CPS 4100 Trigger Repairs

For questions, articles and discussions regarding water blaster maintenance and repairs.
Post Reply
Jadefalcon
Posts: 4
Joined: Fri Jun 13, 2008 8:21 pm
Location: Allentown, PA
Contact:

CPS 4100 Trigger Repairs

Post by Jadefalcon » Fri Jun 13, 2008 8:27 pm

It's been a while since I have visited the soaker community.

Image

The trigger was reinforced previously (not the best job) with a strip of aluminum to eliminate some friction. Now I am planning to add a connector rod to the back of the trigger like most super soakers of earlier design did. This is a major flaw in the design of the gun, and is the main reason why CPS 4100 rifles are so prone to trigger snap. Trigger snapping IS repairable, but it is much more difficult. If that happens or I need a new trigger, I have the capabilities of making brand new triggers. In the future I will draw up outlines to new trigger assemblies in a 1:1 scale so that users can print them out and use them as a starting guideline for shaping new triggers.

The connecting rod will be shortened as long as I need it to, and it will be bent into the spring for added grip (since the shaft is smaller than the inside of the spring). The spring is from an assorted spring box you can find at a hardware supplies store (Home Depot!). There are many springs to choose from. One law must be followed in this respect: Springs always have a constant force which is commonly referred to as "k". The number of turns and the length of the spring greatly impacts it's resistive forces. I can have 5 turns and a one inch spring, and I can have 50 turns on a one inch spring, and clearly one will have more resistive power. The lower the number of turns "n", generally (depending on length) the stronger the spring. In the context of exact lengths, the smaller N is the more powerful a spring is. Some springs are too powerful, and can overwhelm the plastic parts. Care is needed in selecting the right spring, "what feels right" will work here. When I get back to work on it tomorrow I will post information regarding the number of turns and lengths of the spring.

Analyzing where stresses will act upon the (multiple) bodies, from running a quick simulation in my head it seems that there will still be pressure on that thin piece connecting the trigger to the upper trig portion, and there will be stress on the bend rod where it is pulling and pushing the spring- but the ladder probably won't need any attention. To strengthen this area, I am going to superglue the cracks as to fill them and strengthen them. If the spring is installed correctly, it should alleviate some stress on the trigger. In the long run, it is better NOT to use a powerful and short spring on the trigger. Sure you won't have to pull as hard- but the trigger was not meant to withstand such forces. I am going to stick with a longer, but strong spring.

Image
Image
Image

I am currently finishing up a repair on a CPS 4100 that has been lying around for over a year in need of a repair. The repair is on strengthening the trigger and increasing it's liability. CPS 4100s were widely manufactured back at the turn of the century and they are notorious for trigger breaks and pump problems. I will post pictures in a couple of minutes- I need to go take them. Good to be back,

-Rob

User avatar
isoaker
Posts: 7113
Joined: Sun Jul 04, 2004 1:51 pm
Location: Elsewhere
Contact:

Re: CPS 4100 Trigger Repairs

Post by isoaker » Sat Jun 14, 2008 3:52 am

Yo, Jadefalcon,

Welcome back! Good to see you 'round and hope all's been great with you!

On a more thread-related note, nice pics and good repair article; will likely be very useful for some people out there. I also like the style you wrote it in; feels more personal in a way.

May I repost this article and pics on iSoaker.com?

:cool:
:: Leave NO one dry! :: iSoaker.com .:

Jadefalcon
Posts: 4
Joined: Fri Jun 13, 2008 8:21 pm
Location: Allentown, PA
Contact:

Re: CPS 4100 Trigger Repairs

Post by Jadefalcon » Sat Jun 14, 2008 9:46 am

Absoloutely! In the future I may be video recording some repair jobs as well into a 10 minute video- I wouldn't mind if you either linked or embedded the youtube file, either. I have had so many problems in the past with CPS 4100s that I have become almost an expert at repairing them. The super glue has had it's 24 hour drying session (as a precaution) so I will be grinding that brass rod to proper length a little later today, I want to test this thing!

Things are going alright with me. I am finished a year in college and since then I have worked with many hands on projects, which I can say has increased my knowledge on fixing problems (like this gun). I have decided to become a super soaker enthusiast and collector, but also a repairman/restorer (being an engineer and all). Many guns I deal with are vintage and are worth money, so it feels nice to take care of them! I have written my share of guides or two, and I have had to explain a lot of phenomena (word?) and I have had to explain how a lot of mechanical contraptions work, so my technical writing skills are somewhat up there- I like making soaker repair articles, and also my model building articles more personal so that others can understand what I am saying better. There is a hint of technical jargon in there though, with "spring constants" :goofy: . Anyone who has had a Physics course will know what that is, however. Since I am on a roll..... *pulls out Physics text*

Image

The equation I referred to earlier is known as Hooke's Law: [F=kx]. This law does apply to more than just springs: it can apply to the analysis of elastic/plastic regions in test specimen (when you try to bend 'em or rip
'em apart). From Arthur Beiser's Physics: 5th Edition Text:

When we pull out a spring, it resists being stretched, and if we then let go, the spring returns to its original length. As we know, this is typical of elastic behavior. On the other hand, when we pull out a piece of taffy (a type of candy like chewing gum), it also resists being stretched. But, if we let go of the taffy while stretching it then nothing happens (it won't try to reform it's original shape). The deformation is permanent, and this is typical of plastic behavior (this also applies to every single plastic part on the gun, stretch it or bend it in some way and it will eventually fracture).

In the case of the stretched spring, a restoring force comes into being as it tries to return the spring to its original length. The more we stretch the spring, the more restoring force we must overcome. The amount of "x" by which an elastic solid is stretched or compressed by a force is directly proportional to the magnitude F of the force, provided the elastic limit is not exceeded. This proportionality is referred to as hooke's law.

The text goes even further into kinetic energy and other work related issues, but that snippet says a lot. Both the length of the spring and the spring constant are related, the greater either [K] or [X] is, the more force necessary to compress or stretch the spring. I will take the spring arguement one step further and apply some engineering. One thing the physics text neglects to mention is that the number of turns and the length of the spring have a significant impact on the force at which the spring stretches or pushes back against you. Sound familiar? The text is debunked- [K] is parallel in a sense to the number of turns of the spring, and distance is distance is always distance. How does this translate into what we are doing? If we include a spring with too many turns, then we will have a force pushing back against us; instead of this force pushing against our finger it will be pushing on our trigger- which has a weakpoint near the fabled break zone. In short, you will be able to pull the trigger and open the valve, but the trigger will slide back very fast, and eventually WILL fracture. If we introduce the correct number of turns, then the trigger will slide back with ease. Reinforcing the fracture zone and selecting the correct spring will alleviate pressure on that break point. It isn't technically a mechanical advantage per say, but it will help. Please Isoaker, by all means use all of this information if you desire, I tend to get on a roll with things :goofy:

SSCBen
Posts: 1442
Joined: Sun Jul 04, 2004 4:15 pm
Contact:

Re: CPS 4100 Trigger Repairs

Post by SSCBen » Sat Jun 14, 2008 2:37 pm

I like how you analyzed the situation and came up with a different solution. From a statics point of view the crack can be avoided with a force applied at the right point to avoid the internal moment that'll crack the plastic. Great idea. I've updated my guide to snapped triggers with a link to yours. Keep up the good work.

One thing you might want to note is that rubber does not follow Hooke's law. The stress-strain (and likewise force-displacement) curve does not have a linear segment. So you can't approximate the force from a rubber band accurately with Hooke's law.

User avatar
isoaker
Posts: 7113
Joined: Sun Jul 04, 2004 1:51 pm
Location: Elsewhere
Contact:

Re: CPS 4100 Trigger Repairs

Post by isoaker » Sat Jun 14, 2008 5:11 pm

@Jadefalcon: thanks for the reposting permission and additional physics article material! I'll most definitely make use of the info. As for becoming a "super soaker enthusiast and collector", weren't you one in a sense already? :goofy:

At any rate, great stuff and feel free to share your thoughts or ideas on soakers, repairs, and beyond any time!

:cool:
:: Leave NO one dry! :: iSoaker.com .:

User avatar
isoaker
Posts: 7113
Joined: Sun Jul 04, 2004 1:51 pm
Location: Elsewhere
Contact:

Re: CPS 4100 Trigger Repairs

Post by isoaker » Sun Jun 15, 2008 5:58 am

CPS4100 Trigger Repair thread reposted

Thanks again for writing up a rather helpful article on trigger repair and sharing it with the community! If you're ever feeling inspired to write up more in the future, I'd wholeheartedly support the idea and welcome new or even revisited subjects on anything water blaster or water warfare-related. I, too, will also write up additional repair articles on blasters I end up trying to fix as well.

Soak on!

:cool:
:: Leave NO one dry! :: iSoaker.com .:

Jadefalcon
Posts: 4
Joined: Fri Jun 13, 2008 8:21 pm
Location: Allentown, PA
Contact:

Re: CPS 4100 Trigger Repairs

Post by Jadefalcon » Sun Jun 15, 2008 9:54 am

One thing you might want to note is that rubber does not follow Hooke's law. The stress-strain (and likewise force-displacement) curve does not have a linear segment. So you can't approximate the force from a rubber band accurately with Hooke's law.
Yes, Hooke's Law does not apply to elastomers and it will not apply to the plastic region on the stress/strain curve. I should contact ex-Larami engineers and get some fracture stress information :) While I am on a roll......

It's very interesting to look at elastomers and why Hooke's Law will not apply. It lies in the molecular structure- say you have a tangled mess of string- how elastomers work is if you pull the stringy mess, the molecules will stretch and straighten out. Depending further on the material, and how it is shaped and constructed (ex.- rubber bands) it may want to return to it's original shape. Stuff like silly putty (I can get into what is in silly putty, but that is besides the point) does not want to return to it's original shape- it has to do with how the polymers are acting at a molecular level. Although the term "thermoplastic" deals primarily with plastics, there are materials out there made from "thermoplastic elastomers" such as creepy crawlies.

As an additional note- some folks may wonder why Hasbro does not begin producing the older guns anymore. The answer lies in keeping the old molds. To mass produce water guns at the rate they did (the shell, etc)- they had to injection mold items such as the push button, nozzle, and mainly the frame of the guns. The reservoir could have been made with a process known as blow molding. It's no wonder the Monster XL cost so much money because of the amount of plastic involved and the labor required to make these things- you can make literally dozens of parts from a liquid injection molder, but the larger guns probably took some time. These newer, smaller guns are cost effective for them AND for the consumer, so naturally if selling the larger water blasters didn't pay off in the long run, a change was needed- from a business standpoint.

If you guys would like to see the report on Silly Putty I authored, send me a buzz via email and I will let you guys check it out- it is a good read!

Jadefalcon
Posts: 4
Joined: Fri Jun 13, 2008 8:21 pm
Location: Allentown, PA
Contact:

Re: CPS 4100 Trigger Repairs

Post by Jadefalcon » Sun Jun 15, 2008 10:19 am


Post Reply

Who is online

Users browsing this forum: No registered users and 2 guests