Will This Suspension System Work?

[Mastermime]

Hello everyone,
I am building a track system  that uses the suspension very similar (below) to this on my rescue robot

lego tank suspension

The tread setup I'm using is the image below.  I am using brecoflex timing belts. Length from drive wheel to drive wheel (two top wheels) 25"

My question is Will I need a belt tensioning system or will I be fine without the the tensioning system?

Thanks

[rbtying]

If you've got belts, you're going to want to use a tensioning system of sort, otherwise the friction of turning will pull them off the idlers (not fun).

[Mastermime]

If you've got belts, you're going to want to use a tensioning system of sort, otherwise the friction of turning will pull them off the idlers (not fun).

Do you have any ideas on how I coud do this?

[[email protected]]

on your diagram, the two black circles are the top pivot points i guess.  one of them is the power wheel and the other just idles i guess.  instead of having the idler be fixed, you could put it on a spring arm so that it continuously pushes out against the track.  i think this is how normal tanks do it.

[Mastermime]

Wow! Thanks for the idea!  That's something similar to what I had in mind.

[Mastermime]

Do you know where I could find a spring arm like this?

[billhowl]

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=14182

[Mastermime]

Do you know how reliable these shocks are?  I read they're made of plastic.  The robot I am building is about 45 in long and weighs about 200 lbs so I am not sure if these are "robust" enough.  Thanks for the suggestion!

What are your guys thoughts on something like this? http://tinyurl.com/7uevvgr

[Soeren]

Hi,

Don't buy expensive "shocks" which are nothing but glorified springs, just find springs of a suitable strength. Leaf springs would be fine as well.

Cheap springs can be found on a junk yard - car seats, beds etc all have either coiled springs or at least steel frames that makes good leaf springs.
I have made several craft knives out of the flat-steel frame from a bed - very good steel quality.

Why are your 'bot so heavy anyway?

[Mastermime]

Don't buy expensive "shocks" which are nothing but glorified springs, just find springs of a suitable strength. Leaf springs would be fine as well.

I  just don't want the shocks to go out on me in mid operation. 

Cheap springs can be found on a junk yard - car seats, beds etc all have either coiled springs or at least steel frames that makes good leaf springs.
I have made several craft knives out of the flat-steel frame from a bed - very good steel quality.

I'll check at my local surplus store to see what they have.  Unfortunately the closest junkyard is 45 mins away  :-

[

Why are your 'bot so heavy anyway?

The batteries weigh 80 lbs and the steel frame weighs about 40 lbs.  then there is about 15 lbs in other things (motors and other things like that)

[Soeren]

Hi,

I  just don't want the shocks to go out on me in mid operation. 

All the more reason to get good springs, rather than weak R/C springs.

I'll check at my local surplus store to see what they have.  Unfortunately the closest junkyard is 45 mins away  :-

Good to see your huge enthusiasm

The batteries weigh 80 lbs and the steel frame weighs about 40 lbs.  then there is about 15 lbs in other things (motors and other things like that)

Halving the battery size (if possible) will not halve the run time, but will make it faster and using aluminum or carbon fiber would help a lot too.

[Mastermime]

Well fortunately for me the surplus store had an overwhelming amount of options for springs    So I got 3 different sizes (6 springs total) for only a few dollars.

As I said, I am fairly new to this suspension idea.  How would I attach the spring loaded wheel to the frame?  Would I need some sort of slot to allow it to slide back and forth as the spring compresses and expands?

Halving the battery size (if possible) will not halve the run time, but will make it faster and using aluminum or carbon fiber would help a lot too.

Unfortunately I have already bought the batteries.

[Soeren]

Hi,

As I said, I am fairly new to this suspension idea.  How would I attach the spring loaded wheel to the frame?  Would I need some sort of slot to allow it to slide back and forth as the spring compresses and expands?

The easiest way is to mount the (idler) wheel on one end of an arm, with the other end of the arm mounted/hinged on the chassis and the spring pulling the arm away from the belt to tension it.
A roller could be used to push inwards between two wheels on the belt, if that sounds easier.

[Mastermime]

The easiest way is to mount the (idler) wheel on one end of an arm, with the other end of the arm mounted/hinged on the chassis and the spring pulling the arm away from the belt to tension it.
A roller could be used to push inwards between two wheels on the belt, if that sounds easier.

Ok I'm having trouble applying that to my design.  Here is a picture of where the spring loaded wheel will go. 

The wheel will have to protrude out of the frame because the treads are outside the frame, but the spring system should be inside the frame to prevent it from debris hitting it and what not.

[Mastermime]

I recently came across a belt tensioner.  The lightbulb came on. I think I could use something like this http://www.autozone.com/autozone/parts/Duralast-Belt-Tensioner/_/N-apte9?itemIdentifier=421373_0_0_

Do you see any issues of why this may not work?

EDIT: I just went to an auto store and I took a look at one of these and it requires a lot of force to turn one of these.  A little TOO much.  Do you guys know where I could find one of these that would require less force to turn?