Jump to content


Photo

Adding a RPM/Speed Controller to a Stryfe

Control the speed of the Stryfe motors without losing power.

5 replies to this topic

#1 blacklion

blacklion

    Member

  • Members
  • 17 posts
  • Location:Cincinnati
  • State:Ohio
  • Country:United States

Posted 20 May 2013 - 02:12 AM

Hi guys!

I finally got the RM2 motors and UltraFire batteries I ordered. The RM2 motors sure are awesome and deliver plenty of torque and speed. Using either 2,3 or 4 UltraFires you can see the improvement vs. the stock motors and 4 regular AA batteries. However, I was a bit disappointed due to the fact that there was no way of controlling the speed of the motors and that I would have to choose between using 2,3 or 4 batteries at any given time.

Initially I thought about using a good ol' potentiometer to vary the amount of power to be delivered to the motors, however after some research and consulting I discarded this idea since this application would require a quite big potentiometer (with high power rating) and even if I got one, you would lose a lot of power in the form of heat when operating at lower speeds. After some more research I learned about PWM (pulse width modulation). If you're not familiar with this, please visit this site, as I found it very helpful to understand this concept. In a nutshell a PWM modulator is a control device made up of capacitors, resistors, diodes, a potentiometer and a transistor that controls a signal by varying it's frequency. This video helped me understand the concept. Bottom line, you'll be able to control the speed of the Stryfe's motors as you turn a dial.

After some more research I was able to find a PWM controller that was small enough to fit inside the Stryfe and big enough to handle the voltage/current delivered by 3 or 4 UltraFires. I got it on ebay and you can find the link to it on the materials section. All this said, this writeup will briefly cover how I installed the PWM controller in my Stryfe.

MATERIALS

This is the PWM controller (PWMC) I got. Go ahead and pull out the dial, unscrew the locking nut, remove the washer, and proceed to carefully break the white plastic enclosing. You can start by ripping off the the two mounting points with some pliers. When you do so, cut the yellow wire just before the fuse holder and proceed to remove the PWM out of the plastic housing.
Posted Image

I mounted the PWMC just below the Stryfe's jam door. In order to do so, you will need to cut a bigger opening so that the PWMC fits. You'll also need to cut the wires (and probably add more wire) just below the jam door as in the pic below.
Posted Image

Now proceed to cut a bigger opening just as I did.
Posted Image
Posted Image

Look at the difference when compared to the other side of the shell. Now proceed to cut the other side of the shell as well.
Posted Image

When done, the PWMC should fit in the opening without problem.
Posted Image

Note that you will need to drill a hole on the side so that you can get the wires into the Stryfe and make the connections.
Posted Image
Posted Image

IMPORTANT: Once the PWMC is in position (just like in the pic above), you'll need to cut a hole in the center of the jam door such that it matches the position of the shaft. This is not an exact science, so go ahead and using the jam door as reference, roughly find the position where the shaft should go through the jam door. Once you're satisfied, mark the spot and drill a small hole using the dremel drill bit. After that proceed to make a bigger hole using a 1/4" drill bit. Then using the x-acto knife proceed to enlarge the hole one cut at a time unti the shaft goes through and has enough space to wiggle around a bit. Remember that you will need to lock the PWMC in place using the washer and locking nut you removed in the first step. Be careful not to cut the hole too big such that the nut can't lock the PWMC in place. I apologize for not taking pictures of this step.

Once you have done so, lock the PWMC in place. It should look like this. Note that if properly done, there should be no clearance issues between the PWMC and the magazine.
Posted Image

You're done except for the wiring.
Posted Image

You should have two wires coming from the motor (pos and neg), two wires going to the motor (pos and neg), and the three wires from the PWMC. In the following diagram my positive cables coming from and going to the motors are red, and the negatives are black. However, this might not be your case.
Posted Image

WIRING
  • Motor (-) Black ---> PWMC Yellow
  • Motor (+) Red ---> PWMC Red
  • Batteries (-) Black ---> PWMC Black
  • Batteries (+) Red ---> PWMC Red

This is how it should look if wired properly. Notice that the PWMC Black wire I soldered directly to the negative terminal of the battery box. Also try to keep the wires as short as possible such that they do not interfere with the trigger/dart pusher mechanism.
Posted Image

And you're done! This is how it looks once you close the shell.
Posted Image

This is how the PWMC looks from the magazine port.
Posted Image

I apologize in advance for skipping some steps and for not having more pics. I assume most of you can get this done without much more detail. If you have any doubts or questions feel free to PM me. Since I'm still a FNG my post count is limited and might not be able to reply directly on the thread. I do not have ranges yet since I don't have a 100'+ tape measurer, but I can tell you the improvement is significant. Also being able to select your speed/power is pretty sweet and convenient. I also noted that during rapid fire the motors barely lose power. I'm not 100% sure, but I attribute this to the huge capacitor in the PWMC.

Video coming soon.

Hope this helps! Happy nerfing! :lol:

EDIT: Fixed image links.

Edited by blacklion, 21 May 2013 - 12:22 PM.

  • 0
blacklion :. 32

#2 azrael

azrael

    Member

  • Members
  • 393 posts
  • State:California
  • Country:United States

Posted 20 May 2013 - 11:25 AM

The huge capacitor is to smooth out ripple and provide a stable transient response for the active circuit on the controller. I doubt it has anything to do with the lack of recovery time.
TBH, recovery time is something that is rather variable, depending on how rapid your shots are, I'm sure we all define it a bit differently.


I'm not a fan of where you mounted it, but there's not a lot of options, I guess haha. I probably would have mounted it on the outside in a secondary enclosure. Good stuff.
  • 0
Better Nerf By Science!
http://nerfscience.blogspot.com/

#3 Duke Wintermaul

Duke Wintermaul

    Member

  • Members
  • 516 posts
  • Location:Dayton
  • State:Ohio
  • Country:United States

Posted 20 May 2013 - 12:23 PM

I like it.

My jamdoor is occupied at the moment, and always will be, so a different location would be better.

I'm waiting for your tests, as i'm curious as to how much this is needed. Whats the RPM range with the min and max settings? How much of an improvement can this be? Does it reduce torque?

Lots of question's, but i like it.
  • 0

#4 azrael

azrael

    Member

  • Members
  • 393 posts
  • State:California
  • Country:United States

Posted 20 May 2013 - 02:03 PM

Since RPM is something hard or maybe even impossible for most of Nerfers to determine, either a PTG range test or preferably an fps test would yield some relevant results.

Since the stall current draw of the RM2s at these voltages (3s) already significantly exceed the max current supply of Trustfires, and the controller can handle up to 10A, I don't think performance will change from similarly overvolted and motor replaced Stryfes.
  • 0
Better Nerf By Science!
http://nerfscience.blogspot.com/

#5 Hammy

Hammy

    Member

  • Members
  • 104 posts
  • Location:Singapore
  • Country:Singapore

Posted 20 May 2013 - 03:41 PM

That's an itsy bitsy teeny weeny namby pamby electrolytic capacitor.

Anyway, nice mod :)
  • 0

#6 koolman97

koolman97

    Member

  • Members
  • 46 posts

Posted 10 June 2013 - 05:26 PM

Looks amazing, great job!
  • 0


0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users