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Spaceclam
12-13-2005, 01:44 AM
Hello,
i have no familliarity with mechanical speed controls. are they just 3 position, or are they continuosly variable? i just happen to need something what will vary the speed of a motor that draws no more than 2A continuous, 8A peak MECHANICALLY. Electronic ESCs are not an option.
Thanks
-Clam

ForestCam
12-13-2005, 01:49 AM
About the only choice you have as far as a "mechanical" speed control is a good ol' variable resistor. There are better ways that don't waste energy as heat but they fall into the not mechanical catagory.

Spaceclam
12-13-2005, 02:01 AM
those rc car guys had to do something before Electronic switching speed controls happened...

ForestCam
12-13-2005, 02:05 AM
Pulse Width Modulation has been around for a long time.

Spaceclam
12-13-2005, 03:40 AM
look, i am well aware, however mechanical speed conrols DO exist and have been used in cars for some time, and i am curious as to whether they are continuously variable or not.

cyclops2
12-13-2005, 05:02 AM
They are still used in low cost boats and cars. WARNING!! The speed resistor is ALWAYS selected for 1 combination of, motor, voltage, range of control. It is a time consuming process for large runs of the same models. Change ANY part of the model and it can suffer FAST.

Spaceclam
12-13-2005, 05:42 AM
so all it is is a heavy duty resistor then?

Robert53
12-13-2005, 05:39 PM
What your looking for is a wire wound potentiometer (variable resistor). Something with wire wrapped around it, with a wiping arm traveling across the coil. You didn't mention voltage. You can try an appliance repair place. They used to have some but everything is going to computer control. Got an old 110V A/C space heater? The heater wire/element will work. Make sure you're careful. The heater wiring just might get hot. Depends on the load it will be dropping. It will be trial and error but try around 20 ohms to start for low voltage. Got a meter?
Also, you can get a clothes dryer heating coil pretty cheap from that repair place.

Robert

trogdor
12-13-2005, 06:27 PM
If it helps at all, my brother had a Hotshot 4WD car from the mid 80s that I got from my parents house and cleaned up for him a couple years ago. I was about to get a new speed control but decided that the mechanical one was probably ok with the new motor and battery packs I got for it.

Basically it was a rotating metal contact on the top of a servo that made contact with 1 of 4 sets of contacts on a plate. So you had no throttle, a reverse speed that went through two large resistors in heatsinks on the back of the car or three forward speeds using two, one or no resistors. So three speeds forward and one in reverse using combinations of those two big resistors.

The mechanical speed control wasn't too big, just the servo plates and the resistors and on/off switch. I'm sure it could handle a whole lot more amps than you specify. I did look on Tower's site and found one or two other mechanical speed controls similar to it at the time but was able to fix the melted original enough to get it to work (short or something in wiring melted the plasticcase holding the contacts together but some epoxy fixed that.)

Try a search on Tower...

ForestCam
12-13-2005, 06:50 PM
What your looking for is a wire wound potentiometer (variable resistor). Something with wire wrapped around it, with a wiping arm traveling across the coil. You didn't mention voltage. You can try an appliance repair place. They used to have some but everything is going to computer control. Got an old 110V A/C space heater? The heater wire/element will work. Make sure you're careful. The heater wiring just might get hot. Depends on the load it will be dropping. It will be trial and error but try around 20 ohms to start for low voltage. Got a meter?
Also, you can get a clothes dryer heating coil pretty cheap from that repair place.

RobertWhat you're describing is a speed control for a slot car which would work.

savydad
12-13-2005, 08:09 PM
yes, and I'm not sure what your app is, but if for sailplane or plane of any sort, the weight of the mechanical speed controller is gonna be WAY over what an esc will be. If it's just a ground experiment, then no problem, but for planes, you can't get much better than a 2-3g esc...and there are others lighter than that. And almost all the mechanicals I've seen for cars are very limited to either on/off or 3 steps forward and 1 reverse. They are VERY heavy, over 2oz minimum plus the weight of servo. Good luck in what you're looking for, and the slot car control would probably be the best/lightest.

Todd

Robert53
12-13-2005, 09:39 PM
What you're describing is a speed control for a slot car which would work.

Never thought of that but yes. One of the small HO scale should work fine.. I haven't seen one in 20 years. Any kind of wire wound should do. Low voltage and 2 amps ain't much.

Robert

Poof, Landed!
12-14-2005, 11:33 AM
I know this is just a little off course but it could be of interest to you. Why not try a variable output IC (integrated circuit) regulator, whose output is determined by a small potentiometer (low current in the pot circuit) therefore no big resistor or big heat) which could be turned (rotated) with the smallest of servos. It's been awhile since I've made these so I'd have to check the current (not amps) versions of these available. Usually I got all my parts from either a local electrical distributor, but they don't stock much anymore, or Radio Shack. I used a 5 amp three pin Regulator (for size and cost), one small heat sink (or heat dispersing surface prefferably aluminum) to the back of the IC {a MUST}, one potentiometer (value depends on the regulator), and two small capacitors either for filtering DC ripples, or in this case eliminating RF to the IC.
I left alot of the values out of this dicussion, each IC regulator will give you a basic circuit diagram on the back of it's packaging, is available at a website, or may be in a Radio Shack power supply/ voltage regulator hand book $5-10. I'd dig mine out but have no idea where it is.
Using a three pin IC, one pin goes to the battery +, one pin goes to the motor, and one pin goes to ground (battery negative) through the potentiometer via the wiper tab (center tab) and one end of the pots internal resistive circuit (tabs Left or Right of wiper tab) and the other pot tab (L or R) to ground. I once used 2 of these IC's in parallel to assure more current to a child's toy, assuming 5a+5a=10amp max current but at a fixed voltage out put (ajusted by pot[s]?). The last one I made required a 0.1uf cap between the input (Bat+) and ground, a 1uf cap from output to ground (or Bat-), and an additional resistor; in my case 240 Ohms 1/2 watt between the IC's adjustable pin (or at wiper tab circuit) and the output pin (to motor) circuit.The additional resistor's size or nescessity is relavent to the IC being used. The caps in my circuit were both small cerramic's which are usually rated much higher than any RC circuit requires. I mount the IC/ heat sink, caps, additional resistor (if needed) to a miniture circuit board also at RadShk. Mounting the pot and servo on thin ply, adding an arm to the pot, and designing linkage is all ur's.
I would have recomended just a wire wound potentiometer and a servo mounted on thin ply and linked together, BUT I hated to think of what the electrical spikes (glitches) may have interacted with ur radio gear; I'm betting not well especially as the pot got dirty.
ANY ET's out there? I welcome UR thought's on this idea, as I've never used my regulated pwr sup's in RC gear.:eek:

Matt Kirsch
12-14-2005, 02:38 PM
Back to the mechanical speed controls.

Mechanical speed controls are nothing more than a multi-position switch wired to a large ballast resistor. They are not continuously variable. Most only have two speeds, maybe three, and are extremely inefficient because they reduce voltage by burning off some of the energy as heat. ESCs pulse the electricity on and off, varying the rest period between the pulses to simulate partial throttle settings, a much more efficient setup.