Episode 17 – Controls

Quite some time passed after our last epsiode, but we are still here and work on the tractor continues and plans for the upcoming season were made. Basically building the tractor to run the german 3.5T limited modified championship, we were a little sad that the class was only booked for 2 events for the 2020 season. For us this meant, we had to make a choice what to do, if we wanted to run the tractor and collect data and experience. Either we would additionnaly subscribe the tractor for the 3.5T modified or the 2.5T light modified class. Running the 3.5T class would be no problem, but we are lacking lots of power to run that class, so the question was: Can we stay below 2700kg (which we are allowed to run with our engine configuration) to be allowed to run the 2.5T class?

Time to put the tractor and all parts on the scale …

After some math, we think that we can make it. We are actually 30kg below the red line, so that we should be able to make it, without putting everything (and maybe everybody) on a diet, only a few weeks before the start of the season.

The title of this episode suggests, that we will be reporting about the controls on the tractor, so let’s just think what controls will be needed on such a machine. Basically there is no big difference between the basic controls of a car, expect the single rear wheel breaking, as you can find it on stock tractors. But why would you want to break, when you have a 20+ ton sled in your back, who tries to stop you? Well, ass soon as you start to put (enough 😉 )power through the rear wheels into the ground, the front end of the tractor will start to lift and you lose your normal steering. The only way to control the direction in which you are going is by breaking one of your rear wheels, and force the tractor into that direction, similar to driving an excavator or tank. For this purpose, the brakes on the rear axle were changed from drum brakes, which are usually mounted on the planetaries used on our axle, to large diameter disk brakes. We went on and welded flanges to the aluminum planetary housings and mounted laser cut brake disks. The 4 piston hydraulic brake calipers come from a light truck front axle and should provide enough braking force. To control the brakes, we use an individual master clutch cylinder for each side, linked to homemade aluminum pedals.

Of course the tractor is also equipped with a normal steering on the front wheels and a steering wheel. Having build a tractor with a very narrow chassis and a very low center of gravity of the engine, there was no way to pass the engine with some kind of steering column and install a rack and pinion steering. Lots of teams run hydraulic steerings, so that we just wanted to build a similar setup. The basic idea is to just take a hydraulic pump, connect both ends directly to a 2-way hydraulic cylinder and you are good to go. Yeah … that’s just the basic idea and in reality it takes some more tiny bits and tricks to make it work. We ended up with making our own hydraulic cylinder (actually we made two versions, since the first version didn’t provide enough force to turn our wheels), modifying the hydraulic pump (these are basically not made to provide pressure in both directions of rotation), installing one-way valves together with an oil reservoir and having lots of fun to get the air out of the system.

But … we got it to work. It’s always astonishing how such a basically simple problem can take so much time 😉

Now for the must important control of the tractor, throttle control. The throttle has to be controlled by a hand operated, spring loaded lever, which you push into the forward direction. But you are not allowed to just run a wire or rope to your throttle, but the control has to work in both directions. We solved the problem by using a flexible control cable which allows a push/pull operation. Luckily, we were able to scavange this cable from an old fire truck, since these cables are quite expensive. The cable is linked to a homemade adapter, connecting both throttle bodies together.

Actually thinking about the controls, I found, that we need to install some kind of gear shifter …

… so that there is still some work before our first start, which we are planning to do end of April …

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s