Slowing down a Foot switch

[philshevlin]

My bead roller has a foot switch to control the speed. The range of speed is too high/fast. There is about 1.5" of swing. I have to run it by only pressing it 1/4 to 1/2" max. When reaching on larger panels it is easy to accidentally crank down and move the panel too far.

Below is a shot of the switch. I'm hoping for an easy fix . I'm also willing to purchase a new one if they are somewhat universal. If they are universal what should I look for as far as specs.

Thanks.

 

[MBfreak]

The speed is controlled by a potentiometer, which gives a speed reference as a voltage to the power part in the speed controller.
If it is a linear potentiometer you can replace it by a non linear potentiometer which gives you a "softer start" if you get the right curve potentiometer.
Seem to reacall it is called a " negative log " potentiometer, but I am not sure.
A redneck solution is to install a fixed resistor in series with the supply voltage to the pot, ie to the terminal which has a lo-ohm reading to the wiper when pedal is fully pressed. This will hoever reduce the maximum speed you can get.
Ask the supplier of the machine if they have a neg log potentiometer. May cost all of $5.

Ola

 

[Innovate1]

Looks like a simple "pot" or potentiometer - a variable resistor - geared to the pedal. If you measure the resistance between the two outer connections you will get the total resistance - probably 10k ohms but may be higher or lower by several times. You can probably limit the max speed by putting a resistor in the supply lead. Typically the pot will take something like 10V and give a 0 - 10V output to control speed. Putting a resistor equal to the pot value in the lead should give about half speed max. You can put the resistor in the pedal or in the wire at the controller. Put some tubing around the resistor so it doesn't short to anything. Low power 1/4W resistor should be fine.

A new pedal is likely to work the same. You need a mechanical stop for max or modify with an added resistor.

 

[Innovate1]

MBfreak beat me to it.

I doubt the machine supplier is going to be able or at least want to supply an alternate pot. If so they probably want to give you a whole new pedal assembly and in any case it will be more than $5.

I don't consider the added resistor redneck. It's a perfectly legit way to do it.

If you want to limit max speed use the resistor (could even add a switch to short it out for those times when you want full speed). If you want a different speed vs pedal position find a pot with a different "taper". I am guessing the current one is linear.

The pot size looks very standard so finding a different one to fit should be easy from an electronics supply. Digikey is online and a place I use a lot for work.

http://www.resistorguide.com/potentiometer-taper/

 

[MBfreak]

OP
If you are a bit electrically inclined you can make an antilog pot easily.
Disconnect the pot from the controller.
Measure the resistance of the pot between the outer lugs. Say you find it to be 10 kiloOhms ( 10.000 Ohms)
Take a resistor of 10k*0,08=800 Ohms and connect between the wiper and the "ground " pot terminals.
This will give you a anti-log pot at no cost.
If you find out the pot resistance I can mail you the fixed resistor.

Ola

 

[philshevlin]

Wow. More info than I can process. A mechanical stop is probably more my speed. Thank you.

 

[slow]

i would tackle the electrical side with a resistor if it was mine, but I am comfortable with that kind of solution.

Non electrical solution, can you put a rubber pad or dense foam under the foot switch to make the harder to press, or just as a limit to how far it can go down?

 

[Innovate1]

Since the pot turns the opposite way a normal panel pot works you want antilog as Ola says. But I would go with a much larger added resistor. For 10% output at 50% travel you need an added resistor of about 1/20 of the total pot resistance or 500 ohms for a 10k pot. There is some risk the lower resistance value, even the 1/20 value, may cause problems with the controller as it will draw 10 times more current at high settings. The current is still fairly low but hard to say if that's an issue or not. I see he just corrected his resistance calculation to a more reasonable 800 ohms.

Still think the added series resistance is what you want but I may not understand your goals completely.

 

[Lassen Forge]

I was thinking about the resistor idea originally, but then it hit me... put a stop under the pedal and call it done. It's not that the pedal is too fast, it's the high speed that needs a limit.

 

[philshevlin]

I was using a chunk of metal under the lever, but I really like the foam idea. Thanks.

I assumed these switches came in multiple flavors... I'm ignorant to these things. But thats why I came here. Thanks again for all the help.

 

[UTCiv]

I'll go simple (like adjusting the high hat on a drum kit).

Loosen the set screw and clock the pedal/arm so that you limit the initial starting and maximum amounts.

Loosen the arm and push the pedal down with the pot in the initial position. Then when you release you have more give in the start, and less maximum.

You can even loosen and clock the arm to pot as well as arm to pedal, but you may run out of travel. Be careful not to allow the pedal force to be transmitted to the arm/pot stop points.

 

[philshevlin]

Another good idea. I'll start with the foam. then try that.

Otherwise I'll just go back to what I know...

 

[Zeke]

You're a metal guy, shorten the arm and move the pot closer. Or use someone's 3D printer to make a shorter arm.

Also, which way is that under your foot? Might use it the opposite way to see if you get more accurate modulation. I would have trouble using that if the cord was going away from me. It would be easier if the cord ran under my foot.