err, close…both speed and torque can be adjusted through gear ratios, but the output power of the motors stays constant.

with that being said, the winner of your hypothetical pushing match would depend on the gearing of both robots. but assuming that you geared each bot in such a way that they had identical coef. of friction, speed, and efficiency (in short, torque would be the only diff.) the bot powered by drills would come out on top since it is more powerful.

Hang on a second–speed and torque can be adjusted by gears; it’s (mechanical) power that is constant. Once again, rotational speed × torque = power. Since power is constant, speed and torque are varied by the gear ratios.

Also, that little shaft on the drill has a steel pinion (i.e. small gear) pressed onto it. Some teams have managed to get it off, and replaced it with something more suitable to their needs, others elected to use the pinion as supplied. In any case, provided you’re comfortable with assembling gears, the drills are only marginally harder to work with than the CIMs. (Finding a matching 0.7 module, 20° pressure angle gear is, however, quite annoying–try PIC Design, and order very early!)

(Or are you referring to the threaded shaft on the gearbox? That’s another issue entirely.)

As for the CIMs never breaking, that’s a little extravagant, I think! (We had a slightly defective one in the kit this year–it was replaced with a good one.) But you’re absolutely right that they can stand much more abuse than the drills.

I’ve noticed that you seem to be thinking of the drills as the entire drill motor + transmission assembly. We’ve (or at the very least, I’ve) largely been thinking of the motor alone. If you don’t feel like separating them, remember that they have high and low gears by default and therefore their torque and speed will differ in each gear. (In other words, you need to specify either high or low gear, or no gearbox, if you want to describe speed and torque for the drill motors.)

As for the actual question, I have to modify the wording a little:
Q. If the robots were identical, and they were geared to run at the same final drive speed when identically loaded, etc.
A. Theoretically, the drill-powered robot would win, since it is capable of outputting more torque (i.e. more power for a given speed). But that’s not the whole story! Many drivetrains are traction-limited, so that the robot will actually spin its wheels at maximum torque, rather than doing any further useful work. If that’s the case, and both robots are otherwise identical, it could well be that both robots spin their wheels and don’t do anything productive. At this point, it comes down to which robot can sustain this condition the longest–and here’s where it gets interesting. You’d need to look at the graphs and examine the electrical system (including efficiency), and determine which robot will run out of (electrical) power first. (I would tend to favour the drill, even under these circumstances, but that’s an educated guess, since I haven’t done this analysis of which I speak.)

9 ft/s is an average-to-high speed, depending on the year and the game. Without running the calculations through, I would tend to say that this sort of configuration would produce low-to-average torque–which isn’t quite what you had in mind.

Edit: Beaten to it, not once, but twice–but they’re saying the same sort of thing!

From my understanding, this has nothing to do with the gearbox itself, it has to do with the internal motor windings. The gearbox functions the same backwards as forwards, so there shouldn’t be any gearing differences that would cause the difference in speeds.

Hmm… I thought it had to do with the position of the brushes. The way you place the brushes of the motor affects the timing of it. Placing them in differnt positions will affect the speed of the motor and the torque output but power will remain constant. Im 100% sure this has been discussed before.

Simple Gearbox for one chip

Simple Gearbox for two chips


better picture

We did not have a drive train problem all year except for breaking 2 belts.

I see a bit of a problem here (regarding pictures 2 through 4), and I believe that this came up earlier (in this thread). You’ll notice that the CIMs those pictures have (instead of an 8 mm keyed shaft) a sort of small gear built into the shaft (if memory serves, it’s a 25° pressure angle piece–very non-standard). This version of the motor (the Atwood AP801-001 motor by CIM) was supplied in 2002 only. It was specifically legal in 2003, but not supplied in the kit (the FIRST version of the CIM motor, FR801-001 was introduced that year). For 2004, the FIRST-CIM was supplied, and the Atwood-CIM is no longer legal, per <R09> and <R70>. Electrically, they are very similar (but not quite identical, if the specs are to be believed–I’m looking at copies of both), but mechanically, they are different, due to the shaft configuration.

Now, there are pictures of a what appear to be a different version of the gearbox on their website–here, here, and here–was this modified version intended to use the correct CIMs? Or is this something else entirely? Edit: Looking at other photos, those are something else entirely–they’re for the winch.]

Also, note that per <R62>, to make the gearboxes kosher, they could have modified the output shafts on the FR801-001s to have the same profile as those on the old Atwood (this couldn’t have been easy), but they couldn’t replace it part-for-part (certain modifications are allowed, part substitutions are not).

(Note that they said that the problem of legality had been rectified by modifying the shafts, so I can’t accuse them of impropriety–just of posting outdated photographs…)

And yes, this is slightly off-topic, and moot, given that the season is over, but it is of potential relevance to anyone hoping to build one of these systems in the future.

yes its legal. we did nothing wrong. the good picture was taken with other ones while the new ones where being cut. we did nothing wrong. That gearbox is what we used this year and what we will be using in the offseason comp.

Please note that you’re not being accused of wrongdoing–like I said, I’m taking you at your word that you replaced the outdated Atwood Mobile AP801-001 motors shown in those photos with FIRST-legal FR801-001 motors, and made whatever necessary and legal modifications that were required to make it work.

(No need to further derail the topic–for any teams wishing to adapt CIMs to drive systems, the existence of old motors is an issue. I thought you should know.)

First off, good post. We haven’t had one of these in a while. Next, Matt Adams I have one small correction to your motor power calcs for the drill with and without gearboxes. The available mechanical power when you have a gearbox must be lower than the motor by itself due to the efficiency losses. I know you know this because you accounted for them (the reason the drill/drill high/drill low all have different power numbers at the 40 amp limit), but you show that the drill in low has more power than the drill in high and the drill by itself … no way is that possible. I think you may have transposed the data, but the drill by itself has to have more available mechanical power than with a gearbox … Efficiency losses.

Next, shifting and multiple motors (per side) are not a must. However, I think you must use one or the other. If you don’t want multiple motor drives, then shift. If you don’t want to shift, then use multiple motor drives. We shifted and had multiple motors in 2003, but we only used multiple motors in 2004 and we had no noticeable difference in time to the center of the field and pushing performance. With that said, 2002 was a different story. In 2002, the really competitive teams had to shift gears and use multiple motors (and yes, I consider switching drive trains the same as switching gears). My rule of thumb is that switching gears coupled with multiple motors is not necessary when transferring weight to your robot is not possible. When a significant amount of weight can be transferred to your robot, then I recommend doing both. Use multiple motors if your overall design allows for it, because it will help your drive train.


Someone mentioned earlier that the Chips do not run the same speed forward as they do backward. This can be changed. Losen the bolts that hold the motor together (don’t take them out, just losen them one or 2 turns) and hold the motor by the black part in one hand. Have another team member connect the motor to a battery. You will notice that if you turn the back peice of the motor in relation to the black body, the speed will change. With a tach, you can adjust the motors so that they run the same speed in forward and in reverse. This is nice because then you don’t have to worry about which way the motors point. Doing this with the drill motors is MUCH more difficult, and i wouldn’t reccomend it.


I completely agree. I would like to explain how I came about the number for the horsepower.

I found in a post somewhere, that the ratio for low out of the planetary gearset was a ratio of 42.62 : 1.

My calcuation was as follows:

The stall torque of just the drill motor is 7.70 in-lbs, with a free speed of 19,670 RPM.

The expected speed with the gearbox with that gear ratio is 461.52 RPM. Hence, an efficiency of about 97.5%. This is honestly not realistic. However, I kept it uniform and assumed that this same loss would occur in the torque. So, to find the stall torque at 40 amps, I divided the stall torque of the motor times the ratio of the estimated free speed in low (450 RPM) to the ratio of the free speed of just the motor (19,670), then I multiplied that times the ratio of 40 amps / stall current (127 amps) and finally multiplied that by the efficiency of 97.5%.

The mistake of course, isn’t TOO obvious, but here it is: the ratio is fixed and known, and I should have multiplied the stall torque by the true gear ratio, not the after-efficiency loss speed ratio. This would lower the overall output to somewhere around .493 HP in low, and .452 HP in high. This again, is not possible, but the benchmark for the actual motor without the gear box is based on one set of experimental data, the data I used in high gear is from another data set, and the low gear is purely theoretical.

However, I’ll still say that I found these three pieces of data (though from independent sources) to be the most reliable pieces of information available to the general FIRST community at this time on this motor.

I hope this clears up some confusion.


thanks everyone

after reading all ur responses i realized that chips running at 9ft/sec will be destroyed in the matches.(fast but no torque) Even though I want to stay away from drill gearboxes ive decided to give them another chance. Here’s what im thinking. drill in high and chip connected to a output shaft inbetween them, a 3.5:1 ratio between the drill and chip but the gear on the output will be larger(haven’t determined the size yet) Also i was thinking about chain and sprockets and then my dad suggested belts, what do u think, anyone ever used belts in a gearbox?

it will look kinda like this ( o0o )
if that makes sense, drill and chip on outside,output in middle . so what if its crude picture. :cool:

If anyone wants to see the inside of the Chia there are a couple pics here

For a simple drill-chia drivetrain I would recommend something like this
another pic

It uses the drill in high gear

If you are using large wheels, or don’t have room for a large final reduction and would like to run the drills in low with the Chias (or just the Chias by themselves), I would recommend the team 716 2003 single speed gearbox (found in the whitepapers) Team 980 and 696 used it this year with great success. It is a little more complicated to build than the pics I linked to above but it is very reliable, small, efficient and lighter. It has a nice slow output speed of 460 rpm.

Attatched is a pic of ours.



since chips come to a rolling stop, they make a robot much harder to drive than a drill motor robot

I agree with most of what has been said in this thread, but there is one major difference between the Chips and drills that I have not seen mentioned thus far.

The Drills are air cooled motors, cooled by a fan in the back of the motor near the brushes. Since it is air cooled, it will continue to give full power when it heats up, and after it stalls, untill it burns up.

The Chips, on the other hand, are not air cooled. They have a variable resistor (a brass colored plate) in the motor so that as the motor heats up, the resistance increases in the plate, giving the motor less current so that it wont burn itself up. Basicly, as motor heats up, its power output decreases. While this helps greatly with durability of the motor, it hurts in an application such as what we are using them for. If you get in a pushing match and you stall your motors for a 2nd or two, the Chips will heat up, and put out less power for the rest of the match. Do this a a couple times, and you will definately notice the power loss. On our 2003 robot, we had 4 motor drive, with the chips powering the rear wheels and the drills in the front. Due to our weight distribution, our rear wheels had the most traction, so the Chips were mostly responsible for turning. Many times when we got to the end of a match, the robot would have difficulty turining because the chips got hot and therefore their power output was cut accordingly.

Just another thing to think about. Oh yeah…did I mention that those suckers are HEAVY.

[font=&quot]Any motor will do that if you set the speed controller to Coast mode and have a high efficiency gearbox with it. Typically when a team uses the Bosch with its stock gearbox, the drive has lower efficiency than the Atwood does when you make a simple 2 reduction gearbox for it. The lower efficiency causes energy and momentum to be lost faster, which you probably had with your Bosch experiences. Either motor can be incorporated into a high efficiency gearbox and give you plenty of rolling after the power is cut off.

[edit] In further reading of your post, it appears you like the quick stopping feature of the Bosch as opposed to the higher efficiency of the Atwood. High efficiency is always good in your drive. You can create the same stopping effect with the Atwoods by switching the speed controller into Brake mode. [/edit]

Ok lets recap this alittle.
Drills give more power for a longer period of time under stress BUT will burnout
variable speed with gearbox…high rpm without
CIMs dont burn out very easily…or in some cases at all…are more power efficient and are high RPM.

So I guess this means you have to make deicisions. Do you want to risk possibly burning out your drill motors? Or would you rather risk losing some power with the atwoods?

For my team we would rather risk losing some power from the atwoods…

OOO…let me share something with everyone. Last year at river rage we slapped together a new robot to test our new tranny. at one point we lost one cim due to wiring errors and burnt out the last of our drills cept for one(it was a two motor drive) Coincidently the two motors were on oppisite sides of the robot. It drive great with the two motors opposite of each other…had great power and drove the straightest it had all day.

-Thought I’d share…