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Member Since 10 Dec 2015
Offline Last Active Feb 12 2016 10:58 AM

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In Topic: TR-27 GRYPHON - CR-18 Rapidstrike Mod

21 December 2015 - 07:14 AM


Awesome contribution to this thread. My question is, what do you mean by the "Toruk Test"?


Thank you again for your assistance!!


Basically, the Toruk Test is... If the Arduino fails, will the blaster still function as if it were stock, or close to?



Thats cool, I had no idea that the arduino could do that.  But if I'm not mistaken, it will only show you the 5v or 3.3v rail that the Atmega328 is running on.  If you are using an S3 (3 Cell) LiPo battery, then full voltage will be 11.1v.  If you run off of any of fewer cells though, you'll still only get as close as 7.4v, or 3.4v.  I suppose you could run the MCU off of a single cell of the lipo, but there are a few things you need to keep in mind.


1. A fully charged lipo cell runs at 4.2v, and at maximum safe discharge, it will go to down to 3v.  4.2v may be more than a 3.3v MCU can handle.  And 3v may be less than a 5v can handle.


2. Discharging a lipo unevenly (more load on some cells than others) is bad for your lipo.  And if you are only measuring one or two cells to determine the battery's overall power level, then you'll be estimating the unmeasured cell's power level.  (i.e. if cell one is at half discharge, then I'm assuming cells 2 and 3 are as well.)  And while that may work at first, because of the uneven load distribution, you will eventually get faulty readings as the cells deteriorate.


As far as I know, you'll have to regulate the power down from 11.1v to 5v or 3.3v, but if it is regulated, you won't know if the battery is loosing power or not based on the power to the MCU.


If I'm not understanding what you're saying, please let me know because my current understanding says I need to know the voltage of each cell of the lipo individually, in order to properly protect the battery from over discharge.  Hence the circuitry to measure the battery's power.


The rest of your project sounds great though.  Will you be making a project post on Nerf Haven?


Once all my bits arrive, I'll make a build post both here and on the Britnerf forums.  I have already done some stuff using a 3S LiPo to power an Arduino, and I power using full voltage off the JST plug, so I don't severely unbalance the LiPo.  I have considered wiring in my LiPo charge meter in parallel so I just have a low voltage alarm, if not a full volt reading.  Not sure if it will work.


Already going to be using lots of the analogue pins, I2C display, flywheel and pusher MOSFETs, may use a variable resistor or rotary encoder for changing settings, then digital pins for microswitches and navigation... Might have to lose features if I want per-cell health, knocks out 3 analogue pins right away, maybe just one if I can get a clock to toggle between the three cells once per second or so... I really need to get a sketch of the hardware finalized.


I may just re-use that Lipo and current-limit using the MOSFET to keep the max voltage supplied to the motors at or around 6 volts.  Heck, I may make that a programmable feature, along with the dart pusher rate of fire.  Got software control, might as well make the most of it.


For my use, powering off the unregulated supply, I will have to see what happens.  Those particular pins regulate from 6-20V down to the internal required 5V for my board.  This internal regulator will probably stop the function of the on-board voltmeter, as I don't think I can get the pre-regulated voltage using this method.

In Topic: TR-27 GRYPHON - CR-18 Rapidstrike Mod

18 December 2015 - 05:10 AM


1. I'll have to check on the MOSFETs, but I don't recall them being anything particularly special.

2. Runtime on the LiPo has been super.  I think it is realistic to count on a full day of nerf on one battery.  But I havn't yet tested that.  I did do a half day with no issues though.

3. This is a huge question.  One that I'm in the process of answering for myself, but I'll try to condence it and give you something usable.

I should have had a better overall plan and goal.  Because I didn't yet know what I wanted, I tried a lot of things that didn't pan out well.  For instance, I should have skipped right over the 7-seg displays and gone straight for OLED.  Another major issue I wish I had seen in advance is EMI from the Motors and main power lines.


I have already purchased MOFSETs as per advice from the britnerf forums, from the Managing Director of Blastersmiths UK, the IRFZ44N.


I have also ordered a well-supported OLED right off the bat, no mucking about with the bulky segmented display and driver chips.  I'm going to be doing the SMG mod to shorten the barrel and have a relocated battery box, but I will be either putting in a pair of 130 or keeping the stock motors, just with 18AWG wiring for power supply systems.  I am not doing anything to make sure it passes the Toruk test, as I am not a competitive Nerfer.  


Here's an enhancement for you - https://code.google....SecretVoltmeterIf you use the right Atmega chip, then you can find out what the internal voltage is, and from that, you can work out what the current charge state of your LiPo is, without needing additional circuitry.  Personally, I will be powering my nano from the JST balance plug, full voltage, onto the unregulated power pin.


Thanks for mentioning the EMI.  I will make sure to put a ferrite ring around the Arduino power supply. Sure, I'll be feeding it from the unregulated supply pins, 


I suspect that once I get this all prototyped and working on the Nano, I will do the same, and do my own PCB, and use the correct Atmega SMD to get the pack size down.

In Topic: TR-27 GRYPHON - CR-18 Rapidstrike Mod

10 December 2015 - 09:36 AM

I am relatively new to this whole Nerf modding thing but am a programmer by trade, with an electronics hobby on the side.  I am currently pulling together the pieces I need.  Once I get down to Brass Tacks, I will be sure to do my own mod post, but thought I'd ask a few questions.So far, I have 


3 Arduino Nanos - a bit bigger than the Pro, but looking at the shell, so long as I solder and clip pins I can get it to fit.

1x SSD1306 128x64 SPI/I2C OLED screen

Lots of wires of various gauges


Oh... I also have all the source code from this thread.  Not sure if you have made any more modifications to it but I will probably just be drawing inspiration rather than wholesale copying.  Might even put mine on Github.  If I include yours, how do you want attribution?


Here are my hardware questions for you, or anyone else for that matter.


What is the manufacturer and part number of the MOSFET you used? Alternatively, what are the specifications so I can find an equivalent?

How much runtime do you get off the LiPo?

If you could start all over again, what would you do differently?