THE Fisher-Price Motor Spec Sheet
 

Attached is the original motor spec sheet from Mabuchi for the Fisher-Price motors. Notice that Mabuchi also supplied a separate motor. The spec sheet attached is for the motor that is attached to the gearbox. The spec is for the motor only. This is the chart I sent to FIRST in December.

There are two sheets in this file: one for 6 volts and one for 12 volts. This motor was optimized for the 6 volt ride on car, but can be used at 12 volts.

-Paul

Re: THE Fisher-Price Motor Spec Sheet
 

Thanks for posting this Paul, but for some reason I can't open it. I just get a garbled file. Sorry about being a pain in the butt :p

-Bill

Re: THE Fisher-Price Motor Spec Sheet
 

Right Click 'Save Target As...' For some reason, it does that with all *.xls files.

Re: THE Fisher-Price Motor Spec Sheet
 

Gar. I'm a tard... This is what I get for checking robotics stuff before my 8am class... Why am I not a morning person?

Thanks Josh!

-Bill

Re: THE Fisher-Price Motor Spec Sheet
 

So from this data, it looks like we can't really use the motor below about 2/3 free speed or it will draw way too much current and burn something (itself, fuse, etc) very quickly.

Re: THE Fisher-Price Motor Spec Sheet
 

Paul, et al,

How certain are you of this F-P spec?

PEAK POWER: 400+ Watts!

Whoa... ...that's a lot of power. That means that the F-P motors are easily the most powerful motors in the kit. The Chiaphua's (a.k.a. CIM's) are something like 300-350W as I recall.

For those who do not have experience, if you are planning on using anything close to that amount of power, you had better be sure to leave the vents on the front end of the motor open to breath. There is a lot of heat to get out of a small space. Even with the 150W motors from prior years (again from memory not from specs), we used to melt the fans off the armatures. I think we had 200+W motors in 2002 but nothing like this.

Interesting. What was the spec last year -- my memory fades.

FYI PEAK POWER in Watts = (FreeSpeed in RPM) * (Stall Torque in N-m) / 38

This is a useful figure of merit for motor power -- the 1/38 comes from the fact that the peak power happens at 1/2 the stall torque and 1/2 the free speed and that RPM to Radians/Sec ~ 1/10

On another note, the Dewalt whitepaper (see plug below) that explains how to use the F-P motor in a Dewalt Transmission, does not open up these holes. It is possible, even without a mill to leave these holes open. If you are going to drive with a F-P motor, you should definitely open the holes*.

Joe J.

*they are already open on the standard transmission, I really mean this as a note to those who are planning on making your own transmission for these motors -- it make a huge difference the cooling of your motor -- don't be fooled by folks who put fins on the outside of the motor can. While this can be good to improve the amount of power you can put in these motors for long periods of time, FIRST matches are not "long" in heat transfer terms. To give you a perspective: A curling iron is typically 20W. At stall, you are pounding 150Amps at 12V -- that is 1800W of power -- we are talking blowdryer's here. There is just NO WAY you are going to conduct that amount of heat way with fins on the outside of a motor can. You need AIR FLOW to carry that heat away. While I am at it, once you get to stall, there is no way you are going to even blow that much heat away because a stalled motor is not blowing any air!

One final thing, don't tell me that the 40A breaker is going to save you either. This as been discussed 10s fo times on this sight - search "40A breaker trip time" (in fact I just did and there was a lot of talk of burning up F-P motors -- checkit out). You will discover that the 40A breaker can conduct 2 and 3 times their rated current for significant periods of time before they open.

Re: THE Fisher-Price Motor Spec Sheet
 

Something isn't right here. Maybe that's why FIRST hasn't put it out yet?

I think mabuchi has done a mistake (It can't be be Paul's fault ;D)

Re: THE Fisher-Price Motor Spec Sheet
 

I think the mistake is not Pauls or Mabuchi's but F-P's

If the motor is supposed to be used on a 6V car, then it is not unreasonable -- 100*W's is about right -- still high but not too bad. 400W is INSANE in that size motor.

Joe J.

*I don't have the spec open right now, I am going by the theoretical idea that peak power grows like the square of the voltage. So, 1/2 the volts implies 1/4 the peak power.

Re: THE Fisher-Price Motor Spec Sheet
 

All,

When my contact first told me about it being a six volt motor I was a bit disappointed, but I asked him a few questions. Disregard his question to me in the quote below. The Excel grid I attached in my previous post does have the data for 6 volts, too. That data is on another tab in Excel. I can test one of the motors I have and see what it can do, but I bet limiting the voltage to the FP motor is probably a good idea. The thing that bothers me the most is the engineer from Mabuchi did not jump up and down and say, "No way! Do not use it at 12 volts or you will destroy the motor." In my experience, however, the motor will fry near stall conditions at 12 volts. I am confident that the information I have received is accurate, but the missing piece is the robustness at 12 volts.

-Paul

Re: THE Fisher-Price Motor Spec Sheet
 

Mabuchi motors that we have used have also fried near stall conditions. We have not limited the voltage on them, in years past. They definitely don't like to be stalled when full power is being asked for. They tend to give up and let out their white smoke.

So... what we will probably do is run this thing at a maximum of 9.6 volts, as the engineer from Mabuchi suggested. At this stepped-down voltage, we will see these numbers:

2005 Fisher-Price at 9.6 volts
free speed: 19,200 rpm
max power: 325 Watts
stall torque: .518 N-m

Looking at these numbers, at this lower voltage, this motor is less powerful than the 2003-04 drill motor (free speed 19,670, 448 Watts, 0.87 Nm stall torque). It is strikingly similar to the 2002 drill motor (20,000 rpm, 340 watts, 0.65 Nm)

Does this seem reasonable?

Andy B.

Re: THE Fisher-Price Motor Spec Sheet
 

I think there is a better way than to arbitrarily limit the voltage to the motor.

If Mabuchi says 12V is okay, I believe what they are saying is that the armature can stand the 24,000 RPM without "bird caging"*

Given that, I think what is really needed is a way to prevent the build up of heat inside the motor. This can be done more elegantly than simply to limit the voltage of the motor (which is to restrictive at times and not restrictive enough at others).

Here is what I propose to those who want to get the most out of this motor:
1) measure or infer current (you know voltage in from PWM and if you are driving with it, you know the RPM -- that gives you a good method to calculate current).
2) given current and voltage, you can calculate electrical power input and the efficiency of the motor at that speed/load/voltage point
3) given power input and effeciency you can determine how much heat you are generating at that moment in time
4) given the heat input at any moment in time, you know how much energy is put into the system and (assuming initial conditions and the heat out is proportial to the temp of the motor) you can do a basic energy balance calculation temp over time.
5) if you want to get fancy you can even incorporate a motor speed based cooling factor for the motor (faster speed -> more cooling).
6) after the temp rises above a certain number, THEN and only then, I would limit POWER INPUT to the amount that I can dissipate at the current speed

Note that #6 in effect is done by limiting voltage, but the difference is important. You are only limiting voltage when needed and then only by the amount needed to keep the temperature from further.

In theory, this is a pretty easy thing to do. In fact, because temperature is a slow process I think you can do this calculation 3 or 5 times per second and still get good data.

Has anyone implemented a current limit based on such ideas? To be honest we have talked about it for 2-3 years now. We never implemented it mostly because we haven't used the F-P for a drive system in a while.

Any volunteers to share their experience or to take on this subject in a whitepaper?

Joe J.

*where the windings cannot stand the centrifuge effect and they mechanically disconnect from the armature, forming a kind of bird cage.

Re: THE Fisher-Price Motor Spec Sheet
 

side-note:

what is the reduction with the gearbox. i don't have one to look, is it similar to boxes we've had previously? does anyone know for sure what it is? thanks.

Re: THE Fisher-Price Motor Spec Sheet
 

It's a 124:1 reduction. Basic info on the motors in the KOP this year can be found in guidelines_c.pdf off of the FIRST website (look under documents and updates and you should find it. It should be in the robot section if my memory serves me correctly).

Re: THE Fisher-Price Motor Spec Sheet
 

I'd take your gearboxes apart and count the number of teeth on each stage. If we are really getting varied pinnion sizes between teams there may be other variations as well.


Matt's $0.02

Re: THE Fisher-Price Motor Spec Sheet
 

Yes, I had neglected to consider that. Hmm, well, that is what the current documentation states, though it appears it could be incorrect.

Re: THE Fisher-Price Motor Spec Sheet
 

Woburn has a box of F-P gearboxes dating back to the late 90s. There are at least four different kinds in there, and (except for colour--some are white, most are black), they all look identical from the outside. With the issues with differently-sized F-P pinions this year, you should definitely disassemble them and count teeth, if ratio is critical.

Re: THE Fisher-Price Motor Spec Sheet
 

I like your solution better than Dr. Joe's. :ahh: But please tell: Are you proposing a EE solution that steps down the voltage outboard of the Victor, or a software solution where the PWM signal is limited to a precalculated value, so that the effective voltage at the motor is 9.6v? (Or something else? Will the Victors work properly if you limit their input voltage?)

Re: THE Fisher-Price Motor Spec Sheet
 

Do you object to the complexity of the algorithm or to proposed operation? I think several teams did something very like this to stay right on the edge of the 120 Amp breaker from tripping in the 2002 Season. I don't think it is that complicated and I think the performance of the motor would be significantly better than the performance via limiting to 9.6V. 9.6V would still very easily fry this motor under some conditions while at other times (at the beginning of the match for example) it would limit the output needlessly.

As to whether Andy is proposing putting 9.6V on the input side of the Victor or limiting it in software (via max. & min PWM outputs), I don't know how you could actually put 9.6V on the input side of the Victor within the rules of FIRST.

Joe J.

Re: THE Fisher-Price Motor Spec Sheet
 

I was just thinking that we would do it in software, and never run this motor over 80% of full power.

AB

Re: THE Fisher-Price Motor Spec Sheet
 

Limiting the PWM in software is just as effective as limiting the input power to the Victor as far as the motor is concerned. It has the added benefit of being within the rules as well. A PWM limit would be my mitigation choice.

Re: THE Fisher-Price Motor Spec Sheet
 

Andy,

Verify your PWM limit via DVM. Refer to this post: http://www.chiefdelphi.com/forums/sh...168#post310168 and ignore most of the follow on discussion. It is not important why this non-linearity happens... We must deal with it.

Re: THE Fisher-Price Motor Spec Sheet
 

I am just wondering your file say that the motors model number is RS-550PF-8021 while on the first website in there 2005 Specification Sheets section they say the model number for the motor is RS-545SH-2485. Can you clear up this misunderstanding I am having about what these model number mean and why they are different. Thanks

Re: THE Fisher-Price Motor Spec Sheet
 

There are two different types of Mabuchi motors in the kit: the two Fisher-Price motors (Mabuchi part number RS-550PF-8021), and the one
small Mabuchi motor provided directly by Mabuchi (part number RS-545SH-2485). Two separate spec sheets for two different motors, both are in the kit.

-Paul

Re: THE Fisher-Price Motor Spec Sheet
 

Couldn't you just measure the temperature of the motor? (some kind of thermistor or temperature sensor...) Given that it takes only one digital or analog input (depending on how much circuitry and what sensor) and skips 5 steps (and the associated error), that would be my solution. You may have to scale it considering you are measuring the temperature on the outside, and the temperature on the inside is proportionally hotter.

Although it might be useful to have the current for the motors measured anyways...

- Scott

Re: THE Fisher-Price Motor Spec Sheet
 

The only reason I think a model for the temp rise would be better than a thermistor or some other measurement technique is that the temp you really care about is the temp of the armature. This is not so easy to get a real temperature for because it spins. The delay between what you can measure and what the true temp of the armature is could be significant.

This brings up another possible measurement scheme. If you know current and voltage AND speed, you can infer temperature. Basically, you know voltage and speed so you know, theoretically, what your current SHOULD be if the armature were room temp. To the extent that the current is different (in this case lower) than predicted, it must be that the resistance of the motor has increased due to hotter wire in the armature.

Since the resistance of copper wire is pretty well understood, you should be able to get a pretty good estimate of the temperature of the armature using this method, assuming that the current dynamics are fast with respect to the motor dynamics which is typically a pretty good assumption.
Again, this may sound complicated, but once it is worked out, it runs in the background more or less for free, keeping your motors at their peak without allowing them to overheat. I suppose with a bit of tuning, a generic code could be used by any team for any motor that they measure current and speed.

Once I am king and have minions at my disposal, I will be sure to put a few of them on this task ;-)

Joe J.

Re: THE Fisher-Price Motor Spec Sheet
 

Joe,
I don't know if you can get a good view of the armature, but an inferred thermometer may work. With the motor spinning I think you would get the average of the whole armature, and not just the windings. But if you stop it you could get a peak temp reading. Some IR thermometers have a wide measuring spot like a 1/2 inch or more closeup.

Counting teeth?
 

I still have not touched a 2005 Fisher Price motor/transmission (hopefully someone will get one down from the school to work tomorrow).

But... ...I am trying to answer a question tonight. Has anyone actually verified the total gear ratio on this year's F-P?

Share your data and I will share my toot counts tomorrow.

Thanks.

Joe J.

Re: THE Fisher-Price Motor Spec Sheet
 

Here are the ratios for the gearbox with the 13 tooth motor pinion:


1st stage: 72/13 ~ 5.4

2nd stage: 79/25 = 3.16

3rd stage: 62/19 ~ 3.26

4th stage: 38/12 ~ 3.17

Total gear ratio = 58,776/325 ~ 180.849:1

So 24,000/180.849 = 132.7 RPM at free speed assuming no gearbox friction slowing motor down.

-Paul

Re: THE Fisher-Price Motor Spec Sheet
 

Eeeek! The FIRST Tips and Guidelines sheet was wrong. Well that means we've got at least one wasted sprocket...

Re: THE Fisher-Price Motor Spec Sheet
 

I have posted a question on the FIRST Q&A, asking if they will verify/validate the data shown in the Guidelines document. Let's see what they say...

-dave

Re: THE Fisher-Price Motor Spec Sheet
 

If the FP motor gear box is used for an arm, limiting PWM is a bad thing. In certain positions the motor is going to be starting under a considerable load. It might be better to start the motor at full and reduce down once its moving.

Re: THE Fisher-Price Motor Spec Sheet
 

Yeah, I generally do not like hard limiting anything. At least leave a "boost" button on the joystick or something to let you go to max power. Even if you end up frying your motor, you may need that last push at the end of the match.

Data
 

I have some data, not as solid as I might like, but at least I have something.

#1, I counted teeth and I concur with Paul Copioli's count.

#2, I clocked one transmission at 12 V, no load:
100 Revolutions in 49.5 Seconds = 2.0 Rev/Sec = 120 RPM Close enough to Paul's prediction of 132 RPM when you consider that the gears DO actually provide some load to the motor even if the output shaft of the motor is "free"

#3 Current things get murky because of my test set up.
I only had a power supply with a current out meter. Also, I only had aligator clip type jumpers to power the motor -- looking at the data, I think that these must have affected my data.

In theory, the resistance of the motor should be 0.081 Ohm.

Voltage Current A Current B 1 4
2 14
3 22 20 4 30 30 5 40 39 6 48 47 10 75 74 Slope 0.125 0.131
The slopes are much higher than .08 Ohms! I was disappointed but I think it is more a function of my test set up.

I do not have time to repeat the test with a better set up right now, but I think that we can fairly safely say that the motor AS SPECed is the motor AS SHIPPED.

Feel free to confirm my test with your own data. If you do, please share.

Joe J.

Re: THE Fisher-Price Motor Spec Sheet
 

I seem to be kind of slow (midterms are over time to get it together). Does any body have the accurate specs of the F-P motor or are they not avalible because theres confusion over what voltage the motor can be ran at? :eek:

Re: THE Fisher-Price Motor Spec Sheet
 

In my mind, I am convinced that the specs as published are the spec of the motor we have (excepting any mixed lot parts that where shipped by mistake -- but it seems that that is the minority of parts, if any).

The issue of what voltage you can run them at is an open one. The motor can "stand" 12V. If the motor is not loaded too highly, 12V will be just fine. If you load the motor down, you are asking for trouble.

Bottom line for me: Keep V*I Power from becoming m*Cp*(dT/dt) Power and you will keep your motors cool and happy. Run too close to the stall point for too long and the acrid smell of burnt motor windings will fill the air ;-)

Joe J.

Re: THE Fisher-Price Motor Spec Sheet
 

Thx alot dr. joe but i must say after our meeting today i am even more mind bottled. Every body keeps saying "the F-P is the strongest motor in the kit. I know im not the best in the world at math but a some people have checked my math and its correct i got the following


F-P has 5.364 FT LBS @ 126 RPM

The Van Door has 22.1 FT LBS @ 75 RPM

The Denso has 6.78 FT LBS @ 92 RPM

The Jideco has 6.144 FT LBS @ 85 RPM

Please would some body check this information to make sure it is correct because if it isnt i dont want others to use it (me) and i would like to know what mistakes i made in calculating these numbers

Also if these number are correct although at diffrent RMP's isnt the Van Door stronger than the F-P .... thats what makes me think i have made a error.

Also ive read that the van door is not good for arms and needs to be operated at high rpms .... well lets say we needed 90 ft lbs and gave the van door hmmm 5 to 1 ratio would the rpm of the van door drop to about 15 ..... if so is that safe for the van door because i know theres some sort of fan inside

Re: THE Fisher-Price Motor Spec Sheet
 

If you have plans on becoming the President of Harvard, you may what to change your tag line. Some people at Harvard have trouble with the truth.

Re: THE Fisher-Price Motor Spec Sheet
 

I think you may be confusing torque with power. Power is torque times angular rotation.

The FP is the most powerful motor in this year's kit. If you gear all the motors to the same speed, the FP will have more torque (if we are to believe the spec sheets).

Re: THE Fisher-Price Motor Spec Sheet
 

Another thing to think about...

If the FP GB was designed to work with this motor at 6v, what are the plastic gear teeth going to do when you stall it at 12v?

Is it reasonable to expect that they over-designed the gear teeth by a factor of 4x? (2x to account for the 2x of the motor and an additional 2x so that you have your standard safety factor.)

In 2002, we pushed the FP gear teeth beyond their normal operating range and spit out teeth in every match.

Just one more thing to watch out for.

Re: THE Fisher-Price Motor Spec Sheet
 

The last stage of the F-P gearboxes is not strong enough for a drivetrain; not comfortably anyway. Modifications that 188 made in the (distant) past included metal gears in the last stage, and new (metal) shafts for all of the gears, to replace the plastic ones. We've avoided the F-P gearbox altogether since 2000.