Sylvian Tennant Posted July 8, 2015 Share Posted July 8, 2015 Hello I'm currently building a Dave Alexander Q6 and I'm on the way to completing the chassis. I have installed the motor (Mashima 1024) and the (High Level 1:80) gear box. Testing it out I have found that running forward is near perfect, however, reverse running is quite uneven when running slow. I have currently run it with axle only, uncoupled and finally with the couple rods attached but the results are always the same - perfect forward running but uneven reverse running. As I increase the power running improves but as I do plan to have some reverse running as prototypical speeds I would like some advice on what to do next. Link to post Share on other sites More sharing options...
Spitfire2865 Posted July 8, 2015 Share Posted July 8, 2015 What exactly do you mean by uneven. Jittery? Or is the axle wobbling. If the latter, the bearings could be off in such a way it only affects one direction. If the former, Id say the axle is catching on some tiny defect in the bearing. Link to post Share on other sites More sharing options...
Sylvian Tennant Posted July 8, 2015 Author Share Posted July 8, 2015 Whilst it's turning, it slows at a point during the wheels revolution. Link to post Share on other sites More sharing options...
34theletterbetweenB&D Posted July 8, 2015 Share Posted July 8, 2015 This is very common, often an interaction of two or more small defects in the geartrain. why 'one direction good, one direction flawed'? Because of reaction forces, the gear shafts take up slightly different positions. The main defect is most likely to be on the gear shaft that the slowing synchs with once per revolution, and from post 3 it sounds as though this is the geared axle. Is the gear on the axle screw secured? If so always a major suspect: slack off the screw and try running, if it is then smooth running in both directions then it is eccentricity introduced by the screw. Gluing or soldering the axle to the gear is a fix, or drilling through the axle to just clear, and fitting a much longer length of studding so the gear is slgihtly loose. If not that try holding the gear axle against the reaction in the position it is in during forward running, while running in reverse. (Your own fingernail edges bearing on the axle ends lubricated with a little oil will do the trick.) If that delivers constant speed, there's the trouble. Slight relocation of the bearings (often by truing up the gear box assembly closer to all square rather than shifting the bearings relative to the gearbox), or fitting more closely toleranced bearings may be a fix. Link to post Share on other sites More sharing options...
Sylvian Tennant Posted July 8, 2015 Author Share Posted July 8, 2015 brilliants, I'll get on to that tonight and see how it comes along. Link to post Share on other sites More sharing options...
Sylvian Tennant Posted July 8, 2015 Author Share Posted July 8, 2015 Sorted it, I think i screwed the motor on too tight to the gear box, a slight teak and it's running beautifully either way. Cheers for the advice, it's what led me to my discovery. Link to post Share on other sites More sharing options...
34theletterbetweenB&D Posted July 9, 2015 Share Posted July 9, 2015 Now, make a note of it somewhere you will remember to look, because during the body fitting process you may well have the motor off, and you don't want to forget how the motor has to go on... Don't be surprised if other mechanism issues emerge with the body on the mechanism; attaching a body can distort the frame very slightly for example. Link to post Share on other sites More sharing options...
Sylvian Tennant Posted July 9, 2015 Author Share Posted July 9, 2015 I will do, I've tried fitting the body on loose and worked it and don't seem to be getting much of a problem however, these things arise when you think you're safe. Link to post Share on other sites More sharing options...
Sylvian Tennant Posted July 10, 2015 Author Share Posted July 10, 2015 as predicted, just when you think you're safe. Though it running nicely with the body attached I think I'm messed up the pickups as when I fitted them it wouldn't run. I'm thinking I've made them too short and without any springing which in turn prevents the electrical pick up to the motor. I'm going to have another pop at them and will get back to you. Link to post Share on other sites More sharing options...
N15class Posted July 29, 2015 Share Posted July 29, 2015 I would check how much end float you have on the motor shaft. Also put a single washer between the worm and the motor, with no end float. but not so tight it effects the rotation of the motor. If the motor shaft moves back and forth it will lead to poor running no washer makes the worm snatch on the motor. Link to post Share on other sites More sharing options...
Sylvian Tennant Posted August 11, 2015 Author Share Posted August 11, 2015 Ah, ok, I'll give that a go too cheers Peter Link to post Share on other sites More sharing options...
shildonboy Posted August 17, 2015 Share Posted August 17, 2015 the other thing that can cause the motor speed to be different in each direction is the brush location and pressure. Link to post Share on other sites More sharing options...
Sylvian Tennant Posted August 20, 2015 Author Share Posted August 20, 2015 I think she's mostly sorted out now. *hopes* currently the chassis is soldered, painted and meshed together and she's running as good as I can get her, the oly other problem is the pick up which I'm going to add another set in the tender to improve the running. Link to post Share on other sites More sharing options...
Jeff Smith Posted August 20, 2015 Share Posted August 20, 2015 A problem I found is insufficient retention of the motor. In one direction the torque holds the motor down against the frame/chassis - in the other the motor is rotated (lifts) away from the frame. This did not affect running with the chassis alone as it was so light the motor didn't lift, but when the heavy white metal body was on the weight apparently allowed the motor to rotate (around the driven axle) and presumably the opposite end shaft to contact the inside of the body - speed was slower and with a louder sound. The penny dropped and I put a retaining strap around the motor with the result that running in either direction is similar. Link to post Share on other sites More sharing options...
Sylvian Tennant Posted August 20, 2015 Author Share Posted August 20, 2015 Good idea Jeff, might give that ago as well to improve any inconsistencies. Link to post Share on other sites More sharing options...
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