[BAracer]

Running gear installed on the Olifer chassis...

   

   

[Brumos RSR]

Bar, that’s pretty cool!! I assume the shocks are really soft and it’s geared really low?

[BAracer]

The shocks are standard SCX ones, so pretty basic and what you would call soft, although they are held in compression which firms them up a bit. 

(In comparison, the shocks on the Mitoos chassis come in soft, medium or hard springs, and have three compression settings!)

I haven't sorted the gearing yet, but it will probably start at 9/30 and see how it performs

[JMay]

This is on the bench currently, the umpteenth iteration of my tyre truer (details and files in the 3dp section), where as the original one was a simple hinged mechanism that could be lowered on to sandpaper, this one has the sanding medium moving and hence clearing the rubber detritus.

   

   

This iteration was to continuously move the sandpaper at 90 degrees to the tyre, which on other machines is done by reciprocating the sandpaper back and forth using cranks/cams etc. I wanted something different, and this design was a lightbulb moment from repairing my belt sander. By turning a belt sander upside down, and placing the axle carrier over, you get a moving sanding belt at 90 degrees to the tyres. I replicated this with a driven pulley system that runs the sanding belt around a plate over which is the original hinged mechanism. The sanding belts are 10mm wide rotary file belts available for pennies from the right sources and in various grit sizes to suit.

The unit has two motors a Mabuchi 365 to run the sanding belt pulleys at 16:1 via a gear train and a Boxer motor at 9:30 ratio to drive the axle holding the wheels and tyres to be sanded. This was for two reasons, firstly it keeps the motor drive simple and secondly I can vary the rpm of either motor by controlling the voltage supplied.

Still playing with the design as various ideas explored, i.e. a sanding belt tensioner, ball raced pulleys and gears, changeable axle (caters for different axle sizes) cut depth indicator/stop and dial gauge all in the process of being incorporated each time I get round to printing another set of parts.

The model shown has been used for sometime now with various upgrades, and will true pairs of tyres including soft grades, giving a smooth finish concentric to the axle without chunking the tyres.

Cheers
John.

[Kevan]

Ooh yeah, like that idea.

What if the sanded tyre axle is moved at a 15 degree angle so it covers more of the sandpaper to spread the wear area wider?

[Kevan]

...and can we see it in action please 

[DPJ]

Excellent design! The only addition I could ask for would be to have the sandpaper ride over a bar of steel/aluminum so when pressure from the tires is put on the rotating sandpaper, there's no deflection.

edit... Or do I see that in the 2nd picture...?

[JMay]

Some more details on the umpteen Tyre Truer.

See below pics taken from CAD showing the exploded parts of the machine and the assembled unit. The colours show the individual parts and are all 3dp except the metalwork. Shafts are 4mm dia stainless steel with ball races either in the supports or the pulleys/cogs. The mauve support holds the freewheel pulley (marked F) which is on a slide to enable the belt to be fitted then tensioned. The 365 motor is mounted centrally under the axle carrier and drives a pinion and two cogs to increase the torque and lower the rpm to the driven pulley (marked D) on the left hand side. I used threaded brass inserts in the driven pulley, final cog and the axle carrier so that the grubscrews and fixing screws can apply sufficient force repeatedly without chewing up a 3dp thread over time. The axle carrier is on a 6mm stainless steel shaft at the rear acting as a pivot to enable the carrier to swing down onto the belt, controlled by the hex bolt (silver) which has a spring to control the vertical carrier movement. 

   

   


To answer DPJ's question, like a belt sander there is a plate to support the sanding belt at the point of sanding in this case the tyres. The plate rises up from the bed centrally between the two pulley wheels and is @70mm long to cater for various axle/wheel tracks. I added some TPU feet to the unit to reduce the vibration and hence noise when running shown in black.

   

Kevan suggested turning the axis by 15 degrees, this is set at 90 degrees as any deviation from this is limited by the belt width used (10mm wide). Will look into a video as not on YouTube and not sure if I can post direct or have to link to one. 


Cheers
          John

[DPJ]

Great! Love the machine. Question... how do you ensure equal pressure is applied to both tires at the same time so one doesn't get filed more than the other?

I think the single pivot at the Silver bolt will allow the axle carrier to deviate a little either way to favor one tire over the other.

If you used 2 4mm rods as rails that the axle carrier followed instead of the single silver threaded screw, would it ensure equal pressure better?


edit... also, what scale tires are in the picture you posted... they look 1:32. I just sold all my 1:32 and only work with 1:24 now.

[JMay]

On the question of deviation/slop in the tyre carrier leading to uneven tyre truing I went through several print iterations to improve the design. I stiffened the axle/tyre carrier rails (brown) by increasing the side walls and pivot blocks plus shortening the distance from pivot to tyre axle. I also increased the rear pivot shaft from 3mm to 6mm and moved the pivot blocks (dark blue) out more to increase the tripod effect. The pivot shaft is a force fit into the supports and carrier to eliminate slop. The tyre/axle carrier has a top plate (held down by 4 corner bolts in brass inserts) which pushes directly on to the bearings so that the axle is held rigid, to stop the axle twisting in the carrier. The adjusting bolt end is M6 bolt which goes into the tower to a captive nut and again the bolt is a tight fit. A 5mm diameter spring sits internally to control the up/down movement.

   

   

In practice, the compact size and using PLA Tough for the carrier & supports is sufficiently rigid over the entire structure to true a pair of tyres evenly as the force applied is limited by the risk of tearing/chunking the tyres.

Currently only truing 1/32 tyres but I need to make up some bearings with a 3mm shaft hole so I can true my BRM tyres, as there is sufficient width on the sanding support plate to accommodate these.

Cheers John