danlrc

3:1, geardowns, 10 tooth pinion.....
All the terms, but what is the actual ratio of some of these gearboxes?

Even a close estimate?

I was going to count motor revs (turning by hand) and count wheels revs to get teh ratio on a Tamiya box with Schumo reducer, but its really high- too high to count it like I tried.

Reason I ask is I want to play with trying to make a belt drive (mini-timing belts) like we use on scale R/C boats - very quiet, strong, no lube, easy to ajust, flexible location of output shaft, will slip with no damage if overloaded.
I suppose somebody might have looked at this before?
Thanks.

BIGMIG

I did a 1/12 scale abrams using geared tooth belt and pulleys and it worked OK.Most likely a lot different set up than what you have in mind.It was something different,but i did two more of them the same way a typical HL tank is set up and it was a lot cheaper and easyer for me that way.Not sure how your boats are set up,but hope you post your project on hear as it sounds interesting.

BIGMIG

Should note here I still used the standard metal gearbox with a pulley on the gearbox and a belt from there to a pulley on the drive shaft.One setup like that for each track.

1sgt

Could you post some pics of the belt drive that you us e in your boats.

Jim

danlrc

Here's a quick sketch of a typical boat drive set-up and a first cut at a design for a tank. Also some pics of the components and one of the online sources.
For my 3ft tugboat, I have only a 4:1 reduction - that's plenty to slow the prop at the desired RPM. But in tanks, the reduction has to be much greater to get the power and very slow RPM needed. I just guessed at a reduction of 500 or 600:1. The tank drive box can be much smaller than I show with a smaller motor sheave. If the ratio required isn't bigger than the assumed 600:1, the setup can be pretty small.
One source of parts here, but I find parts at a surplus store and in the R/C car section of the hobby shop.

http://www.sdp-si.com/eStore/CoverPg/Drive_Components.htm

WhiteWolf McBride

My Feedback: (3)

Dan:

When the DMD drives first came out, I was one that went to the trouble of marking the gears, and then calculating the ratios. I was the one who also 'tagged' the types, the Type 1 being those in the first Sherman (56005) without a black cover, and then the black-covered Type 2's and 3's.

The initial ratios were about 1:48 to 1:60... but adding another 3:1 to that would crank it down to about 1:150 to 1:180, depending on which 'Type' of gearbox you are adding it to. And has anyone really counted to see if its actually 3:1, and not 'close' to 3:1 (like 42:14) or summat?

I MAY still have my diagrams of the DMD drives in my archives... if anyone is that interested, I could drag 'em out and post 'em.

As for 'what is best' I think that depends on a combination of application, and the user's opinion of how they want the vehicle in question to behave. PatMat once said worm-drives were the worst, as when you don't power the gearbox, the unit 'stops dead' because the right-angle drive issue makes the gears lock up, for lack of a better term, and there is no gradual slowing of the drive.

One other possible issue is the 'loading' on the gearbox. A tank of X weight driving up a slope, or getting a twig jamming the sprocket, is comparable to a weed-clog on a boat prop. Too fine a gear-tooth will cause teeth to shear, not a motor stall. I've had a weed-clog literally unscrew props from a shaft, costing me two hard-to-match (left/right pitch) props drop to the bottom of a pond on the first ruun at a display.

As for calculating the reduction of any unit, its just a matter of manually (or looking up) the teeth of each relevant gear, and doing the math. The motor pinion to 1st half of gear #1, then 2nd half of #1 to 1st of #2, and onward, and finally then tallying all the ratios calculated. You could even calculate motor RPM to distance travelled by factoring in the drive sprocket and # of track links, and size of link.

WhiteWolf

danlrc

I got my hands on a tachometer and measured motor speed and drive wheel RPM. Motor speed was fixed and averaged about 2000RPM (varied about1900 -2100) and drive wheel was 20.5 RPM. Total gear reduction then is about 98:1.
The gearbox is a Tamiya with a Schumo "geardown" unit on it. Standard Tamiya motor.
To get about 100:1 is easy with standard miniature drive belt parts. Only three reductions are needed. A LOT of advantages over gears I think for R/C tanks.
Sketch of a 107:1 belt drive attached. Slightly smaller than a Tamiya gearbox.
This looks like it will work.....maybe time to start scavenging for belt drive parts....

heavyaslead

The tank drive is primarily concerned with torque (power) under load at a wide range of speeds unlike a prop with constant speed at relatively low torque.

If you utilize a belted drive it would be better to use chain (bicycle chain) for the drive as the final drive has a high tension which will stretch belts and prematurely break or slip.

kclank

I second that. chain, or latter type reinforced belts, not cog or smooth belts. I did a custom 10 years ago with cogged belts, and it was quiet and smooth but would not handle the real tough stuff and started slipping.

Panther G

Belts at these scales would be near impossible to find. Chain is a much better alternative since there is many sizes readily available with ready made sprockets of different tooth counts. Even double drives.

danlrc

Yes, chain would be better than belt, but not necessary. I talked to a head engineer at the company that makes the gears for Caterpillar and other heavy equipment manufacturers. He said new belt materials and proper selection of wheel sizes should handle any load from a model tank. So chain would be better, but belt would work too. Short belts of newer materials would not stretch, and sufficient belt tension would stall a motor before the belt slipped (with a large enough number of engaged teeth on the smaller wheel.) Composite/engineering plastic wheels would work - metal not necessary.
Anyway, either belt or chain would be more efficient, quieter, simpler than gears.
This guy also said the Nissan Murano has a CVT transmission - uses belts - and they are workng flawlessly in many super high mileage Muranos. Seems that at 1/16 scale this is something to pursue.
Belts and wheels of all sizesand many materials at this site and others. Belts I'm looking atare 1/4" (6mm) wide.
https://sdp-si.com/eStore/Direct.asp?GroupID=218
I'm going to build a test unit and see how much abuse it can take. May take a couple of weeks, but stay posted.

BIGMIG

1/4 inch cog-timing belt and pulleys..............

danlrc

BigMig - Outstanding!
So what do you think of the belts? Wear? Slippage? Adjustability? etc.
Thanks,
Dan

BIGMIG

Well this was just to try something different for fun.It works allright and there is no slipping with these belts... I mounted these in place and there is no adjustment.........One thing it is very easy to gear this down as slow as you want it to go.Small pulley on the gearbox drive shaft.....and the bigger the pulley on the sprocket drive shaft the slower it goes.Guess you could gear it down slow enough where it would climb a wall if you could figure out how to hold it on there.

BIGMIG

Panther G

That is a very clever way to Up scale a vehicle with readilly acssesable parts. No need to get big gear motors with their added cost. Don't know if i would go that route on something really heavy but you certainly could go 1:6th scale that way if you keep it on the lighter side of things.

heavyaslead

OK so this engineer says it will work, sure I believe that, but he is comming from the industrial quality veiwpoint. Counsumer belts will not be the grade of automotive or heavy machinery.

Notice some added space in the hull may be needed for belting, space is usually a premium at this scale.

Another point that cannot be underestimated is the constant tension needed to maintain belt traction, the faster or more load the higher tension is needed. This will be extra load on the bearings and motors that may not be necessary.

These belts will likely be vacuum beater brush type cogged belts. And though run a high speed compared to tank gears, they break and storage over years will cause old belts to crack.

danlrc

Eric,
Dude - way negative. The stuff I'm looking atis industrial quality, is not "vacuum beater brush belt". Belt is 6mm wide low profile. Polyamide (like kevlar) reinforced, almost zero stretch, etc etc.
You may be right, but my current belt drive design is smaller pkg than a Tamiya drive.Pulleys are engineering plastic - way overkill for 1/16 tank applications.
Think about it - full drive shaftload incurrentTamiya and similargearboxes is taken by a single brass gear toothat a time.One skinny little brass tooth.Load on a belt drive is disributed around the full belt contact area around the circumference of the pulley - many teeth engaged at any given time, and material strength isMUCH greater than the load requires.
And it's a hobby - I want to try something fo fun. I'm an engineer - a lot of patentsetc, so why assume I'm using cheap stuff, that it's too big, that it will rot over time, that bearings will be overloaded (that's why they are there), that I don't understand force/velocity/load relationshipsetc etc.
Should be fun to see how it works...
Thanks for encouraging me to move ahead.

Panther G

I think it's a great concept. Especially if the parts neede can be obtained in the scale sizes we are used to using. I was not awhere that belts and cogs of that grade where available. The ratio combinations are endless . Those that hate the noise made by the "metal" gear boxes would love this. You couls actually make a 2 or 3 speed transmision much easier with belts. Different combinations on one shaft switched by a servo.

heavyaslead

Sorry danlrc, did not intend to be negative. You obviously have done your homework and should make a great build.

Just curious, will you have some way of tensioner for the belts? (As an automobile)

danlrc

Eric, sorry, I came back a little heavy. Seeing the SEAD thing and your experience, you would be a btter judge than me on how tougha drive needs to be. After some reserach on all this, a relatively small gear motor going thru a couple wheel/belt reductions wuld be a very strong, quiet, shock isolated system.
I'm in the process of working with a fairly high tech drive system company to get the specific design pulled together based on the original sketch I posted. I hate the skreechy, whinysound of the Tam gearboxes. A belt drive would be quieter and would not slip. Tensioners are not necessary on these very short transfer belts. But since only two shafts are required,one would haveadjustable position fortension adjustment.

Should have something ina week or two.

Being optimistic, I'll thenhave two Tamiya gearboxeswith Schumo reducers for sale relatively cheap......

Panther G

Uh, Tam gear boxes are quiet compared to most.

RSEA

Dan,

In my opinion, your belt drive design looks very promising. I find that it is too easy to strip out gears in the Tamiya gearboxes. I've already had 2 gear failures in my Tiger during the course of 7 battles on a rock covered, dirt field (DAK). That is a 28.5% failure rate, 2 out of 7 battles ended with a stripped out gear. And that was when running plastic tracks! Metal tracks would have even been worse. The modified, airplane gear-reduction units (by Schumo) leave a lot to be desired as well.

I wish you success in your belt-drive design endeavours! I would welcome a new alternative to the current available gearboxes / gear reduction units..

Steve

danlrc

Here's the latest cut at a design using 1/4" (6mm) wide timing belt (urethane reinforced with Kevlar) and with 3 reductions for a final ratio of 120:1. For comparison, a stock Tamiya gearbox with a Schumo reducer delivers about 100:1.
Sheaves and belts are up to about $60 and no bearings, shafts or frame costed out yet.
I'm looking at narrower sheaves and more compact alignment design to make the footprint smaller. Current desgn is 2 x 3.5". Should be able to get to at least 2"W x 2.75"L

Will likely order parts for a test unit.

tomhugill

I have some junked tamiya kt boxes I can donate if needed

heavyaslead

You know danlrc, I would really be interested to hear your ideas on a turret rotation using the belted system.

Seems (at least to me) the turret rotation is an area that could use a simple but reliable drive!

danlrc

Funny you mention belt drive for turret rotation. I just changed out my Tam KT gunelevation to using a 1/16" diameter bungee drive. No more stuttering with that stupid arm system. The bungee slips on the pulley at the end of travel, so no need for fancy end of travel devices.
I'll post some pics later. Basically remounted the Tam gun elevation gearbox on a foam pad (for vibration/sound reduction), added a small pulley made of small servo wheels in place of the final gear and drive the gun end up and down a shaft with the travelling bungee. Very quick sketch attached..
I have a much simpler solution for turret rotation - pic slater. A small surplus gear drive with a perfectly fitting gear.