Re: White Paper Discuss: Nothing But Dewalts
 

Thanks for the advice. We will check it out further.

Re: White Paper Discuss: Nothing But Dewalts
 

Whoops, looks like our problem is the missing motor plate, sor some reason in our haste we forgot to make that, will have to see if we can get it in tomorrow.

Brian, we don't have that plate in front of the FP so it is probably in too far

Re: White Paper Discuss: Nothing But Dewalts
 

Is anyone using these for their drive motors and shifting them? I wondering if you use one on each side, will they simultaneously shift with the servos? What if you use four, one for each wheel? Will all four shift simultaneously?

Also, can a flex coupling (lovejoy) be placed on the end of the shaft? Will the threads in an aluminum one strip out?

Last, can the Chia gear be reamed on a manual lathe (with a proper reamer of course) instead of EDMed? If so, what size reamer would you recommend (considering the lathe is old and probably not incredibly perfect anymore).

Re: White Paper Discuss: Nothing But Dewalts
 

We used them last year, and again this, at all four wheels. We learned from last year's prototype that YES, all four would shift simutaniously, but it was a struggle. A giant servo was used via cables to shift them, but the #4-40 threads would pull out of the linkage.

We considered shifting again this year with one continuous cable (spectra cord) and a short throw pnumatic. But decided that the risk of getting one or more wheels caught out of gear was not worth it. I.E., six robots and nine goals on the field may not leave many fast lanes open - so we're locked in first gear.

Re: White Paper Discuss: Nothing But Dewalts
 

As to shifting wit a "Giant Servo," I don't know under what theory a Giant Servo would be legal under this year's rules or last year's rules.

But... ...be that as it may, if you shift with one Hitec 311 servo (i.e. a legal servo) per transmission in the manner shown in the white paper, the shifters have enough "guts" to shift. They sometimes need to have the gears moving to find the right mesh, but this has not been a problem. Eventually, the drivers move the joysticks, which allow the gears to mesh if a jam occurs.

As to shift on the fly, I have discussed elsewhere that this is possible. The transmissions don't sound like they like it, but they didn't fail either. We told our drivers to do it when they needed to and not to if they didn't. Also, as I've said before, the shifting can be enhanced with software if you monitor the speed of the output shaft and try to pick the right voltage to make the mesh go smoothly. It is not very complex code.

As to simultaneousness of shifting multiple transmissions, they shift close enough to at the same time that it didn't cause us any problems.

Some thoughts from THE Dr Joe... ...accept no substitutes ;-)

Joe J.

Re: White Paper Discuss: Nothing But Dewalts
 

same info here.....

we're using four dechip's(thats short hand for a cim and dewalt combo) to drive our base. we have one servo per tranny, to whitepaper specs.

we shift them on the fly repeatedly, at full speed, and even while turning. we've beat these things to death on our practice robot for over two weeks and have had no problems.

Re: White Paper Discuss: Nothing But Dewalts
 

Does anybody have the Drawings of the "Chiaphua Plate", "Plastic Top Hat", "Top Hat Carrier", and "Top Hat Chiaphua Assembly" i would like to make a large copy of the drawings for reference and other things but it is hard with the small copy on the whitepaper if anybody can help it would be greatly appreciated. Thanks


Bill Hancock

Re: White Paper Discuss: Nothing But Dewalts
 

Since this thread is resurrected anyways...

As a heads up to any teams planning on buying the CIM NBD kits from Capital Die, Lou Oudin is still doing them, but it's been a year since he last did, and he didn't get all that many orders last year, so you'll need to work with him a little more and have the white paper in front of you when you call. No problems otherwise.

Re: White Paper Discuss: Nothing But Dewalts
 

for everyone shifting plz rd if ur having problems (giant servo theory) http://www.chiefdelphi.com/forums/sh...ad.php?t=42461

Re: White Paper Discuss: Nothing But Dewalts
 

Years later, I'm finally looking at this and wondering if it'd be a good project for our team. We'd planned on building something similar on our own, but our driving directive for the future is, as I've probably mentioned elsewhere, the "12 Hour Drive." If we can't manufacture and assemble a drivetrain in 12 hours, I don't want to know from it.

So, I've got a few questions for folks that I've not seen answered elsewhere -- though I'll keep looking.

1. Is it possible to mount the servo plate (Drawing No. 5) onto the opposite side of the transmission housing than what is shown? I like symmetry and using as little space as possible for anything and everything.
   
2. Is mounting the assembly by a shaft collar genuinely sufficient? It seems like these assemblies can put out quite a bit of torque in first gear at stall and holding it place only by friction seems daring. Might it be better to adapt the Chiaphua Plate (Drawing No. 1) to mount directly to the robot in addition to the collar? I want to mount a gear to the output rather than a sprocket and am concerned that a collar will allow too much play in the center-center distance between the gears and create problems there.
   
3. We can laser cut .125" and .0625" delrin pieces and chemically bond them together to create a plastic top hat as shown in much less time than it'll take to set up and mill them. Will undersizing the .125" piece by as much as .003" be a disaster? The drawing calls for .128". I'd love to laser cut them, since I can then add a keyway in addition to the pressfit.
   
4. Is there a particular reason the modifications to the top hat carrier call for a counterbored hole rather than a countersink? Again, it seems to be it might be easier to countersink the hole than to counterbore it given our tools and desire to get it done quickly.
   
5. Is first gear really all that useful, or should I be treating this as a two-speed transmission? It seems like with gearing designed to make the two higher gears useful -- 1:2.5 at the output, resulting in about 1:7.5 and 1:10 -- the first stage reduction then becomes 1:30 and produces way more torque than even the stickiest of FIRST tires can be bothered with. Perhaps it'd be wiser to ignore that first gear all together, since I'm going to be spinning tires there in any case, and gear the second and third speeds down a bit more. 1:10 is awfully fast and 1:7.5 might be illegal on the Autobahn, even.
   
   

This looks like a really straightforward modification and I think we ought to be able to get two of these setups up and running in the time it'd take to set up and manufacture the parts for one of the gearboxes we'd otherwise been considering.

Re: White Paper Discuss: Nothing But Dewalts
 

Yeah, it's definitely doable. We've always put them on the same side because we would have a default setting on the servos which we used to calibrate them. If you have the servos on opposite sides. If you have the plates on opposite sides then one transmission might have a bias toward 1st gear, and the other might have a bias toward 3rd gear.

We had a debate about this on our team a couple years back, and trust me, those collars are more than sufficient. After 3 years of relying on the DeWalts for our drive train and arms, we've never has a single problem with the collars not being able to take the stress of competition.

Since they don't do anything else, I don't see why .003" would make any noticeable difference.

I think it just has to do with the type of screws they recommend in the whitepaper, but I'm not sure.

First gear is very useful. If anything, you might have more of a problem with the lack of difference between 2nd and 3rd. We designed our drive train to slip the wheels in 1st gear (using rough top on a 6wd). This maximized our speed while allowing us to still use the wheels' coefficient of friction as the limiting factor. In 2nd gear the robot would zip across the field, so we found that 3rd gear wasn't that useful, since 2nd gear was sufficiently fast for all practical purposes.

Re: White Paper Discuss: Nothing But Dewalts
 

I don't trust our ability to make a reliable press fit onto the CIM shaft, so I've been looking at alternatives. It seems like there's enough space on the shaft to allow for the "top hat" piece to be extended back to the motor mounting plate and keyed. Has anyone tried this?

Because we cannot conveniently (or, really, inconveniently) key hubs, I instead was considering that we build up a keyed "top hat" from layers of delrin or some other plastic. We can laser cut 1/8" and 1/16" layers as necessary and extend the overall length of the finished piece into the gap that currently exists between the motor mounting plate and the carrier/pinion gear. This'll get us about 1/2" of key and I'm going by gut when I assume that we can find a plastic that'll hold up sufficiently well this far up the gearing. We could then loosen or eliminate completely the press fit.



We'd be looking at stacking up this assembly on the motor shaft, gluing the layers togethers, then tapping through all of the pieces of plastic at once. Conceivably, we could try plasma cutting these same pieces from aluminum, but we've had mixed results with the plasma cutter, particularly because of its relatively large kerf. It's difficult to get it to make small cuts and holes cleanly.

Also, I'd love it if someone was able to tell me what the distance is between the back of the "top hat" and the motor mounting plate if this is built according to spec. in the whitepaper. The drawing doesn't include that information, nor the face width of the gears in the transmission, from what I've been able to tell. Based on the drawing below, I know only that the overall dimension from the face of the carrier gear to the motor mounting plate is .647" and that the top hat is .188".



I love the idea of making these work for us, but the build out called for in the white paper seems to call for all of our weakest abilities -- press fits, welding, accuracy ( ;) )... and the changes we're making to accomodate that seem significantly vast that we have some concerns. Still, for the weight and price, this arrangement can't be beat, it seems.

Re: White Paper Discuss: Nothing But Dewalts
 

Madison I respect your posts here on CD and I see your doing your best to try and make this work for your team. I don't think that using plastic as a key is such a great idea. This is coming from my background in machining and dealing with different types of plastic. I don't profess to be an engineer but my team has been machining plastic and using it for wheels,turrets and bushings for quite a long time. I have seen this set up and it just seems to me that in a application with the cim motor like you have shown the plastic keys just won't hold up through the whole season. I am only a first year engineering student but whenever there is metal on plastic, plastic usually loses no matter how strong it is after a certain period of time. I think your best bet would be to find someone who can make that size keyway which I believe is 2mm if your talking about the cim. Either that or make the Keyseat on the cim bigger and adjust the plate accordingly. Just a few ideas and I think aluminum would definitely be the way to go as far as the key. I like the idea it just doesn't seem efficient manufacturing wise and from what I read and I reread the post 3 times, that it just won't be durable enough. I do like an idea of a keyway in the top hat instead of a press fit, good thinking.

Just some input and ideas like you asked for,
Drew D.

Re: White Paper Discuss: Nothing But Dewalts
 

Drew,

Sorry if there was confusion -- I should've made this more clear -- but we'll be using a steel key seated between the CIM shaft and the plastic spacers. Last season, we built clutches for the 256:1 Banebots gearboxes that were delrin and acrylic and included the key in the delrin parts. Those keys didn't last very long at all and repairing them on the fly would've been impossible if we hadn't realized early on that we'd made a really dumb decision.

I'm not sure if we'd see better results with a steel key into a plastic keyway, though. It could end up being six of one and half a dozen of another.

Re: White Paper Discuss: Nothing But Dewalts
 

Madison,

Two years ago, we used a NDB CIM to spin up a shooter wheel. We too had a problem getting a good press fit on the shaft and ended up keying the unmodified top hat. Mind you, this was a last minute fix and the key ended up also being wedged somewhat under the metal gear... But it worked fairly well for us in that application. I'd probably be a little more worried about its use in a higher torque application, but not too terribly worried if you're lengthening the keyway. Seeing as how this is the off-season and all, I'd just recommend mocking up a similar keyed hole in something like a long, thin(ish) rectangle that you can rigidly attach to something. Then you can hook up a CIM (preferably that you don't like) and rig up something to stall it at 12V rapidly cycling from CW to CCW. One other thing I'd recommend is cutting your keyway as a semi-tight fit. Any slop you have there is going to increase shock loading by that little bit and make things that little bit less reliable.