FRT curcuit design, for the wigwag on a mobility scooter, pls.

Thread Starter

Dumb-ton

Joined Oct 16, 2022
10
for the wigwag on a mobility scooter, [Shoprider ERSF, Circa 2014?] where i'm modding controls, and unavoidably reducing wigwag swing range. i wish to increase the rate of change on the 5K pot/voltage divider by between 1.5 and 3 times [selectable?], largely independent of supply voltage, which varies from v to v/10. v/ something less is acceptable.

quiescent state amplifier Vin=Vout=V/2 ==wigwag pot centralised, or unit disabled.

an unknown is the rest of the cctry response to an increase in total current by voltage divider [doubled? as output reistor prob needs to be 2.5K]

a 50K pot is in series wth the wigwag to lower max possible speed range as needed.

i thought FET because it's a voltage sensing system, and i can't reconcile that with bjt', as i've forgotten too much.


if a cheap kit/module exists [in Oz?] pls recommend. .

thx
 
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MisterBill2

Joined Jan 23, 2018
13,689
WHAT?????
The question is not clear , and I am not sure what the "wig-wag" referenced actually is. My mind-reading ability is very poor, especially at a distance.
But what is certain is that a voltage divider will not produce an increase in the delivered current.
Aside from that, what moves a "wig-wag"??? I am not familiar with anything by that name, except the tail of a dog.
 

DickCappels

Joined Aug 21, 2008
9,505
Just a guess: Is a wig-wag the steering handle?

I imagine that if we knew exactly what you need it could be done with an inexpensive operational amplifier. Being a 5K pot suggests that the load is fairly high impedance -probably thousand of ohms. How many volts is supplied to the pot?
 

MisterBill2

Joined Jan 23, 2018
13,689
My guess is that the TS has not enough experience to accomplish the project attempted. And I will not even guess how "wigwag" relates to a mobility scooter.
 

BobTPH

Joined Jun 5, 2013
6,046
I think he means a flashing light pattern where one light flashes several times, then the other. Often seen on emergency vehicles.
 

Tonyr1084

Joined Sep 24, 2015
7,190
Wigwag (click on it) as I know it is a train crossing signal where flashing lights and a hanging physical sign begins flashing and swinging the WW back and forth. If we discount a moving sign, we're left with an alternating set of flashing lights like what you see when a train is coming but before the gates come down.

For such a circuit, one can be built from a simple 555 timer where one light flashes for a set period of time then the other.
Here's one such circuit. Modifications would be needed to achieve the timing you want.
1670515320439.png
 

Thread Starter

Dumb-ton

Joined Oct 16, 2022
10
wigwag:
the push-pull or see-saw lever used for combined speed and direction control. a center stable lever, the more it moves the faster it goes. nb the rehostats used here are special, being weatherproof and only some 70deg total rotation. in the mod, i doubt i'll get 25deg. the mod will shift my wrists from horizontal to vertical planes, thus reducing damages from tiller shaking on uneven surfaces. i can't believe i'm the first so afflicted, but no-one here has a mod kit for this after >20yrs production. Manufacturers don't use their product, or they'd know what's wrong with it. older clients die or deteriorate and complaints never get back to HQ. i cannot change the wigwag pot, but i know its range can be amplified elrctronicaly.
it is low current, and a voltage divider, not current divider. i'm just unable to design a suitable FET circuit from first principles. BJT I think i can do, but i have doubts there's enough current capacity in the supply circuitry to drive it safely. i fear damaging the mobo. i don't know if supply is 5v or 12v. memory says 5v - but memory is unreliable, and i can't do any testing for some time. the motor is 50A, controller is abt 90A, of the prev to current type?. it is the last type before automatic decent braking was installed and has a hi/lo speed range switch as well as the 50K speed limiting pot.
 

Thread Starter

Dumb-ton

Joined Oct 16, 2022
10
wigwag:
the push-pull or see-saw lever used for combined speed and direction control. a center stable lever, the more it moves the faster it goes. nb the rehostats used here are special, being weatherproof and only some 70deg total rotation. in the mod, i doubt i'll get 25deg. the mod will shift my wrists from horizontal to vertical planes, thus reducing damages from tiller shaking on uneven surfaces.

i can't believe i'm the first so afflicted, but no-one here has a mod kit for this after >20yrs production. Manufacturers don't use their product, or they'd know what's wrong with it. older clients die or deteriorate and complaints never get back to HQ.

i cannot change the wigwag pot, but i know its range can be amplified electronically.
it is low current, and a voltage divider, not current divider. i'm just unable to design a suitable FET circuit from first principles. it will have to be biased :Class A.. it's probable that the now output be similar to the originalie total quiescent resistance 5K, centrally tapped at the source/collector..
BJT I think i can do, but i have doubts there's enough current capacity in the supply circuitry to drive it safely. i fear damaging the mobo.
i don't know if supply is 5v or 12v. memory says 5v - but memory is unreliable, and i can't do any testing for some time. the motor is 50A, controller is abt 90A, of the prev to current type?.
it is the last type before automatic decent braking was installed and has a hi/lo speed range switch as well as the 50K speed limiting pot.
 

MisterBill2

Joined Jan 23, 2018
13,689
OK, now that what it is has been made clear, in my locality it is called a control-stick or a Joystick. So it handles two axis for both speed and direction. The outputs are small voltages that control the driving electronics. I have seen versions of that which respond to force, not motion, I believe that they use strain gage sensors and a circuit know as an instrument amplifier to convert the output to voltage signals.
The amplifier for the voltage would most conveniently be an integrated circuit op-amp, set for some small amount of gain. The benefit being simple gain adjustment capability and also the simple ability to adjust the DC offset voltage when no output is required.
The serious challenge being that you will need to know just what the output voltage is in both the neutral position ( no speed and straight forward, and at the extremes of the commands. But when those values are known the rest of the changing will not be unknowns.
Information about the present control system is what will be most useful now.
 

Alec_t

Joined Sep 17, 2013
13,224
Are the 5k pot and 50k pots mentioned really separate, or is there a typo somewhere?
If the wig-wag controls both speed and direction, won't there be two pots involved?
 

MisterBill2

Joined Jan 23, 2018
13,689
Measurements are in order at this point. The difficulty will be in locating the reference point for the measurements, the control system common connection. When the voltages at each end of each pot are known, along with the voltages at the movable point, when at rest are known that will be the required information. All sorts of control stick devices are available if a replacement would be better, or adding amplification in the form of an op-amp IC is an option. I have seen a heavy-duty mobility device with a control that needed to only move a few degrees in each direction. The ramp I assembled for that user will easily support a passenger car.
 

DickCappels

Joined Aug 21, 2008
9,505
@Dumb-ton I think that if you can provide some more details we can recommend a circuit.

Do we need to consider the 50k speed limiting pot? If so, where does it figure into the circuit?
Battery voltage and range of the voltage output by the other pot?
 

Thread Starter

Dumb-ton

Joined Oct 16, 2022
10
direction:
FWD/REV only, steering by tiller. 50k pot not relevant atm, but does reduce max voltage to wigwag pot for lower max speed down to abt 1/10th.. wigwag is a 2D see/saw with full movement, and when modded, will have << movement. the pmw mobo is difficult to alter. it is digital. the input could be ADC, and internal in the processor? it uses some SMT. i think it best to leave it alone and make a transferable plugin [for my next one too.] mobo's are replaced, not repaired, so there's no depth of local info to draw on. new ones are expensive, used not common, espec the one being sought [Murphy's Law]. only some direct interchangability exists to upgrade power rating in same series controller.
 
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Dodgydave

Joined Jun 22, 2012
10,585
direction:
FWD/REV only, steering by tiller. 50k pot not relevant atm, but does reduce max voltage to wigwag pot for lower max speed down to abt 1/10th.. wigwag is a 2D see/saw with full movement, and when modded, will have << movement. the pmw mobo is difficult to alter. it is digital. the input could be ADC, and internal in the processor? it uses some SMT. i think it best to leave it alone and make a transferable plugin [for my next one too.] mobo's are replaced, not repaired, so there's no depth of local info to draw on. new ones are expensive, used not common, espec the one being sought [Murphy's Law]. only some direct interchangability exists to upgrade power rating in same series controller.
Can you post any pictures of this as it's hard to work out what is required?
 

Thread Starter

Dumb-ton

Joined Oct 16, 2022
10
quiescent state, relative to 0 not grounded.
V2=Vo=V1/2
5k pot has perhaps 1k movement from center, and from that, Vo must vary between V1 and 0., without phase inversion?
 

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