pic: Floating Zip Tie Chain Tensioner

[Joe G.]

Originally Posted by UndergroundVoid

Umm, so let me get this straight if you used this as a chain tension device than how long would it last due to the chain grinding against it. Also chain has that special pattern to it with that wouldn't it get locked up on the edges of this device? might want some sort of bearingS to prevent friction but that is just me.

Its obviously not as efficient as something that rotates, but the plastic used is relatively low friction. I also imagine that the side walls do not hit the side of the chain unless the chain is moving side to side somewhat.

[UndergroundVoid]

I would have to see some test data before i make any real judgment on things since the world is full surprises.

[R.C.]

Go to mcmaster.com and type in 5973K1. My idea is based off of this but has a different way of tightening it and is superior in price and quality. Here is my final design of it:



We have been using Mcmaster Carr tensioners and chain does not get locked into the tensioner. UHMW is a very good plastic for this application and the side walls are usually never hit due to the smaller side walls. It is fit for both #25 and #35 chain.

[Joe G.]

what is the purpose of the holes on the front and back?

[R.C.]

Originally Posted by rocketperson44

what is the purpose of the holes on the front and back?

Say that you want to tension the chain on an arm robot. The chain is going vertically, so you add springs to each side of holes and the tensioner now just hangs: suspended by springs and it still tensions the chain. Also you can attach zip ties or springs to limit how far it floats or if you just want it to stay stationary. Example shown below:


Look at the white tensioner on the lift mechanism, it is suspended by springs and zip ties. The sprockets lifting the arm were of different sizes (a 60 tooth and a 15 tooth), so the tensioner had a tendency of diving down to the smaller sprocket.

[dtengineering]

Originally Posted by rc_cola1323

Here is my final design of it:

I can see why you would want two different sized grooves for the chain to accommodate both #25 and #35 chain, but do you need the different sized grooves for the zip ties, too?

I ask only because it would seem to save a few manufacturing steps to put only a single groove in for each zip tie.

In a similar vein, would it, perhaps, be easier to drill the holes ALL the way through the tensioner? That way you would only need to do two drilling operations rather than four.

You may have a different production path in mind than I envision (as I've mentioned, I see this being an ideal shape to cut on a table saw). For instance with a CNC router, putting in extra grooves would require little in the way of additional manufacturing time. But if you are going to be kicking these out by the hundred using some manual production method, you probably want to include optimizing the production path as part of your design process.

Just a few thoughts that occurred to me without having "seen inside your head" to know why you made these design choices... perhaps I have overlooked something perfectly obvious to you. If so, my apologies.

Jason

[NickE]

Originally Posted by dtengineering

I can see why you would want two different sized grooves for the chain to accommodate both #25 and #35 chain, but do you need the different sized grooves for the zip ties, too?

I ask only because it would seem to save a few manufacturing steps to put only a single groove in for each zip tie.

In a similar vein, would it, perhaps, be easier to drill the holes ALL the way through the tensioner? That way you would only need to do two drilling operations rather than four.

I agree that the 2 grooves for zipties seems unneccesary, and that the holes could go all the way through.

Another thing to consider:
If you were to make 2 different models for two different sizes of chain, it would simplify your design immensely.
I doubt many teams will be switching their tensioners between different sizes of chain very often.
Just because there is demand for more than one chain size, doesn't mean you need to incorporate all sizes into one product

Honestly, I liked your original design better. I think the most recent one you posted looks too complicated and time-consuming to machine.

[R.C.]

Guys, the reason for one tensioner is that we used the #25 Tensioner for both 25 and 35 chain and it worked perfectly. There will be no machining, i am probably going to have a mold for this made. I will probably end up changing the final design after all the comments and after more test runs of this tensioner.

Thanks Cd

[dtengineering]

Originally Posted by rc_cola1323

Guys, the reason for one tensioner is that we used the #25 Tensioner for both 25 and 35 chain and it worked perfectly. There will be no machining, i am probably going to have a mold for this made. I will probably end up changing the final design after all the comments and after more test runs of this tensioner.

Thanks Cd

If you are molding it then I would suggest rounding the exterior edges and corners. You might also want to think about putting some draft in to your design, and possibly stamping a product name, website or trademark in to the side as part of the molding process.

I hope that the sales volume is sufficient to cover the up-front cost of the tooling.

Jason

[Cory]

Originally Posted by dtengineering

If you are molding it then I would suggest rounding the exterior edges and corners. You might also want to think about putting some draft in to your design, and possibly stamping a product name, website or trademark in to the side as part of the molding process.

I hope that the sales volume is sufficient to cover the up-front cost of the tooling.

Jason

Unless he's got someone to make him a mold for free, there's just no way he can make a profit off these. The cost of getting a mold made is going to be extremely extremely high if it's being paid for.

[R.C.]

Originally Posted by Cory

Unless he's got someone to make him a mold for free, there's just no way he can make a profit off these. The cost of getting a mold made is going to be extremely extremely high if it's being paid for.

I have a company in mind

[Gary.C]

Really cool invention, so this year we can replace the mcmaster carr tensioners. Will buy

[R.C.]

This product is finally going to be released. Andymark is going to mold and sell this. So thank you everyone that replied and helped me. The final design is not shown.

Thanks CD

[Elgin Clock]

Looks like AndyMark is stocking these now!

http://andymark.biz/am-0286.html

[artdutra04]

Originally Posted by UndergroundVoid

I would have to see some test data before i make any real judgment on things since the world is full surprises.

While you can do a lot of engineering and material science related equations, there are a lot of good approximations and rules of thumb that high school students can use on FIRST robots. (Just don't use that practice IRL ).

Delrin (and UHMW) are both engineering plastics that have very low friction, and both work great for chain tensioners of various kinds. I prefer Delrin where possible since it machines very nicely (you can mill it really fast too), but it does cost quite a bit.

But if you want proof of plastic chain tensioners, here's a photo from Team 228's 2007 robot.



The white plastic circles are either Delrin (back one) or UHMW (front one). You can also see a third Delrin one on the drivetrain through one of the chassis rail lightening holes in the back. These are really simple ones: plastic rod with an off-center hole. As you rotate it around, it varies the radius; and by cranking down the bolt, it will hold its position.

The Delrin ones held up the entire year (about five competitions and a lot of other random driving) with barely any noticeable surface scratches. The UHMW ones had small (about 1/16") grooves in them from the chain. (There was no particular reason why certain ones were Delrin and others UHMW; they just happened to be whichever our machinist mentor grabbed from the stockpile when making them.)