The OpenSimWheel direct drive steering wheel I built recently has completely outclassed the Logitech G27 pedals and shifter, so I’ve decided to upgrade my pedals. I’m after hydraulic pedal feel, smooth action, long pedal arms, and a more realistic progressive brake pedal. I’d like some Heusinkveld Ultimate pedals, but they’re out of my price range. So I built some pedals with similar features and layout, out of recycled timber.
I built them using scraps of some leftover 100 year old fence palings, which are a nice hardwood when you’ve taken off the rough surface and old paint.
I laminated three pieces of this 15mm thick hardwood for each of the pedal arms, cut out with a jigsaw, shaped with a coarse sanding disc on the angle grinder, and finally smoothed with an orbital sander and finishing sander.
I couldn’t find any suitable bronze or nylon bushings for the main pivots, so I’m using some 608-2RS sealed cartridge bearings. These are the same size bearings which are used in skateboards, and readily available. I drilled holes for the bearings with a 22mm Irwin Speedbor Max drill bit, because I found that a standard spade drill bit doesn’t give an accurate enough hole size. The bearings are epoxied into place. I was debating what to use to space the bearings apart, and I could have used a couple of 10mm skateboard bearing spacers. I needed about 25mm of spacing between the bearings to fit the pedal arms. In a moment of inspiration, I realized that M10 nuts were just the right diameter, with a flat surface the ideal diameter for sitting against the inner race of the bearings. The bearings are sitting on an M8 bolt.
I’m using a Century C838 spring for the throttle (2.45Nm/mm), a stiffer spring for the clutch (initially a stock G27 brake spring, but it works better with a GT Eye progressive spring – approx. 6Nm/mm), and a short spring (approx. 6Nm/mm) combined with 72mm of 70A Fibroelast urethane elastomers for the brake. The white Fibroelasts urethane springs are 20mm outer diameter and 8.5mm inner diameter.
The springs are sitting over a 6mm threaded rod cut to length. To allow the 6mm threaded rod to slide smoothly inside the fibroelasts, I discovered some 8mm Teflon (PTFE) tube with a 6mm inner diameter on eBay, which works a treat. It allows the rod to slide smoothly through the hole in the timber backplate of the load cell, allowing the springs to compress with minimal friction. The throttle feels eerily friction-less prior to adding the hydraulic damper. I’m using good quality Rose joints (rod ends) where the spring stack connects to the pedal arm, which have a 6mm female threaded end to fit the threaded rod, and a Teflon liner to make them smooth and slop-free.
I’m using a load cell for each of the pedals, in an angled arrangement. These are reliable and durable. Pots also would have also worked ok for gas and clutch. The brake uses a 70kg load cell, clutch 30kg, and throttle uses a small 20kg load cell. To make the pedals quiet when returning to the extended position, I’ve used some white eva foam from an old running shoe mid-sole. I drilled a hole in the centre of a cube of this foam, mounted it on a bolt in my power drill, and sanded it into a circular shape so that I could make thick foam ‘washers’ to sit on the back side of the spring stack and quieten the extension.
The picture below shows the brake spring stack at the top, throttle on the right, and clutch spring on the left. The brake and throttle pedals geometry is such that the spring pivot stays approximately perpendicular to the pedal travel. When the brake and throttle pedal are half way through their travel, the spring stack is perpendicular to an imaginary line between the rose joint and the main pedal arm pivot.
Some might say that the throttle could use a potentiometer, since it is position sensitive, unlike a brake which should be pressure sensitive. However, I like the durability of load cells, and it’s much easier to keep it all in nice alignment when you’re making it out of wood. A tiny little linkage to a potentiometer might not work well with timber construction. In terms of linearity, the coil spring on the throttle will be increasing in force in a roughly linear manner, which means that the force measurement by the load cell will actually be a close approximation of position.
The brake pedal spring stack is exploded below. The elastomers slide smoothly over the PTFE tube. I have used two nuts and a small m6 washer as a stop for the coil spring (just above the coil spring in the photo below), as well as holding the length of PTFE tubing in place. I cut the length of the PTFE tubing precisely so that the coil spring can compress about 6mm before the m6 washer hits into the m8 washer of the first fibroelast. This means the coil spring is only compressed 6mm, before the load is entirely supported by the urethane fibroelast bumpers. This gives the brake a two stage feel.
The spring support for the load cell on the brake and throttle is made up of several pieces of timber glued together and sanded into a suitable shape. It sets the spring at 45 degrees to the load cell. This allows the load cell to be hidden in the base of the pedals, where it is bolted to another piece of timber glued across the base.
The clutch has a regressive action, with a linkage that pivots upwards on a couple of sealed bearings. The load cell is anchored at the top rear of the base. As the pedal moves into it’s travel, the stiffness decreases and the spring rotates upwards on a pair of bearings (hidden behind the bolts which are covering the spring in the pic below).
You can see the 608-2RS bearings in the spring backplate, epoxied in place. I used a long 8mm bolt and some m10 nuts and m8 washers to hold the bearings straight while gluing them in place. They need to be properly aligned to run smoothly.
A pair of 8mm bolts hold the bearings onto the outer support which is then bolted the load cell. The clutch spring backplate will tilt upwards as the pedal is compressed, so that it has less leverage the further you press the clutch pedal into it’s travel. The spring will be more perpendicular to the load cell as it rotates upwards at the end of the pedal stroke, so the signal from the load cell isn’t linear with clutch pedal movement – but it makes no practical difference on the clutch, which is usually just pushed in or out.
I purchased three adjustable Bansbach oil dampers, which have damping that can be adjusted. They aren’t cheap, and form a large part of the cost of these pedals. I’m using a compression-only damper for the throttle, and bidirectional damping for the clutch / brake. The throttle damper is the small one. It isn’t as smooth and durable feeling as the big chunky ones for the clutch and brake due to it’s smaller diameter, but it also has less damping which is better suited to the throttle. The more spring force being used, the more damping you want. The brake feels very damped the way I have it set up, with the damper pivot sitting above the spring stack, but it seems quite realistic and easy to modulate. I bought all the dampers off ebay. The large dampers were surplus stock I bought for a good price. I bought the small one with compression only damping from bansbach USA, and it was quite expensive at around $80 USD. Make sure you understand the model numbers before you buy dampers, you don’t want gas springs for example. It is important to choose dampers that have sufficient travel to suit your design geometry. I sketched accurate drawings of the pedal geometry, and the distance they travel. I went for a 50mm travel damper for the gas pedal, and 100mm travel on the other two. It depends how high up the pedal arm they are attached, and how much pedal movement you need, but I probably wouldn’t recommend 25mm travel dampers. Keep in mind that these ‘X’ models of Bansbach damper do not have a floating piston, which means they will move about 20% before engaging the oil damping (at either the start or end of travel depending on which way up they are sitting). These ones are fully adjustable, you pull the rod out to full extension and then you can turn it to fine tune the damping rate. I have the damping at minimum on the large dampers, and mid range adjustment on the throttle damper.
I made some donut wooden spacers for the back pivot of the clutch and brake dampers, and cut a piece of 8mm PTFE tubing to act as a bushing between the damper ends and a 6mm bolt.
These pedals work really well. I like having nice long pedal arms and the curved pedal foot plates are really comfortable. The dual stage brake spring stack is nicely progressive, and it combines with the damping to make them more realistic and predictable than the G27 pedals. The damper on the throttle makes me apply the throttle a bit more smoothly out of corners, rather than stomp it down. The regressive clutch is nice, and it feels more realistic with damping. However, I wonder if the clutch would be faster for iracing without a damper, because you only need to punch the clutch straight in and out as fast as you can. It has been a complex build, and an enjoyable challenge. The geometry of the pedal arms, load cell angle, spring rates (which go up by the square of the leverage ratio), damping, and clutch linkage are all important to get just right.
I think they look a lot nicer made out of wood rather than plates of stainless steel bolted together.
I have wired up three DIY load cell amplifiers with low pass RC filters, connected to the STM32F4 Discovery USB controller board in my OSW. An easier option for load cell amplifiers is to buy some from Leo Bodnar. I’m not getting any EMI interference at all from my direct drive wheel with this setup, an advantage of using wood.
Here’s a pic of the brake pedal. You can just see the timber brace which holds the load cell in the base, roughly half way along the base, under the spring. The brown outlines show the timber supports bolted to each end of the support. The support closest to the pedal arm is glued into the base, and is actually several pieces of timber shaped to wrap around the sides of the load cell end for strength and a larger gluing surface onto the base (it has to support 70kg). The support on the left side is not attached to the base, and it takes the load at a 45 degree angle from the spring stack and applies force to the load cell. The yellow lines are roughly where the bolts are holding the load cell in place. Both the brake and accelerator pedal have a similar arrangement, the brake just has stronger/chunkier timber supports to handle the 70kg force being applied to the load cell. The 70kg load cell seems about right for the brake pedal, I have to push very hard to get maximum force.
They work great. Predictable braking feel, plenty of feedback from the throttle, and they feel really nice on the feet.