Suitable Ratio for PF XL with Power Puller Wheels

[andythenorth]

So what's a good ratio for PF XL motor with power puller wheels?

Intended design

- one motor per wheel (8 in total)

- portal axle frame (for the strength of hub mounts, rather than for reduction or ground clearance)

- no shredded 8t gears

- not intending to go rock crawling, power puller wheels unsuitable for that, want balance of moderate speed and ability to climb small obstacles

Building one of these https://www.nov.com/Brands/Rolligon/Rolligon_8X8_Model_Brute.aspx

With smaller (81.6) wheels 20:12:24:8:24 has worked perfectly, but it's not enough reduction with power pullers.

[Zerobricks]

I suggest you to use 12:20 :) and keep the gearing simple!

[AndyCW]

3:1

The fewer gears you use the better. You could build it to try both 3:1 and 1.67:1. It will depend on the weight of the final product.

5:1 makes a great crawler, but may be overkill.

v/r

Andy

[andythenorth]

It's an interesting challenge. The frame width is very narrow (9 studs), and I want to get a motor to each wheel. Suspension and steering are not required which helps.

I was hoping to use L motors, but they don't have enough torque without a lot of reduction. XL needed.

Turning anything through 90º will need a rectangular frame and 1 stud bevels or knob wheels, best avoided.

For another smaller truck using diffs I found a pretty clean structure (picture attached). It has 3:1 reduction hubs also, with easily access to replace 8t gears.

This next project is bigger though

With the PF wheels, the XL motor will eat 12t single bevels for breakfast. I broke one already just testing. Diffs are out of the question (and there's no space to lock them either).

Any ideas?

Edited May 11, 2014 by andythenorth

[Tommy Styrvoky]

Knob gears would work well because almost any type of bevel gear will get shredded by XL motors

[AndyCW]

Placing the bevel gears in double shear helps prolong their lifespans. The GM 14 bolt axle uses double shear on the pinion gear. It is used as a heavy duty axle in rock crawlers.

This setup prevents the pinion or ring gear from deflecting away from each other. The deflection is what causes them to eat each other.

Knob gears are robust, but eat up efficiency.

v/r

Andy

[andythenorth]

Double shear = trapped in liftarms both sides of the gear? Which reduces the bending moment on the axle when the gears try to climb away from each other?

[AndyCW]

Yes that is what I mean by double shear and it prevents the pinion from "walking" up the ring. It also prevents the rings from deflecting away from the pinion.

v/r

Andy

[andythenorth]

Evolved this now to 1 PF Large motor per Power Puller wheel.

Gearing is 12:20 then 8:24. Is that 5:1? Anyway it works well. With 4 powered wheels the chassis will climb a wall then stall out (or fall on its head).

Chassis is 4 studs wider than I wanted, but I managed to get double shear in. Trade off. Also more stable.

I managed the narrow chassis with a PF XL per wheel, but it was actually overkill, and would have needed a heavily overbuilt axle to contain the torque.

The L motors have a nice balance, with enough torque, but won't destroy the axle. \o/

[AndyCW]

1 PF large per wheel at 5:1sounds pretty robust.

v/r

Andrew

[andythenorth]

L motors offer excellent mounting options, shame they couldn't be one stud shorter for same power

Axles turned out pretty robust. Parallel walking beams for suspension. Brutally simple.

Battery box center and low down, counteracts tendency to flip.

Rear unit will clone front unit, just waiting on an expensive L motor order.

Untitled by andythenorth, on Flickr

Edited May 18, 2014 by andythenorth

[andythenorth]

More motors arrived today...

Uno: a v1 PF receiver will power 8 L motors from a single AA battery box without cutting out. Kinda. Until you put any serious load through the setup. In case anyone wanted to.

Duo: Are 4 powered axles (8 L motors) enough? How about 7 powered axles (14 L motors)? http://s4.e-monsite....14-khan-pdf.pdf

Edited May 21, 2014 by andythenorth

[BondemandClausen]

I like your project, but i think you are shooting over the target with the amount of motors. Two XL motors per batterybox, is as much the safety switch in both the batterybox as well as the PF reciever can handle.

My Ropa Sugar beet harvester http://www.eurobricks.com/forum/index.php?showtopic=81575&hl is powered by only one XL motor per axle, on the two first axles with power pullers. The rear axle is powered by a L motor.

To avoid overload on batterybox/PF reciever, the first axle has its own box and reciever, and the two rear axles are sharing a box and reciever.

The ratio on the powerpullers are 1:2,334, and the smaller rear ones is 1:3,89.

I am using the train remote, with 7 steps. That helps starting and stopping smoothly, without smashing gears.

It weighs 8,4 kilo, and still runs with a nice speed, with the above gear ratio. I am using lithium batteries with high voltage, and long durability.

[Zerobricks]

As a rule of thumb there should be 4M motors or 2Xl motors on battery box max. Seeing L motor is somewhere in the middle I'd say you could use max 3 motors per battery box. Any more than that and you run out of current.

[andythenorth]

As a rule of thumb there should be 4M motors or 2Xl motors on battery box max. Seeing L motor is somewhere in the middle I'd say you could use max 3 motors per battery box. Any more than that and you run out of current.

Yup, agreed. Current set up is 8 L motors, 2 v2 receivers and 2 battery boxes.

The v2 receiver takes 4 motors ok under light load, but stalls out quite easily. Not sure if it's battery box or receiver protection kicking in (it's not the motor). Or maybe it's just not enough juice available.

I'll try a third battery box and receiver, need one for the steering anyway.

Using multiple battery boxes only really works with matched batteries in each (type + charge level). Shame there's no easy way to gang battery boxes together. Definitely one reason against doing the 14x14 version of this truck.

Just been re-reading your Fox thread. A beast

Edited May 22, 2014 by andythenorth

[Cwetqo]

I still think that 4 L motors would be enough. The model you are trying to build doesnt have large superstructure so it wont be THAT heavy. I tried driving 9398 offroader with PP wheels and it drives ok and can even do some light offroading (tested on our TT course). Your model would be just that times two but with lower weight.

If you insist on using 8 L motors, I suggest using 4 V2 receivers and 4 battery boxes (preferably LiPo type which is realy light and powerful enough). 4 L motors per receiver will just stall it (as you already found out). Both suggested combinations will also enble you to drive it with one remote (for using both A and B ports you will need two remotes just for forward which could be problematic, because you might not be able to control both exactly in sync)

[andythenorth]

If you insist on using 8 L motors, I suggest using 4 V2 receivers and 4 battery boxes (preferably LiPo type which is realy light and powerful enough).

I do insist I'm going for pulling power rather than trial-truck (crawler) performance, so more batteries actually helps. I haven't built a trial truck, but I've looked at a lot posted here, and I would guess power puller wheels are disadvantaged in trial trucks - too heavy, too much inertia?

Original plan was 8 XL, but it's actually too much power and will tear up the chassis and drive train, which is kind of boring to keep fixing (I prototyped).

I could do 4 XL instead of 8L. But I want to avoid diffs, and I want left / right sides on separate channels to aid turning. I could run spur gears along the walking beams, so each motor drives 2 wheels on same side, but it would be a lot of power lost to gears. Chains are out, too weak

Intrigued to see how much it will pull. I have another smaller 8x8 with 3 XL motors and locking diffs, that will pull a 15KG toddler on a scooter.

I'l post some more pictures when I have something worth showing.

Edited May 23, 2014 by andythenorth

[andythenorth]

Gonzo video, with blooper at the end

Anyone know how to embed flickr videos on EB? I had a search, but found no answers, only other people with same question.

Edited May 24, 2014 by andythenorth

[Doc_Brown]

https://flic.kr/p/nrqokT

That might work.

Wow that thing hauls! May need to reinforce a bit, hehe

EDIT: nope sorry no idea.

It does say Sharing is restricted for this video

Edited May 25, 2014 by Doc_Brown

[andythenorth]

Got steering in. Needs 2 LAs, both on same side. Tried one on each side, they bind. The XL is overkill and drives through the clutches constantly, also slow. A single M is too gutless for this, and as for L...I've run out (8 in the chassis).

Although the turning circle is eventually tight, the steering performance is dreadful because the Power Puller wheels are so resistant to side-scrubbing. So it's slow, and twists up the chassis unless the wheels are also rotating (i.e. driving forwards or backwards). Kind of expected, the Commander has same issue with fewer wheels.. Still, if you want to turn you'd better block out some time in your diary.

Also the chassis has a swivel (roll) joint with the large turntable.

Currently 3KG. With ~2000mAh NiMH, 12 batteries are lasting about an hour.

I'll probably add 2 more battery boxes, 1 per receiver. Currently on 3x v2 receivers and a v1 receiver. It stalls out right about where you'd want it to, any more and it would tear something up.

Edited May 25, 2014 by andythenorth

[andythenorth]

Hmm. I'm using a large turntable as the roll joint in the center of the chassis. http://www.bricklink....asp?P=48452cx1

Problem: the truck pulls the turntable apart easily. Ideas for reinforcing it, or alternative solutions for roll joint?

Maybe sandwich the large turntable and a small one, with a liftarm through the centre to retain the two sides?

[

Edited May 31, 2014 by andythenorth

[2LegoOrNot2Lego...]

Impressive wheel/motor setup! You might want to use an old turntable, these are "stronger" in my humble opinion. Not that easy to fit, but it might work...

[andythenorth]

Thanks.

The newer small turntable also seems to be insanely strong. I've tried to pull one apart by hand, can't split it. Going to try using that instead

[Bzroom]

What camera and settings did you use for this? Nice picture.

[andythenorth]

Camera details are on Flickr page https://www.flickr.c...th/14264965852/ (scroll down)

It's just iPhone, taken on a bright day, but not in direct sunlight.

Edited August 3, 2014 by andythenorth