Team 47... Alchemists...

FIRST Robot Showcase
#1

I don’t have any real pictures of our robot, (look for that soon – hopefully no later than Monday March 1).

I will say this much now that the build is over: Our machine uses 8 Dewalt XRP transmissions. The engineers at Dewalt really know there stuff.

In my opinion, the XRP drill is head and shoulders the best cordless drill I have seen out there. There are a few very useful features of this drill trans.

  1. First of all, it has a 3 speed transmission (47 to 1, 16 to 1, and 12 to 1).
  2. The shifter is designed such that a servo can easily and reliably shift it with parts you can make using a band saw, drill press and pliers.
  3. The output shaft is 1/2 inch (easy to interface to) AND it is designed to take a side load – notice the handle on the picture – this baby is intended for a 300 pound construction worker to be able to “lean into it”
  4. Because it is designed for a clamp on handle, a simple standard aluminum clamp collar is all you need to hold this drill in place (1 11/16" ID available from McMaster.com)
  5. All metal gears and lots of them.
  6. Built in torque limiting feature – no worries about impact loading breaking your gears or you arm or whatever.
  7. Oh yeah, if you lift with one, you can leave the anti-backdrive pins in and viola! you don’t fall when power is removed.

All this and it cost less and is lighter than any similar transmission I have ever designed for FIRST.

It has all this and a lot of other great things going for it, the only problem is that the motors are not legal for FIRST.

But fear not… …we were able to interface the Chiaphua, Bosch, Fisher Price, Globe and Keyang motors to this transmission!

We will see how it turns out, but so far, we are very happy with the results.

Stop by our pits in Detroit, San Jose or Atlanta. We plan on having a display showing how we performed this alchemy.

Joe J.

#2

Sounds extremely interesting, how much do the transmissions cost?

#3

That is really cool. I’m assuming you ordered the transmissions all as replacement parts from DeWalt and used them that way. I’m hoping you didn’t buy 8 drills and take them apart! :ahh: Seems really neat, and if I remember, I’ll be stopping by your pit in Atlanta, since that is the only time Cyber Blue 234 will see you all. We even have one of those drills! :stuck_out_tongue:

#4

Yep, Jim (Zondag) has one and was showing us one of those gearboxes that he has before the season, those things are nice.

#5

#%&^#%@(^!!! Dang it, Joe! It sounds like you just made our entire transmission design obsolete in one shot! Now we have to start all over again! :slight_smile:

I can hardly wait to see this bad boy in action!

-dave

#6

The drill kit goes for about $180 with all the batteries, etc. I wish they would sell the drill alone, I think it would be cheaper than buying the parts I need.

The transmission is about $20, the bearing housing is about $30, the clamshell is about $15, the back of the housing is about $5 as I recall, the motor adaptor and misc. screws are about another $10, when you add in that you have to buy 1 transmission for every 4 gearboxes (to get the input pinions you need – luckily the planets from stage 2 work as suns from stage 1, if not, we’d need to buy a motor too for each gearbox adding another $30 or so). So far I have about $85 into the gearbox.

The only thing left is $20 to wire EDM the hole in the planets to a press fit on the motor in question (.125 dia for the FP, .155 dia for the Globe, 4.98mm dia for the Bosch, .160 square for the seat motor, .312 dia for the Chiaphua, don’t quote me, but these are appr. right). The reason that the hole has to be EDM’ed is that the planets are hard (really hard).

As to mounting, the aluminum clamp collar is about $17 (part #6436K151 from McMaster.com)

All you have left is to weld (or perhap bolt, though I’d recommend welding) the clamp collar to a bracket on your robot and you’re done.

Well, not quite, you also have to drill and tap a 1/2-20 hole in a sprocket (we used a standard #35 sprocket with 8 teeth – cheap $7), screw it on to the drill output shaft, make a small spacer, and put in your left hand screw to keep the sprocket from unscewing.

I figure the whole drive unit cost under $130 each. On a typical FIRST gearbox on a typical year, I would spend more than that just on the gears alone.

I think that this is going to be a huge success and that many many more teams will do this next year.

Look for a white paper after the season is over.

Joe J.

#7

One more thing, Ridgid Tool has a similar design in terms of the handle being a clamp on affair. They almost won my “Best Drill for use in a FIRST Robot” Award, but got edged out by 4 factors:

  1. The distance from the clamp surface to the output shaft was lower on the Dewalt – Torque = Force X Distance – lower distance, lower torque on my mounting brackets.
  2. Three speeds on the Dewalt vs. 2 on the Ridgid Tool drill (more options for ratios without having to bother with changing anything but a setting on a yellow housing).
  3. The method Dewalt uses for shifting is more reliable than the method that Ridgid (or Bosch for that matter) uses. They planetary rings move axially just like in all the other, but the shifter works by rotating a camming device that is just plain gorgeous in its simplicity and reliability. I don’t recommend it, but these babies can be shifted on the fly without the gearbox complaining at all hardly.
  4. Finally, the Dewalt Service Network is AWESOME – easy to order parts online, easy to get parts breakdowns, easy to find local dealers, etc. It is like they are designed to be FIRST friendly.

I am not an owner or stockholder of Dewalt, but I cannot say enough good things about them and this product.

I have already started pestering them to get to a FIRST competition (and to sponsor FIRST with drills next year ;-).

If anyone has any inside connections to Dewalt, give them a call and try to get them turned on to FIRST.

Joe J.

#8

Random 229er: “You’re obsolete”
Me: “Yes I am”

Joe… serious kudos are due.
I am seeing implications that will shake the entire FIRST design world.

I will DEFINITELY be interested in more details.

Poor Baker. :wink:

John

#9

You are a “Clever Sheep” indeed.

And the three-speed feature is a neat trick. Did you remove the shifting ability for use on the arm, or just securely lock out the shifter?

#10

Do these gearboxes require a full stop before shifting, or are they capable of shifting “on-the-fly”?

#11

The cam that shifts, does not let them shift without moving the shifter. All we have had to do is put them in the gear we want and SURPRISE! they stay there – make you wonder what all those other drill gearbox designer were thinking.

Joe J.

#12

Yes they can shift on the fly but they sometimes don’t sound like they are happy about it. We are only going to use shift on the fly sparingly (though we have yet to blow one, so what do I know?).

In fact, I have some relatively minor modifications in mind that I think will make them better at shifting on the fly but I am loath to try it unless and until I am convinced that it is a vital feature to have and that the system I have now will eventually quit shifting if we shift on the fly too often. At this point both issues are open questions.

Joe J.

#13

Thanks for sharing all of this, Joe. Definitely filing this away in the “things to remember for my team’s first year” file. I’m looking forward to your white paper.

#14

Hey Joe! As always you’re always thinking outside the FIRST Kit of Parts Box!

Anything to make this competition more economical and reliable will help FIRST spread new technology to more rookies to help everyone be more competitive.

Love to check it out!
See you in Atlanta!

Ellery

#15

…almost nothing actually.

Many of you stopped by the pits in Atlanta to look at our Dewalt drill transmission and our modifications that allow us to drive the drill transmission with either a Chiaphua motor, Bosch drill motor, Fisher Price motor, Globe motor, or Keyang motor.

I told many of you that I was worried half to death that this transmission would end up being not as robust as I had hoped and then I would have 8 times as many problems. But in actual fact, we had almost zero problems with this transmissions. With 3 competitions on our “real” robot and hours and hours on our practice robot, I can’t think of a single time we took a transmission off the robot because we had a problem with the motor or the transmission. I have never had as few problems with gearboxes and motors on a FIRST robot.

I am definitely going to be publishing a paper on these transmissions this summer. With some luck, we may even make contact with Dewalt in time to get some of these beauties in the kit next year.

They were awesome.

Joe J.

#16

Have you done any efficiency tests on them yet? I know the Bosch one was very low efficiency, i think less than 75% (its on one of the data sheets on www.usfirst.org). Of course i dont know how efficient a typical FIRST home made gearbox is, so its hard to compare. I just have to find some reason to build a shiny new gearbox… Howabout weight? tell me it weighs a ton. (yeah, i know, its gotta be pretty light…)

#17

Joe, did you have any problems controlling the drives with this unit? As a typical planetary gear system the backlash is typically what most software guys complain about. Was the controllability of the drives at a high enough resolution? Adding encoders to this unit wouldn’t seem to help it much becuase of that slop in the gear system.

Thanks Joe.

Ellery

#18

There is some backlash, but to be honest, it is not all that much. With #35 Chain, it was often on the order of magnitude of our chain slack (if we let it get loose, which we did from time to time).

But, yes, the additional backlash can cause some problems for control loops at times. It is not that bad though. We ended up either living with the oscillations or adding damping to the system. The only joint we took steps to do something about were are fingers – they are over powered and very lightly damped. We actually used some set screws on our finger axles, not to transfer torque (which everyone knows sucks) but to add drag to our pivots so that the extra damping removed the oscillations – not exactly elegant but it worked.

Joe J.

#19

Joe,
I saw the “magic” in Atlanta and was very impressed.
I’m just wondering how long until you have that whitepaper out?

I understand you’re busy (aren’t we all)… but I’m eager to learn more.

Thanks in Advance,
John

#20

Somethings got to give…

If I start to list the things I have going I will sound like a whiner so I will just leave it at that…

…I want to do it…

I think I will just have to get some pictures taken by one of our students. That should help me get the ball rolling.

Time will tell.

Joe J.