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

[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]

[Gdeaver]

If teams have the parts, perfboard and kludge it. There are also 1 chip solutions from digikey.

[Joe Ross]

Originally Posted by Mike Betts

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]

This post may be helpfull for people trying to account for the cost: http://www.chiefdelphi.com/forums/sh...7&postcount=42

Another option for teams electing to run the 6 volt motor is to limit the peak voltage going into the PWM to avoid over heating the motor. I tested running a Blue Victor using a 6 volt supply and it appeared to run well. I am not an EE, so I can't say if this is safe for the PWM - I would continue to run the PWM fan on a separate 12v circuit. I also am not sure if this violates some other safety/construction rule. So I'd appreciate it if an EE and someone from the rules committee would chime in. I checked on Digikey, and there are many solid state voltage regulators at 5, 6, 7 volts and up to 20 amps. There is a cheap hobbiest trick that uses 2 diodes to float the center tap of a 5 volt regulator. This should result in a 6.2 volt output on the regulated supply.

Even the 12v FP motors and transmissions tend to heat up in competition - so I would consider using a fan to cool them. A simple trick is to position the PWM near the motor so that air is always blowing over the motor.

[Mike Betts]

Alan,

Just limit the PWM signal to a 50% duty cycle (verify with a good analog meter like a Simpson) and you do the same thing (and stay within the rules to boot).

[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??