I’m making a test rig for accelerator pedal and need to apply a force between 15 Nm -50Nm to the pedal.
Currently I am considering how suitable the Invenscience i00600 Torxis Servo 1600 oz.in. 1.5 sec/90 deg
SKU: POLOLU-1390 would be to apply the force to the pedal.
Alternatively I’m happy to use linear actuators but have found in the past they lack the position control I require. It is possible alternative linear actuators with position control may solve this issue.
Does anyone have any advice as to what approach would be most suitable and the tradeoffs for either method?
To hit 50Nm of force with a linear actuator shouldn’t be too difficult. The weakest Glideforce linear actuators we stock have a max dynamic load of more than double that. We also have linear actuators available both with and without position feedback. The position feedback in this case is provided by a potentiometer linked to the shaft position.
Was position feedback of your actuator/servo the only feedback you required for your system, or do you need to know the force applied to the pedal?
Hi @Glenn193950 - you could apply a torque directly to the pedal axle but that requires a very beefy servo indeed. Trent’s suggestion of a linear actuator will allow you to use the pedal as a lever arm and rely on mechanical advantage of the pedal to generate the torque you desire.
You mentioned you’ve had trouble with linear actuators in the past because they lack position control. I would say that you should be more interested in pressure feedback from the brake line. While these methods will generate force quite well, they won’t have any force feedback. Without monitoring the brake pressure you’ll have no way of knowing what the true force being applied to the pedal is. Your pedal master cylinder should have a datasheet that will be helpful in converting between pressure/displacement/force/torque and an brake pressure sensor is the missing piece of the puzzle. By measuring brake pressure you could work backwards to find the torque that’s being applied.
There are torque feedback servos out there, but it’ll be up to you to do the mechanical advantage conversions to make their feedback translate to a torque at the pedal. A beefy servo with a cam coupled onto the horn could press on the pedal. The cam would convert the rotary motion of the servo into a precise linear motion at the face of the cam.
What an interesting project! Can you provide any more context as to the “why”? Why might somebody need to be measuring brake pedal torque?
This sounds like it could be related to Formulae SAE - is that the case?
Who mentioned brake pedal. I can’t find a mention of that anywhere above except in your reply.
As an answer to your question as to who would want to do this, when did you last have a rego inspection on you car. That little slip stapled to your rego check report not only records deceleration but the pedal force to obtain that deceleration on what used to be known as a “Tapley” meter. Don’t know what the modern equivalent is called but it is that important looking box the mechanic puts in the car when taken for a test drive.
Cheers Bob
What sort of position control do you want. The mechanics driving 3D print heads and milling / laser heads
are usually linear actuators of some description and the positioning of these is pretty fine. Usually driven by steppers but sometimes by 2 wire DC motors with obviously some form of positional sensing as distinct from steppers which are driven a specific number of steps to reach a pre-defined position.
I agree with Trent that a of linear actuator with some form of position feedback would be your answer here. As he says I don’t think most of the commonly available hobby servos would have enough grunt for this task.
As for relative precision I think the linear actuator would win. The word “precision” has been bandied around a bit regarding servos. I don’t profess to know the definition of “precision” but most servos require a pulse width change of 1000µsec to move 180º. Now 1000 / 180 = 5.55555.which would be the number of µsec per degree. I could be wrong ( haven’t looked yet) but I don’t know that the Arduino “Servo” libraries would get down to this accuracy so when I get time I am going to do a bit of experimenting to find out one way or another. It might be a case of it is very close. That may be but my interpretation of “precision” might differ.
Seems i misread and this is for an accelerator pedal
so pressure sensing is out. Perhaps load-cell feedback would be appropriate then? There are disc versions available that look like they will work well in-line. Or a classic bar-style load cell
Thank you all.
I would like to operate an accelerator pedal preferably using a servo and would like to understand if this servo would suit ’ i00600 Torxis’.
The force required to start the pedal movement is around 15N and builds up to around 50N
“N” what. Newton metre or newton centimetre.
Here is a handy conversion site.
That seems to be a very hefty servo when they are lifting 100lbs to test it. If you Google “i00600 Torxis” you will find a data sheet which I assume you have already done. You should be able to make a judgement once you establish what your Newton units are.
Cheers Bob
It seems @Glenn193950 means a linear force applied to the pedal of 15-50N
A servo could totally do that @Glenn193950 but you’ll need to either:
convert the rotary motion into a linear motion to press on the pedal eg. with a cam or linkage
couple the servo directly to the pedal shaft
Both have their advantages and disadvantages, both have their own failure modes. Do you just set a position and trust the servo will drive the pedal or do you have some feedback mechanism to safely constrain the system within a certain angle?
How far does the pedal need to travel? if you are pressing the pedal with a linkage that will determine your linkage design and mechanical advantage. The servo you have specced is certainly powerful enough - probably a bit overpowered to press 5kg through a linkage.
I’m imagining something similar to this (source)
where the servo horn is the crank. The travel distance of the slider (pedal pusher) will be determined by the length of the crank, which also affects mechanical advantage, which will determine what torque rated servo you need to use.
Hi Michael
Force is Nm and the set up is similar to your image from the servo horn to the pedal via a crank and push rod. I was looking for if anyone had experience using the Torxis servos.
I dont have direct experience with the Torxis servo’s, but any staff members should be able to help with questions about them, what were you after?
Liam
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