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

[Garauld]

It would be nice to engineer in a little more speed than 20 MPH at 6K

-> I agree, but I don't plan to drive it down the interstate. If I didn't weld up the diff, then the speed would be doubled but the spider gears might not hold up as other posters have mentioned. Got any ideas for a speed increaser?

 

[airbiscuit]

Isn't your speed going to be the same as the vehicle the transaxle came out of times a ratio of
drive sprocket diameter/original tire diameter?

 

[Garauld]

No - there are now two differentials in the drivetrain - the original one in the engine tranny and the one I put in the front feeding the drive sprockets.

 

[airbiscuit]

Got it

 

[ArlyA]

Interesting project! Here is a few photos of one a buddy assembled. Its FS if anyone is interested. I did have some construction photos if it but I can not locate them.

 

[The Fred]

I would think seriously before assembling that transaxle to a rear diff. It's early enough to replace the drivetrain with something from a very small 2 wheel drive pickup or something similar.

I've been thinking all morning but I'm no engineer. I wish I was because I have built a bunch of crap over the years. Some worked excellent and some didn't.

Obviously it's not my project but measure twice, cut once is a good lesson.

Think about this, at 6000 RPM your machine should be approaching say 50-60 MPH (which sounds way too fast for your preference) to be able to crawl around at 10-20 miles per hour at a reasonable RPM.

The other thing I highly recommend is a Catalytic converter because there's not much worse than crawling around the woods smelling raw exhaust and possibly chancing getting sick. The technology is so good for the last 15 years that you won't lose anything by installing a good CAT but maybe extra heat in the exhaust to deal with.

I guess I would recommend buying a complete car or truck and use the instrument cluster as your gauges, everything will work as it should.

Regards, Fred

 

[Garauld]

Hi Fred -

It's early enough to replace the drivetrain with something from a very small 2 wheel drive pickup or something similar.

-> I looked over the various options early on in the design phase and decided a rear engine location was how I wanted to do it. I could always add a transfer case or some other kind of speed increaser to bump up the top speed. There's enough room in the tub frame. At this time, I just want to get it driving.

I highly recommend is a Catalytic converter...

-> I saved all the parts I thought I would ever need including the cat from the Toyota Echo. I had it stripped down to the bare unibody. I planned to install it but not the OEM muffler.

 

[The Fred]

I wonder how much work it would be to tap the mainshaft for your power before the diff reduction. I know this sounds like a bunch of work but your trans is a simple one.

http://natpronet.com/trans/U340.pdf

Didn't the Echo have a center mounted instrument cluster? You might be able to use the antilock brake computer to have more function like speedometer that could be reprogrammed or using the ABS sensors tracking a homemade toothed wheel to get your speed accurately. You might have a working cruise control too.

Such a cool project, I'm so jealous.

Electric throttle or cable? Electric throttles are so much easier.

 

[Garauld]

I have the instrument cluster but have no plans for it yet. I was looking at bicycle speedometers - there are lots of options out there using GPS. I planned to use a throttle cable as I have the OEM pedal but an electric cable sounds interesting. I have no skills in setting one of them up.

 

[MossRoad]

Speaking from personal experience with our 2013 Impala and electric throttle.... I hate that thing!

There's no feedback in your foot, and there's a noticeable time delay between foot movement and engine response. Now I know most of the delay can be prorammed out with tweaks to the program and re-burning the chip..... why do it on this machine if you don't have to? You're just over-complicating the thing and adding electronic components that do and will go bad in time.

Besides the noticeable delay in foot feedback, there is also no movement of the pedal at all as the cruise control altered speed. So you're cruising along and hit a steep hill, the old mechanical linkage throttle pedal would pull away from your foot as the cruise control added throttle to increase engine speed to keep you going up the hill, and, on the downhill side, the pedal would lift away from the floor. With electronic throttle (on the Chevy, at least), this doesn't happen. The pedal never moves. The computer increases and decreases the fuel flow without moving the pedal in either direction.

Stick with mechanical linkage if you can. It's simpler and there's less electronics to fail.