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large scale wiper motor servo

Old 04-06-2015, 12:12 PM
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superchip
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Default large scale wiper motor servo

Hi everyone, I'm new to this site and I'm really impressed with the wealth of knowledge on offer. I am currently in the middle of a large scale build in the form of a Baja style buggy although it doesn't look remotely like a Baja lol. Seeing as I have zero welding skills I have had to resort to bolting everything together in these early stages and once I have something that I'm satisfied with I'll be looking to weld and reinforce the chassis and other bits. I'm using a 2 stroke engine from a mini moto, the size of the car must measure 4 1/2 feet long and 3 feet wide at its widest, the wheels I'm using are the ones used on sack barrows so that gives you a rough I idea how big this thing is lol. Together with no welding skill I also have no real metal working tools like a lathe, but I do have access to a press drill and angle grinder which have proved invaluable. The frame and chassis has been made entirely from lawn mower handles cut at certain places to give me the shape I want and the whole thing has gone together pretty well, I would say I'm around 65-70% finished. Now to my question. I am an absolute noob with electronics but can learn fast, I am currently trying to put together my steering servo which comprises a wiper motor and a controller called a Servo Thor-15 which is designed for my application. Now I have been able to proportionally control the speed of the motor in both directions both with the rc tx and the potentiometer and all seems fine until I link the ou output shaft to the pot after which the output shaft loves to rip the linkage to pieces. In other words I can't make the set up to behave like a normal servo ie;
Neutral-left-auto centre-right-auto centre. I know the controller should work how I want as I've seen quite a few videos on YouTube where people are using the same motor controller and the wiper motor shouldn't be the issue either. Any brain boxes on here that can shed some light as to what I'm doing wrong would be appreciated, pics to come and many thanks
Old 04-07-2015, 09:22 AM
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superchip
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After reading through my post, it seems like I may not have made my specific problem clear. Now my aim is pretty much the same as what some other people in this forum have proposed to incorporate in their projects and that is to use a wiper motor as a steering servo but while they're using a scratch built h bridge or a polulu board(sorry if that's miss spelt), I'm going a different and I think more cost affective route by using a unit called a servo Thor-15 which is basically the electronics that you find in a normal hobby servo but can take voltages up to around 16v. This unit is specific to my goal in that the unit is designed to control a large motor (in my case a 12v wiper motor) just like a normal servo. The unit has an input for up to around 16v and incorporates it's own potentiometer for position feedback. In addition the unit also powers the receiver so I only need to worry about one battery which is a small 12v lead acid battery. Now my problem is that no matter what I try I simply can't make the motor behave like a servo, I can control the direction left and right via the potentiometer or the tx but when I link pot to the motors output shaft it just destroys itself. It doesn't matter either way when the pot reaches it's max travel because either way the motor just keeps turning until the linkage breaks. One thing I have noticed with the attached pot and that is there seems to be a huge dead area in the pots neutral position, I have to turn the pot quite a bit either way before the motor starts to turn, added to the problem is that I don't seem to have auto centre either. I don't know if that's an issue or not but I thought I'd mention it. Like I've said before, I have seen a few videos where people have used the same controller and have achieved what I want to achieve but I can't help thinking that I'm missing something....

Last edited by superchip; 04-07-2015 at 09:26 AM.
Old 04-07-2015, 10:57 AM
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I found a couple of early pics, I hope they uploaded properly lol
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Old 04-07-2015, 11:00 AM
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These pictures show my project in it's early stages and as such isn't as polished as it will be once finished
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Last edited by superchip; 04-07-2015 at 11:02 AM.
Old 04-15-2015, 05:02 PM
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Nice project! It is coming along very nicely and lots of work done already.

If you test the motor disconnected from any linkage, and you actuate the potentiometer manually, does it react to your potentiometer manual input? Does it change direction at some point? From your description, it sounds like when you are in the middle it does stop moving? It seems odd that you have to move the pot quite a bit before you get a reaction of the motor. I think it should be very sensitive as to keep the servo in position. Think of a regular servo, if you try to force it it does not even move yet and it already senses it and torques in the opposite direction to keep it there.

Regarding that middle spot where nothing is happening, is it a lag issue, or really a position issue? I mean, if you move the pot extremely slowly, it does the same thing ?
Old 04-16-2015, 12:57 AM
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Hi Frederick! Yes the motor changes direction in accordance to manual input from the potentiometer. When I say dead area I'm not quite sure if that's the right turn of phrase, the motor rotates left and right and stops once the pot is in centre. But to get any movement to begin with, the pot shaft has to be moved at least 1mm either way from centre which I don't think is right, and it's the same story with a few other pots I've used trying to make this work. I think it might be a good idea to post a video of what's going on so I'll try and do that later on.

What I can't understand is, having the exact same controller and very similar motor to others who have made this setup work, what am I doing that's so different? At first glaces the answer would be that I'm not doing anything different at all and I may be closer to getting it to work than I thought. But at this time I find that hard to believe lol
Old 04-16-2015, 05:29 AM
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Is there any chance the closed loop mode with linkage activates the pot on the wrong side? Leading the servo to conpensate, on the wrong side (aggravating the difference between the setpoint and the current position, instead of actually correcting)?

When you say 1mm dead spot, is that at the tip of the servo arm? If so what is the lenght of the arm? It seems ok that the arm moves 1mm on such a large scale before any movement is made as to avoid oscillation (overreacting of the controls)
Old 04-16-2015, 10:11 AM
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Hi thanks for getting back, prior to actually mounting the pot I made sure I got the orientation correct, good thought though and I can tell I have set your thinking gears into motion lol. When I estimated 1mm that was actually by twisting the pot shaft. Once a servo horn was installed, say a small one 20mm long? , it would increase to maybe 5mm or around 20 degrees either way at the end of the servo horn (not good at angles lol). And all the while the engine wasn't running so it rules out any potential suppressor interference. It's almost as though the pot isn't sending any positional feedback because it won't auto centre. But the pot must be fine because I can change the direction using the pot. I went back to the site where I bought the controller from just to make sure I purchased the right one as there's many models, and the description, although in German so I had to translate through Google, clearly states the controller I have is designed for my purpose. Making me even more confused as to why it isn't working as desired. Would soldering the pot wires onto the the wrong pins be the issue? I am 80% sure I soldered them to the right pins but I can't think of anything else, and if this is the case, how can I check to make sure I soldered the right wires to the right pins?
Old 04-16-2015, 01:11 PM
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I am pretty interested in getting one of these, sounds like a nice simple setup for large scale projects. When you test in open loop (not mechanically connected), if you play with the trims on the remote until the motor starts moving, can you confirm the direction you have to move the pot to stop the motor movement corresponds to the direction the motor turns?

Regarding pot wiring, there is a cursor on a pot, that is the wire attached to the piece moving across the resistor. If you have a larger pot, usually the cursor is the center pin. You should be able to confirm with an ohm meter (tester set to resistance testing). The cursor is the only pin that will show a varying resistance between it and any of the other two pins.

If you test the resistance between the two other pins (not the cursor) you should read a constant resistance nonmatter the pot position. Once that all tested you should know for a fact which is the pot cursor.


If you have the documentation of the thor 15 it probably shows where the cursor should go. But then again, if you have a proper response to your input on the pot it sounds as if it is wired with the cursor at the right place. I would triple check the pot direction of rotation to make sure it provides a feedback in the proper direction.
Old 04-17-2015, 12:45 AM
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Hi there, I shall do as you suggest and double check the pot orientation. Meanwhile here is the translated instructions for the servo Thor-15, Google translate isn't the best IMO lol.

THOR 15 servo servo electronics Operating Instructions for Power Thor 15 Maximum voltage is 16 volts. RDSON 25 milliohms. Maximum continuous current is 18 amps. Momentary Power up to 50 amps. For battery and motor connection 1qmm Silicone cables are attached. Dimensions: 24 * 20 * 6mm BEC supply for receiver and servos 5 volts for receiver and servos are mounted on the servo connector available (thin red wire). Maximum current is 1000mA (enough for 1 servo, but is dependent on the cell number). This voltage is short circuit proof and protected against overheating. Warning: This means when overtemperature switch off this voltage and thus the receiver would be a power interruption (risk of accident)! So, perform extensive testing, preferably with loaded servos (rubber rings the servo load can simulate). Terminal of the servo Thor: The servo THOR 15 is gem. Switching scheme (analogous Thor 15 HC) connected as shown below. The potentiometer must be mechanically driven. If a different size of the pots facilitates the installation and the mechanical drive, so it can be unsoldered and replaced by another pot. The mechanical rotational movement of the pots should not be too fast, since the scheme otherwise "swings" and it comes to permanent readjustment of the movement. It is important to design the mechanical control play as possible and easily. OFF THE RECEIVER IF NO ADDITIONAL RECEIVER BATTERY USED: by tweaking the red wire in the power cord and connect a switch. Caution: • Before the first ride the range of the RC system should be checked, as this control is very hard switching edges! • If a fault of the regulator, it may happen that the motor starts even when the receiver!
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Last edited by superchip; 04-17-2015 at 03:25 AM.

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