MRC / Academy SB Sport 4wd Buggy
07-06-2004, 04:55 AM
#436
Tech Apprentice
Just to keep you updated:
the servo horn of the Losi XXX Buggy works as a direct drop in, just have to use a short neck ball stud and a 4-40 mini-locknut.
The steering is much stiffer now, with the only flex coming from the steering arm (in stock, the flex from the servo mounts and servo horn will add up creating a very soft steering)
I'll get my broken axle machined from some high grade hardened mangane steel or some highest grade hardened stainless steel (both better than titanium in this place) - think that should last a pretty long time
the servo horn of the Losi XXX Buggy works as a direct drop in, just have to use a short neck ball stud and a 4-40 mini-locknut.
The steering is much stiffer now, with the only flex coming from the steering arm (in stock, the flex from the servo mounts and servo horn will add up creating a very soft steering)
I'll get my broken axle machined from some high grade hardened mangane steel or some highest grade hardened stainless steel (both better than titanium in this place) - think that should last a pretty long time
07-06-2004, 06:25 AM
#437
I got some info from the www.raceacademy.net boards, anyone interested in this vehicle should check it out, helpful people there. To solve the nut tightening issue for the front and rear ( haven't noticed it on the rear ) here are the spacer dimensions you need.
Front
width: 2.9mm
inner diameter: 5mm
outer diamter: Less than or equal to 8mm
Rear
width: 1.9mm
inner diameter: 5mm
outer diamter: Less than or equal to 8mm
These will go between the two bearings, similar to how it is done on AE kits and I believe Losi kits. I have posted a message to AE to see if they have anything similar in dimensions that will work, if someone else could contact some of the bigger companies like Losi that would be great too. Or, if you know of an online machine shop that you can get parts like this from feel free to post.
Front
width: 2.9mm
inner diameter: 5mm
outer diamter: Less than or equal to 8mm
Rear
width: 1.9mm
inner diameter: 5mm
outer diamter: Less than or equal to 8mm
These will go between the two bearings, similar to how it is done on AE kits and I believe Losi kits. I have posted a message to AE to see if they have anything similar in dimensions that will work, if someone else could contact some of the bigger companies like Losi that would be great too. Or, if you know of an online machine shop that you can get parts like this from feel free to post.
07-06-2004, 06:33 AM
#438
Tech Apprentice
Do you use the axle 5x8x0,2mm shims between the bearing and the 2x10mm hex shaft as stated in the manual?
I tried without them (the hex prevents the small shaft from rubbing against the bearing anyways) and only 1 in the rear and I didn't notice any binding without these Losi-type spacers no matter how hard I crank down the wheel nut
I tried without them (the hex prevents the small shaft from rubbing against the bearing anyways) and only 1 in the rear and I didn't notice any binding without these Losi-type spacers no matter how hard I crank down the wheel nut
07-06-2004, 06:47 AM
#440
Tech Apprentice
Well then you know why your axles are binding.
I don't use the shims in front and only 1 in the rear (as 1fr/2re I think the manual suggests) and my axles have little play - not more than on a Losi XXX or some other buggies.
The point is, that the wheel hex slides on the axle just till it reaches the area, where the inner diameter of the hex goes from 5mm down to 4.
So when this point is reached, you can crank down the wheel nut and you won't get any binding because the hex can't slide onto the axle any further.
When you add the shims, the hex can't slide onto the axle that far, so that it locks itself axially. As a result, thightening the wheel nut will result in enormous axial bearing load (=binding)
The problem is, that the academy shims are 0,2mm in thickness.
To take out any play in the axles without binding in the bearings, you'll need 0,1mm in the front and 0,3mm in the rear I guess, (depending on manufacturing tolerances of the axle and the hub carrier) because 1 0,2mm shim front and 2x0,2mm shims in the rear is just a bit to much.
I don't use the shims in front and only 1 in the rear (as 1fr/2re I think the manual suggests) and my axles have little play - not more than on a Losi XXX or some other buggies.
The point is, that the wheel hex slides on the axle just till it reaches the area, where the inner diameter of the hex goes from 5mm down to 4.
So when this point is reached, you can crank down the wheel nut and you won't get any binding because the hex can't slide onto the axle any further.
When you add the shims, the hex can't slide onto the axle that far, so that it locks itself axially. As a result, thightening the wheel nut will result in enormous axial bearing load (=binding)
The problem is, that the academy shims are 0,2mm in thickness.
To take out any play in the axles without binding in the bearings, you'll need 0,1mm in the front and 0,3mm in the rear I guess, (depending on manufacturing tolerances of the axle and the hub carrier) because 1 0,2mm shim front and 2x0,2mm shims in the rear is just a bit to much.
07-06-2004, 06:49 AM
#441
Can you post your thoughts on this to www.radiocontrolzone.com as well as www.raceacademy.net .
I will give your suggestion a try and see. Are you using the plastic hexes or the aluminum ones?
I will give your suggestion a try and see. Are you using the plastic hexes or the aluminum ones?
07-06-2004, 06:51 AM
#442
Tech Apprentice
I use the aluminium ones.
The trick won't work with the plastic ones very good, and they didn't come with my kit either
The trick won't work with the plastic ones very good, and they didn't come with my kit either
07-06-2004, 06:55 AM
#443
Tech Master
iTrader: (21)
Just got one
Just got one of these,traded my GT for it(sucka/lol).Couple of questions. Is anyone running the cvd/universals in the rear?The dogbones,even with springs etc. seem to bind and not rotate properly. Has anyone had any problems with the diffs loosening?The other guy at my LHS running one has that problem with the rear diff.When I got this one,first run the rear was loose,front wheel drive only.Tightened it and it seemed to hold.Am currently rebuilding the whole car,so that should take care of that,I hope.As far as the binding,so far it only seems to be on the front.Will definately try to find/make the spacers tho. Gotta say tho,The one good run my daughter got in with the car,it rocks.Any other info on gearing is appreciated.Will post my findings next week after we run sunday. We had a 19 turn in it,geared at 19/70 and it seemed pretty good,could be better tho,I think.Great info here BTW.Thanks guys.Mario.
07-06-2004, 06:56 AM
#444
Its a tough call then. I can eliminate the tightening problem, but at the same time the plastic ones from what I have been told will help the axle shearing off problem.
If you want I can post your thoughts on the shims to the raceacademy.net board if you don't have a chance to do it. Right now the gentleman who came up with the spacer is on there posting.
If you want I can post your thoughts on the shims to the raceacademy.net board if you don't have a chance to do it. Right now the gentleman who came up with the spacer is on there posting.
07-06-2004, 07:05 AM
#445
Glad to see another academy driver!
you should check out www.raceacademy.net for more info. I haven't had any diff issues, I do plan however to do a teardown this wednesday, never got the chance last week.
As for dogbones binding, I haven't had any issue with this. They feel pretty smooth but just sound horrible when running.
As for gearing,about 6 pages back I posted a gearing chart based on what info i got from various drivers. Here is the chart:
( assuming 70T spur used )
Motor Pinion
10 turn 20
11 turn 21
12 turn 22
13 turn 23
14 turn 24
19 turn 23 - 24
24 stock ( torque based ) 24
24 stock ( rpm based ) 23
Depending on your 19T motor, I would start at 23T with the stock 70T spur. If its a chameleon motor, probably going with a 22 or 21 would be a better starting spot.
Just watch the temp on your motor since it is pretty sealed up. I am thinking of drilling some cooling holes, not sure exactly where would be a good spot.
you should check out www.raceacademy.net for more info. I haven't had any diff issues, I do plan however to do a teardown this wednesday, never got the chance last week.
As for dogbones binding, I haven't had any issue with this. They feel pretty smooth but just sound horrible when running.
As for gearing,about 6 pages back I posted a gearing chart based on what info i got from various drivers. Here is the chart:
( assuming 70T spur used )
Motor Pinion
10 turn 20
11 turn 21
12 turn 22
13 turn 23
14 turn 24
19 turn 23 - 24
24 stock ( torque based ) 24
24 stock ( rpm based ) 23
Depending on your 19T motor, I would start at 23T with the stock 70T spur. If its a chameleon motor, probably going with a 22 or 21 would be a better starting spot.
Just watch the temp on your motor since it is pretty sealed up. I am thinking of drilling some cooling holes, not sure exactly where would be a good spot.
07-06-2004, 07:07 AM
#446
Tech Apprentice
I'm registered at raceacademy, but you can post at radiocontrolzone if you want.
I personally don't understand why the plastic hexes should prevent the axles from breaking?
I think, it's just the other way round, because the plastic ones will slightly deform when cranking down the wheel nut, so they will add axial preassure to the 2x10mm shaft that itself will transfer the load to the axle where it's thinnest making it even more prone to breakage.
But again, I didn't have a chance to try the plastic hexes because they were missing - that's just what I'm thinking from a mechanical point of view.
To Lotus1
If you're just bashing, do yourself a favor and get the Academy RT-4 Gear diffs, 2x RG039 and ST-17 and ST-18.
The academy ball diffs are good, better than the old Losi XXX ones, but at least they do not have the durability of a gear diff.
You won't need any spacers for the rear dogbones when using gear diffs.
As for the ball diffs, the springs are not good, to much axial load and binding!
Instead, cut an ear plug to an appropriate lenght and stuff it into the outdrives (will make a nice dust cover for the thrust bearing btw
)
But remember, you never want the ear plug foam to press against the dogbone! It should just prevent it from falling out.
I personally don't understand why the plastic hexes should prevent the axles from breaking?
I think, it's just the other way round, because the plastic ones will slightly deform when cranking down the wheel nut, so they will add axial preassure to the 2x10mm shaft that itself will transfer the load to the axle where it's thinnest making it even more prone to breakage.
But again, I didn't have a chance to try the plastic hexes because they were missing - that's just what I'm thinking from a mechanical point of view.
To Lotus1
If you're just bashing, do yourself a favor and get the Academy RT-4 Gear diffs, 2x RG039 and ST-17 and ST-18.
The academy ball diffs are good, better than the old Losi XXX ones, but at least they do not have the durability of a gear diff.
You won't need any spacers for the rear dogbones when using gear diffs.
As for the ball diffs, the springs are not good, to much axial load and binding!
Instead, cut an ear plug to an appropriate lenght and stuff it into the outdrives (will make a nice dust cover for the thrust bearing btw
) But remember, you never want the ear plug foam to press against the dogbone! It should just prevent it from falling out.
07-06-2004, 07:17 AM
#447
good info re-inferno!
I am right now just reading up on the threads again. I will post your statement on radiocontrolzone for you. That is another big board for the vehicle.
I also try and keep www.4wdrc.com filled with info as well.
I am right now just reading up on the threads again. I will post your statement on radiocontrolzone for you. That is another big board for the vehicle.
I also try and keep www.4wdrc.com filled with info as well.
07-06-2004, 07:38 AM
#448
I just noticed we have a section on www.raceacademy.net for US drivers. I was made the Forum leader, so here are your marching orders, go post! 
Feel free to post your experiences, thoughts, etc there.
Feel free to post your experiences, thoughts, etc there.
07-06-2004, 08:34 AM
#449
Tech Master
iTrader: (1)
re: axle spacers
The reason for running the spacers is to be able to tighten the whole unit up, wheel, hex, axle and inner races of the bearing as one unit.
The only problemwith not running a spacer is that it makes it harder to set suspension geometry and there will be excessive play in the ahxle assembly resulting in premature bearing wear, maybe axle failure.
With running the spacer, the whole axle assembly rotates as one with no play in it, makes the suspension geometry more consistent.
The only problemwith not running a spacer is that it makes it harder to set suspension geometry and there will be excessive play in the ahxle assembly resulting in premature bearing wear, maybe axle failure.
With running the spacer, the whole axle assembly rotates as one with no play in it, makes the suspension geometry more consistent.
07-06-2004, 08:42 AM
#450
Tech Rookie
raceacademy.net
To all Academy USA owners:-
I am very glad to hear you are going to use Race Academy, my idea is for all Academy owners through out the world to share the knowledge and experiances of this car. I know this sounds like a quote for a perfect world, but if everyone helps each other and shares information then the enjoyment for the owners must be better.
We are getting some good info on there now, and there is also a chat room for all the Academy owners to discuss their views. I myself will be on there from time to time to answer qustions, so feel free to ask.
We have set up a US section, and if there are anymore sections you would like added to this please say.
At the moment I am working on an upgrade for the steering arm which we will test this weekend and I will keep you posted of the results.
And finally many thanks to all you who have posted your views and thoughts, thanks again for your feedback on the Academy products as this is vital for future projects.
Thanks
Nick Isaac
Academy UK
I am very glad to hear you are going to use Race Academy, my idea is for all Academy owners through out the world to share the knowledge and experiances of this car. I know this sounds like a quote for a perfect world, but if everyone helps each other and shares information then the enjoyment for the owners must be better.
We are getting some good info on there now, and there is also a chat room for all the Academy owners to discuss their views. I myself will be on there from time to time to answer qustions, so feel free to ask.
We have set up a US section, and if there are anymore sections you would like added to this please say.
At the moment I am working on an upgrade for the steering arm which we will test this weekend and I will keep you posted of the results.
And finally many thanks to all you who have posted your views and thoughts, thanks again for your feedback on the Academy products as this is vital for future projects.
Thanks
Nick Isaac
Academy UK