CHIPS
 

Ive been thinking about doing a chip only drive system. It appears that the chip has more speed than the drill(5500 to 1000ish) Wouldn't it make more sense to use the chip over the drill. Chips have more torque too I believe. Why do many teams use only drills when chips are more powerful (besides mounting and placing a gear on it.) In terms of power shouldn't u use just chips over drills. thanks :cool:

P.S. I know both is better than just one

BAM!

Re: CHIPS
 

Well I belive the ships stall before the drills do. So there for i belive the drills have more power. For example. We run drills on one side chips on the other side. We only rip our belts(breco flex timing belts) on the drill side. That makes me belive that the drills are stronger then the chips or that the drills have a higher stall current.

Re: CHIPS
 

I think a lot of teams have used the chips for drive. Part of the problems for some is that they are high rpm while the drills come with the transmission to gear them down. They are geared down to like 1000 and 500 (not exact) from 19000 rpm (again not exact). For teams that don't have the resources to build the chips into their drive the drills are a very nice option. I also thought the drills had more stall torque. It all depends on what you want to do but both work well. I think for many teams the drills are just easier to deal with because it is the easiest to put into a drive straight out of the kit.

Re: CHIPS
 

My assumption all along has been that the chips have more power, but that could be wrong. The reason I think a lot of teams don't use them is the need to build a gearbox for them. Until this year, our team didn't use chips because of that same reason. The drill motors have a simple and reliable gearbox, so if no-one is going to really care/work on the drivetrain, those are the best choice. You could put one of those together in 20 minutes right out of the kit.

Re: CHIPS
 

I have to assume that you are referring to the drills with their stock gearboxes. both the drill and the CIM output close to the same power. with its gearbox on, the drill loses some of its power to friction in the gearbox, and is therefore (i believe) slghtly less powerful than the CIM. without its gearbox, it has slightly more power than a CIM. likewise as you said, coming out of the gearbox, the drills have a slower speed, but more torque than a stock CIM. once again if you take the gearboxes off, these numbers are reversed. the CIM is more powerful, yet slower.

the main reason people use drills with their gearboxes is because its alot easier. you don't need much of a reduction coming out of them, and they have two speeds built right in. in addition, they're pretty light.

Re: CHIPS
 

There seem to be a lot of half-truths floating around here....
While the CIM has up to 346.9 oz-in of torque (2.450 N m), the Bosch has 0.870 N m of torque, and the Johnson F-P has 0.6375 N m of torque, all of these numbers are measured at different rotational speeds. To get a comparable measure of which motor is strongest, you should compare the (mechanical) power of the motors, which equals speed × torque.
At 12 V, the CIM has up to 343 W (0.46 HP) of power, the Bosch has up to 448 W (0.60 HP) of power, and the Johnson F-P has up to 262 W (0.35 HP) of power. Therefore, the Bosch drills are the most powerful, followed by the CIMs, then the F-Ps. (I say "up to", because the maximum power of an electric motor occurs at a single point, in the middle of the power vs. torque curve. Everywhere else, it makes less power.)
Note that these numbers assume that the drill gearbox is not being used.
While the only way to really examine this in detail is to look at the graphs, this should be enough to base your assumptions on.
And if you're wondering, 188 used all of the above motors to drive its robot (all at once, of course).

2004 Motor Statistics in US Units
 

To post something very brief... I'm going to get on a bit of a soap box.

Not having information is better than wrong information. I've seen a few people in this post (and other posts recently as well) post things they "believe" to be true.. or that they're "pretty sure about" or this is "close enough to right."

I'm going to correct a bunch of mistakes written here in hopes that we can continue with something worthwhile... I'm just going to tell it how it is, don't be offended.

Here's the stats, all converted to English units, by me a while back.
(1) - 12 Volts motor curve. Stall specs taken at 40.4 Amps, and assumed linear relationship to approximate at 40 Amps
(2) - Free speed from Gearbox performance, at 11.98 volts. Stall torque estimated at same efficiency as free speed
(3) - Free speed from 2003 manual page 5 reference, stall torque estimated using speed ratio efficiency. No solid available data, hence cause of higher power in Low than possible. Accurate free speed data would help immensely.
(4) - 2004 Motor data from CCL Industrial Motor Limited sheet
(5) - All data taken from 2004 Johnson Electric Manufacturing Specs
(6) - All data taken from 2003 competition specs, adjusted to 12 volts from 10 volts, assuming linear relationship
(7) - All data taken from 2003 competition specs.

Okay, so there are the specs... now to correct/comment on some people's comments.

Stall current isn't related to power.... the max power in an ideal DC motor like the one's we're using is at half the stall (max) torque (and hence half the free speed). Power output = torque x angular velocity. This varies depending on the load to the motor. You often want to design such that you're gearing to get the most power out of your motors.

Something you need to consider is that the max power output of these motors is well beyond the Amp circuit breaker limit. I have already done the calculation at the breaker limit above so that you don't make the mistake trying to design around something that will trip breakers.

Good luck everyone!

Matt

Re: 2004 Motor Statistics in US Units
 

First off, thank you for the concrete data.

Now to pull the thread somewhat off topic.

Taking into account that the breakers have a fair amount of tolernece, in that they can tolerate varing amounts of current for varing amounts of time before opening, perhaps it would be possible to gear a motor for a higher power output then might otherwise be possible if you stuck to a strict amprage budget.

In otherwords, if you knew that the 40 amp breaker takes 30 seconds to trip when passing 60 amps, and the motors duty cycle was perhaps only 20 seconds why not gear the motor to produce peak power at 60 amps rather then limiting your self to 40 amps?

Is there any good data on the trip curves for these new breakrs? I just did a quick search, and didn't turn up anything, although I easily could have missed it. Aslo, is there any data on thier cooling? Any data on how quickly they derate after repeated trips (I noticed this was a major problem for my team this year)?

I guess what I am really asking is for some good data on the 40 amp breakers, and just how much we can push them before we get in trouble.

Anyone have any thoughts?

-Andy A.

Re: 2004 Motor Statistics in US Units
 

The 40 amp breakers trip VERY quickly after 40 Amps. The only data I can verify this with is that from personal experience, noting that at a ratio of 25:12 our machine was tripping against a wall, and at a ratio of 25:10 on the final sprocket reduction, they wouldn't trip... this means that around 20% past thier rating, they trip quickly (5 or 6 seconds). I wouldn't even try messing with these.

The 120 Amp breaker is another story. Dr. Joe and I had a lively discussion on this preseason. He was convinved that those 120 Amp breakers wouldn't trip even throwing boatloads of current through them. We found this to be true. We were running (at peak) somewhere in the range of 160 amps and had no problems.

Until the finals.

In the last round of our last match, after playing in the order of a 10 or more consecutive matches, our main 120 Amp breaker tripped in the finals of Currie, costing us the match, and perhaps much more. These breakers have a thermal element to them, and after back to back matches, they were starting out a bit too warm... and tripped about a minute into the match.

Lesson Learned:
Be sure that you cool your breakers in the finals, as well as your motors.

Matt

Re: CHIPS
 

IMHO chip only drive is the way to go. You get very good power and speed along with a very simple mount(two 10-32 holes). The chip is also a very reliable motor. I rarely hear or people damaging the motor or burning it out(doesn't mean it doesn't happen) where as drills have a tendency to wear out faster and burnout or blow through clutches.

I also am not an advocate for the two motor drive with the electrical system that we are given to work with. It seems to take too much current draw and the robot 'runs out of gas' before the finish. I've formulated this based off my 2003 experience with multiple motor drives.

-Pat

-p.s.: Rmmbr keep it simple stupid

Re: CHIPS
 

The cool thing about those 120 amp breakers is because of their thermal element you could cool them and run at higher than 120 for a fair amount of time.

Because 2 of our lead mentors are Electrical Engineers and Thermodynamics engineers they often talked about if they were to put a sort of heat sink near the breaker module itself and were able to cool it, then you might be able to run at high current for a period, we called it like hitting the nas.

This might be beneficial if you are using something like a 6 motor drive in a high torque game.

But to get more on track about the topic. Our team has never used anything but chips on our drive since they were introduced in 2002. The reason being, is the first year soo many teams had problems smoking their drills. The big and beefy chips never had this problem so we tended to use them, then because of familiarity we used them.

Some of the students and mentors did some number crunching on the motors, to come up with a motor efficiency number. I wasn't involved with this as much but I was told that the Chips where the number 1 rated motor for their curve efficiency level. I would have to find out what they used to determine that and get back to you.

Re: CHIPS
 

I guess I'll just throw the comment out there that you simply can't be competitive with just one pair of motors and no transmission. You simply won't be able to move fast enough or be able to apply enough pushing force.

On another topic

Efficiency isn't really a concern for these motors. You don't worry about running out of juice in a match, you worry about moving faster and pushing harder than other machines. You want more power out of your motors. I'll take getting .5 HP out at 60% efficiency over .45 HP out at 99%. The batteries are rechargeable!!

Just some thoughts,

Matt

Re: CHIPS
 

The chips are good motors with the proper gearbox. I like the drills becuase they are practical for a drive system. The only problem with them is the mechanical error in the stock gearbox. It rotates faster going forward then in reverse. We had that problem but you can fix that in programming. And yes the best way to use both those motors is to actually use both the motors.

Re: CHIPS
 

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.

Matt

Re: CHIPS
 

actually, this problem is not in the gearbox, but in the drill motor itself. the CIMs also have a slight bias, but it isn't nearly as noticable as in the drills. theres a couple threads on this subject out there...

Re: CHIPS
 

you are contradicting yourself, in a way. If running out of juice in a match is a factor, than efficiency is important. But i havent seena ny problems with running low on batteries so yes, i'd agree, max power at a reasonable current is more important.

Re: CHIPS
 

sorry about the double post...

this is the second time that i've seen these 'windings' mentioned, and while i think i know what they are, i'm not sure, and i am curious about what is done to them that makes them cause this. does anyone have a (relatively) simple explanation they can give me?

Re: CHIPS
 

The stock gearboxes are designed so that both drill motors will run the same way. On the other hand...if your using chips, I would recommend you get them running the same way. I listened to the good old "it's not a big difference"...but it became a very annoying problem on our robot this year. We would always drift right...making setting up autonomus to hit the tee ball a pain.

Re: CHIPS
 

wow

ok, the reason for this post was because i want to keep the gearbox very simple adn achieve a speed of 9 ft/sec. also torque. This is the first time im designing a drive train and i want it to run smoothly. Im also scared of dual motors because theree is like a .5 mm shaft on the drill and i don't want it to crap out and its too complex for my first time. The reason i thought the chips would be better because they seem like they never break, and they have almost 5 time the rpm of a drill. From what im hearing is that the chip is only slightly less powerful, speed can be adjusted in gears but torque cannot, right? So, here's my question, if two robots were identical and one had chips and the other drills with gearbox(high and low) who would win in a pushing match?

thanks :cool:

Re: CHIPS
 

Assuming that you designed each drivetrain to take advantage of the maximum power available, and efficiency and gear ratios were identical, the drills would win. Wheels would need to be the same too, as would weight.

If you gear just the Chippy's to 9 fps, you won't have any torque (Well, you will, but you wont be pushing much of anyone)

Cory

Re: CHIPS
 

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.

Re: CHIPS
 

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!

Re: CHIPS
 

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.

Re: CHIPS
 

Simple Gearbox for one chip

http://www.valleytech.k12.ma.us/robo...2%20Gears1.jpg

Simple Gearbox for two chips

http://www.valleytech.k12.ma.us/robo...4_24wheels.JPG

or

http://www.valleytech.k12.ma.us/robo...ectronics2.JPG

better picture

http://www.valleytech.k12.ma.us/robo...4chipgear2.JPG

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

Re: CHIPS
 

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.

Re: CHIPS
 

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.

Re: CHIPS
 

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.)

Re: CHIPS
 

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.

-Paul

Re: CHIPS
 

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.

Re: CHIPS
 

Paul-

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.

Matt

Re: CHIPS
 

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:

Re: CHIPS
 

If anyone wants to see the inside of the Chia there are a couple pics here http://team696.org/forum/category.php?cid=5&page=3

For a simple drill-chia drivetrain I would recommend something like this http://team696.org/forum/image.php?iid=166
another pic http://team696.org/forum/image.php?iid=164

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.

Re: CHIPS
 

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

Re: CHIPS
 

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.

Re: CHIPS
 

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]

Re: CHIPS
 

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...


-Pat