Watched the demo video, this is excellent.
Earlier you mentioned this would work,
Do I need the one for communication, and the other to program and drive the motor? All can be powered by one or two 9 volt batteries?
I've switched 20W loads with an SOT-23 part. No problem. On resistance is low, dissipation in the part was just a few mW.
I wouldn't design an SOT-23 to dissipate more than about 1/4W without worrying about heat sinking (large copper plain on the PCB)
You're mixing up things, badly.
That's a LiPo cell with a boost converter in a PP3 package.
Why don't you use a standard LiPo battery? They come in many different sizes and shapes, and can deliver a lot of current. If the 3.7V is no enough (it probably is - measure the voltage across your motors while they run to get an idea of what's really going on), use two smaller ones in series. I expect you measure way less than 9V across the motor terminals thanks to the internal resistance of the battery. Otherwise those motors would be running pretty hot, fast.
If using a single LiPo cell you can also run all your logic from the same battery. No need for a second set of batteries, save space and weight.
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You should not buy electronic components on amazon for two reasons:
- most sellers on amazon provide not that kind of technical data that is needed
- amazon often offers not the lowest price
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"But your motors only want six volts."
Lol! Yup, but tractor pulling is ALL about pushing the limits, finding ways to keep all the parts in their respective place, yet squeezing every bit of horsepower out of the engine. Watch some videos of pro stock tractors doing their thing, it is mind blowing. 5000 HP coming out of a relatively small engine.
But what you say has peeked my interest. If there is a way to get more power out of these little gearmotors without simply feeding more voltage, I am all ears! I'm blissfully ignorant, but would love to gain in-depth knowledge.
Just want to thank everyone for your help and knowledge. I am breaking new personal ground, but you all do this as easy as I eat toast.
I will be posting links to my website which hopefully will be up and running next week.
The specifics we are discussing here are only to make it easier for us to produce videos, and will not be for sale. Once we have a working system, i may only build a dozen or so different models for the studio.
I grew up on a farm and spent a huge part of my young life on an 88 Oliver. Dad bought it new in 1948. I always joke that my butt is shaped like the seat on the ol' 88! Enjoy my recreation of the 88 as a pulling tractor, rather than a field ready workhorse.
Here she is as a micro electric pro stock, doing her thing!
I do not understand electricity very well, so i am completely open to advice. Generally speaking in a petroleum powered engine, more power means more fuel, more fuel means more heat.
For this project what i really need is more speed, i can adjust other dynamics to compensate for lack of power. We will not be competing, we are only making videos.
I belive I am assuming correctly that what we come up with, I will be able to adjust or program to mimick the "throttle" on a real tractor.
This whole project, which started in June of this year, but kicked into "road gear" in the last 3 months is a fascinating study of physics. We are hoping to bring this project to high schools for science fair competition just like the rocket cars, mouse trap cars and such.
Is the tractor motor running on 18V? Does the sled load increase as the tractor moves down the course? I can't determine what limits the pulled distance.
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Ah, okay, that's what the pulley arrangement on the sled is for. I wondered about that.
You are correct
If you spent that much time on it, perhaps the seat on the ol' 88 is shaped like your butt. 
Looking forward to video or whatever you share. Fun!
a7
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analogy about too much voltage applied to a certain DC-Motor.
You can imagine this as if you would use nitromethan in a standard gazoline motor.
Too much energy for what the motor is build for.
You would have to add / modify the cooling system heavily so the bigger heat could be carried away from the motor.
Same thing with too high voltage for a DC-motor.
If you want high power in a small space you could use a brushless motor.
brushless motors have a much heigher watts per weight ratio than DC-motors.
Using a brushless motor would require a completely different motor-driver module. A so called ESC (electronic speed controller) and I guess a much higher gear-ratio.
Brushless motors of small size like a diameter of 15 to 30 mm run with 8000 to 20000 rpm as outrunner.
Outrunner means the housing is the rotation part.
Here is a small one
diamater 18 mm length 21 mm
weight 13 gram
Power up to 35 W !
Now look at your DC-motor what is it rated for:
6V and but for sure not 5 A
The no-load RPM of the brushless motor will be 2000 kV * 12 V = 24000 rpm
As such motors are widely used in RC-models cars, ships airplanes
this leads me to another idea
RC-servos are also available with brushess motors.
If these vehicles are the same as dragsters
build whatever big-block or airplane-turbine you find suitable
you could power this tractor with whatever brushless-motor you want
hm why not using a brushless-motors with a multistage planetary gear?
best regards Stefan
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Oh yeah! That's what I'm talkin' 'bout!
'"If you spent that much time on it, perhaps the seat on the ol' 88 is shaped like your butt." 
EmilyJane, there are several women involved with tractor pulling.
Please enjoy, this little girl represents Breast Cancer Awareness, and reminds all women to get regular exams, and for us men who love our wives and daughters, to encourage them to do so. https://photos.app.goo.gl/STunuf4pQGoGZwMu9
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Good for her! More pink tractors! 
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Do any of the tractors have any kind of line following logic?
For competition, no, part of the drivers job is to keep the tractor from going out of bounds. This application has no rules so-to-speak. I've seen line following demonstrated in a video I watched yesterday, if we employed that technology, we could really make it look realistic. We could even stage a wreck!
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