pic: FRC294 Prototype base almost done

[AdamHeard]

Originally Posted by Greg Needel

Adam,
it looks really good, the machining is obviously top notch. I am wondering if you have put any thought into the amount of chain wrap on a sprocket? best rule of thumb is that you need at least 120 degrees wrap on each sprocket, I have a feeling that the center wheel is just about at 120 degrees. If you have the option have you considered moving the idler on the bottom left towards the center wheel which will increase the wrap on the center while keeping your left wheel with plenty.

Greg

Yes, I am a little concerned about the chain wrap. It is pretty close to 120 degrees, and it is a prototype (294 cover your ears; I also didn't want to fix everything that might be a issue because I wanted the new kids to work with the more experienced ones to fix it and learn. But also, a lot of the mistakes were me legitimately messing up ) so I left it to see how it turns out.

Kind of funny story about the pins. One of the mentors that was advising told me to add a bunch of pins rather than bolts.... So, once the design had a 5" tall plate one each side, I decided, why not just put a bunch of pins? It's not going to hurt, and If the base is run without bumpers those corners will be taking lot of shear on impacts.

EDIT: techtiger; what do you mean about chassis plate shifting back and forth? Do you mean the left and right modules, or the inner and outer plate of each module. On the 2007 base which had very similar framing, neither was an issue. The entire frame was very, very stiff.

EDIT2: spazdemon548, sorry I missed you. I'm not sure what you mean by clockwork spacers; but, for the gearbox standoffs, and all the other spacers standoffs we bought a whole bunch of spacers from mcmaster for cheap. We bought two different outer diameters, and the inner undersized (so we can just chuck it in a lathe and open it to what we want real fast) and in a whole bunch of lengths from 1/32" to 1". In the past I had them make some really funky spacers; now they can get almost any spacing with off the shelf parts. FYI, borisdamole can testify to the painful amount of spacers I had cut .

Also, the wheel drop is either 3/16" or .2. I don't remember which but they're pretty close. That's about what we ran all year with our adjustable height.

M Krass; Allways look forward to your input. I don't have the CAD with me, so I can't pull a weight from that. I know some of the components off the top of my head though; each panel ~ 3, each wheel ~ .4. We're weighing the finished assembly this weekend for some real world data.

It is pretty easy to adjust the tension on the chain, just turn the thumb screws. So, it should be done every match. Hopefully it can't loosen enough in one match to cause the failure.

Hmmmm. the 3/8" plate is just what we've been using since the original design (this is the 3rd iteration). The machining time isn't that bad because it can be run while they're simultaneously cutting on the manual machines. I guess 1/4" would save a lot of time, but would it be worth the strength loss? Weight isn't a big issue, each panel is only 3 lbs right now. But now you've got me curious, I'll look into 1/4" and see how it will compare in weight, strength and the amount of material removed.


Once again, thanks to everyone for all the input. Really, your opinions mean a lot.