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  #16   Spotlight this post!  
Unread 01-13-2005, 11:02 AM
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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.
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Unread 01-13-2005, 11:28 AM
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Re: THE Fisher-Price Motor Spec Sheet

Quote:
Originally Posted by Andy Baker
So... what we will probably do is run this thing at a maximum of 9.6 volts, as the engineer from Mabuchi suggested.
I like your solution better than Dr. Joe's. 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?)
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Last edited by Greg Ross : 01-13-2005 at 12:00 PM.
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Unread 01-13-2005, 12:07 PM
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Re: THE Fisher-Price Motor Spec Sheet

Quote:
Originally Posted by gwross
I like your solution better than Dr. Joe's. 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 if you limit their input voltage?)
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.

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Last edited by Joe Johnson : 01-13-2005 at 12:13 PM.
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Unread 01-13-2005, 12:12 PM
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Re: THE Fisher-Price Motor Spec Sheet

Quote:
Originally Posted by Joe Johnson
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.
I was just thinking that we would do it in software, and never run this motor over 80% of full power.

AB
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Unread 01-13-2005, 12:12 PM
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Re: THE Fisher-Price Motor Spec Sheet

Quote:
Originally Posted by Joe Johnson
Do you object to the complexity of the algorithm or to proposed operation?

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.
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.
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As easy as 355/113...
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Unread 01-13-2005, 12:21 PM
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Re: THE Fisher-Price Motor Spec Sheet

Quote:
Originally Posted by Andy Baker
I was just thinking that we would do it in software, and never run this motor over 80% of full power.

AB
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.
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Unread 01-15-2005, 07:19 PM
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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
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Unread 01-16-2005, 10:43 AM
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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
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Unread 01-17-2005, 11:46 AM
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Re: THE Fisher-Price Motor Spec Sheet

Quote:
Originally Posted by Joe Johnson
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
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
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Unread 01-17-2005, 03:27 PM
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Re: THE Fisher-Price Motor Spec Sheet

Quote:
Originally Posted by scottm87
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
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.
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Last edited by Joe Johnson : 01-17-2005 at 03:31 PM.
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Unread 01-17-2005, 06:20 PM
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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.
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Unread 01-17-2005, 08:14 PM
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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.
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Unread 01-17-2005, 10:12 PM
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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
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Unread 01-17-2005, 10:30 PM
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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...
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Unread 01-17-2005, 11:54 PM
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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
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