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

[Garauld]

I've been thinking about the second caliper idea. Obviously, I still want to keep the service brakes but I was wondering if it was possible on each caliper to take a tee plumbed so fluid can come from both the service MC and the steering MC and insert a small "shuttle" into the straight run of the tee. The branch of the tee would be piped to the caliper. The shuttle would be a small cylinder with tapered ends that would be able to slide back and forth as it is pushed by pressure from the active MC to seal off (plug) the inactive caliper piping port. Hmmm. Do they make these? I'll look for a couple later.

 

[pmsmechanic]

I know you can purchase single piston rear calipers that have a mechanical park brake built in. VW's and Audi's come to mind as I'm familiar with those models.

 

[Garauld]

Good idea but in this case, there's no room for utilizing the parking brake hardware. I found some 3-way shuttle valves which is what I was thinking of.

 

[Garauld]

Another option I am looking into - bolting a smallish diameter rotor (9") onto the input flange of the front differential and use it for my service brake. A 1985 Honda Civic rotor will fit nicely. I would then repipe the ports from each steering MC to the two existing calipers on each side of the diff. I think this may end up being the best solution by doubling the brake surface area. Here's a model layout.

 

[Garauld]

I am looking into another slight modification that will provide better access to the track tensioners as shown in the attached image. I plan to accomplish this by lowering the support wheel axles by 1" effectively raising the chassis.

 

[Garauld]

If you have seen some of the running gear photos, you may have seen that there is no real "suspension" in my current design. Each set of two support wheels are attached to a walking beam that pivots around a central axle and has hard stops to limit travel. I've felt strong whacks when the beam hits the stop when traveling over bumps. I fired up the cad system yesterday to come up with some kind of springing that might soften the end stops. I might add a fork gaiter (not shown) to protect them from debris. Comments?

 

[MTGreen]

That seems to be pretty close to the pivot point of your rocking beam fulcrum and from lever mechanics you may need a very strong spring assembly (and correspondingly very rigid mounting points) to make a difference depending on the articulating mass distal to the spring/strut attachment point. You also may find you would need a progressive type spring for the application that may be challenging to calculate for and locate. Another thought is do you really want a spring on a rocking axle? It seems it may actually make for a rougher ride as I thought the suspension's ability to adapt to terrain depends on the free articulation of the rocking beam?

I also think that as you recognized the open strut assembly is unlikely to stay clean and unencumbered during operation.

Another alternative is to make springed bump stops where you have short/stiff springs topped with a traditional rubber stop. Pros here are reduced bump stop slamming/banging and simpler design/lower cost, while cons are you don't have the shock dampening effect at partial articulation that the strut would provide. You also would have more mounting flexibility as these could be installed either on the frame or on the articulating beam.

A third alternative is to use the springed bump stops in combination with shock absorbers instead of struts. This will allow articulation dampening coupled with bump stop dampening but may have fewer downsides than the struts.

Regardless of the direction you go, thanks for sharing your ideas here

 

[Garauld]

Great feedback - thanks! Those spring you see are pretty stiff at 313 #/in. As this is a prototype project (as well as something to keep me busy during retirement) keeping costs down is important so I bought a set of (16) high (.600) lift valve springs for an LS engine for $35 delivered. The full travel is calculated to be about 1.3" hence the need for two springs on each side. I could move them away from the pivot for more travel if needed. I wanted to have the springs in hand before I finalized the design.

 

[MTGreen]

Great feedback - thanks! Those spring you see are pretty stiff at 313 #/in. As this is a prototype project (as well as something to keep me busy during retirement) keeping costs down is important so I bought a set of (16) high (.600) lift valve springs for an LS engine for $35 delivered. The full travel is calculated to be about 1.3" hence the need for two springs on each side. I could move them away from the pivot for more travel if needed. I wanted to have the springs in hand before I finalized the design.

I edited the post and put in a few more thoughts while you were writing that might be useful
Edit: If keeping costs down I imagine repurposed valve springs - maybe a cluster of 4 would be ideal for the springed bump stops as well

 

[Williy]

Back in the 50's my grandpa toke an old 18 wheeler tractor
toke old tires and wrapped them around the back rims and
wired them on so no air needed and it worked great for him
as a tractor.

For your wooden wheels I would have bolted some metal on
the outside of the wood for more support.

I don't know if you have checked out tractor supply for wheels?

willy