dream, pull the trigger and it goes, release the trigger and it starts acting like a half squashed daddy long legs with bursts of life, you think the pusher is going to stop this time but then out it pops again.
So I know the theory is that once the pusher is returned the circuit 'shorts' the motor to itself causing it to stop rapidly before it can go forward again. This works fine with stock motors and stock 6 volts, but with faster motors and 2s lipo the motor doesn't stop in time.
I had thought if playing has to at their own game and using the diodes to drop the voltage as soon as the trigger is released, my hope is that the lower voltage will slow the motor enough to cause it to stop in time.
Anyone else go any ideas?
Wed Mar 29, 2017 1:21 am View user's profile Send private message
SSGT
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Joined: 12 Jan 2013
Posts: 1289
Fav. Blaster: 'Rave-N' CS-18, Elite Alpha Trooper (EAT) CS-12
Location: Durham



Post Reply with quote
EDIT

Moved to Q&A and New Members -SSGT



What motors and switchgear setup are you using? How quickly a motor can stop under dynamic braking is dependant on the speed it's spinning at before you start braking it and how much torque it can produce under braking (which, in of itself, is also tied to how fast it is spinning). The faster the motor is spinning the more torque it needs to produce to come to a complete stop before it overruns the cycle control switch. The switch/follower setup you use is important aswell - if you can make the switch close earlier, and similarly open later, in the cycle then the pusher motor has more time to come to a complete stop. You can't do a lot to tune the standard switch/follower setup but you can if you custom mount your own microswitches/use BSUK's kit.

You could put diodes in the live-centre feed (connection from battery +ve to cycle control switch Normally Closed) to reduce the speed of the pusher motor only when releasing the trigger but you may still find that the pusher overruns occasionally and fires off an extra full shot (depending on when you release the trigger and how many diodes you use). Running a "dead-centre" circuit (same as live-centre except you cut the connection mentioned above) is a viable option if you continue having issues with runaways as it relies on the inertia of the motor-gearbox to retract the pusher before it closes the CC switch and initiates braking. With a dead-centre circuit a runaway scenario is physically impossible as the pusher motor will never receive power unless you're pressing the trigger - if the pusher does overrun the CC switch it'll just stop ever so slightly extended. The downside, depending on the speed of the motor, is that a quick flick of the trigger may not always fire off a shot - if it does you may experience a delay before firing off the next shot as the pusher may be partially/fully extended. I personally try to tune live-centre circuits to cycle reliably rather than running dead-centre but if you're after very high RoF, and the motor you're using to achieve it simply cannot stop quickly enough within the narrow braking window, then dead-centre will probably be the way to go.

Common RS wiring schemes (including "live" and "dead" centre) are described on toruk's blog here.

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Wed Mar 29, 2017 2:29 am View user's profile Send private message
OldNoob
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Joined: 07 May 2013
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Fav. Blaster: Xtreme 180 Rapidstrike
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Post Reply with quote
If you have a honeybadger pusher then that is usually the problem if none of the above is an issue.
They have rubbish torque and I have never got one to cycle correctly on live or dead centre with three switches.

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Big_Poppa_Nerf wrote:

Boff whats the damage? I have spent over 3 times my Nerf budget this month already. Part of me is trying to be a responsible parent/husband/house owner. The other half is just says 'Ahhhh, Screw it!'.
Wed Mar 29, 2017 7:01 am View user's profile Send private message Send e-mail
TheDon808
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Joined: 16 Mar 2017
Posts: 16
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Location: Bristol



Post Reply with quote
The motors I've got are anonymous 30k @6v motors from aliexpress, I'm not looking for a really high RoF the motors are around 7-9 dps. I may try the stock RS motors with carbon brushes tonight and see if i get a good RoF (7 dps I think) and the motor braking as required.
I think i'm going to be running it on burst fire mode once I've fully finished the mod, it would be nice to have a fast 'double tap' but i guess a few milliseconds more will give me time to re-adjust the aim.
I'll read the post on the RS circuits on my lunchbreak.
I did forget to mention in the OP (its was late and i was falling alseep writing it) that the switches are running a relay which is switching the motor so i'm not sure if that is giving a longer delay in braking the motor.
I don't really want to bother with new switches as i'm planning to use a motor driver with an arduino on the second phase on the mod, which I think I may be starting soon anyway, so im not sure what other problems that will lead too.
Wed Mar 29, 2017 10:47 am View user's profile Send private message
OldNoob
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Joined: 07 May 2013
Posts: 4886
Fav. Blaster: Xtreme 180 Rapidstrike
Location: In the Boonies



Post Reply with quote
I would always change the switches, the stock ones are really awful quality.

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Big_Poppa_Nerf wrote:

Boff whats the damage? I have spent over 3 times my Nerf budget this month already. Part of me is trying to be a responsible parent/husband/house owner. The other half is just says 'Ahhhh, Screw it!'.
Wed Mar 29, 2017 11:26 am View user's profile Send private message Send e-mail
SSGT
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Joined: 12 Jan 2013
Posts: 1289
Fav. Blaster: 'Rave-N' CS-18, Elite Alpha Trooper (EAT) CS-12
Location: Durham



Post Reply with quote
TheDon808 wrote:
The motors I've got are anonymous 30k @6v motors from aliexpress, I'm not looking for a really high RoF the motors are around 7-9 dps.

Link? A 30kRPM @ 6V motor should spin closer to 37kRPM @ 7.4V. That's definitely into the "too fast to stop" region for most 130s although that does depend on how much torque an individual motor is able to produce - the standard RS 130 pusher motor struggles to stop when run at much above 9V (at which point it'll only spinning around 25-27kRPM). Running the RS pusher motor on 2S would be OK but it won't quite get the sort of RoF you're after (it should be around the 5-6dps mark).

The relay will add a small delay but it shouldn't make too much of a difference unless the motor is already on the edge of stability. Like ON said, replacing the switchgear is recommended even if FETs or relays are doing the high current switching as they simply aren't very good and often don't take long to fail (especially when being cycled rapidly at higher rates of fire).

The easiest fix would probably be to use a higher torque motor (this is why it's commonly recommended to use 180s all around - since they often produce significantly more torque they can brake more quickly and so offer extremely crisp and controllable cycling) but if you will be sticking with your current switches and motors, and want to maintain a live-centre setup, then you can try modifying/replacing the cycle control follower so that it engages the switch earlier/disengages the switch later in the cycle. Alternatively, depending on how you'll be controlling the motors with the Arduino, you may not need to do anything else at all (you can just program the microcontroller to brake the motor and not start it again until you pull the trigger - effectively like a dead-centre circuit).



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Trust me, I'm an engineer! Very Happy

Antonius wrote:
Compoooter bits make shiny Nerf blaster go whoosh!
Wed Mar 29, 2017 5:57 pm View user's profile Send private message
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