2005 Motor Information

[jaustin]

Can anyone help with a question related to the "Intro to Motors" [Heinzmann & Mikus] presentation posted on the 2005 Kick Off Workshop List? Near the end they list a "simple strategy" of assuming a higher motor resistance to calculate a new power curve. They then say to "operate at half the new peak power". I'm wondering if it was supposed to say "... half the new peak torque". Half of the already greatly reduced power seems REALLY low.

Thanks!
Jeff Austin
Team 372
Mukilteo, WA

[ErinColleen]

So are we in agreement then with the specs that were in the excel sheet?

~Erin

[petek]

Originally Posted by ErinColleen

So are we in agreement then with the specs that were in the excel sheet?

~Erin

I updated the spreadsheet, with a few corrections and new data - attached here. I haven't heard from Brandon if I can update the link in my post earlier in this thread.

[Joe Johnson]

I would use THIS SPEC for the Taigene motor.

Joe J.

[sciguy125]

Originally Posted by petek

I updated the spreadsheet, with a few corrections and new data - attached here. I haven't heard from Brandon if I can update the link in my post earlier in this thread.

Hold on a sec...
I think the oz-in numbers are wrong on the van door, jideco and denso. They're WAY too low. lb-ft numbers look right though.

ok...maybe I should investigate before I speak... When the numbers were converted from Nm to oz-in, they used mNm to oz-in conversion. I've fixed them, assuming that the spec actually is Nm and not mNm.

[petek]

Originally Posted by sciguy125

Hold on a sec...
I think the oz-in numbers are wrong on the van door, jideco and denso. They're WAY too low. lb-ft numbers look right though.

ok...maybe I should investigate before I speak... When the numbers were converted from Nm to oz-in, they used mNm to oz-in conversion. I've fixed them, assuming that the spec actually is Nm and not mNm.

Good catch! Funny how simple conversions can get screwed up at 10 at night... I hadn't paid too much attention to the oz-in numbers (obviously).

[Tom McCurdy]

I have had members of our team who are saying the gear ratio is wrong still instead of 1:124 for fisher price is 1:12.4 would this make any difference.... basically right now we are looking for the torque on the fischer price motors

[petek]

It would appear there are a couple of other errors in the data:
- According to other threads, this year's Van Door motor apparently has a no-load speed of about 50 rpm;
- The Globe gearmotor stall torque is way off - it is lower than the window motors', but I don't know what is the real value.

If and when I get "real" data, I'll update the spreadsheet. Sorry for posting bogus data.

[HPA_Robotics_13]

I don't understand this data.
I find it impossible to believe that the torque from the FPs is less than one Nm. Can someone explain what "stall torque" is? And then, what is the motor's "normal" torque?

[jgannon]

Originally Posted by HPA_Robotics_13

I don't understand this data.
I find it impossible to believe that the torque from the FPs is less than one Nm. Can someone explain what "stall torque" is? And then, what is the motor's "normal" torque?

The torque from the FP without the gearbox is less than 1Nm. With the gearbox, it's a whole lot more. The data for the FP with gearbox is wrong on that sheet, as pointed out by Dr. Joe earlier. Stall torque is the amount of torque provided when you are at 0 RPM. When you are at maximum RPM, you have 0 Nm of torque. There really is no "normal" torque... it depends on what speed the motor is going. I think there are power curves for the motors around here somewhere, which will tell you how much torque you get for a certain speed. If not, you can probably construct one yourself.

[sciguy125]

Originally Posted by jgannon

I think there are power curves for the motors around here somewhere, which will tell you how much torque you get for a certain speed. If not, you can probably construct one yourself.

As far as I know, brushed motors are linear. Plot torque vs speed. 0 speed, stall torque is your first point. Full speed, 0 torque is your other point. Draw a straight line and you have your "curve."

[russell]

I dont think thats right. Dont know why, but something seems funny about it. For I think because you are plotting the speed at stall at the beginning then the rest of the time you plot the free speed. Something like that.

[Tristan Lall]

Originally Posted by russell

I dont think thats right. Dont know why, but something seems funny about it. For I think because you are plotting the speed at stall at the beginning then the rest of the time you plot the free speed. Something like that.

Originally Posted by sciguy125

As far as I know, brushed motors are linear. Plot torque vs speed. 0 speed, stall torque is your first point. Full speed, 0 torque is your other point. Draw a straight line and you have your "curve."

In fact, sciguy125 is mostly right, except that usually, you plot speed vs. torque with stall torque (the max.) at the extreme right of the x-axis, and the torque corresponding to free speed (i.e. 0 torque) at the origin.

Maybe you were thinking of current?

[HPA_Robotics_13]

So, then what is the stall torque on the Fisher-Price motors (with gearbox)?

[jgannon]

Originally Posted by HPA_Robotics_13

So, then what is the stall torque on the Fisher-Price motors (with gearbox)?

We don't have any official numbers, but Paul Copioli figured the gearbox reduction to be about 180:1. Take the torque listed on the data sheet for the motor alone, multiply it by 180, and subtract a bit for energy losses. That will give you a ballpark figure.