unpowered magnetic brake advice needed
unpowered magnetic brake advice needed
(OP)
I'm designing a motion damping system. I can't say what for, but I can tell you where I got the inspiration from. I've noticed that when my force feedback video game steering wheel is unpowered, the DC motor and gear train create a smooth motion with strong resistance when the wheel is rotated. Since I don't really need my rotational mechanism to be powered, I would prefer a similar system comprised of some sort of DC-motor-like magnetic brake and gear set to achieve a similar function, preferably with variable resistance. Furthermore, it is imperative that the magnetic field is contained and doesn't interfere with nearby electronics. Seeing as this was accomplished in the force feedback wheel, I see no reason it couldn't be done in the project I am attempting.
here's a few pictures of a disassembled force feedback wheel to show what I'm talking about:
http:// simpleparc el.com/cat alog/was/l ogitech%20 formula%20 force.html
here's a few pictures of a disassembled force feedback wheel to show what I'm talking about:
http://





RE: unpowered magnetic brake advice needed
Using a belt drive to speed up the disk will help.
Using a belt drive to spin a fan will also work well.
If you use the motor you are actually making a generator out of it. Experiment with different value loading resistors across the motor terminals.
A permanent magnet doesn't create much interference and a fan even less.
Belts will work much better than gears. Little or no backlash.
Read fast, this sounds like a hobby post and hobby posts are not allowed. This thread may disappear soon.
Bill
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"Why not the best?"
Jimmy Carter
RE: unpowered magnetic brake advice needed
RE: unpowered magnetic brake advice needed
RE: unpowered magnetic brake advice needed
RE: unpowered magnetic brake advice needed
RE: unpowered magnetic brake advice needed
Bill
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"Why not the best?"
Jimmy Carter
RE: unpowered magnetic brake advice needed
At any rate, I don't need it to be a carbon film potentiometer, I was thinking more along the lines of this type (wire wound):
http://u
http://u
I'm sure I would need some sort of heat-dissipating element in line like the load resistor mentioned a few posts up, but there needs to be adjustability in the torque of the DC motor output.
RE: unpowered magnetic brake advice needed
We don't want to be overwhelmed by hobbyists seeking free information.
We expect posters to be professionals and we expect them to do a little research on their own and not bother us with every little detail. Hence comments such as "You should know this."
But you have been allowed to stay, so far. Welcome to the forum, there is an unbelievable amount of expertise available here.
Back to the question at hand.
The resistor across the motor terminals is not a secondary control device. It is the heat dissipating element that you correctly surmised would be needed. It must be sized to handle the output of the motor.
A small permanent magnet DC motor is also a generator. As a motor the no-load speed is closely proportional to the applied voltage and as a generator the open circuit terminal voltage is closely proportional to the speed. On a larger motor, at a higher voltage (1 HP, 120 V and up) there is often only a few percent difference between Volts and/or RPM going from motoring to generating. The percentage difference will be greater with a small toy sized motor, but you get the idea. When selecting a rheostat I recommend looking at the Wattage rating and calculate the corresponding current. (Watts = current squared times resistance) you may need to use an external resister (check the current capability as above) to avoid burning out your rheostat when only a small percentage of the resistance is in the circuit.
On another track; a strong horse shoe magnet in close proximity to a spinning disk is easy. The drag may be varied by placing an iron bar on the other side of the disk. The bar may be movable, the smaller the air gap in the flux path the greater drag on the spinning disk.
Bill
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"Why not the best?"
Jimmy Carter
RE: unpowered magnetic brake advice needed
RE: unpowered magnetic brake advice needed
You may cut and twist paddles on the edge of the disk and also use magnetic braking.
Bill
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"Why not the best?"
Jimmy Carter
RE: unpowered magnetic brake advice needed
RE: unpowered magnetic brake advice needed
As I've looked into it more, I believe I'll be able to get the torque I need via some timing belts and pulleys to adjust the ratios, the only issue is that I need to be able to vary the resistance on the motor for variable motion dampening.
Is there a variable version of load resistors like this one? http
If so, what would it be called when I searched for it? I feel like I'll need something with an integrated heat sink, but perhaps not since motion will occur in short bursts rather than long consistent stints, but I'm not very well versed in electro-thermal properties.
RE: unpowered magnetic brake advice needed
ht
RE: unpowered magnetic brake advice needed
How about an AC motor, could I get more force using an AC electric motor?
RE: unpowered magnetic brake advice needed
Mike Halloran
Pembroke Pines, FL, USA
RE: unpowered magnetic brake advice needed
You have not told os what torques and speeds are involved. The reference to game consoles indicates that we are talking low speeds and rather low torques. Similar to what you have in a game kind of thing. If that is correct, you do not need to worry about power and heat.
If that is not correct and if you need to handle more power, then just calculate what kind of speed and torque you expect. Then make a worst case estimate of duty cycle and take it from there. Power in your resistor can never exceed that number.
Re the remarks that you feel are 'degrading, belittling, or condescending'. It is something you can expect when you are putting questions outside of your expertise in a forum where we are used to (and the site rules also indicates that) that the members have done their own research to a degree where elementary technical details have already been dealt with and that the continued work needs clarification of details or selecting between principles or just getting a verification that work is moving in sound directions.
Many of us are long-term members. I, for one have been around for six-seven years and many of the others are members for more than ten years. It is only natural that a 'hobbyish' question is questioned and that most of us also think that you 'ought to know this'. We are a nice bunch. But we are also humans that get irritated by the sometimes blatant laziness and lack of fundamental insight that is reflected in many questions that newcomers put.
Accept that - and you will grow as you learn. We all have done that in one or several ways.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: unpowered magnetic brake advice needed