Subject:
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Re: Aviation Tractor MOC
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Newsgroups:
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lugnet.technic
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Date:
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Mon, 17 Jun 2002 13:16:38 GMT
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Viewed:
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1490 times
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Yes, nice job. Well done!
In lugnet.technic, Jennifer Clark writes:
> Nice job Simon! I always like watching these machines at the airport too,
> did the spec sheets you received state what sort of horsepower and max speed
> these things have?
>
> As for the power problem, two 9V gear motors should be able to drive a
> machine of that size and weight quite well. Off the top of my head I'd
> suggest a gear ratio of around 24:1 from motors to drive axles; it will be
> pretty slow, but then the real things are pretty slow anyway. The double
> diff is probably superflous, certainly I've been able to gang two motors
> together without using a diff beforehand, and as long as the RPMs don't
> differ too much I can't see there being any great efficiency losses.
If you're going for a real power puller, then a ratio of 24:1 sounds good.
But beware! You'll be getting into gear-breaking torques. Be sure to use the
new style 24t gears, if you should need 24t gears.
I agree with Jennifer about connecting motors together. I've connected (i.e.
directly geared together) up to 4 motors and they've worked well.
> I don't have an 8880 but I remember people mentioning that the CV joints
> have a lot friction in them, so perhaps this is causing some problems?
If the 8880 CV joints are the problem, then perhaps you could try the new
4x4 parts from the 8466 off roader. These seem to work well and are about as
efficient as a normal u-joint. You can connect just about any tire to these
new parts. You only need a few small pulleys.
Another potential problem with gear trains is the stiffness of the chassis.
If your chassis (or supporting structure around your gear train) flexes,
then your axles will rub hard against the sides of their supporting holes.
I ran into this problem over and over with my tractor. As I operated it,
things would flex and move around, resulting in "warping" the gear train.
You could hear the effect in the motors as they would strain and the RPMs
would slow.
The thing I like to do when building is to turn the output shaft with my
fingers. Before you connect the motor(s), everthing should spin freely in
the gear train. Squeeze the supporting structure a little to simulate
operational loads. If the gear train becomes more difficult to turn, then it
is being warped a little.
> Another thing I've come across, especially with multi motors setups, is the
> requirement for the batteries to be delivering enough current. A 9V PP3 just
> cannot cut it, but 6 normal AAs in parallel are great. Another combination
> I've used recently to surprisingly good effect is 8 AA NiMH rechargables in
> parallel using a battery box from Maplin (about 70p). This gives a total of
> 9.6V and really shifts the motors; motor power goes up as the square of the
> voltage, so if you had previously been using 6 NiMH giving 7.2V, going to
> 9.6V makes a serious difference. Of course the motors are only rated at 9V
> so there may be some risk in this... I'd be interested to hear opinions on
> this.
My opinion is that it won't hurt the motor. I've run my 9v's using a 12v
power supply before and they've worked great. I imagine the motors would not
have any problems with 9.6 volts. But this is just my simple observation,
I'm no electrical engineer!
TJ
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Message is in Reply To:
 | | Re: Aviation Tractor MOC
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| Nice job Simon! I always like watching these machines at the airport too, did the spec sheets you received state what sort of horsepower and max speed these things have? As for the power problem, two 9V gear motors should be able to drive a machine (...) (22 years ago, 17-Jun-02, to lugnet.technic)
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