George Foreman's Lean Mean Chiaphua Machine...

[dlavery]

There has been some discussion about how hot the Bosch motors can get, and when the thermisters kick in. But has anyone noticed their Chiaphua motors running really hot?

We started breaking in our new gearbox bolted to the front of the Chiaphuas the other night. The plan was to let them run in for at least 10 hours. But after about 20 minutes, I noticed that the motors were running very hot. The first reaction was excessive binding in our gearbox, so we popped those off and just let the motors run "naked" with no load @ about 10 volts. After ten minutes of running they were VERY HOT - to the point that you could not pick them up in your bare hands, and they were a burn hazard.

I know that the normal application for these motors (powered car jacks) do not require them to run for this long. However, I was surprised that no-load running would stress them that much. If it was just one, I would think that one of the motors was bad. But the heating was consistent on both motors. Has anyone else seen this? The duty cycle during the competition will not be as harsh, but the loading will be much more severe. Will we see a lot of these motors turning into space heaters?

-dave

[Jordan A.]

I think the real problem is the method by which the chiphua's get rid of heat. Radiation is ALOT slower than convection.

[AdamT]

There are some really cool looking heat sinks that are extruded aluminum and leagal. They were on another thread....somewhere. But that makes a very valid point: making sure your whole robot is very cooled. Those muffin fans are in there for a purpose, and I highly recommend using them and other means of cooling your robot.

Thanks for the info Dave...

[Joe Johnson]

I just ran one of our Chiaphua motors under no load for 10 minutes at 12.5 Volts.

The motor was luke warm.

Our motor was only drawing between 1-2 Amps. That works out to under 25 Watts of electrical power. At the size these motors are, I would not expect the motors to get much hotter than they got in the 10 minutes.

I think something must be wrong with your motors OR you had built up a lot of heat in your earlier test and it took that long for the heat to conduct through the case.

In any case, I don't think teams should panic about overheating Chiaphua's just yet.

Joe J.

Interesting to know what the projected lifetime use of the motor was.


The Chiaphua motors are similar to starter motors - they are designed for infrequent but hard use lifting a trailer - maybe two minutes a day.

Running them under load (even low) for hours is certainly not a use the designer intended. The people who build Battlebots don't use automotive starter motors for this reason. Also note how fast you can run down an automotive battery by cranking a car that won't start.

Also running them at ten volts (Though a PWM?) might cause a heat problem.

So Dave - like the patient who asked the Doctor about "my arm hurts when I do this......"

Dr. Bot says: "Don't do that."


(Darn NASA guys test too much - what happened to
FASTER-BETTER-CHEAPER>)

[dlavery]

Alan -

To paraphrase Artie Johnson "Why do I keep hitting myself in the head with a hammer? Because it feels SO GOOD when I stop!"

The reason that the trial was conducted in the first place was to break in the gear train, so that the loads experienced during the competition would be limited to match-induced loads and minimally affected by alignment/meshing problems with the gearbox. But now that I have seen a possible overheating problem with the Chiaphua, I do want to see if it is worth characterizing the thermal behaviour of the motor to understand if we will see any performance-limiting effects during the competitions.

So here are the results of a totally unscientific test that I just completed to try and document the Chiaphua heating.

The set up: Chiaphua motor with one reduction stage installed in the gearbox (i.e. motor pinion meshing with the cluster gear supplied in the kit.) Gear center-to-center distance is 0.742", with minor backlash (~2 degrees). There is little to no load on the motor, so any loads on the rotor must be caused by mechanical and/or elelctrical interference within the motor itself. The motor is directly connected to a 12 volt, 10 amp DC power supply from my shop (ie. no speed controller or PWM). It is not connected to a dynamometer, so I will not be able to document any torque fall off as the temperature increases. No special heat removal methods were employed (i.e. no cooling fans or forced air). I am sitting in my basement, eating a Pop Tart (frosted cherry) and sucking down a Diet Coke (sorry Joe, I don't do Dew).

The data log:

1:06am - Power on. Motor case is at ambient tempterature of 74 degrees.

1:16am - After 10 minutes, the motor case is luke warm. The digital thermometer says it is 82 degrees. The Pop Tart is now gone, so I hold the motor. Pamela Anderson is the guest on Conan O'Brian.

1:26am - After 20 minutes, the case is getting warmer. The thermometer reads 90 degrees on the black portion of the case. No problem to hold in my hand. Mulder is chasing Krichek through an abandoned railway station on X-Files.

1:31am - After 25 minutes there is a big temperature spike. The thermometer I am using maxes out at 110 degrees F. The hottest portion of the case is the (zinc?) housing on the back end of the motor, where the temp has cruised well beyond the thermometers ability to track it, and is still rising. Holding the motor in my hand is definitely uncomfortable, and the motor cannot be gripped tightly. My Diet Coke is gone, and Steve Irwin is playing with a rattle snake on Animal Planet.

1:36am - 30 minutes into the test, the motor case is so hot that it can't be held without some pain. The back end of the motor is very hot - I would estimate it is over 160 degrees. Without the can of Diet Coke to periodically cool off my hand, the palm is now getting very red from the heat of the motor. Kid Rock is on After Hours.

1:46am - After 40 minutes, it is time to end the test. Only a true dedication to see this test through to the grisly end has kept me holding the motor this long. The motor is very hot, although it seems to be running with no ill effects from the heating. The back of the motor is hot enough to cause blisters. My hand is very red, and has a possible first-degree burn near the base of the thumb. I realize that holding on to the motor for this long was pretty stupid, but we must all sacrifice for the sake of science. Debbie Harry is singing "Maria" on a SNL re-run on Comedy Central.

2:00am - postlog: after turning off the motor, it cooled faily quickly. Within 15 minutes after the end of the test, the motor is back to room temperature, and appears to have dissipated all excess heat without problem.

So what have we learned from all this? I have drawn the following conclusions:

1) The motor does not appear to have any serious heating problems during short-duration use, and we MAY not have any heating problems during the two minute matches (this experiment wasn't enough to prove this, as I did not apply a load to the motor that would be comparable to the loads they will see during the matches).
2) The motors can cool quickly, which bodes well for their performance at the competitions as long as there are a few minutes between matches to thermally recover.
3) Human hands make really crappy heat sinks.
3) Dave does really strange things at 2:00 in the morning, and obviously needs to get more sleep.

I don't intend to do any further testing at this point, but am curious if any other teams have noticed heating of the Chiaphuas during their use of the motors.

-dave

[Jason Morrella]

All I can say Dave is.........

Thank you so very, very much. That is certainly near the top of the "top ten laughs I've had during FIRST this year" list.

Your team is in good, slightly burnt, but good hands.

Hope all is going well with the team - see you in March.

JM

[Joe Johnson]

In honor of the skin cells on our beloved Mr. Lavery's thumb who gave their vary LIVES in the furtherance of our knowledge, I have begun another test...

First of all, I took a motor apart (not recommended for you folks at home since removing the armature from the magnets can cause you to loose up to 10% of your motor output).

From what I can tell, the motor seems pretty heat resistant on the insides. There are no plastic components that seem likely to melt or catch fire. In fact, the only plastic at all is the insulation on the wires and the gromets that the wires run through. The brushes are mounted to a circuit board type material that looks very fire resistant indeed.

Anyway, I am running the motor at 20V with no load. I have no sensors on the motor, I just want to run it until it is extremely hot and keep it there for a good long while, then let it cool down and see what ill effects I observe.

The only data I can give you at present is that it is drawing just under 2Amps (the readout on the power supply is flickering between 1 and 2 as it runs -- sorry I don't have a more elaborate set up).

I will keep you posted.

Joe J.

[Joe Johnson]

The motor has been running for about 1.5 hours now.

Other than it being very hot (too hot for me to pick up and hold), it seems no worse for wear.

Current is still right at the 1-2 amp border.

Joe J.

[Joe Johnson]

The motors stopped getting hotter after about 20 minutes (based on my calibrated hand ;-).

After that, the motor just ran and ran.

After 4 hours I stopped the test and took the motor apart again.

Nothing changed really on the inside other than it was clear that the oil impregnated bearing dripped a bit of its oil down the inside of the end cap.

I suppose that everything will be just fine with these bad boys.

Joe J.

P.S. In another note, someone asked in a separate note whether it was safe to press something onto the motor shaft. I think so. The shaft is a 8mm shaft all the way through the motor. The back of the shaft is held against the inside wall of the casting. I think as long a you don't go crazy with a very tight press fit you should be fine. But... ...as always, your mileage may vary.

Joe J.

I am really looking forward to how teams adapt these motors and use them for the competition.
Thanks a lot to Joe J. for getting these included in the kit. It is also cool that the rookie teams can be competitive with just the FPs this year.

I admit to being a bit jealous - I don't have a dynometer in my custom lab/workshop. Can't watch TV
and chew on pop tarts while my computer controlled
milling machine spits out custom cluster gears.
Can't feed the online temp - voltage - amperage -
torque data into my POWER GRID super computer to analyze the thermal efficiency to the 20th significant digit.

[Jordan A.]

Dr. Bot, I think if anything can be learnt from this thread is that all the crazy expensive sensory equipment in this world can be replaced by a very well calibrated and sensitive hand.

Another use for the all sensing hand I found out today is determining RPM by the pain the burn from touching a spinning gear gives you (Just FYI it was the FP motor, I know im an idiot, but I just couldnt help it, curiosity burnt the cat)

[JoeJ]

Our Chiaphua motors got a bit hot after test driving our 'bot. But I don't think the motors will suffer.

I am adding active cooling to the circuit breakers.

Tank steer with two motors geared for speed does suck current when turning. It is probably just under 30 amps when spinning 360's at full speed. Of course we are using the skyway 10x3 tires with a modified tread. That does have a fair bit of traction.

When the custom circuit box is finished we will have the current feed back in place so I will have a better understanding of our power.

I wish we could use 60 amp breakers then we would be near peak power for these motors.

Just for my sanity - what kind of gear reductions are you using for your motors?

Our plan is use a 48 tooth gear off the 16 tooth
cluster, and take that directly to a chain sprocket
for a further 2 fold reduction to the wheel.

This should add up to about a 20 fold reduction -
Using an 8 inch wheel I predict our speed to be 3 fps.

What are you guys clocking in at?

[JoeJ]

We built aluminum motor/gear housings.

We ground off the 32 pitch side of the Chiaphua adapter gear. Then we drilled and pinned the gear to a 1/4" shaft.
The we added a 15 tooth 24 pitch gear to the 1/4" shaft and pinned that.

A 3/4" shaft goes over the motor on two flange bearings. A 24 pitch 48 tooth gear couples it to the 15 tooth gear on the 14" shaft. At one end of the shaft is a 3.5" pulley for a 3/8" cog belt. At the other end of the shaft is the 10x3" Skyway wheel with the 3/4" hub and the 5/16" keyway.

An identical aluminum housing sans motor and gears supports a second 3/4" shaft, wheel and pulley. The belt couples the two wheels together.

Total reduction is 15.64 to 1
With our wheels the final FPS = 15.34
When pulling the goal, accelerate slowly ~ 5 seconds to full speed