RE: [CAD_CAM_EDM_DRO] Re: Problems in Timing Belt drive system in 6WD robot

Hi John,

I disagree. The principal of independent drive to both sides is used pretty
well all tracked vehicles. Just watch a dozer or tank turn in place with
one side turning one direction while the other side turns the other.
Control is often with two levers, one for each side, forward and backwards.

Alan's first step is to verify his chassis isn't flexing under adverse load.
All the belt tension in the world won't help if the chassis twists under
certain conditions that allow the belts to loosen.

Next test is to lock the driven wheels and place a lever on the motor shaft
and measure the maximum torque you can apply before the belts skip. If they
skip at all. If they skip under the static load you now have a number that
you can use with the belt specifications to determine if they are too small
for the job.

Does a toothed belt have different torque values when it's moving as opposed
to static. Also, there are toothed belts with round teeth and ones with
dear shaped type teeth. There are some that are better for timing
applications like servo positioning and others that are more adequate for
load transfer.

I don't know which is which but the XL series I bought for my Mill are
apparently not the best for the CNC positioning and better for driving a
load. Of course I read that somewhere after I'd bought all the belts and
pulleys.

John Dammeyer

-----Original Message-----
From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of picengraver
Sent: January-26-13 4:43 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Re: Problems in Timing Belt drive system in 6WD
robot

Alan,
Beautiful work. But I don't think you will stop the belt problem with this
design, if I understand what I'm seeing from the pictures. There appears to
be no differential, so either the belts or the tires, or something, has to
slip for the robot to turn, IMHO.

I'm not sure what to suggest to improve your robot. Perhaps some one-way
clutch drives may help, but they may interfere with running in reverse if on
all wheels.

Please advise if I haven't understood the design correctly.

Regards,
John Champlain

--- In CAD_CAM_EDM_DRO@yahoogroups.com, KM6VV wrote:
>
> Sorry for the cross-posting,
>
> I'm having problems with the timing belt drive system in a 6WD robot
> I'm building for Robomagellan competition in the upcoming Robogames.
> (Mechanical design courtesy DPA).
>
> Pictures in LM forum:
>
> http://www.lynxmotion.net/viewtopic.php?f=9&t=7839&hilit=6WD&start=45
>
> There are a pair of DC servo motors, each driving a short (3") 037
> (3/8") .2" pitch timing belt from the 2nd level down to the first,
> 23:15 ratio for a 1.33 speed increase. The motors are mounted on
> opposite ends
>
> On the first level are three short axles on each side of the 'bot,
> connected on 8" centers by the same timing belts, and 20 tooth pulleys.
> There are belt tensioners (4) between each pair of pulleys pressing
> down on the top of the belt. (I do remember hearing that the
> tensioner pulleys should be on the driven side of the pulley, so one
> pair is on the wrong side).
>
> The belt system appears to run fine in straight runs, grass, concrete,
> etc., even when moving quite fast. The problem arises when the 'bot
> starts to make a turn (more torque required). I start hearing loud
> "popping" sounds, which I take to be the belt(s) jumping teeth.
>
> I can't determine which belt(s) is jumping. Since I first observed
> (heard) the problem, I've strengthened up the bearing supports between
> the axles, made a better tensioning nut for the belt tensioners
> (idlers), and increased the tension on the upper drive belts as well.
> Specs say 3-4 oz at 3/64" deflection on the belts, although I don't
> have a way to accurately measure it. The belts "sing" when they run,
> like they are being "plucked", so I think they're pretty tight.
>
> The angle of the upper motor belt is about 50 degrees, and I haven't
> yet figured out a way to add a tensioner to it.
>
> Any ideas?
>
> Thanks!
>
> Alan KM6VV
>




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