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Avi_Y
2009.06.28, 05:28 AM
Hi,
I would like to try a motor that would present as much drag braking as possible. I am currently using the Stok-R motor, which has a great punch, and great braking as well. Top speed is of less importance, and there is no current limit (aftermarket speed controller). Any ideas for another choice of motor?
Thanks,
Avi

color01
2009.06.28, 06:05 AM
If you want more drag brake, you can shim the magnets on your Stock-R to move them closer to the armature. That'll give you a lot more drag brake, but make sure that the rotor still has plenty of clearance! You could probably break a magnet if the rotor hits it at 30k RPM's. :eek:

Avi_Y
2009.06.28, 06:48 AM
I thought about this solution, but I don't think I will be able to fabricate accurate spacers to move the magnets square and equal.
Are the grades of magnet strenght? If so, where can I get different grades of magnets? And what are the ones used in the Stok-R?

MantisMMA
2009.06.28, 08:44 AM
get a PN70 or an old xeric

Avi_Y
2009.06.28, 09:37 AM
Isn't the PN70 supposed to be a "weaker" motor? What are its characteristics?

MantisMMA
2009.06.28, 01:30 PM
Isn't the PN70 supposed to be a "weaker" motor? What are its characteristics?

its a spec stock motor for all of the PN events it has loads of torque and mega drag brake. lap times on our track with the pn 70 is around 10.4 and the modified cars are about 9.8. its a good motor.

color01
2009.06.28, 05:45 PM
Marcus, I'm fairly certain that the neodymium magnets in a Stock-R provide more drag brake than a PN Stock 70t... it just doesn't feel quite that way because the Stock-R rockets the car forward given any small amount of space. :eek: The Xeric may be comparable though, haven't tried that one yet.

Avi, Shimming magnets can be done with paper. So as long as you cut from the same sheet with a sharp pair of scissors, you can't really mess up the thicknesses too much. ;)

Avi_Y
2009.06.29, 01:40 AM
From what I have read around, the the PN70 has excess drag due to friction with the brushes, rather than magnetic field. I prefer strongger magnetic force, which also translates to acceleration.
I will give the paper shim a try, as my motor is already old, so I don't mind experimenting with it.
Thank you both for your ideas.
Avi

MantisMMA
2009.06.29, 01:56 PM
From what I have read around, the the PN70 has excess drag due to friction with the brushes, rather than magnetic field. I prefer strongger magnetic force, which also translates to acceleration.
I will give the paper shim a try, as my motor is already old, so I don't mind experimenting with it.
Thank you both for your ideas.
Avi


its not brush friction it is the hard springs but even after the brushes have worn down that motor still has a good amount of drag brake!

color01 doesnt that depend on the air gap of each motor? i have both of those motors and the pn70 always feels like it has more brake than any of my stock r's:confused:

color01
2009.06.29, 03:45 PM
Brush friction does play a part, but 1) it goes down as the brushes wear and 2) I don't think it's as strong as the magnetic drag. You're right, the air gap between magnet and rotor plays a large part in this, that's why I suggested shimming the magnets. But magnet composition matters even more, and while the PN70 uses ferrite magnets, the Stock-R has neodymiums -- they generate a heck of a lot more drag, and a heck of a lot more torque.

We both missed one thing though, the PN70 is a bushing-can motor. :o That would increase the drag brake a bit, although in this case I'd rather use bearings in the can...



Anyways, to recap, the primary ways of increasing drag brake on a tunable motor are harder brush springs and stronger/closer magnets. If you want to decrease the drag brake on the PN70 you can actually bend the brushes back a little bit to reduce the force with which they push on the comm, and vice versa. :)