Adding FP Motor to '05 KOP Transmission

[Tom Bottiglieri]

Would adding a Fisher Price motor, run through an AndyMark Planetary reducer, put enough strain on the existing KOP transmission to the point where it would not work, or to the point where the efficiency of the system is so low it wouldn't be worth using?

If you can answer this question with the math and/or know-how to back it up, could you also please explain the principles used to find this answer, or direct me to some further reading on this topic?

Thanks alot,
Tom

[sanddrag]

What do you mean adding? You want your robot to run on two FPs and two CIMs? That would be perfectly fine. However, as I recall the 6V FP running at 12V going through the AM planetary will give you a no lload speed of something like 6500 rpm where the CIMs are closer down to 5500 rpm. Quite a difference, but you could just pwm limit the FPs perhaps. Also, I think the shaft on the AM planetary is slightly longer than the CIM so you may have to trim it. Other than that, I'd say you're good to go.

[Veselin Kolev]

The gear reduction in the AM planetry is 3.67:1. The no load speed of the FP I use is 20,000 (I dont think this is the 6V, because my team replaced all of ours with 2004 FPs). The gear reduction on the FP motor brings its speed down to about 5500 RPM which is a good mate speed with the CIM, of course as long as you use the same motor pinion.

However, what are you trying to do exactly? As Sanddrag said, a drive train with 2 CIMs and 2 FPs running through the KOP? If you use the 2004 FPs (the ones that dont burn out) you will actually be getting less power, so there is no reason why it wouldn't work. If you are using the 2005 FPs (the ones that burn out rather easily) it will be a little more power than a CIM, about 60 watts per drive train. However, if you use the '05 you also have to limit its speed as Sanddrag said, to match its speed with the CIM, so you might not be getting any more power than a regular CIM. Also, you have to take into account the inefficiency of the AM planetary reduction.

If you are using two 2004 FPs and two CIMs for your drive train, you should be absolutely fine.

Hope that helps.

[Doug G]

That's a great idea - just make sure to use the 12V type of FP, either from 2004 or the ones you could've exchanged for at your first 2005 competition. The AM planetary outputs about the same speed as the CIM if you use those 12V FPs, and the great thing is that they also use the same output shaft and mounting holes as the CIM as well. Also note that the type of FP has been different in each of the past 4 years (maybe more?); in 2002 it was a Johnson FP (~274 Watt) with a 20 tooth pinion and a free speed of 20,000. In 2003 it was a Mabuchi FP (~150 Watt) with a 24 tooth pinion and with a free speed of 15,000. Then in 2004 it was a Johnson FP (~263 Watt) with a 19 tooth pinion and a free speed of 15,700. Last year was the 6V debacle which we hope doesn't happen again.

All the above data is thanks to Paul C, Joe J, Andy B, and others on CD.

[sanddrag]

Originally Posted by Doug G

just make sure to use the 12V type of FP... Last year was the 6V debacle which we hope doesn't happen again.

Our 6V motors didn't mind one bit running at a full 12V. One of them even lost its internal fand blades and it still didn't even get warm. It is all in how you use them. I hate such generalizations as (for example) "the 6V FPs burn out, you should use the 12V ones." We had great success with the 6V ones and enjoy every Watt of power we have over everyone else.

[Doug G]

Originally Posted by sanddrag

Our 6V motors didn't mind one bit running at a full 12V. One of them even lost its internal fand blades and it still didn't even get warm. It is all in how you use them. I hate such generalizations as (for example) "the 6V FPs burn out, you should use the 12V ones." We had great success with the 6V ones and enjoy every Watt of power we have over everyone else.

You are absolutely correct, because we customized a gearbox for the 6V FPs we had like 900:1 reduction to actuate our arm, and then when we got to our competition to switch out our FP's, they had a different number of teeth on them, and without the resources to swap the pinions, we stayed with our 6 V FPs and they held up just fine. However the AM Planetary is not enough reduction for the 6V motors running at 12 V.

I 'm banking on them not giving us 6V motors again.

[Andy Brockway]

We joined the fisher price with gearbox to the KOP transmission last year and used it for our arm shoulder joint. No issues at all.

But back to your question. I have to point you to some greater minds.

here

and

here

[Paul Copioli]

The KOP transmission was designed to take the torque loading in the arm configuration. If you stay below the max torque at the output stage in the arm configuration, then you can use the FP motor to drive the KOP transmission.

We used the globe motor with one KOP gearbox to drive our arm last year and it worked fine. The KOP transmission manual has the output torque curve for the arm configuration in the Appendix. If you stay below that maximum output torque, then you should be good to go.

-Paul

[Tom Bottiglieri]

Thanks for the replies everyone.

Just to clear things up, I was talking about modifying the back plate of the transmission to accept a 3 motor input. (2 CIM, 1 FP)

[sanddrag]

Oh, NOW you tell us. Those gears are 1/2" face width if I'm not mistaken. IMHO, shouldn't be a problem as long as it is done with care and precision.

[Paul Copioli]

Tom,

Again, refer to my post above. Do the math. If you are at, or near the limit on the chart in the manual, then you will be fine. My initial numbers tell me you should be O.K using the one stage option.

-Paul

[Stephen.Yanczura]

Okay, I’ll chime in with a question.

Looking at the KOP FP motors that my team received the part number on the can is 00968-9003.

**searches through FIRST specs**

Those motors apparently have a free speed of 16,320 RPM at 12.000V. Thats all well and good but when you apply that to the andymark planetary gearset with a reduction of 3.67:1. That yields a free speed of 4446.87 RPM. Okay so what, right? Well being as the andymark planetary gear set fits up in the same mounting dimensions as the CIM motor I think most people (myself included) assume that the speed would match up. The CIM motor free wheels at 5310 RPM; that’s over an 800 RPM difference from the FP/AM. Clearly you cannot just say replace one of the CIMs in the KOP transmission with a FP/AM combo and have it work. Unless maybe the andymark gear set was designed for a different FP motor, perhaps one that spun about 20k RPM. If you run that number through the gearbox you get 5449.59 RPM, much closer to the CIM. I don't remember which of the ten or so different FP motors made 20k RPM (maybe 2004?). Anyway I guess I was just seeking some input on this, because I can see some people (myself included) possibly running into a problem here.

[Rick TYler]

Originally Posted by Stephen.Yanczura

That yields a free speed of 4446.87 RPM. Okay so what, right? The CIM motor free wheels at 5310 RPM; that’s over an 800 RPM difference from the FP/AM. Clearly you cannot just say replace one of the CIMs in the KOP transmission with a FP/AM combo and have it work.

Sure you can -- I think. There is no absolute reason they have to both have the same free speed. Through much of the match both motors will be running outside their most efficient range anyways. As I understand the wonderful world of DC motors, the free speed differential won't make any difference, as long as you arent' trying to make that FP motor run past its maximum free speed (something you can insure in software). You could even argue that with two motors of slightly different torque characteristics on each transmission that you might get an aggregate torque curve that is better over a wider range of speeds.

I encourage someone who actually knows what they are talking about to correct me if I'm wrong (which is entirely likely -- I'm really more of a software and program management kind of mentor).

[Andy Baker]

Originally Posted by Stephen.Yanczura

Okay, I’ll chime in with a question.

Looking at the KOP FP motors that my team received the part number on the can is 00968-9003.

**searches through FIRST specs**

Those motors apparently have a free speed of 16,320 RPM at 12.000V. Thats all well and good but when you apply that to the andymark planetary gearset with a reduction of 3.67:1. That yields a free speed of 4446.87 RPM. Okay so what, right? Well being as the andymark planetary gear set fits up in the same mounting dimensions as the CIM motor I think most people (myself included) assume that the speed would match up. The CIM motor free wheels at 5310 RPM; that’s over an 800 RPM difference from the FP/AM. Clearly you cannot just say replace one of the CIMs in the KOP transmission with a FP/AM combo and have it work. Unless maybe the andymark gear set was designed for a different FP motor, perhaps one that spun about 20k RPM. If you run that number through the gearbox you get 5449.59 RPM, much closer to the CIM. I don't remember which of the ten or so different FP motors made 20k RPM (maybe 2004?). Anyway I guess I was just seeking some input on this, because I can see some people (myself included) possibly running into a problem here.

Mark and I are looking into this. This lower rpm FP motor is definitely a suprise to us. We need to do some tests and report back soon. My initial reaction is that the FP motor will still be a boost of torque, but with a lower efficiency compared to a FP motor with a 20,000 free speed rpm.

Andy

[Stephen.Yanczura]

Thanks for the input Rick and thanks for looking into the problem Andy. Always nice to see people standing behind their products.