Just some random thoughts that may be helpful...
using a regular 9 volt battery, test each axle of the SPUD to ensure that all 4 wheels are picking up power correctly
(With only 4 wheels to work with,
dropping even 1 "wheel" worth of pickup reduces the loco to effectively "1 pickup point per side",
which ain't great odds in any Modeller's language...
2 - Everything else being equalk, The H&M should work fine with a decent mech. (They have a good reputation, and are fairly robust. They also tend to "play nice" with hi-precision motors, which has won them some fans...)
3 - THe SPUD and basic Black Beetle have 14:1 ratio gearing, which is waaay too high for smooth slow running under NG conditions IMHO. The custom 27:1 Black Beetles are a SERIOUS improvement, and are the only valid BB gear ratio for my $$$
4 - Black Beetles have nickel silver treads, which aids in pickup behaviour. However, as a result, they should NEVER be "slid",
(either by moving the vehicle down the rails with wheels locked, or by "power sliding"). This will wear away the nickel silver, and create a pitted surface which attracts and holds dust/dirt.
5 - In contrast, SPUDS do NOT have such coatings IIRC. This means their overall pickup is worse, and are Always susceptible to dirt/dust pickup
6 - added weight is GOOD, as long as it is Balanced over the 2 axles of the SPUD. having it "nose or tail heavy", or heavy Left <> right is only going to weight down one wheel/pickup point, and break contact with the other. Ergo, No Go!
7 - watch for PVA or other scenery adhesives creeping up the rail and creating issues, esp in the days after ballasting!
8 - this one has a number of both fans and naysayers, but I personally use graphite in "stick" form to coat freshly cleaned rails. This helps avoid dust pickup, benefits electrical pickup, and improves overall analog DC layout behaviour. I clean my track maybe twice a year, and do at least 4 shows a year. (I clean my Loco wheels once a year, and have Never needed to clean rollingstock wheels).
I have fairly high reliability and "crawl speed" specifications for my personal layouts and equipment, and graphite allows me to hit or exceed those reqquirements without significant stress mid-show...
NB the only real downside to graphite is that it is a lubricant, and as such WILL affect adhesion on grades. This can be a benefit to those of us using screamingly tight corners, as it helps the gear "slide round" the sub 9" radii curves...
9 - the Gaugemaster Throttles have already gotten a mention. I'll put my hand up to say that the tiny Gaugemaster model HH handheld throttle is THE test crawling throttle I have ever used. Don't know how it does it, but I could be very happy if it was the only throttle I was permitted to use. It's held up for me under show conditions on N, HO, HOn30, HOn3, HO, On30, and On3 use, even when subjected to "1 sleeper/minute or slower" torture tests such as crawling multiple MDC open-frame-motor-powered Shays, or a pair of seriously worn out brass Tenshodo 0-4-0 locos, (each loco measured out later at 1.2 amps under "crawl" conditions!!!)
The HH is also very well protected, and has kepth the show going where larger and much more $$$ throttles have crashed and burned....
10 - no-ones asked the question yet, but what track/rail material are you using? Nickel Silver(Peco)? Steel? Brass?
Hope this Helps,
let us know what transpires...
and remember, achieving "Good Reliable Running" is simply a case of methodically working thru the chain from one end to the other...
(try not to get disheartened, we've all been there...
Aim to Improve,
"...Just tried to test a pair of Athearn SW1500s on a layout tuned for Atlas S1/4s and Kato NW2s,
and sorely disappointed with their "track holding" behaviour,
somewhere deep in the Aussie Bush..."