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Unread 08-03-2010, 09:34
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FP ok to stall?

I know in years past, FP motors loved to produce magic smoke when they stall (now replaced by thermal trip). My dilemma this year is our roller (single fp) isn't geared down enough (2500rpm) and we are having trouble controlling the ball.

Question: If we run the FP motor at 30% power and stall it for no more than 10 seconds, will this still cause thermal trip/magic smoke or is this a "safe" option?
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Unread 08-03-2010, 09:43
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Re: FP ok to stall?

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Originally Posted by ADZDEBLICK View Post
I know in years past, FP motors loved to produce magic smoke when they stall (now replaced by thermal trip). My dilemma this year is our roller (single fp) isn't geared down enough (2500rpm) and we are having trouble controlling the ball.

Question: If we run the FP motor at 30% power and stall it for no more than 10 seconds, will this still cause thermal trip/magic smoke or is this a "safe" option?
The FPs have an external fan attached to their output shaft to keep them cool. Stalling the FP not only causes high current, but also stops this cooling fan. Not a good idea.

I would not suggest running an FP in stall for very long at all (not even 10 seconds).

Just my opinion.
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Unread 08-03-2010, 09:52
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Re: FP ok to stall?

I'm going to have to say this is a bad idea. FP motors are super sensitive to stalls, and will go up in smoke in seconds.

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Unread 08-03-2010, 09:59
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Re: FP ok to stall?

The only thing that makes me consider this is that when I have seen FP motors go to smoke, they have been at 100% power and stalled for at least 2 seconds. By running them at 30%, the motor would be drawing significantly less power.
I'm just wondering if anyone has tried running the FP at less than full power and still fried it?
(If not, I can resort to destructive testing but I rather ask here first)
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Unread 08-03-2010, 15:34
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Re: FP ok to stall?

The only way to effectively use fisher price motors and not product magical white smoke is to have enough gear reduction built into the system so it doesn' stall. If you manage to do that, then the motors will produce magic in the form of winning matches otherwise, there is no real solution to the problem your team is having. The window motors or cimz would be better suited for the solution you previously mentioned
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Unread 08-03-2010, 15:45
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Re: FP ok to stall?

The FP have a thermally activated switch that protects them from getting too hot but it also prevents you from pushing them to the limits of their capability.

I thought it was fine to have intermittent use at 1/2 stall torque, but I have heard war stories that make me believe otherwise. I am planning on having a modification that will allow me to drop my motor current to 1/4 to 1/3 of the stall value during lift.

As I said, I think I should be okay for 4 seconds at 1/2 stall but I don't dare bet the farm on it...

So... ...we make contingency plans and hope we don't need them...


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Unread 08-03-2010, 16:42
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Re: FP ok to stall?

Our FP is geared down 108:1, powering a 2" roller. It was stalled for about 10 seconds, there was no smoke, but a strong burning smell came out. Thankfully neither the motor nor the wires were hot, but we have a spare one ready to go just in case.

Our roller and back plate are design such that the ball doesn't get jammed in too far. The material is chosen such that it brushes a ball like getting a car wash at a gas station. The height have been modified a hundred times before it was finalized in one of the later matches at SD. All of this and we are still fine tuning it as time goes on.

Be very gentle to your FP motors... Be very gentle.
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Unread 08-03-2010, 16:54
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Re: FP ok to stall?

Fisher price are not a nice motor to use effectively. They are just too fast. The pinion (and gear) is a real pain if you need to change it for whatever reason and they hate being stalled. Personally, I'm not a fan. Can I have my big cim back please?
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Unread 08-03-2010, 17:33
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Re: FP ok to stall?

What Daniel meant above is the fan is internal. Frequently teams have loaded the motor significantly which slows the shaft speed to the point at which the fan is inefficient. (or they block the open slots at both ends of the motor) Regardless, stalling the motor is bad even at low throttle values. The thermal device gives no warning, the motor just stops.
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Unread 08-03-2010, 18:57
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Re: FP ok to stall?

Quote:
Originally Posted by Ross340 View Post
Fisher price are not a nice motor to use effectively. They are just too fast. The pinion (and gear) is a real pain if you need to change it for whatever reason and they hate being stalled. Personally, I'm not a fan. Can I have my big cim back please?
We've had great luck using a FP by cutting down the gearbox to whatever state best fits our application. Two years in a row, we have rollers powered by FPs with the third stage on the plastic gearbox removed, and they have been tremendously reliable.

That said, I don't know that *any* motor likes to stall for very long when hooked to a 12V battery...
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Unread 08-03-2010, 19:30
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Re: FP ok to stall?

ChrisH,
I'm probably wrong, but I thought you guys used the BaneBot motors on your ramps and the fps on your arm in 2007.

Another option if your still worried about stalling though, is to put some kind of slip clutch into your system so that if the ball jams the fp motor will not stall.
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Unread 08-03-2010, 21:42
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Re: FP ok to stall?

Quote:
Originally Posted by Ross340 View Post
Fisher price are not a nice motor to use effectively. They are just too fast. The pinion (and gear) is a real pain if you need to change it for whatever reason and they hate being stalled. Personally, I'm not a fan. Can I have my big cim back please?
I love the FP motors. At least I did before the Thermal protection was added. I think I will end up liking it just as much with the breaker, if not more. They are easily the most power dense motors in the kit. Used with a Dewalt transmission or a Banebot transmission designed to be loaded properly (<1/3 stall torque if planned to be stalled for any duration of time) the motor is a real work horse.

Just one man's opinion.

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Unread 09-03-2010, 01:20
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Re: FP ok to stall?

Quote:
Originally Posted by Joe Johnson View Post
I love the FP motors. At least I did before the Thermal protection was added. I think I will end up liking it just as much with the breaker, if not more. They are easily the most power dense motors in the kit. Used with a Dewalt transmission or a Banebot transmission designed to be loaded properly (<1/3 stall torque if planned to be stalled for any duration of time) the motor is a real work horse.

Just one man's opinion.

Joe J.
Seconded! You can't beat them for sheer power. Especially because you actually have the option of running them at 1/2 stall, even if it's not the best idea. You won't run a CIM at 1/2 stall for more than a few seconds before you trip a breaker.

That said, we're using an FP to hold up a ramp this year. We've currently settled on 25% speed as a semi-safe value. We tried 30%, but after a long session of unintentional idling in the pits, the motor was producing some distressing odors. In the interests of my sanity, the students backed it down to 25% and promised to not leave it idling in the pits.
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Unread 09-03-2010, 03:16
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Re: FP ok to stall?

We learned this the hard way this year.

We tried to use a FP to run a centrifigal fan out of a dewalt vaccuum. It functioned o.k. 1:1 but didn't give us the speed we needed. We geared it up 1:2 and after running 30 seconds wide opened the Fish smoked a bit and thermal-tripped. We thought we had a bad motor since there wasn't that much load on it (it was spinning at a REALLY good clip) so we wired up another and prompty toasted that.

That's how we learned that you don't run an FP at 100% of rated power if you can help it - even if it is not stalled and is still turning pretty darn fast.
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Unread 11-03-2010, 14:03
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Re: FP ok to stall?

Quote:
Originally Posted by Kevin Sevcik View Post
We've currently settled on 25% speed as a semi-safe value. We tried 30%, but after a long session of unintentional idling in the pits, the motor was producing some distressing odors.
Kevin, could you clarify what you meant here please? When you say "25% speed", did you mean "the voltage that produces 25% of the rated 12 volt no load speed" ?

In other words, adjust the PWM to the unloaded FP to produce a speed of 25% of the rated 12V no-load speed, then - while keeping the same PWM - add load to stall the motor; and it is OK ?


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