what motor did you use(arm)
 

Hello, im wondering what motor your teams used for the arm, the cim or the window motor.

Re: what motor did you use(arm)
 

648 used the fisher price motor. It turned an arm, which was connected to another rod fixed to the arm. When the motor turned, the first arm raised the second, raising the arm, pretty much a large cam system. The arm had a telescoping feature driven by the banebots motor. We used the four small CIMS to power the drive system, and the window motors to turn the wheels in our swerve drive.

Re: what motor did you use(arm)
 

1714 used the Keyang window motor through a bane bots 56mm 12:1 transmission (the one meant for the cim). The motor worked great, but the transmission gave us problems all season.
For the second joint on our arm, we used a Nippon Denso window motor. We mounter the motor on the opposite side of the arm as the gripper to be used as counterweight. We ran a chain down the arm and used a 4:1 ratio. This section of the arm worked great all season.

Re: what motor did you use(arm)
 

108 used a globe motor on a 1.75:1 rack and pinion assembly to control the telescoping part of the arm and the other globe motor on a 30:1 worm gear reduction to rotate the arm. Although it was pretty slow, it was controllable and reliable. In fact, the arm assembly never failed through 3 competitions, it just never worked great to begin with :p . Hope this helps.
-Evan

Re: what motor did you use(arm)
 

Which arm? our first telescoping 1 used a fischer price through 64:1 42mm banebots. the second 1 used a globe motor with 2 sprockets and the rebuild of the second one now uses the fischer price through a lead screw it works amazingly well

Re: what motor did you use(arm)
 

1726 used the small Banebots motor and a 125:1 Banebots gearbox. this drives an 8:1 chain reduction, and the arm is mostly supported by a gas spring. it worked all season, and is still working (they're playing with autonomous programming now).

AJ R--I'm not at all surprised that you're having trouble with the 56mm Banebots transmission...think about what you are doing to it, you are driving it with a gear reduction motor that can put out way more torque than the transmission is designed to handle.

Re: what motor did you use(arm)
 

Gael Force used two FP motors this year, one for the lift and one for the extension. Both powered a ball-screw through repackaged FP trannies. The extension simply slide back and forth on bearings while the lift worked through a sliding four bar linkage.

Re: what motor did you use(arm)
 

364 used the small banebots gearbox with the default motor (mabuchi?), and we used a globe motor for our extension.

Re: what motor did you use(arm)
 

we used an AM Planetary Cim gearbox at 181:1. The arm can lift the whole robot.

Re: what motor did you use(arm)
 

Our first stage was a CIM and a 12:1 BaneBots gearbox, reduced another 1:3 (as I recall) through chain to the actual arm. The second stage alternated between a Denso and Keyang motor, although we never quite nailed that.

Re: what motor did you use(arm)
 

We used two Fisher price motors to move our two jointed arm, and then used a globe motor to rotate it and a window motor to open and close the claw. The problem with using a globe motor for the rotation was that it had no backdriving on it so we eventually broke the gear that was on the arm and had to lock the arm rotation half way through Curie.

Re: what motor did you use(arm)
 

One FP Motor (without original FP transmission) on a 64:1 BB transmission driving a 40:1 worm gear assembly for both the base and the arm.

BB RS540 motor in the 64:1 BB transmission that came with the kit for the wrist.

Re: what motor did you use(arm)
 

The Fischer price had more than enough power to move the arm. At our test days, I accidently snagged the corner of a tote full of tools and wire with our tube funnels on the arm, and when i tried to free it up, it flipped the tote over like it wasn't there. After competition, I was dinking around with the robot, and the arm was strong enough to lift the front of our robot off of the ground without a problem. For our wrist, we used the globe motors on a PID loop with a slight reduction.

Re: what motor did you use(arm)
 

1885 Used a window motor connected to parachute chord with no xmission/reduction in the pulleys to power a simple elevator. We then used the Globe motor for the "shoulder" joint and the 2 tiny motors (the ones that smoke if they're run for more than 20 seconds at at time) for the claw movement.

Re: what motor did you use(arm)
 

S.P.A.M had a 2 link arm with a grabber, this year. We used an F.P. for each link and an N.D. window motor for the grabber. We burned up a grabber motor or two during build and competition season.

Eric

Re: what motor did you use(arm)
 

We made 2 arms this year:
our first one used:
globe - shoulder
globe - elbow
Nippon-Denso window - wrist

our second (better) arm used:
BaneBots 25:1 - Elevator
BaneBots 64:1 - Wrist
Nippon-Denso window - claw

Re: what motor did you use(arm)
 

If there is something to be learned here it is that any motor in the kit (even the globe) can be used to power the arm.

I like the philosophy of 330 on arms though; keep them simple, and then gear them down A LOT so that they have so much torque you never have to worry about it. A mentor of theirs, Chris Husmann, gave a great presentation last fall on arms that I would love to get a copy of.

When we had to redo our arm after a regional this year, we took that advice and used a small CIM paired with an AM planetary for each joint (the "team 60" arm).

Re: what motor did you use(arm)
 

Turret - Keyang with a sprocket attached, the chain wrapped around the turret base, which had about a 16" diameter.
Lift - Fisher Price using the plastic gearbox it comes with, modified for mounting and to accept a sprocket for the chain that drove the lift.
Shoulder - Globe geared down through a chain reduction, I can't remember the exact ratio, but it was something around 5:1.
Wrist - Another Globe with a chain reduction, this time more like 2:1.
Gripper - 3/4" pneumatic cylinder.

Overall the motor selections/reductions worked nicely, the wrist is a bit fast though.

Re: what motor did you use(arm)
 

I can't emphasize this enough. Over design the power transmission on the arm. If calculations show that you need 30 ft-lbs of torque to lift the arm and object at the end of the arm, then design a motor/transmission combination that can supply that while drawing < 10 Amps! (somewhat dependant on the motor choice)

If you need 30 ft-lbs, then stall torque should be at least 120-150!! Also this way, you can throw in some feedback and PID will have lots of headroom for tuning and working correctly.

In the 7 years of doing FIRST ... In my opinion the ratio of "under-designed arms" to "over-designed (or simply well-designed) arms" is at least 25 to 1.

Re: what motor did you use(arm)
 

We made the mistake of calculating the reduction required when the motor is being run with ~60 amps. These motors were only ran with 20 amps. So we ordered new Banebots transmissions and that set us back a whole week... (good thing we were doing pretty well schedule-wise until then :ahh: ).

Well, that's what happens when you make mistakes: you learn from them.

Re: what motor did you use(arm)
 

Exactly... definately a lesson learned there....

Another interesting tidbit I forgot to mention. Our original system w/ FPs wasn't geared low enough and was a pain to tune in PID because it was sooooo fast. The new system with the CIMs (not that the motors make a difference, there were other reasons for the change in motor type) was much slower and torqu-ier so we were able to tune a two jointed arm w/ straight P control in 15 minutes at a San Diego with even better accuracy the the original.

Re: what motor did you use(arm)
 

Power = force x distance / time

Think about the weight you are lifting. That's the force, The height you have to lift it to is the distance. Those are pretty straight forward.

What many teams forget is that it will take time to move from where you pick up an object to where you have to place it. Typically that time is 3-4 seconds. Give your arm operator something to do while the driver is moving from place to place. The joint of a single joint arm will typically move 90-120 degrees. Even if you want to pick up really fast, you can still design a joint that will take 9 seconds for a full rotation or 6.66 rpm. It will then take about 3 seconds to raise the arm to the correct height. The 05 and 07 BeachBot arms are running at more like 4 or 5 rpm and they are plenty fast enough. The arm almost always gets to "place" position before the rest of the robot.

Use a gear reduction such that your motor is running at 75% of free speed and your arm is moving at 4-6 rpm and you will get the most out of whichever motor you use.

The BeachBots have developed a very slick way of using the FP motors and a stock FP gearbox to power our arms. (actually I think we modified an idea we stole from Team 60) In 07 we started out using two FPs to power our arm as we did in 05. This set-up can and has lifted other robots silly enough to get entangled with our arm. But after a competition or two this year we decided we didn't need all that power in the arm as much as we needed the extra pound or two so we could have both ramps. So we removed one of the motors and its gearbox.

In 07, because the objects were so lightweight, virtually any motor in the kit could have driven an arm if it was properly geared.

As an example let's run the numbers:

We want to move a 0.5N object approximately 3 meters in 4 seconds. That will take 0.375 watts. The least powerful kit motor is the Mabuchi at 16W. The Mabuchi has a free speed of 4700 rpm. So you want it turning at 3500 rpm or 59 rps.

At this speed the output torque should be 25% of 61mNm or 0.015Nm. Assuming a 120 degree rotation for the final output, it should take 12 seconds for one revolution or 0.083 rps. Dividing the motor speed by the output speed, 59rps/0.083rps gives a reduction of 710:1. But that provides plenty of torque: 0.015Nm*710= 10.65Nm. If we assume a 2m arm, we only actually need 0.5N *2m = 1Nm.

That looks like a big reduction, but 20:1 is easily done using chain and sprockets and Banebots puts out a 56:1 gearbox that would work nicely. Using these together gets 1120:1 which should make the motor even happier.

There will be some losses in the drive train, but even with 50% loss there will be way more torque than needed. I puposely left out the power required to move the arm itself as that can be adjusted by using counter balances or springs.

So it really does not matter too much which motor you use as long as you use it correctly and keep all hardware within its operating limits.

Re: what motor did you use(arm)
 

We used a Fischer Price into a 64:1 Banebots 42mm planetary to a 30:1 reduction Rino Mechanical worm drive (that pretty little anodized box many of you asked about).

We stuck with our why make it from scratch when you can buy existing parts and adapt them to your purpose philosophy.

Pete

Re: what motor did you use(arm)
 

We used the Fisher Price with the Nothing But DeWalt concept. It was plenty strong for the job and we did not have to touch it all season long. Great motor for an arm with the right gear ratio.:)

Re: what motor did you use(arm)
 

We didn't use a window motor this year. We CAD'd up a plastic insert for the FP motor/transmission that accepted the triangular lead screw nut. It was quite a contraption once the entire mechanism was done using some iGus linear slides inside of a 4 inch PVC tube all connected to ansi 35 roller chain and and IFI mechanism sprocket on the arm.

Re: what motor did you use(arm)
 

Team 1902 used two banebot motors, one on each side, at 125:1 reduction and chain and sprocket. also to keep the motors from staling out we used a forty pound gas strut on our arm, it also helped stabilize it's movement.

Re: what motor did you use(arm)
 

2 cims (we could have use one but i did want it to back drive ) on a winch that powered and system of slides that pushed the arm up

Re: what motor did you use(arm)
 

2158 first used two Banebots with 256:1 gearboxes, which worked for several rotations of our arm over a two day period, but we quickly realized they weren't going to work when they began to smoke during a stall (they were stalled while the arm wasn't moving since they are backdrivable motors.

Then we switched to two keyang window motors for our arm since they were not backdrivable and they held up quite well for Lone Star and Atlanta, but shortly after during a demonstration, the gear inside one of the motors stripped out. It's been difficult finding a replacement because they're not commercially available, so next year we'll probably try and stay with motors that are replaceable.

Re: what motor did you use(arm)
 

When building our arm we first thought about using the Keyang motors. However, after a little testing we discovered that they are not as strong as their aluminum housings make them appear... The Keyangs contain little plastic gears, which are easily broken.

Our decision then became to build a worm-gearbox for the Big CIM and run our arm off of that. The gearbox would be made entirely from metal to limit the chance of anything breaking.

Our manipulator weighed a lot this year - roughly 10 lbs. But we didn't really need much arm power! We balanced the weight of the manipulator with a gas piston. If we had wanted to we could have used a tiny banebots planetary! But the big CIM gave us lots of extra power.

Re: what motor did you use(arm)
 

The 1st joint of our arm was powered by two 256:1 FPs, one on each side, plus a 5:1 sprocket reduction. Strong enough to lift the robot (and it tried quite a few times because of PID errors). The 2nd joint locked up, glitched, and was otherwise a pain to maintain. I think it ran off a BB at 64:1, but we also experimented with several sprocket configurations for additional torque so I don't remember what the final reduction was.

Re: what motor did you use(arm)
 

Team 233 used one large CIM through a custum gear box to rotate our arm, and another large CIM through a custum gear box to extend the arm

Re: what motor did you use(arm)
 

We used a CIM motor to drive te arm with the help of a andy-mark planetary gear system. we also used two globe motors on our end effector. We had to save our fisher-price motors for our lift.

Re: what motor did you use(arm)
 

Excellent points, Chris. I'm a physics teacher, so I get all geeked up when this stuff comes up. I see a mistake some teams make is under-estimating the amount of torque required to move not the game piece, but their robot's ARM! True any motor could be used to pick up the 1 lb tube, but what about that 1x1 box tubing and the grabber assembly at the end? 16 W Mabuchi motor?? Well, if the arm weighs a modest 10 lbs with its CM located 2 ft from the pivot = 20 ft-lbs (27 N-m)... That means that mabuchi would need to be geared down at least 1800:1 and moving 0.033 rps or 12 degrees/sec. Yikes or better yet, Yawn!!

I know Chris was simply making a point to look at the physics, specifically mechanical advantage of gearboxes. Hmmm... maybe we could re-write the Archimedes quote ... "if I had a big enough gearbox for my 16 W mabuchi, I could move the world". Another hmmm.. makes me think of an off-season project!!!

Re: what motor did you use(arm)
 

Then again you could also consider the arms moment of inertia because many of these arms have a large weight at the end of a long stick. So even if the motor can move the arm fast, it might take too long to get up the speed.

We didn't use an arm this year but we used one in 2005 and each joint was powered by a fischer price. I forget the reduction on the lower arm but the upper arm somehow got to 1157:1. Not by design, but hay it was a highly entertaining fluke.

Alex

Re: what motor did you use(arm)
 

Quixilver used the window motor for the shoulder joint and a globe motor on the elbow joint.

Re: what motor did you use(arm)
 

1741 used five motors on the arm assembly of our first robot. One keyang to move a shuttle up and down. Two fischer prices and one that ended up having to be changed multiple times (started as a keyang, then went to a globe on a custom worm drive gear box, and finally the banebots planetary on that same gear box). Finally we used one globe to adjust the pitch of our gripper via a screw drive. This system was extremely complicated and we chose to build an entire new robot for IRI. This new one used two banebots planetarys one on either end of a worm gear that moved the arm around a fixed gear on the shaft which was also fixed to our tower.

The moral of the story simple is almost always equal to better.

Re: what motor did you use(arm)
 

1024 Used both large CIMs for the manipulator... worked out well, 0->12ft on the elevator in 0.9 seconds.

-q

Re: what motor did you use(arm)
 

We used the large CIM motor with 3 to 1 belt drive to a 2 in pully to wench up 8020 slid on a slide. The claw we used was large enough to grab a tube from the outside. When the tube was in the claw it took no time for it to go to the top spur. We did not want to wait for it to crank up so we made sure it would get thier fast. For the claw we used pneumatics pulling steel cables to close the claw and springs to open. http://team1322.org/DESIGN1.jpg

Re: what motor did you use(arm)
 

We used a CIM motor straight into an AM Gearbox which drove the arm.

Re: what motor did you use(arm)
 

We raised and lowered our arm with the Keyang window motor. We attached the motor to the arm itself, so we could use it as a counterweight. Originally, we planned to use another window motor to telescope our arm, but we swapped that for pneumatics late in the build season.