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Old 11-14-2007, 07:06 PM   #1
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Cool BMV-style TLT-crawler - reworked

Hi!

Today I received a parcel with a new tranny from the AX10 in it:


Click pic 4 gallery!

This cute little tranny is very good! It weights almost nothing and keeps the cg very low...

Tomorrow I´ll do the body mounts. The last thing to do on this little project...


Manuel


Edit: Btw, here´s the old thread: BMV-style TLT-crawler with BTA-steering / 2-speed tranny

Last edited by Uncle_Manuel; 11-15-2007 at 06:37 AM.
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Old 11-15-2007, 01:55 AM   #2
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hey I have a couple of questions about your rig...what kind of metal are you using for your suspension rods? also whats the diameter of it and the size of the collets you are using? I love your truck by the way...I have a tlt here begging for the same treatment!
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Old 11-15-2007, 06:35 AM   #3
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Morning! *yawn*

The rods are made of 3mm spring steel, the collars are fitting to them (3mm hole). I bought them from a local hobby shop...
But the spring steel is very stiff and I haveīnt tried on rods made of solid carbon fibre...

But Iīm also thinking about to reduce the width of the rods on the tail to gain more flex. Perhaps Iīll try a little on that...


Quote:
I love your truck by the way
Thanks!


Manuel
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Old 11-15-2007, 01:50 PM   #4
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Hi!

Worked a litte bit further on today:


Click pic 4 gallery!


And this is how itīs look like now:


Click pic 4 big!

Drives well but the rear axle now can twist almost 90° wich is a problem with the body in the way. And the notorious "torque twist" is a major problem at climbing (especially when I turn right the right wheel goes up into the air)...

Tomorrow Iīll try a different setup with new spring steel rods. Hopefully this will turn out better...


Manuel
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Old 07-14-2008, 03:50 PM   #5
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Default BMV wire/position choices

So the motor induced torque twist was caused by the how close the wires are together when they entered the rear plate, or the angle you put on them in the second design?

I have the stock BMVII chassis and wires. I don't want to drill up the stock chassis plates. Despite them being delrin, I have heard of them cracking because of too many holes.
Local hardware has a few dia of music wire for $3/4ft length. I might try the next size smaller I can find. Stock size (need to remic it) gives about 30-35 deg of flex. I do not want to go too small where the whole chassis springs around or torque flexes under power.

Which, BTW, 55t Novak, 14/84 gears in a Stealth trans, does lift the front wheel a little if you are still rolling in reverse and then goose it forward.
Doesn't lift the whole front, just one wheel.
What if you made one of the two wires the next size smaller? Play with one side then the other to see what gives you flex without torque twist.

thx
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Old 07-23-2008, 12:15 PM   #6
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These BMV2 type chassis work best with quit a bit of weight in the wheels, that's where you get your flex. the front plate was desinged for the servo to go on the driver side and the heavy batteries to go on the passenger side to help fight the torque twist. You can also slide the trany plate front to back to help tune and dial in your weight transfer, with it more centered your gonna get even flex front/rear. with it pushed farther forward you'll get more rear flex, etc... I had mine set up as far forward my pede shafts would allow without binding, if I was to rebuild it I would get some clocked C's for the front or maybee clock the trany forward a little to help with the drive line issues. You also want to make sure the rods spin freely in the mounting plates so it can twist when flexxing.
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Old 07-24-2008, 10:40 AM   #7
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Quote:
Originally Posted by LIKES2CRAWL View Post
These BMV2 type chassis work best with quit a bit of weight in the wheels, that's where you get your flex. the front plate was desinged for the servo to go on the driver side and the heavy batteries to go on the passenger side to help fight the torque twist. You can also slide the trany plate front to back to help tune and dial in your weight transfer, with it more centered your gonna get even flex front/rear. with it pushed farther forward you'll get more rear flex, etc... I had mine set up as far forward my pede shafts would allow without binding, if I was to rebuild it I would get some clocked C's for the front or maybee clock the trany forward a little to help with the drive line issues. You also want to make sure the rods spin freely in the mounting plates so it can twist when flexxing.
^Straight knowledge being dropped by Eddie^.



I have never owned one of these chassis's but I have seen them in action at comps. Once you get it tuned properly, they work very well. It's torsion style chassis so you have to learn to drive it more than a sprung suspension. The torsion chassis in my clod was that way. Easy lines for sprung crawlers were hard for the torsion, but hard lines for sprung crawlers were easy for the torsion. Torsion designs take more of a finesse style of driving. Nice crawler and best of luck.
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Old 07-24-2008, 10:55 AM   #8
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Thanks guys...

Setting up a BMV-chassis is really a science - if you drive competitions. But I only drive 4 fun so it doesīnt really matter for me...


And I thought about one thing: Clocked axle Cīs would be nice to solve the problem with the extreme angle of the front drive shaft. But then the steering linkage gets in the way of the spring steel rods of the chassis... :-(
So with the straight front axle I can only mount a AX10- or Stampede-style driveshaft...


Manuel
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Old 07-25-2008, 11:51 PM   #9
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Default BMVII, wire size, driveline angle

Uncle Manuel,

Did you get this set up the way you wanted for flex?
Did you stay with the 3mm rod?

My BMVII has 3 or 3.1+mm rod. I was considering the next size lower, but it is 3/32, or 2.38. Quite a drop in size. I think I'll try it around the yard and see. I bet I'll see some torque twist.

The steep driveline angle on mine, from a stealth tranny to the front has caused the stampede drivelines to pop the yokes loose.
Hate to say a little bailing wire did the trick.

Next week link was this angle pulling the axle pinion away from the ring gear when under high loads (TLT axles). Started to strip the front pinion. Tore down now with a new one about to go back in. Bearing was fine, without slop, but I think the torque just overcame the strength of the axle around the bearings. Nothing broke yet.
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Old 07-26-2008, 12:53 AM   #10
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Quote:
Originally Posted by sweli View Post
Uncle Manuel,

Did you get this set up the way you wanted for flex?
Did you stay with the 3mm rod?

My BMVII has 3 or 3.1+mm rod. I was considering the next size lower, but it is 3/32, or 2.38. Quite a drop in size. I think I'll try it around the yard and see. I bet I'll see some torque twist.

The steep driveline angle on mine, from a stealth tranny to the front has caused the stampede drivelines to pop the yokes loose.
Hate to say a little bailing wire did the trick.

Next week link was this angle pulling the axle pinion away from the ring gear when under high loads (TLT axles). Started to strip the front pinion. Tore down now with a new one about to go back in. Bearing was fine, without slop, but I think the torque just overcame the strength of the axle around the bearings. Nothing broke yet.
Did you shim the R&P on your axles? I've never had that problem with mine.
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Old 11-17-2009, 01:17 AM   #11
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Morning! ;)

After quiet a while there are some news:


Click pic 4 gallery! (scroll all the way down)

Iīve lengthened the rods about 5cm (1.97 in) to make room for the front driveshaft. I also tested a setup with a 3S LiPo & a Turnigy 15A UBEC. Works fine with the old Jamara No Limit (6-10 cells, 4kHz)...
The Orion 80T isnīt quiet perfect, it will be replaced by a LRP Truck Puller 2...

Talking about amps: The motor doesnīt have a large consumption (6A), but the servo was shocking me! It takes massively 7A at maximum load!
--> http://www.manuel-aka-mdk.net/galler...2_itemId=32525


Things left to do:
-add rear wheel steering
-do a proper mount for the UBEC
-solder a direct feed-in for both servos
-drive


Manuel
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Old 11-17-2009, 05:33 AM   #12
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Nice build!
Post some natrual flex shots.
How much do your front and rear wheels weigh?

I played with smaller dia piano wire on my BMV, then moving closer. But I went back to the original design.
Too narrow, and the thing wants to twist up. To small wire and you get chassis bowing.

I run 16oz front and 14oz rear total weight (tire, foam, weight, wheel).


Your body is mounted in the middle of the sides only? Works well?

I have two posts rear upper, and single loose post middle front. So body pivots with rear axle twist. I wondered if there was a better way out there.

Nice build!!
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Old 11-17-2009, 06:44 AM   #13
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Quote:
Originally Posted by sweli View Post
Your body is mounted in the middle of the sides only? Works well?
Jepp, middle-mount only. Quickīnīdirty...
And yeah, it works fine because the body doesnīt flex. Itīs only shakin a little bit from the bumps. And because the hollow shell is a good resonator I taped it from the inside. Also works fine...

Manuel
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Old 11-22-2009, 05:19 PM   #14
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Hi!

Worked a little bit further on: ;)


Click pic 4 gallery! (and the following pictures)

Yeah, I added rear wheel steering...
The battery of the remote control is currently charging so I can testdrive it later. Will see how the rear ws turn out...


Manuel
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Old 12-03-2009, 01:04 PM   #15
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Hi!

Today I installed the new digital servos:


Click pic 4 gallery! (scroll down)

Massive torque at 6 volts and extreme holding forces. These servos are just perfekt...


Manuel
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Old 12-03-2009, 10:01 PM   #16
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Nice rig. I find it funny that the BMVII style rigs are still kicking. I figured that with this setup well over 3 years old, many would have moved onto the new hotness of setups.

Keep up the work!
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Old 12-04-2009, 09:41 AM   #17
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Simplicity always works...

I donīt know I just got stuck with this torsion chassis since June 2007. I tried different types before but this simple chassis just works fine...


Manuel
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Old 01-02-2017, 10:48 PM   #18
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Default Re: BMV-style TLT-crawler - reworked

Fun to read about our design after all the years. It would be fun to know if any of these chassis are still around.

Jeff
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Old 01-02-2017, 11:32 PM   #19
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Default Re: BMV-style TLT-crawler - reworked

Yeah. Kinda neat.
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Old 01-24-2017, 08:09 AM   #20
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Default Re: BMV-style TLT-crawler - reworked

I'm actually getting ready to rebuild my BMVII chassis. Haven't decided yet whether to stick with TLT axles or go with XR mod SCX10 axles so I can clock the front. Going to print me off a wedge to clock the rear.
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