My Senior design project - a "Swamp Thing" tracked vehicle clone

[Garauld]

...have you considered laminated wheels?

Thanks for the link. I have seen these but have not really considered using them. I wonder how effective they would be to handle the side loading they would experience. In any case, I am nearing completion of installing four wooden wheels on Snowzer. Here's a couple of images showing them.

 

[MTGreen]

My first thought here is what happens when you hit a substantial bump at speed? A tire alone will deform considerably and provides a cushioning effect on the rest of the suspension and ride. I understand that cushioning is not the goal here; but when that tire deforms in response to said bump it would seem that the wooden portion will strike the tracks and experience shock loading as well as having lateral forces applied from the tire bulging.

 

[Garauld]

A valid point - look closely at the middle photo and you'll see the rubber tread that I cut off the original tire - that should add some cushioning. There should be no direct wood-to-metal contact occurring on except on the sides. I am not worrying about the wooden construction too much as it is made from multi-ply plywood with cherry and oak on the outside faces for wear resistance. It is all glued together with Gorilla urethane glue and should not come apart. I'd gladly like to hear if anyone has a different suggestion on how to make a 5" wide, 16" OD flat-proof tire to handle side loading. Keep in mind I did look into filling the original trailer tires with 2-part rigid foam but it was expensive at about $130 per tire. As a side note, I plan to install the previously defined chain drive system to the rear sprockets this spring. Due to the tight spacing between the tire supports and the frame, I have to reduce side-to-side movement of the tracks so collisions do not occur. The new wider wooden wheels should do that (I hope).

 

[ArlyA]

Did you guys get snow there?? And thanks for posting updates.

 

[Garauld]

6" a week ago. Just a dusting last night.

 

[Garauld]

One of the things I think can be improved is the feel of the brake steering sticks. I think I initially used the wrong kind of master cylinder (MC) - one that is used to operate a clutch. The feel is very mushy as though there's air in the system. I've tried numerous times to bleed it and nothing made it better. The sticks also have to travel a ways before enough pressure is generated to initiate a turn. I wonder if the MC, when it retracts, is pulling the caliper pistons back from the pads/rotors too far. The Echo OEM MC has two plungers, each 13/16" dia. I played with cad today and laid out how I could install and plumb the Echo MC. Looking at the attached image, the pink cylinders are small check valves. When the steering lever is pulled, both MC plungers push fluid to the caliper pistons to take up any gap between the pads and the rotor. As pressure builds, one of the check valves acts as a PRV (at about 14 psi crack pressure ) and vents fluid back to the reservoir. The second plunger continues to act normally. Suggestions / comments?

 

[pmsmechanic]

If you had a clutch MC there would only be one outlet port for the slave cylinder. What I would try is to plumb the lines so that both outlet ports operate the slave cylinder. Eliminate the return to the reservoir. I don't know why you have 14 psi residual pressure valves. It would be like having your brakes partially on all the time. Disc brakes in an automotive application normally operate with no residual pressure valves. Drum brakes usually run with about 5 psi residual pressure valve. There are different residual pressure valves if the master cylinder is on the firewall or under the floor boards but I don't remember which requires what.

 

[Garauld]

If you had a clutch MC there would only be one outlet port for the slave cylinder.

Yes - that is what I have currently installed. The image shows the OEM Toyota Echo brake MCs. I need the return to pass flow and bleed excess pressure off the primary plunger so I get full pressure from using only the secondary plunger area. The primary plunger is only there to help push the caliper piston quickly up against the pads - does that make sense? The check valves crack at 14 psi. In the image, the line to the caliper bleeds off return back pressure thru the secondary plunger port which does not have a check valve in it.

 

[pmsmechanic]

Ok I see what you are doing.

Do you have single piston calipers? I'd almost be tempted to add a second caliper and use the brake MC to activate both calipers.

Is the mushiness from flex in the linkage? Maybe some ceramic brake pads would give enough grip to enable you to turn with less effort.

I'm just tossing out ideas.

 

[Garauld]

Thanks for the ideas. There's not enough room for another caliper as I already have two on each rotor. The second one is for a service brake - see image. I may try the ceramic pads.