CHIPS

[roboteer49]

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

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

BAM!

[BillyGoats]

Originally Posted by roboteer49

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

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

BAM!

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.

[ngreen]

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.

[Ryan F.]

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.

[RogerR]

Originally Posted by roboteer49

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

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

BAM!

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.

[Tristan Lall]

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).

[Matt Adams]

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.

 
Motor Name			Free Speed	Stall Torque	Stall Current	Circuit Breaker	Torque at Breaker Speed at Breaker Power at Breaker
				(RPM)		(in-lbs)	(A)		(A)		(in-lbs)	(RPM)			(HP)
Drill (1)			19,670		7.70		127.0		40		2.18		14190.5			0.491
Drill in High (2)		1,521		48.64		127.0		40		29.27		1041.9			0.484
Drill in Low (3)		450		319.95		127.0		40		103.35		308.3			0.506
Atwood / Chip / CIM (4)		5,342		21.68		114.0		40		7.61		3467.6			0.419
Fisher Price (5)		15,694		3.54		61.0		30		1.74		7980.9			0.220
Globe Motor with Gearbox (6)	104		180.00		18.5		30		180.00		0.0			0.000
Van Door Motor (7)		75		300.88		44		30		205.15		23.9			0.078
Window Motor (8)		86		83.19		24.5		20		67.91		15.7			0.017

(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.

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.

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

[Andy A.]

Originally Posted by Matt Adams

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

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.

[Matt Adams]

Originally Posted by Andy A.

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?

Anyone have any thoughts?

-Andy A.

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

[Pat Roche]

Originally Posted by roboteer49

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

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

BAM!

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

[Dan Richardson]

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.

[Matt Adams]

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

[Ali Ahmed]

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.

[Matt Adams]

Originally Posted by ali_rockon22

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.

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

[RogerR]

Originally Posted by ali_rockon22

...The only problem with them is the mechanical error in the stock gearbox. It rotates faster going forward then in reverse...

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...