11-28-2008 07:30 AM

Sam2197

Re: pic: Madtown Robotics Drive Proto

looks nice and clean. good design

11-28-2008 12:08 PM

Akash Rastogi

Re: pic: Madtown Robotics Drive Proto

What cut of Al are you using for those front bumper-like thing? I've never seen anyone use that before. Looks clean and light. All welded I'm assuming?

11-28-2008 12:18 PM

gorrilla

Re: pic: Madtown Robotics Drive Proto

are those gearboxes custom?

11-28-2008 03:29 PM

R.C.

Re: pic: Madtown Robotics Drive Proto

The front bumpers are extremely funny, our teacher 3 years ago thought it would be cool if our bumpers weren't rectangular. So he got a piece of 1x2 aluminum and made slits on the ends, then bent the pieces to that U shape on the front and left the back flat. Then we weld them shut. You can't notice the welds on the front due to powder coating. BTW, we weld everything.

Yes, those gearboxes are custom. For some reason we lost sponsorships but got some weird grants over the summer. We have a brand new CNC, a ton of broaches for keyways and hexes, and other random stuff in our shop. So we figured to start making custom stuff, it's pretty fun. Especially when CD gives such brilliant suggestions.

I forgot, in the grant that we wrote for our CNC, it stated that we had to help other teams machine out parts. So i don't know if i should start another thread, but if any teams needs anything milled (can be possible to do with a 3 axis) we would do it for free (you pay for shipping, the product and $1 for the labor/SO as close to free machining.) Contact Me

11-28-2008 04:30 PM

gorrilla

Re: pic: Madtown Robotics Drive Proto

where do you get powder-coating done? isent that really expensive?

11-28-2008 05:53 PM

ironbears

Re: pic: Madtown Robotics Drive Proto

I work in a custom machine shop that has full CNC capabilities as long with powder coating. Is there a rule against powdercoating in FIRST/ or anything like it?

My employer has allowed us to use all equipment during build season. Do you guys always do that drive train?

11-28-2008 06:03 PM

rutzman

Re: pic: Madtown Robotics Drive Proto

I'm sorry if I'm missing something, but what are those shafts extending from the gearboxes? They don't appear to be attached to anything.

11-28-2008 06:10 PM

AdamHeard

Re: pic: Madtown Robotics Drive Proto

The 1.5 lb gearbox seems fishy to me. What are the gears? Are you accounting for fasteners, cylinder, bearings, shafts, etc...

11-28-2008 06:31 PM

Re: pic: Madtown Robotics Drive Proto

I can see them being 1.5 lbs without motors. Two motors are more than 1.5lbs.

That being said: Due to all the changes being made to the kit, with electronics and all, don't secure yourself on the CIM motors. Whatever you do, be ready for a change in case it comes.

11-28-2008 08:18 PM

EricH

Re: pic: Madtown Robotics Drive Proto

Not for as long as I can remember. Any team that has wanted to powdercoat/anodize/paint/otherwise treat their metal has pretty much been free to (aside from the cost limits).

This may change in 2009.

11-28-2008 10:25 PM

R.C.

Re: pic: Madtown Robotics Drive Proto

We have a wide range of sponsors that do not donate money, instead they offer resources such as powder coating, we have gotten it for free and yes it is pretty expensive.

No, there is no rule against it. The pink team, poofs and a handful of other teams do it.

The shafts are attached to the gears, it is an andymark supershifter without the last stage of gears.

The gears are all steel, but they have been faced down (from a 3/8 to a 3/16) and they have holes drilled into them by using an index. The weight is accurate but it does not include motors. BTW, there are only five gears (exclude cim gears) in this assembly and we have found a sponsor that will anodize the gears for us.
I was thinking the same thing, I created this drive before Bill's statement. It would be kinda cool to get some Mag Motors. lol.

11-29-2008 12:12 AM

Brandon Holley

Re: pic: Madtown Robotics Drive Proto

What grade steel were you planning on using? Did you feel that this grade was not going to be strong enough? I was under the assumption that its not possible to anodize steel.

11-29-2008 01:26 AM

Cory

Re: pic: Madtown Robotics Drive Proto

Have you done the math on this? 3/16, while probably OK on the first stage of reduction is scary thin for your output stage.

Also as Brandon pointed out, you can't anodize steel.

11-29-2008 04:22 AM

R.C.

Re: pic: Madtown Robotics Drive Proto

Sorry, I didn't mean steel. I was thinking about the aluminum gears.

11-29-2008 04:36 AM

Cory

Re: pic: Madtown Robotics Drive Proto

You're making aluminum gears? I would think very hard about that before committing to a design that revolves around them. Travis has posted on here how there's no way we would have attempted the gearbox we did in 2007 if it hadn't been able to take care of his and Kirk's senior design project as well. There's hundreds of hours of machining alone put into them. The resources are really better spent elsewhere.

Regardless of the material, you need to do the math to see if 3/16" face width will work for you. It probably will for the initial reduction, but my gut instinct is there's no way it will hold up on the output.

11-29-2008 04:42 AM

R.C.

Re: pic: Madtown Robotics Drive Proto

Cory I was thinking about this, what if we used a 3/16 face on the first reduction. Then moved up to 3/8 face for the rest, shouldn't that be fine. We are not going to go with an aluminum gearbox yet. In the offseason we will be attempting and testing one out, but for the season it will be steel. I just pointed out that we could anodize if we needed to harden up the aluminum gears(if we used it). I have already checked out your aluminum gearboxes and Cory, if we wanted to make an aluminum gearbox, what steps do you recommend or what is your opinion about creating an aluminum gearbox. We have the time and resources to make one over winter break. But not during the season it we don't make a proto, thanks Cory.

11-29-2008 08:12 PM

AdamHeard

Re: pic: Madtown Robotics Drive Proto

They spent hundreds of hours. Hundreds. If you worked nonstop for a week, that's 168 hours.

You know what your best bet is if you want a nice, light, simple to make gearbox? Make custom sideplates for the AM supershifters, pocket them like you did, and use standoffs rather than the extrusion casing, like you did. It'll be real fast to make, and you *know* it will work and be very reliable. It may not technically be the lightest gearbox out there, but it will be done fast and done right. You could probably drop the 4.6 lb super shifter to at least 3.5, probably closer to 3 if you lighten the gears (but do not, do not reduce the face width unless you really know what you're doing). A 3-3.5 pound, 2-speed, bulletproof gearbox is still pretty light overall.

This is our exact plan on 973. We technically have the resources to make lighter gearboxes (from Steel gears, we won't dabble in aluminum without some serious effort and planning), but it's not worth the additional time and risk in our opinion.

11-29-2008 08:45 PM

R.C.

Re: pic: Madtown Robotics Drive Proto

I totally agree, but we will be facing down steel gears b/c

a. we have the resources
b. engineers are gonna help us with details
c. a great learning experience for the team

11-30-2008 10:48 PM

Re: pic: Madtown Robotics Drive Proto

Oooh, CAD! Shiny! If criticism is welcome, then I offer up the following. I ensure you that my intentions are not to denigrate your design, but instead to offer some criticism. PM me if anything here doesn't make sense, I'd love to explain it to you over PM, without the pressure of an open channel.

First off: Cheeseholing your drive frame. Why? The weight saving there is minimal, and the time it would take to machine those parts could be better spent doing something with more impact, such as more time in design to make sure your robot will reach maximum effectiveness during competition. Instead of spending time hobbing the structure of your robot away for those precious few pounds, I suggest spending the time doing some FEA on your chassis to make sure it can withstand the forces of the game, while still using the minimal materials possible. I'm sure you can chop the weight down without needing to spend an enormous amount of time machining key structural components.

Second: Gearbox mounting. It makes me nervous having only two bolts holding something that critical to an already weakened member. If you move the gearbox down, so more of the sideplate face is flush against the chassis member. This allows the bolts to take less of the load when the gearbox is under stress.

Third: Gearbox sideplates. Yes, milling out enormous pockets on the gearbox plates look cool. Yes, it provides bragging points to other teams. Is it necessary? Not if the design is done well enough. If your goal is to lose weight, look at designing your side plates around a different material. I highly recommend Delrin or UHMW. You will (most likely) save machining time as well as cost and weight.

Fourth: Gears. Aluminum gears, unless they're pre-fabricated, are not worth the work. Your team MIGHT save some weight by going with this option, but is the insane cost and manufacturing time worth the weight? Instead of going with exotic materials, it might be a better design decision to go with something strong and proven.

I might be designing a little to "conservatively," but I've yet to have a gearbox failure by working with these principles. As a great mentor taught my old team, the most important question is not what can we build with this, but Why are we building this with that?

I really like the design you have going for the chassis, assuming you make a few tweaks. You've got a cool and innovative "crumple point" in the form of those rounded bumper plates. You're also going to get a lot of strength out of the triangles you've created in the frame. However, you might gain even more if you design in a chassis member across the front of the frame, and tweak the superstructure to suit.

Good work on the CAD, it's a valuable skill. Never stop designing things!

11-30-2008 11:09 PM

R.C.

Re: pic: Madtown Robotics Drive Proto

Craig, Thanks a lot. That advice helped a lot. We did run FEA on the frame when I finished the design. I had more pocketed out way too much, including the top. The engineer told me that was way too much and it crumbled under the FEA tests. So that is why we have the bracing setup it like that and you can see that the top of the tubing is not pocketed out.

The gearbox won't be mounted like that, last year we mounted the gearbox with more support. I was hoping to add more support when I included the mast of the forklift or Arm. I had a question about the plates, if i use delrin. How thick should it be and do i leave everything solid except the holes for the bearings? (I will be moving the bolts down)

My purpose was to lose weight, I will redesign them after i get feedback on the thickness of those plates.

The gears will be prefabricated, http://www.chiefdelphi.com/forums/sh...threadid=70259. This sponsor would do it for us. But we are thinking that it would be better to use steel and use an index to make some holes.

Craig thanks for all the suggestions. I am going to be redesigning to your suggestions. If you have any more suggestions, please post it. The reason for shaving so much weight is. Every pound matters to our team, we always add stuff and every year and bearly make the weight limit. But that was because our stuff was way too solid.

11-30-2008 11:26 PM

Re: pic: Madtown Robotics Drive Proto

Cool. It's good to see that you've been doing the right calculations. Many teams skip over this and end up with some nicely bent frames that would look quite nice in a modern art museum, but won't function for robotics. My motto has always been that my bot should be able to be dropped wheels down off a roof, and still be able to drive itself into the shop to have the flimsy manipulator fixed from the damage. Driving is everything in FIRST.

Delrin is awesome. We used the 1/4" thick from McMaster (I don't have the part number on me, let me get back to you on that), and didn't have any problems with strength. The material is so light, cheeseholing the plates isn't even necessary. Just make sure you put washers on EVERY bolt and nut that goes into the stuff. It's also nice to machine, as CNC's cut the stuff like butter. If you think Aluminum is nice to cut, wait till you see delrin get cut. It has a tendency to load the smaller bits, but you can work around that.

Ah, I didn't make the connection between threads.. Well, if the gears are built for you, then go for it.

12-01-2008 12:42 AM

roboticWanderor

Re: pic: Madtown Robotics Drive Proto

Hey there!
Not sure what is gonna go on top of the robot and whether it will provide any extra support, but there does not seem to be much keeping the two halves of the drive train parallel. putting a triangular support on the upper back corners, or bridging the gap about halfway up the chassis would do a lot to keep the two halves stuck together.
If you did that, you could reduce the beefy super structure you have and save more weight than cheese-holes ever could.
Someone else already mentioned my other concerns, good luck!

PS: nice to see you back Craig!

12-01-2008 12:51 AM

R.C.

Re: pic: Madtown Robotics Drive Proto

Yeah those were going (bridging the gap) to be added as soon as the rest of the bot was decided upon. We will probably do three to four beams across and one across the top of it.

12-01-2008 03:44 AM

AdamHeard

Re: pic: Madtown Robotics Drive Proto

You may have the resources, but keep in mind there is a lot more to a robot than a base.

If you can make the base that performs the same for 40 units of weight, and 10 units of work as one that is 30 units of weight and 100 units of work, the first is probably a better option. It looks like with this design concept, you can get a competitively light and strong base in short amount of time, don't try to go to far and shoot yourself in the foot. Use that nice start to get a decent base done for sure, which will free up machining resources and allow assembly and test to begin sooner.