**FIRST EMAIL**/Fisher-Price Motor Information

[Alex1072]

Originally Posted by HPA_Robotics_13

So how is team 1072 making sure that the motor doesn't stall? I suppose you have to have the torque from the arm when the arm is in the position you want, transferred to some other mechanism. With our arm design, and the way that team 833 has played FIRST in the past, I know that our arm will need to be up in the air many many times, for long periods of time.

So if you do a gear reduction from the motor to your arms pivot point this will reduce the strain on the motor at stall? is 7:1 enough? Also, if you put a heatsink on the motor along with a muffin fan, can you make up for the problem of heat enough that there shouldn't be a problem or are there other issues than the heat?

What is the reason that this is not an issue for the other motors provided?

We're not using it for rotation, so our problem is much simpler. Since the new specs of the van door came out, we redesigned our elevator to be powered by 2 fisher prices. Basically we're using two of them at a reletivly low spool diameter to make SURE that it won't stall. I think our grabber would actually break before it stalls.

EDIT: I just remembered that one solution we came up with in our brainstorming (at one point were were thinking of doing a rotating arm), we were going to extend the bar past the pivot point and attach a cable to the back end, and a point equally far away from the pivot at the front of the arm. A cable would go down to a spool, wrap around it a bunch of times, and then go back up the other attachment point. That may pose entanglement issues though. Just a though.

[Kevin Sevcik]

Probably too late to pull it off, but if you used the DeWalt transmission for the FP, you could leave in the anti-backdrive pins and just not run the motor when you don't need to.

[HPA_Robotics_13]

What would any of you say about having a reduction on your system so great that you would just rely on the torque it takes to backdrive the motor being greater than the force of the tetra and your arm? This way you do not stall the motor, and it holds position.

[Jack Jones]

Back on topic - I.E. the unavailability of the kit FP.

They promised more information to follow, yet none has come this way.

All who plan to use - or misuse - the FP motor had better e-mail frcteams@usfirst.org and Sharon Gele <sgele@usfirst.org> in particular and implore them to let us use last year's motor as well. That would solve the availability problem and the 6v motor in a 12v system problems as well.

I do not understand why they have not done so already.

Some people asked about the 2004 254 robot. Yes, we did use The FP motors last year to power our arm, and no we are not using them for our arm this year. It was our original intent to use them, but we have changed our design, based on the FIRST blast information. We will be using the FP motors as supplied by first in our drive drain, but will use in tandem with other motors.

We are planning to use them through a unmodified PWM - We have no plans at this time to regulate the voltage down to six volts before sending it to the PWM, because 1) we don't know if that's legal (would require addition of some inexpensive electronics -a couple of high amperage solid state voltage
regulators) 2) We don't know if the PWMs would work correctly, if only 6 volts is being fed into them( I don't see why they wouldn't, but I am not a EE!). Our plan is to run the FPs and replace or remove them if they fail. We did have to fine tune our gearing so that the other motor overdrives the FP and not the other way around. We are estimating the FPs are contributing < 25% of the power to our drive.

To everyone struggling with this - good luck. Overcoming limitations in your
supplied equipment is part of the challenge.

[Paul Copioli]

Jack,

Please relax. I assure you that FIRST (and others) are doing everything they can to get the situation resolved. It is the number one priority for the engineering department at FIRST. Fisher-Price and Mabuchi are also scrambling to get a solution. Things are not always as simple as they seem.

-Paul

[sanddrag]

Thanks Paul.

I have one question. Everyone says that the FPs will inevitable fail. Besides JVN's beating, has anyone actually had this year's motor fail yet? If so, can we hear about the situation it was used in and the failure that occurred?

[Mike Betts]

Originally Posted by sanddrag

Thanks Paul.

I have one question. Everyone says that the FPs will inevitable fail. Besides JVN's beating, has anyone actually had this year's motor fail yet? If so, can we hear about the situation it was used in and the failure that occurred?

If designed in correctly, the FPs should not fail.

What has been discussed is that if you stall an FP at 12V it will fail very quickly. Stalling an FP at 6V should be OK for quite a while. Operation at high voltage and high torque (low speed) is problematic but you have an increased chance of failure the higher in voltage/torque you go.

At issue is that these are self cooling motors (you can see the fan in the end). If you put enough torque to slow the fan (motor) above 6V, you are at risk.

Regards,

[ahecht]

Everyone should read this before continuing discussion here.

[Mike Betts]

Originally Posted by ahecht

Everyone should read this before continuing discussion here.

Zan,

IMHO, how to address the design issue of a 6V FP is still relevant.

[Gdeaver]

Last year First included a current sensor as part of the kit. If any teams still have the current sensor, they could use it to monitor and control the current to this years Fisher price motor and gear box. It could be used as a fixed point limit or with a little more programing starting curves could be implemented.

[Mike Betts]

Originally Posted by Gdeaver

Last year First included a current sensor as part of the kit. If any teams still have the current sensor, they could use it to monitor and control the current to this years Fisher price motor and gear box. It could be used as a fixed point limit or with a little more programing starting curves could be implemented.

While the individual components would qualify, I'm not sure that last year's printed circuit board is available to all teams... If not, it would be illegal...

[edit] Not really illegal, but you would have to cost account a custom PCB... Not trivial... [/edit]

[jrocket567]

Originally Posted by ahecht

Everyone should read this before continuing discussion here.

hmmm... back to the drawing board, and digging around in previous year's junk.. i think were gonna attempt to put in the old motors.. what's everyone else planning on doing this late in the game??