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A throttle resistor card converts only the motion and electrical network presented to it. Pedal or valve position, shaft angle, contact position, track resistance, receiver voltage and reported percentage are related but not interchangeable quantities. Mechanical stops, backlash, eccentricity, wiper footprint, source resistance and input loading can each alter the result. This guide defines how to select a track law for the useful angular sector. Product construction remains owned by the rotary-card page, while detailed center-offset geometry remains a separate calculation owner.
Key design decisions
- Define commanded position, shaft angle and contact travel in one shared datum before selecting active arc and inactive zones.
- Calculate the receiver's loaded voltage or resistance at controlled angular points, including finite input and stable series terms.
- Allocate repeatable curve error separately from backlash, contact interruptions, eccentricity and system diagnostic behavior.
Define the complete command-to-readout chain
Build a table that relates commanded throttle position, mechanical input travel, shaft angle, wiper center position, required electrical output and controller interpretation. Name direction, reference temperature and electrical state. The useful sector may be smaller than the physical rotation because landing zones and overtravel protect contact at the stops. Do not normalize an undefined mechanical span to zero and one hundred percent; first establish what the system owner means by closed, idle, active range and fully open.
Identify which conversion owns intentional nonlinearity. Cam or linkage geometry may transform command into angle, printed geometry may transform angle into resistance, and controller software may transform voltage into reported position. Applying correction in more than one location can distort the required response. The card selection record states the intended angle-to-electrical law and preserves upstream and downstream maps as controlled interfaces rather than silently compensating them in artwork.
Reserve active arc, landings and overtravel
Locate the shaft center, printed arc center, mechanical stops and mounting features from common datums. Define useful angle, assembly tolerance, stop variation, wiper width and the earliest and latest positions that must retain valid contact. Provide nonfunctional landing or collector regions where required by the mechanism. A nominal contact center inside the track does not prove that the complete footprint retains edge margin through tolerance, vibration and wear.
Center offset can create both angular-coordinate error and radial movement. Use the dedicated eccentricity analysis when those effects matter, then carry its allocations into selection. Backlash and compliance are different: they create direction-dependent or load-dependent angle rather than a fixed printed-center relationship. A shaped electrical curve may correct a repeatable coordinate map, but it cannot recover a contact that crosses an edge or a mechanism that does not return to the same angle.
Calculate the electrical output under actual loading
For a three-terminal track, define R1 from the supply end to the wiper and R2 from the wiper to reference at each angle. With receiver resistance RL connected from output to reference, the lower leg becomes R2 in parallel with RL. The output is Vs multiplied by that parallel value divided by R1 plus the parallel value. If the real topology differs, use the project schematic rather than forcing it into this example.
Include source resistance, leads, connector and stable contact terms at their actual locations when their contribution is not negligible. Keep variable contact resistance or interruptions separate because they are not a predictable curve term. State ADC input behavior, sampling, filtering and diagnostic currents. An unloaded ohmmeter sweep characterizes the card, but it does not establish the voltage seen by the controller when its load changes the divider ratio.
Vo(θ) = Vs × [R2(θ) || RL] / {R1(θ) + [R2(θ) || RL]}
- θ is shaft angle within the defined active sector.
- R1 and R2 are the track segments on either side of the wiper.
- RL is receiver resistance to the reference node for this topology.
- Vo is loaded output before controller conversion and filtering.
Static divider behavior with a declared wiring topology; contact interruptions, ADC dynamics and mechanism error are evaluated separately.
Check one angular point before fitting a curve
Consider a hypothetical 5 V track at one angle. Let the upper leg R1 be 400 ohms and the lower leg R2 be 600 ohms. With an ideal high-impedance receiver, output is 3.000 V. If RL is 20 kilohms to reference, the effective lower leg is approximately 582.5 ohms and output is approximately 2.964 V. The 36 mV difference comes from loading and must not be assigned automatically to printed-track tolerance.
Convert the voltage difference through the controller's approved position map before judging significance. A 36 mV shift may be acceptable in one system and unacceptable in another. Raising total track resistance can increase loading error for the same receiver, while lowering it changes current and the contact's electrical condition. Select the resistance range and curve together with the receiver rather than optimizing either in isolation.
| Input | Illustrative value | Review point |
|---|---|---|
| Supply | 5.000 V | Include source tolerance and diagnostic states |
| Upper track segment | R1 = 400 Ω | Value at the named angle |
| Lower track segment | R2 = 600 Ω | Value at the same angle |
| Ideal output | 3.000 V | Assumes infinite receiver impedance |
| RL = 20 kΩ | R2 || RL ≈ 582.5 Ω | Finite loading changes the fraction |
| Loaded output | Vo ≈ 2.964 V | About 36 mV below ideal |
Choose the track law and point density
Use the controlled angle-to-output table to choose a linear, shaped, segmented or multi-track architecture. Add points where required output slope changes, near diagnostic boundaries and near the ends of useful travel. Equal angular spacing may miss a sharp change in the commanded relationship. Retain independent check points that were not used to fit the artwork; a curve can pass all fitting knots while deviating between them.
For multiple channels, define each transfer independently and state permitted correlation or separation. Channel relationships, plausibility logic and fault reaction are system-level requirements; the card does not certify functional safety. Avoid routing or terminal choices that make supposedly independent signals share an uncontrolled failure path without system review. The selection record should show track count, collector and terminal ownership, but final diagnostics remain with the controller and system design authority.
Identify curve, mechanism and contact signatures
A smooth repeatable residual at the same angle in both directions can indicate track law, datum or receiver-model error. A consistent direction gap suggests backlash, friction or contact hysteresis. A periodic residual can be associated with center offset or shaft runout and should be compared with geometry. A sharp local discontinuity may arise from segmentation, a print feature, contamination or contact crossing. Random short dropouts require time-resolved acquisition rather than a polynomial curve correction.
An endpoint fault only at one assembly extreme may indicate stop tolerance or insufficient landing margin. Output that changes with receiver connection but not with unloaded resistance identifies electrical loading. Output that changes after remounting points toward alignment or support. Preserve raw angle, direction, output and contact observation so these signatures remain distinguishable. Trimming or reshaping artwork against a mixed error can create a card that compensates one fixture but fails in the controlled mechanism.
Verify from card fixture to complete throttle assembly
Measure the card on a controlled fixture with an independent angle reference and the actual receiver or equivalent load. Sweep in both directions at defined speed, sampling and electrical state. Then repeat on the complete mechanism through useful travel and overtravel without forcing the stops. Compare output, residual, hysteresis and interruptions at independent angles. Record temperature because both track resistance and mechanism behavior can vary with condition.
The system owner defines vibration, contamination, humidity, temperature, cycling, electrical transient and diagnostic tests. Measure contact events with sufficient bandwidth and state how filtering is applied. A bench sweep can establish static transfer and reveal local defects, but it does not prove lifecycle, installed airflow, safety behavior or valve response. Recheck after assembly changes, because support, shaft alignment, wiper force and connector routing can alter the result without changing printed artwork.
Release angle, circuit and acceptance as one record
The drawing package identifies shaft and printed datums, active sector, landing zones, overtravel, wiper trajectory, track and collector geometry, terminals and mounting features. Attach the angle-to-resistance or loaded-output table with direction, excitation, receiver impedance, reference temperature and local tolerances. Allocate repeatable curve error, mechanical hysteresis, contact interruption and electronic conversion separately.
For quotation, provide the mechanism drawing, schematic and validation requirements rather than only endpoint resistance. Changes to stops, shaft, carrier, wiper, track center, receiver load, ADC reference, diagnostic strategy or software map can reopen selection. This bounded handoff lets artwork be reviewed against the intended throttle system while avoiding an unsupported claim that the resistor card alone determines system accuracy, safety or service life.
Review a throttle-position resistor-card transfer
Send the angular envelope, contact geometry and loaded receiver requirements so the track law can be reviewed for the actual mechanism.
- Mechanism drawing with shaft center, printed center, stops, useful angle, overtravel and shared datums.
- Wiper footprint, radius, force, material, direction, speed and expected tolerance stack.
- Required angle-to-resistance or loaded-output table, interpolation and local allowable error.
- Schematic with supply, source resistance, receiver impedance, ADC range, terminals and diagnostics.
- Track count, channel relationship, collector layout, landing zones and mounting constraints.
- Temperature, vibration, contamination, cycling, contact-interruption and complete-system validation requirements.
The drawing-upload form loads as you reach this section.