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

[Garauld]

Not much to report this past week. I've been evaluating the cab dimensions and decided it needs to be several inches longer and wider and 4" shorter. After building the stick cab, I noticed the drive sprocket teeth would be closer to the cab than I would like. It wouldn't take a very big stick or rock to get jammed in there. Subsequently, I plan to raise the cab by adding some 1" sq. tube on top of the frame. I hope to get some of the tube today for the frame and cab and start welding.

 

[Garauld]

Being a back-burner project, it's slowly coming along. I finished the seat supports and the exhaust system is piped. I made up some misc brackets and got the radiator hoses completed. I have the foot service brake calipers and pads on order so I plan to make the support brackets for them this week.

 

[balsam]

Being a back-burner project, it's slowly coming along. I finished the seat supports and the exhaust system is piped. I made up some misc brackets and got the radiator hoses completed. I have the foot service brake calipers and pads on order so I plan to make the support brackets for them this week.

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Hi Garauld: like you, I am retired and looking for a project. Years ago I was involved with a ski hill operation where we had a Thiokol Imp to do the grooming.
I always thought it would be fun to build a lighter, 2 person cab tracked vehicle, similar to the one youæ±*e working on.
Are you still involve with it and would you allow me to pick your brain and run some of my ideas by you?

 

[Garauld]

Are you still involve with it and would you allow me to pick your brain and run some of my ideas by you?

-> Yes, I am and ask away. Other forum members may have a better idea too that they may want to share. If you wait a while until after I work the bugs out, I hope to make some extra cash selling complete drawing packages so you can built one like it.

 

[balsam]

-> Yes, I am and ask away. Other forum members may have a better idea too that they may want to share. If you wait a while until after I work the bugs out, I hope to make some extra cash selling complete drawing packages so you can built one like it.

Great! I have my design pretty well worked out except for the steering. I have a background in hydraulics, so I have decided to go that route.
Most guys seem to use an open differential with brakes and from I read it痴 a simple reliable system. I am pretty sure this was the system used on the Imp, way back.
I think I have worked out a very simple hydraulic circuit by using a variable displacement pump and runnning the two track motors via of a parallel circuit. Instead of using brakes I would, with a valve, restrict flow on side or the other to slow(or stop) one track or the other, causing the turn. The flow not going to the restricted side would go to other, speeding it up as in a mechanical differential. I couldn稚 achieve 奴ero turn radius with only one pump but that痴 not impotyant to me.
In my mind, and please correct me if I知 wrong, this would work exactly like a differential system without any brake pads to wear out or freeze up.
I remember having to pull very hard on the joy sticks to engage the brakes on the Imp, which would not be the case with a hydraulic valve.
Achieving reverse would be an inherent part of the pump itself, or a directional control valve could be used also.
I know introducing hydraulics creates a few problems in terms of efficiency and cold oil etc. but think the syplicity, reliability and compactness is a fair trade off.
I would appreciate any thoughts you might have. Too bad we couldn稚 chat about this over a beer.

 

[Garauld]

Hi - I do not have any background in hydraulics and wondered how to get enough hp into such a vehicle. Care to define some of your performance & design parameters? Got an image of your design? My biggest concern at this point is the strength and durability of the driveshaft and half axles which I plan to fabricate myself from stock Echo and Rav4 axles. I could always buy stronger custom units if they don't hold up. I had the axles tested for hardness and found them to be case hardened. If I need more force to brake steer, I could readily add a vacuum booster to each circuit - there is room under the cab in the tub to put them.

 

[The Fred]

NVH

Noise Vibration Harshness; Think before you apply to the final assembly. It's no fun driving around the woods with ear protection because your contraption is too noisy, either from hydraulics or a poor exhaust system design.

Get the exhaust heat out of the compartment sooner, maybe through the side, you'll be sorry there is no catalyst on the thing, unlike a car at speed your machine will be slow and the fumes will be difficult to handle, not to mention dangerous. Maybe run your muffler outside like a tractor or big truck.

Regards and nice work, Fred

 

[texasranger556]

The more conventional setup for hydraulic drive is two variable displacement pumps and two wheel motors, a pair for left and a pair for right. As I'm sure you know zero turn mowers, skid loaders, etc work this way. The plumbing is dead simple since the pump functions as the valve, offering infinite flow variation and reverse simply by tilting the swash plate. Two high pressure hoses per side, case drain(s), and suction.

To achieve similar flow with one pump you'd obviously need a pump twice as big and associated larger hoses, fittings etc. And like you say come up with some way to reverse flow if the pump doesn't provide it.

I have some scrap zero turn pumps that I've rebuilt and set aside for a project like this in the future, but if I was buying new, this pump is the right price albeit small depending on your design requirements:

.43 cu in Hydrostatic Kanzaki DUP-7A Tandem Pump | Piston Hydraulic Pumps | Hydraulic Pumps | Hydraulics | www.surpluscenter.com

 

[MossRoad]

The more conventional setup for hydraulic drive is two variable displacement pumps and two wheel motors, a pair for left and a pair for right. As I'm sure you know zero turn mowers, skid loaders, etc work this way. The plumbing is dead simple since the pump functions as the valve, offering infinite flow variation and reverse simply by tilting the swash plate. Two high pressure hoses per side, case drain(s), and suction.

To achieve similar flow with one pump you'd obviously need a pump twice as big and associated larger hoses, fittings etc. And like you say come up with some way to reverse flow if the pump doesn't provide it.

I have some scrap zero turn pumps that I've rebuilt and set aside for a project like this in the future, but if I was buying new, this pump is the right price albeit small depending on your design requirements:

�.43 cu in Hydrostatic Kanzaki DUP-7A Tandem Pump | Piston Hydraulic Pumps | Hydraulic Pumps | Hydraulics | www.surpluscenter.com

This is the way I would do it, too, for a skid steer type machine. Two variable volume pumps and two wheel motors. Two levers and you can control direction and speed independantly. Also, when you return the levers to the neutral position, it is effectively brakes. When you turn, it won't force the other side to double in speed, either. You could push one lever forward and the other lever backwards and spin 360 in your own length.

A disadvantage of this setup is you'll have to pick a speed range/power range that suits most of your needs. There's no two-speed range selector. So you can have low speed and tons of power or high speed and a lot less power. It's a compromise unless you come up with a two-speed setup. I know small tracked loaders have two speeds, one for working and the other for tramming between locations. Don't know how those work, myself.

My current machine is a Power Trac PT425. It has a variable volume pump and four wheel motors. It'll do 8mph tops. Fine for mowing, brush cutting, and pulling small diameter logs out of the woods, snow plowing, etc... It's an excellent speed for a front end loader. But it is not strong enough to pull large logs, pull a dirt plow, etc.... Some people have put larger wheel motors on them for lower top end speed and more power to the ground and hill climbing ability.

One put larger wheel motors, which cut down his top speed, but larger tires for flotation on the sandy beach he had. There's all kinds of stuff to figure to determine your top desired speed and low desired grunt pulling power.

 

[ArlyA]

Here is a great video explaining how variable pumps and drive motors operate for the driving of machines. Personally I think Garauld is reinventing the wheel but i'm still watching his thread!

Hydrostatic Demonstrator | Tigercat TV