Modified steering brakes

[Mike Keenan]

Yes have just finished testing, brakes now more progressive,button screws also removed and I have thought of drilling the disc as per motorcycle which would aid with cleaning and a reduction in surface area which helps with brake force. In my opinion don't think UC is going to be much of an off roader at the moment, diff. may need some work. Hope this helps Dennis.

[Peter Withers]

Mike, have you retained the original servo linkages in your setup?

Thanks,
Pete W

[Mike Keenan]

Yes Peter have retained the original linkage but have removed the button head screws,also when fitting the disc push it with your thumbs and make sure it doesn't rub on the back face of part ER0219. I had to shim mine out to clear and also when the disc retaining nut is tightened it locks up against the disc so no float on disc and check it is running true. If you do this then you are getting the full effect of the servo and still free travel for no burn out. My next job is to drill a series of small holes on the disc where the pad makes contact this should help with self cleaning and slightly reduce the surface area which aids for slightly better pressure, think about it.

[Peter Withers]

My discs are shimmed to just miss the housing and even with full servo force I don't get any contact. The discs were a tight press fit on the threaded part anyway so there is little possibility of contact developing. Interesting on the drilled disc idea, it did cross my mind. Some while ago my 1/6th scale petrol buggy (insane!) had drilled discs and they worked very well in all kinds of conditions.

[Peter Withers]

The UC ambulance is up and running with the modified brakes and a fairly significant additional mod. I have swapped the rear sprockets for some homemade ones with 8mm pitch. This engages far better with the tracks when under tension (whenever it is under power basically). The original sprockets have a 7mm pitch and work OK when the tracks are tight and not under tension(!) but I found they were slipping and generally misbehaving when under load. The new sprockets are modified roller chain sprockets with 8mm pitch. I'm down to 30 teeth but the rolling diameter is only about 4mm less so it has little effect on speed. The sprocket is shown in the picture, I filed the teeth to the correct profile and turned down the hub to get the correct alignment. It is all reversible if I ever decide to go back to original.

Next big mod will be a new motor and gearbox. The existing motor is 12V rated but being run at 7.4V reduces the torque. I have a 18V 550 size motor with gearbox which has about double the torque for the same output shaft speed so that will get swapped in. The plan is to fit a 18V drill battery for main power, a homemade speed controller good for 18V , and keep a 7.2V NiMH pack for the servos and electronics. Depending on how that goes, I have a pair of similar motors with gearboxes and some 3:1 skew gears, I'm really tempted to do a dual motor setup...

Pete W

[Dennis Jones]

Hi Peter,

I was thinking of dual motors but I haven't found any that would fit under the back end, so I would be interested if you ever go down that route.

The guy that I am building the 2nd one for already has a scratch built UC in 1/6th scale made mostly of wood and plastic tracks they used two motors on the rear of that one with 540 motors with 50:1 gearbox on the end but I don't think that those gear boxes would stand up to the extra weight of the Armortek one. The motors I was looking at with gearboxes attached were about 105mm in length and as there is only about 205mm between the hull sides at the rear it would be a tight fit.

Dennis.

[Peter Withers]

Hi Dennis, my thoughts regarding motors and placement are to use 18V RS550 sized motors from a cordless drills complete with 16:1 gearbox. I have a pair of 3:1 reduction 90 degree gearsets so in combination I get the right kind of sprocket speed when the motors run at 18V. Those 3:1 gears are about the size of what you would get in a 4 1/2in angle grinder head. I was aiming to put the motors in longitudinally (basically replacing the existing servos with motors and gearboxes) and mounting the output gear of the 3:1 gearset on the drive axle. This would mean losing the back axle machining but I'd keep the outer bells with the bearings and just make new inner bearings etc to support the inboard side of the axles. The space gained inside the engine cover by deleting the central motor would free off some space for the 18V main drive battery.

If you wanted the motors across the chassis you could put one behind the other and run small chains to sprockets on the drive axles maybe?

I hope that all makes some kind of sense.

Pete