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

Garauld · Dec 27, 2020

While I am waiting for my plc to be delivered, I thought I would spend a bit of gray matter computer time thinking of a possible door vent window. Here's the concept I am leaning on. The window panes will be 1/8" acrylic which is colored green in the attached image. The small slider window measures about 5.5" high x 11" wide. This view is inside looking out and right is forward. Your thoughts?

ArlyA · Dec 27, 2020

Garauld said:
While I am waiting for my plc to be delivered, I thought I would spend a bit of gray matter computer time thinking of a possible door vent window. Here's the concept I am leaning on. The window panes will be 1/8" acrylic which is colored green in the attached image. The small slider window measures about 5.5" high x 11" wide. This view is inside looking out and right is forward. Your thoughts?

A window that slides and has a channel to do that in, is problematic in snow.

Garauld · Dec 27, 2020

A window that slides and has a channel to do that in, is problematic in snow.

-> I cannot disagree with you Arly. I'll look into a hinged awning-type window.

Garauld · Dec 31, 2020

My PLC for the track slippage warning system (TSWS) came yesterday and I got to play with it and get it working on my desk. Here's my bench-test setup. The PLC is the black square box at bottom left. To recap, the PLC will receive pulses from a sensor monitoring each drive axle rpm and compare them. A substantial difference in the counters will light up the appropriate LED on the dash to show which track is slipping from lack of traction. I can then brake that side to add torque to the opposite track. I hope to get the system installed before the next big storm. Does anyone need a system like this? Happy New Year everyone! :thumbsup:

Xfaxman · Jan 1, 2021

Don't need one.

strantor · Jan 4, 2021

Garauld said:
My PLC for the track slippage warning system (TSWS) came yesterday and I got to play with it and get it working on my desk. Here's my bench-test setup. The PLC is the black square box at bottom left. To recap, the PLC will receive pulses from a sensor monitoring each drive axle rpm and compare them. A substantial difference in the counters will light up the appropriate LED on the dash to show which track is slipping from lack of traction. I can then brake that side to add torque to the opposite track. I hope to get the system installed before the next big storm. Does anyone need a system like this? Happy New Year everyone! :thumbsup:

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I've devoted a lot of thought to high speed skid-steer vehicle control over the past few years, heck I guess it's been a decade, or ever since Ripsaw came along. I have lots of ideas but no time to try them. It seems you have a lot more time than I do, so I'll throw a couple of ideas out and maybe you'll find one of them promising.

Hydraulics are horribly inefficient compared to the mechanical drive that you have. The efficiency of the mechanical drive is diminished by side-braking to steer. IMO it would be best to redirect power from one side to the other rather than dissipate it into a brake on one side. Yes, I realize that when you brake one side, the diff "redirects" the power to the other side, but you're still wasting an appreciable amount of energy (I think - never done the math - have you?)

To redirect the power you could use a number of means. Hydraulic solutions, mechanical solutions, electrical solutions. The Hydraulic solution would involve a pair of variable displacement swashplate pumps, hydraulically cross-connected, and mechanically one pump coupled to each side of the diff. I know I said hydraulics are inefficient, but this wouldn't be so bad because the hydraulics aren't driving the locomotion, just augmenting it. Cruising in a straight line, the swashplates of both pumps are straight, no fluid is being pumped. You want to turn, you pull a stick that's connected to both swashplates, one pump turns into a pump and the other one turns into a motor. The pump feeds the motor. Basically a hydrostatic supplemental system. The power is redirected in a controlled manner and the jerkiness of mechanical side-braking is gone.

The electrical solution is probably the best, and the most expensive. Same concept, a pair of wound field DC motors is coupled to either side of the diff. You move a joystick which turns a rheostat controlling the field current of one motor and it starts producing higher voltage (power (drag)) which feeds the other side; one side turns into a generator and the other side a motor powered by it, resulting once again in a smooth turn. You could do this with more advanced technology, induction motors and VFDs, servo motors and amplifiers, BLDCs, the more advanced you go, the more control you have. You could program it to have steering force proportional to cruising speed, so can turn on a dime in your driveway without turning on a dime on the interstate and flipping.

I think my favorite is the mechanical solution. Simple, cheap. A variator is coupled via intermediate shafts to both sides of the diff. Maybe variator isn't the right word... CVT? I'm sure you're familiar with the "torque converter" setups that snowmobiles use? Two variable diameter pulleys whose diameters vary by opening or closing half-sheaves. The belt naturally conforms to the pulleys as they change. These are normally outfitted with a centrifugal clutch in the driving pulley and spring closer in the driven pulley, but you could roll your own where the two pulleys are opened/closed on demand from a cable or a lever. They could be arranged so that they ride on a fulcrum; when one opens the other closes and vise versa.

The point of these ideas is to maximize efficiency and improve high speed control. I didn't think you would need that until you mentioned it now being capable of 50mph. Can you imagine driving that thing 50mph and squeezing the brake on one side? Honest question, you have more experience with tracked vehicles than I do, especially in the design. To me it seems scary as ****, but maybe it isn't.

Garauld · Jan 4, 2021

Awesome feedback - thanks! Yes, theoretically, it could go up to 50 mph and it would probably be a bit scary unless it was on a really smooth location like a lake. I was more interested in getting the rpms lowered at a more reasonable travel speed of 20 mph. Prior to installing the inverted transfer case, at 20 mph, the rpms would have been approx. 6500. Now, I calculate them to be about 2300. I have had little experience with tracked vehicles unless you consider operating my mini excavator or an old Terratrac dozer.

strantor · Jan 4, 2021

Garauld said:
Awesome feedback - thanks! Yes, theoretically, it could go up to 50 mph and it would probably be a bit scary unless it was on a really smooth location like a lake. I was more interested in getting the rpms lowered at a more reasonable travel speed of 20 mph. Prior to installing the inverted transfer case, at 20 mph, the rpms would have been approx. 6500. Now, I calculate them to be about 2300. I have had little experience with tracked vehicles unless you consider operating my mini excavator or an old Terratrac dozer.

Ok I understand. Well you can go fast now if you ever want to. I thought of a better way to say what I meant: If you want to go fast, (I think) you're going to need an efficient way to finely control the ratio of left:right side rotational speed. Something that doesn't involve mashing brakes. But I could be wrong. I believe the original ripsaw still used left/right braking, and it was pretty dang fast. But I never did learn how they controlled the brakes, and I don't think they're using brakes anymore.

Fallon · Jan 4, 2021

strantor said:
I've devoted a lot of thought to high speed skid-steer vehicle control over the past few years, heck I guess it's been a decade, or ever since Ripsaw came along. I have lots of ideas but no time to try them. It seems you have a lot more time than I do, so I'll throw a couple of ideas out and maybe you'll find one of them promising.

Notes on Tracked Vehilcle Steering is a cool look at the many diff steering types for tanks. Most are pretty complex.

Wit electric cars becoming common, I bet it's not to long until we can start foraging electrical drive trains for this kind of stuff. Not going to be that long range for a while, but plenty for some joyride & recreational stuff. Trivial to vary the speed on a pair, or even do neutral turns. Matching speed on a pair of electroc motors is pretty trivial (just look how much it took the OP to make his track slip detector).