The Soft-Launch of DeWut and the Motorama Robot Conflict 2013 Recap

So about that Motorama liveblog…

Anyways, now that the event is done and everything has settled into normalcy again, and with the completion of the best user manual / instruction guide I’ve ever made (I think so anyway…), I’d like to make the DeWut publicly available. Get yours today!

At Motorama, 8 of them were run in various fashions. The three in Überclocker, as well as five in a revamped version of Blitz. Five 3-pound motors in a 30 pound bot. That thing was made of motors. Moto was a great durability test of the gearboxes and outputs under various loading conditions. In Clocker, they were indirect driving wheels and gear-driving the fork. In Blitz, however, they were each direct driving a hard rubber wheel. One gearbox grenaded at the event when Blitz took a pneumatic flipper directly to a corner and bounced a few times. Clocker’s fork drive held up great, to my amazement, because there were points during the tournament when I was basically using the fork as a hammer.

DeWut is one of the two love babies I’ve been working on for the past few months (RageBridge being the other…) and it was great to see my parts actually being able to stand up to some use. Speaking of RB itself, I had no issues at all with my two boards on Clocker, but a few other folks were running the beta version and I recovered some of those when they succumbed to strange issues, to be diagnosed. Blitz also lost one production board to suspected thermal overload (from driving two DeWalt motors in parallel with the current limit maxed out) and another due to possibly a metal chip short from drilling the frame. Another bot’s suffered some kind of strange failure where the board itself looks totally fine, powers on fine, but never exits failsafe mode no matter what radio is connected! I’ll diagnose all of those and hopefully find that there’s nothing seriously wrong with my hardware.

Moving, on, here’s what went down at Motorama 2013.

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DeWuts are the Most Beautiful Things to have Ever Existed. Ever.

A few days ago, I received a package.

Okay, more like five packages. The shop made a concerted effort to ship my parts out before the Chinese (lunar) New Year vacation, and they at least managed to get out of the country in time!

And they are gorgeous.

This picture doesn’t do the quality of finish justice. They’re really, really, really shiny. There’s 4 total parts to a DeWut assembly: the output bearing block, the motor mount (in the back), the motor clamp, and the shaft.

Investigating the intersections of cutting paths and machined surfaces was quite enjoyable as I deduced in which order the features must have been machined. For instance, on the fancy flower end of the shaft, the valleys of the lobes have clearly been bead-blasted and are dull, while the rest of the shaft has a machined finish. Short of somehow forging and finish machining these (highly unlikely), I bet they milled the profile into an entire bar of ~1″ steel first, then machined that down to form the 1/2″ diameter shaft body.

With the Dewalt 3 speed gearbox, motor, and output bearings installed, it looks like a thing that exists!! Like, a real product.

Missing here still is the Nifty Barrel Shifter lock. I laser-cut them out of some 1/4″ Delrin, though I strongly believe 1/8″ is sufficient as they do not take any sturctural loads.

Okay, so that was sort of fail.

First, the raw plate came very warped from McMaster. Second, the action of cutting alone made it even more warped. As a result, I only got a handful of NBS locks from this plate since warping ruins the focus of the laser beam. For now, this is more than enough, but for production purposes, I will probably just hire these out to Big Blue Saw for convenience.

Check out this veritable forest of DeWut output assemblies.

Originally, the plan was to sell complete knockdown kits that have to be assembled by the user. Problem is, after pushing a few of the shafts through the bearings, I realized you really needed an arbor press of 2 or more tons capacity to do it correctly. I sized these shafts for a proper bearing fit – that is, you’re not sliding it in by hand, it’s actually a tight fit. I attempted using a deadblow hammer or just banging it on the table – two methods I’ve historically used to fit shafts into bearings prior to having a few different sizes of arbor press within one wireless router’ coverage – to no avail.

So asking any random builder to do so might be a little too much. The bearings into their housings, too, are troublesome for someone not press-equipped.

Therefore, I’m thinking the new plan is to sell a partial knockdown kit with the front end assembled, the motor mount and clamp (& other residual hardware) separate. Maybe offer an option that includes the transmission already, so you just need to pop in a motor of your choice (DeWalt makes this style motor in 12, 14.4, and 18 volts).

Enough about product, though. Here’s more pretty motor pictures.

These are the 3 motors that I’ve prepared with NBS locks and all which will go into Überclocker. Speaking of which, I really need to post about it. It’s practically finished, which given my recent robot practices, is kind of weird – Motorama ain’t even until Saturday. A week early? Come on now…


The Semi-Official Launch of RageBridge

After months of design, iteration, and testing (most of which has ended up on this very website), I’m proud to introduce RageBridge for general sale to the robot-inclined public.

Get yours today!

Now, this isn’t a launch announcement per se – I’m waiting for the DeWut CNC mounts to arrive, then a more official announcement will be done once those are ready. But, given that some events like Motorama are coming up, I figured this pre-grand-opening-grand-opening will be helpful.

Here’s roughly what the DeWuts will look like in component form; this preview was sent to me by the CNC ship a few weeks ago when the order was not yet complete.

And thusly, Big Chuck’s Robot Warehouse begins humbly. 2013 is shaping up to be a great year so far…

The latest on the DeWut? project

It’s been a little while since I went “Make it your damn self!” on the DeWuts and left everyone hanging with the waterjettable pieces. Since then, the billet style design has evolved some. I’m proud to announce that it has been sent off for manufacturing by Sketchy-Ass Chinese CNC Co. Ltd., to return to me hopefully by mid January. This is a product which is in immediate need by robotland  ever since the old style 18v DeWalt “Team Delta” systems stopped manufacture, so, oddly enough, it might be my “launch product” instead of Ragebridge! Here’s what’s been going down.

This is the fully modeled design as of two weeks ago or so. As can be seen, I’ve actually bothered to model the DeWalt 3-speed gearbox! I’ve made the gearbox and motor available as a downloadable widget, if you want come up with your own design. The files are in Autodesk Inventor 2012 format, as well as a STEP and Parasolid.

While I tried to make a workable output shaft for the motor, I began to realize that it was perhaps more fruitful to replace the final output stage altogether. The 3 speed DeWalts have an advantage here because their antibackdrive (“that thing which makes it so you can’t crank on a drill’s chuck and have the motor turn”) system is very simple and planar. The idea would be to replace that ABD stage with a custom-machined ‘socket’ of sorts that wraps around the output carrier and has an integrated 1/2″ keyed bore, so in principle any 1/2″ keyed shaft can be used with the motor. If this is not clear from the above picture, then it will surely be elucidated by…

So, basically, the output stage planetary carrier has 5 little claw things. It’s easy enough to make a doohickey that wraps around those 5 claws. Normally, roll pins fit between those claws which are just barely smaller than the distance between one face of the weird decagon output coupler and the outer ring with 4 nubs on it (seen in the previous image). If you attempt to backdrive the drill, the decagon hub turn just enough to wedge the roll pins against the outer ring, locking the whole thing up solid.

This whole arrangement of course contributes much backlash to the system. While I could just say “take these 5 little derpy pins out”, that’s one more step in the instructions which, if not followed, would surely result in undesired behavior as the ABD rapidly alternates between locked and unlocked. A custom output coupler would also alleviate those concerns.

This is what the output coupler looks like, a 5-sided flower thing. In real life, this would be waterjet-cut from a high alloy steel like 4140 and moderately hardened. The shafting is a piece of stock McMaster 1045 steel shaft I bought to test fits.

The new output carrier pushes right against the inside of the inner ball bearing due to a chance alignment of English and Metric units. So, it truly is bring-your-own-shaft – the motor doesn’t provide any retainment force.

With this problem taken care of, I began addressing some fine details. With larger, heavier motors like this, face mounting screw holes are often not enough to keep the whole assembly planted under shock loads. A second set of mounting holes is provided at the rear to keep the heavy motor end anchored. These holes are designed to be 3″ apart and 1.375″ between centers. Why the weird dimensions? Because it’s compatible with a Banebots P80, just like the front mounting hole pattern.

This revision of the design also saw these little gearbox-retaining nubs on the inside, which help with setting the torque clutch tightness without having the motor installed yet. It allows more modularity in the assembly since previously the motor was the only thing pushing back against the torque clutch plunger (pressing on the spring steel wear washer immediately next to the gears, anyway).

The next logical step in the design was to combine the 5-sided flower thing with a shaft. This would fully constrain the output shaft, allowing direct coupling to a wheel.

Here’s what the whole thing looks like in mushy 3d printed plastic form:

This is the version I’m sending out to be manufactured. The integrated shaft is specified to be made from 1566 steel as-rolled 1″ (/25mm…) round, which should offer a yield strength in the mid 50s to 60ksi (400-ish MPa in Unamerican Units). So, the total setup if I were to kit this up would be:

  • Integrated output shaft
  • Output mount with 2 FR8 type ball bearings
  • Motor mount
  • Motor clamp
  • The nifty barrel shifter holder
  • 4 hex nuts to constrain the NBS holder
  • 4 long cap screws to hold the output and motor mounts together
  • 2 short cap screws to screw down the motor clamp
  • 1 set screw to adjust the torque clutch
  • A retaining ring, because retaining ring.

I’m wondering if I should make a version that has the “socket” output carrier such that the motor can hitch into any existing 1/2″ keyed shaft. The 5-sided flower thing will likely be available separately. I’m also going to pre-emptively make it available in downloadable form for your own waterjetting amusement (Inventor, ready-to-cut-DXF, STEP, and Parasolid). I strongly advise making it out of a high carbon or alloy steel for strength reasons.

For now, enough product development. I need to turn my attention to more pressing matters…

The DeWut Motor: Next Steps, and Design Files for Making Your Own DeWalt 3-Speed Motor Mount

Alright, with the Long Weekend of Nobody Being Open coming to a close, I’ve pretty much finished the ‘version 1’ of this project and am moving onto another fork of it. As discussed previously, the DeWut is an effort to make the new generation DeWalt 3-speed hammerdrill gearbox actually useful. The ‘old generation’, according to my sources, has totally stopped production, and are getting harder to purchase spares for. DeWalt has been the foundation of so many robots I’m surprised they don’t straight up sponsor events.

The short story is that I am skipping over a waterjet-plate stacking version (… what? Are you out of your mind?!) directly to investigating an all-billet, CNC machined version. That seems a very not-me thing to do, and actually I’m going to build a few of the aforementioned waterjet-compatible mounts for my own amusement, but as a potential product, I am in the process of gathering quotes and potential suppliers.

The long story…

After completing the body of the first version gearbox, I went ahead and carved the future shaft out of some 1566 precision-ground steel stock. Luckily for me, the new generation DeWalt gearbox has a rather normal double-D shaped output adapter, so it was a short mill pass to turn the round shaft into the proper mating shape. Unlike the old style gearbox, which had a…. what the hell is that? Apparently a massive stress riser. This would be only a manufacturability test, because untreated steel is going to be far too weak to handle the torque output of the motor. Based on a few FEA torque simulations, to hold the torque of the motor at stall in low gear at 100 amps, the double-D area is going to see about 180ksi of shear stress.

Ouch. That’s some serious steel – comparatively few alloys can heat treat to the 200ksi+ range and not be brittle as glass, and we all know how my last adventure with “heat treating” went. This is a subject I’m not so familiar with and so will probably have to leave to the professionals when I make these into production parts. For my own amusement, though, I’m probably going to buy a sampler plate of steel rods, make the axles, and try heat treating the ends to various degrees.

I also came up with a new arrangement for the motor’s rear retaining plate. Previously, it only held onto that little nub that the motor’s tailshaft sticks into, and was fairly unstable. A more stable method is enveloping the ‘nub’ and pressing entirely against the motor’s endcap. Unfortunately, the brush holders have conductive crimps that end flush with the endcap surface, but can still short on metal. Hence, a ‘gasket’ of sorts is necessary, shaped to the endcap’s outline, and I’ve modeled that as the little yellow-beige-brown thing to be made out of a thin insulating material.

Additionally, the structure of the Nifty Barrel Shifter retainer has changed. It’s now removable from the side and the idea is to hold onto it with a nut from either side. The bolt slotting narrow a little before opening up to the proper center, so it ‘snaps’ into place and is less likely to fall off. This arrangement makes it easier to change gearing (if needed) but also allows the whole thing to be assembled before picking the gear ratio, since it does not have to be stuffed onto the gearbox while it is being lowered into position.

But the most important addition conducive towards kitting this assembly up is the alignment marks on the side. Starting with 1 little indent slot on the side, just line the plates up in incrementing slot count order. I figure the X shaped motor back end is obvious enough on its own. There’s 9 in the structure, then the gasket, then the motor retainer, for 11 total.

This is what the retaining plate looks like now. Of course, one option to bypass the need of a sketchy nonconductive shim which COULD conceivably become conductive by accident, is to make the thing out of a nonconductive material. Garolite (G10/FR-4 grade) was my prime candidate, but electrical grade fiberglass ought to work too. Anything in 1/4″ short of nonfiberous squishy plastics ought to be stiff enough to hold the motor in place.

Moving the retainer plate onto the motor endcap means the whole assembly becomes basically 6″ long minus the shaft length. A nice, even number to work with!

For the purposes of easy cutting, I arranged these plates into separate 1/4″ and 1/8″ assembly files with little “sprues” in between the plates. This ensures that they stay together and cut as one part, and can be extracted whole.  It’s a little more dangerous than individual parts, but machine time is billable by the second and precious seconds are spent cycling the nozzle, so continuous cutting is marginally cheaper too. For small parts, the sprues prevent them from falling into the tank.

However, I think that’s as far as I’m going to go with this design. Here’s why:

Huh. Well then.

That’s just for the 1/4″ parts! Note that I tiled 4 of the assemblies together, so the real cost is about $38 per set. Add to that the 1/8″ plates (another $20 per set) and the heat treated, custom machined steel shaft (estimating $30+ each), plus all the hardware and the laser-cut gasket. I’m basically looking at a hair under $100 just in cost. And only in quantities 10 and up, assuming I have like $8000 to drop on this right now.

As funny as modern digital manufacturing is, and as great as it is if I really just needed 1 of something, I think I can get a much better price by falling back to good ol’ subtractive machining. Hey, as it turns out, waterjetting in real life is expensive.

So, as previously mentioned, even though I could pop out a few for my own use, I won’t be able to introduce these as a viable product (in my opinion – feel free to differ). So what’s next?

DeWut? Design Files

I’m going to make everyone else do it. Contained in the above ZIP file is the two tiled parts to be cut (0.25″ and .125″ aluminum) and a 2D drawing of the gasket to be made from something nonconductive, in DXF version 2000. Also included are the original Autodesk Inventor 2012 3d models of the assembly and an exported version in X_T (Parasolid) which can be imported back into individual solids.

The assembly should only fit together one way, basically described in the first post.

There are a few #4-40 holes to tap in order to make blocks from the plates at first.

The mounting holes up front are properly sized to be threaded 1/4″-20, no more than 3/8″ deep.

The shaft solution, however, is left as an exercise to the reader (the shaft model is included).

The model as-cut should fit the new-style DeWalt transmissions (397892 series), possibly with a little stuffing.

There’s no warranty expressed or implied.

Next Stage

Based on my experiences sourcing the hub motor parts for Chibikart, I believe I can get billet mounts for the gearboxes contracted out through a Sketchy Chinese Dude With a CNC Machine for substantially less price. Leaving the thickness quantum domain also means I can make the gearbox mounts better fitting and have multiple threaded mounting holes, etc.

I basically began translating features found in the stacked plates into a single, solid model. There were optimizations for weight reduction made, as well as thicknesses and details changed to fit the manufacturing technology.

This is the end result. Now, it’s not totally free of potential laserjetted parts, because I’m keeping the Nifty Barrel Shifter holder. It will still rest on the tie rods that hold the thing together.

Check out that new motor mount. It’s a 2-piece clamp affair out of necessity because the DeWalt motors don’t face mount to the transmissions, they stick into them a good 1/4″ or so. Hence, the idea is to tighten together the gearbox and shaft portion, then stuff the motor in, then tighten the mounting collar. With a 1/2″ of support on the collar and additionally 3/8″ of support in the aluminum block, I think the motor’s not going to go anywhere short of having the output shaft shoved through it (by which time, terrible things have happened). This obviates the need for a rear retainer.

Overall, I’m looking at 3 aluminum machined parts, 1 heat treated steel part, and a derpy laser-cut thing. Because the NBS holder is not structural, I’m content with making it from Delrin or ABS plastic.

Incidentally, the mounting holes match a Banebots P80, at least on the front. This whole thing is basically a lighter P80 type motor with 3 speeds!

Of course, I’m not leaving the world of 3DRP forever. I wasn’t going to send anything out without a sanity check for the critical mounting dimensions. I turned, appropriately, to a Dimension 1200ES to produce these mostly hollow plastic shell representations of the gearbox. The Dimension printer is much better at making parts ….. on dimension…. than the Makerbot Flock.

Since it cost 3 times more than the aforementioned Makerbot Flock combined, I would expect nothing less…

And hey, everything fits! I verified that the little slots and cutouts to cater to the DeWalt housing were within reason – if they fit in slightly shrinky plastic, then they will be a little looser in aluminum unless Sketchy Chinese Dude with a CNC Machine is really that sketchy. The overall length has remained essentially the same – this was basically a direct plate translation, after all. The Nifty Barrel Shifter holder is not seen in this picture, nor are the #10 cap screws that will keep the two halves firmly locked together.

The next step from here is to pitch all of these parts to my favorite SCDwCNCM as well as (my new favorite snack) to compare prices vs. features. At this point in the year, I’m going to consider getting prototypes in before the holiday breaks a total not-happening, so expect some more news on these DeWuts in January.

By the way, this is what is inside an allegedly “empty” Stratasys Dimension ABS build cartridge.

…seriously? That’s like 50 feet. I only feel slightly ripped off.

Luckily, this filament is 1.75mm diameter just like the latest generation Makerbot Flock feed, so I’ve been making heart gears using the Replicator. Productivity!