More Mule then Rover?

[Tommy_T]

gotta wonder....
this season's task was a standup mower using (2) 4 pole 1000W servo motors(mowing 2 acres a week).

the frame used was a commercial 48" brand(gravely) that weighed 300lb alone, with
me ,batteries,servo motors and brackets, and gas engine the weight of that task was
greater then the mule's winter weight(with empty bucket).

the mule is now using (4) 2 pole open-loop motor(watt rating not supplied), if the
sabertooth 2x60 can survive the standup mower task, it should survive running (2) 2 pole motors in parallel.

the main drive train is 10 teeth on the motor output shaft, and 30 teeth on the drive axle with 18" tires,
the front uses 10 teeth on the motor output shaft, and 21 teeth on the drive axle with 13" tires, so they
should respond at the same ground speed.

using 1 sabertooth 2x60 and fused at 160Amp to power all four motors would be sweet.




from the manual of the sabertooth 2x60

Out of the box, the Sabertooth can supply two DC brushed motors with up to 60A each. Peak currents of 120A per channel are achievable for a few seconds.
Overcurrent and thermal protection means you'll never have to worry about killing the driver with accidental stalls or by hooking up too big a motor.

[Tommy_T]

not even going to try it...

if I could pick the mule up and bring it back home if it fails when it's dark and -20degf outside
then it would be worth looking at. but I currently can't.

having two different drive systems would at least give me a way to limp back home if one fails.

the drive never failed last winter, last failure was a 17mm axle, now using 25mm axles.

[Tommy_T]

found a small briggs engine with 12vdc starter motor on craigslist for $100 to power the 24Vdc 100A alternator for the mule.


started first try and doesn't smoke (sweet!)

seems to be a 1982 engine that has not seen much use.

hope to use the engine's 12vdc charging system to charge the 12vdc battery used
to power the mule's control/lighting systems and starting the engine.

24vdc batteries only going to power the (3) Sabertooth speed controllers
(1) 2x60 (rear drive motors)
(1) 2x32 (front drive motors)
(1) 1x50 (lift/dump) plan to replace with a 2x60 at some point(powers 1000W motors)

[jwatte]

started first try

Nice!

Also, looks like just the right size to run that 2.4 kW generator. And at $100, it sounds like you got a good deal!

[tician]

Just needs a new boot on the spark plug connector... and might be a bit under-powered for that alternator at full load. 1[hp] is 746[W], so even 100% conversion efficiency won't give you full 24V 100A. Worse still is that the nameplate ratings are usually quite optimistic with output significantly decreasing over time, and the 12V starter battery charger may cut that rating further.

Lost power again for several hours Friday night because of an unexpected storm, so that reinforced my desire to turn the engine from my current pull-start push-mower into an emergency generator whenever I finally get my rover mower up and running safely - been neglecting projects because of work. Honda being Honda, the engine still runs quite well after ~15 years of use (30~80 hours a year) with only ~3 attempts at maintenance over that period (two in the last three years). Ran the first blade without sharpening/balancing until it finally wore so thin hitting pine cones and sticks that a chunk broke off 2~3 years ago, and that was also when I finally changed the spark plug for the first time... Given that prolonged abuse, it could use a full rebuild to clear out the grunge that has undoubtedly built up, which would also let me figure out the exact source of the oil that sometimes collects on the cutting deck when left in storage. As part of the rebuild, it would also get a larger intake filter system and a proper muffler because it is a loud little 5.5[hp] engine.

[Tommy_T]

And at $100, it sounds like you got a good deal!

jwatte, I don't get buyers remorse too much anymore, now I just think what's plan B.

might be a bit under-powered for that alternator at full load.

tician, it just got even more under-powered for this build, the documentation for the engine
lists the on-board charging system as 6W, to continuously run the cameras/lighting and control
systems I'm going to need 100W charging. so I'm going to have to add a small 10A 12v alternator also.

proper muffler because it is a loud little 5.5[hp] engine.

when I started the 3.5hp engine, the first thought was how quite it was compared
to the noise my 14hp motors make.

the hardest part of this upgrade(gas engine) is going to be controlling the noise, because the
mule has to operate late at night, and early in the morning.

[jwatte]

I'm going to have to add a small 10A 12v alternator also

I would look into a DC/DC converter that outputs 12V 10A from the 24V rail instead. A little bit of electronics is generally lighter and more robust than anything mechanical ...

[Tommy_T]

I would look into a DC/DC converter

jwatte, that's what I used last winter, but had problem when a high load on the drives
dropped the 24v too low, and the dc/dc converters shut down causing the cameras to reset.

not a big problem but, I had to wait for them to reset.

this winter the load on the battery should be even worse with the four wheel drive connected.

so I'm running all control/cameras/lighting on a separate battery(12v)

it's possible with the alternator running it may not happen, but I'm not always going to have
the alternator running.

[jwatte]

I imagine you could use a diode and a 12V DC converter to keep the 12V battery topped off while the motors aren't stalling out? Or do you think you'll just have < 15V on the 24V rail most of the time?
Even if the 3.5 HP doesn't manage to generate 2.4 kW, it will still presumably extend the runtime somewhat significantly, as long as the 24V converter/alternator generates charging current even when not running at full rate.

[Tommy_T]

< 15V on the 24V rail most of the time?

jwatte, it's possible with four wheel skid steering that it could drop below the dc/dc cutout
voltage every time I do a ZRT(takes lots of current).

Even if the 3.5 HP doesn't manage to generate 2.4 kW, it will still presumably extend the runtime somewhat significantly

because the four drive motors are 500W motors I'm betting the 3.5hp engine can keep the battery system at 27.1v
most of the time, and also power a small 12v alternator which is going to have very small load(100W).

if not, plan B is 6hp

the mule is also going to have 500cfm blower to control the alternators temperatures (on when over 150degf).

the question of how much of the alternators temperature is due to belt friction has been on my mind, so for this
build I'm using #20 chain to power the alternators.